Merge pull request #84800 from xedin/remove-csapply-operator-devirt

[CSApply] Don't attempt operator devirtualization
2025-12-14 20:36:38 +01:00 · 2025-10-18 23:09:23 +09:00
parent c23de594fc 2943d63ce5
commit 2b7adbc4ff
16 changed files with 989 additions and 367 deletions
--- a/lib/SILOptimizer/Mandatory/Differentiation.cpp
+++ b/lib/SILOptimizer/Mandatory/Differentiation.cpp
@@ -43,6 +43,7 @@
 #include "swift/SILOptimizer/Differentiation/VJPCloner.h"
 #include "swift/SILOptimizer/PassManager/Passes.h"
 #include "swift/SILOptimizer/PassManager/Transforms.h"
+#include "swift/SILOptimizer/Utils/Devirtualize.h"
 #include "swift/SILOptimizer/Utils/DifferentiationMangler.h"
 #include "swift/SILOptimizer/Utils/SILOptFunctionBuilder.h"
 #include "llvm/ADT/APSInt.h"
@@ -100,6 +101,24 @@ private:
                                   SILBuilder &builder, SILLocation loc,
                                   DifferentiationInvoker invoker);

+  /// Creates and canonicalizes private differentiability witness for
+  /// `originalFn`, differentiating with respect to
+  /// `desiredParameterIndices`. Returns `nullptr` on failure signifying that a
+  /// diagnostic has been emitted using `invoker`.
+  SILDifferentiabilityWitness *createPrivateDifferentiabilityWitness(
+      CanSILFunctionType originalFnTy, SILFunction *originalFn,
+      IndexSubset *desiredParameterIndices, IndexSubset *desiredResultIndices,
+      SILValue original, DifferentiationInvoker invoker);
+
+  /// Resolves differentiability witness for `originalFn`. Either by looking up
+  /// for registered one with respect to posible superset of `desiredIndices`,
+  /// or creating a new private one. Returns `nullptr` on failure signifying
+  /// that a diagnostic has been emitted using `invoker`.
+  SILDifferentiabilityWitness *getOrCreateMinimalDifferentiabilitywitness(
+      CanSILFunctionType originalFnTy, SILFunction *originalFn,
+      IndexSubset *desiredParameterIndices, IndexSubset *desiredResultIndices,
+      SILValue original, DifferentiationInvoker invoker);
+
  /// Emits a reference to a derivative function of `original`, differentiated
  /// with respect to a superset of `desiredIndices`. Returns the `SILValue` for
  /// the derivative function and the actual indices that the derivative
@@ -527,12 +546,142 @@ SILFunction *DifferentiationTransformer::getUnwrappedCurryThunkFunction(
  return silFnIt->second;
 }

+SILDifferentiabilityWitness *
+DifferentiationTransformer::createPrivateDifferentiabilityWitness(
+    CanSILFunctionType originalFnTy, SILFunction *originalFn,
+    IndexSubset *desiredParameterIndices, IndexSubset *desiredResultIndices,
+    SILValue original, DifferentiationInvoker invoker) {
+
+  // Check non-differentiable cases before creating a new private
+  // differentiability witness.
+
+  // If the function is intentionally marked as being opaque to
+  // differentiation, then we should not create a task for it.
+  if (originalFn->hasSemanticsAttr("autodiff.opaque")) {
+    context.emitNondifferentiabilityError(
+        original, invoker, diag::autodiff_opaque_function_not_differentiable);
+    return nullptr;
+  }
+
+  // Check and diagnose non-differentiable arguments.
+  for (auto [paramIndex, param] :
+       llvm::enumerate(originalFnTy->getParameters())) {
+    if (!desiredParameterIndices->contains(paramIndex))
+      continue;
+
+    SILType paramType = param.getSILStorageInterfaceType();
+    if (!paramType.isDifferentiable(context.getModule())) {
+      context.emitNondifferentiabilityError(
+          original, invoker, diag::autodiff_nondifferentiable_argument);
+      return nullptr;
+    }
+  }
+
+  // Check and diagnose non-differentiable results.
+  unsigned firstSemanticParamResultIdx = originalFnTy->getNumResults();
+  unsigned firstYieldResultIndex =
+      firstSemanticParamResultIdx +
+      originalFnTy->getNumAutoDiffSemanticResultsParameters();
+  for (auto resultIndex : desiredResultIndices->getIndices()) {
+    SILType resultType;
+    if (resultIndex >= firstYieldResultIndex) {
+      auto yieldResultIndex = resultIndex - firstYieldResultIndex;
+      auto yield = originalFnTy->getYields()[yieldResultIndex];
+      // We can only differentiate indirect yields. This should be diagnosed
+      // earlier in VJPCloner.
+      assert(yield.isAutoDiffSemanticResult() && "unsupported result");
+      resultType = yield.getSILStorageInterfaceType();
+    } else if (resultIndex >= firstSemanticParamResultIdx) {
+      auto semanticResultParamIdx = resultIndex - firstSemanticParamResultIdx;
+      auto semanticResultParam = *std::next(
+          originalFnTy->getAutoDiffSemanticResultsParameters().begin(),
+          semanticResultParamIdx);
+      resultType = semanticResultParam.getSILStorageInterfaceType();
+    } else {
+      resultType =
+          originalFnTy->getResults()[resultIndex].getSILStorageInterfaceType();
+    }
+
+    if (!resultType || !resultType.isDifferentiable(context.getModule())) {
+      context.emitNondifferentiabilityError(
+          original, invoker, diag::autodiff_nondifferentiable_result);
+      return nullptr;
+    }
+  }
+
+  // Check and diagnose external declarations.
+  if (originalFn->isExternalDeclaration()) {
+    context.emitNondifferentiabilityError(
+        original, invoker, diag::autodiff_external_nondifferentiable_function);
+    return nullptr;
+  }
+
+  // Soundness check passed. Create a new differentiability witness
+  GenericSignature contextualDerivativeGenSig = GenericSignature();
+  if (invoker.getKind() ==
+      DifferentiationInvoker::Kind::IndirectDifferentiation)
+    contextualDerivativeGenSig = invoker.getIndirectDifferentiation()
+                                     .second->getDerivativeGenericSignature();
+  auto derivativeConstrainedGenSig =
+      autodiff::getConstrainedDerivativeGenericSignature(
+          originalFnTy, desiredParameterIndices, desiredResultIndices,
+          contextualDerivativeGenSig, LookUpConformanceInModule());
+
+  auto *witness = SILDifferentiabilityWitness::createDefinition(
+      context.getModule(), SILLinkage::Private, originalFn,
+      DifferentiabilityKind::Reverse, desiredParameterIndices,
+      desiredResultIndices, derivativeConstrainedGenSig, /*jvp*/ nullptr,
+      /*vjp*/ nullptr, /*isSerialized*/ false);
+  if (canonicalizeDifferentiabilityWitness(witness, invoker, IsNotSerialized))
+    return nullptr;
+
+  return witness;
+}
+
+SILDifferentiabilityWitness *
+DifferentiationTransformer::getOrCreateMinimalDifferentiabilitywitness(
+    CanSILFunctionType originalFnTy, SILFunction *originalFn,
+    IndexSubset *desiredParameterIndices, IndexSubset *desiredResultIndices,
+    SILValue original, DifferentiationInvoker invoker) {
+  // NOTE(TF-893): Extending capacity is necessary when `originalFnTy` has
+  // parameters corresponding to captured variables.
+  // TODO: If possible, change `autodiff::getLoweredParameterIndices` to
+  // take `CaptureInfo` into account.
+  if (originalFnTy->getNumParameters() >
+      desiredParameterIndices->getCapacity()) {
+    desiredParameterIndices = desiredParameterIndices->extendingCapacity(
+        context.getASTContext(), originalFnTy->getNumParameters());
+  }
+
+  // Look up a differentiability witness with the exact configuration.
+  auto *minimalWitness = getExactDifferentiabilityWitness(
+      context.getModule(), originalFn, desiredParameterIndices,
+      desiredResultIndices);
+
+  // Otherwise, look up a differentiability witness with a minimal superset
+  // configuration.
+  if (!minimalWitness)
+    minimalWitness = getOrCreateMinimalASTDifferentiabilityWitness(
+        context.getModule(), originalFn, DifferentiabilityKind::Reverse,
+        desiredParameterIndices, desiredResultIndices);
+
+  // Finally, try to create private differentiability witness
+  if (!minimalWitness)
+    minimalWitness = createPrivateDifferentiabilityWitness(
+        originalFnTy, originalFn, desiredParameterIndices, desiredResultIndices,
+        original, invoker);
+
+  return minimalWitness;
+}
+
 std::optional<std::pair<SILValue, AutoDiffConfig>>
 DifferentiationTransformer::emitDerivativeFunctionReference(
    SILBuilder &builder, const AutoDiffConfig &desiredConfig,
    AutoDiffDerivativeFunctionKind kind, SILValue original,
    DifferentiationInvoker invoker,
    SmallVectorImpl<AllocStackInst *> &newBuffersToDealloc) {
+  SILFunction *parentFn = original->getFunction();
+
  // If `original` is itself an `DifferentiableFunctionExtractInst` whose kind
  // matches the given kind and desired differentiation parameter indices,
  // simply extract the derivative function of its function operand, retain the
@@ -576,111 +725,16 @@ DifferentiationTransformer::emitDerivativeFunctionReference(
    auto loc = originalFRI->getLoc();
    auto *originalFn = originalFRI->getReferencedFunction();
    auto originalFnTy = originalFn->getLoweredFunctionType();
-    auto *desiredParameterIndices = desiredConfig.parameterIndices;
-    auto *desiredResultIndices = desiredConfig.resultIndices;
-    // NOTE(TF-893): Extending capacity is necessary when `originalFnTy` has
-    // parameters corresponding to captured variables.
-    // TODO: If possible, change `autodiff::getLoweredParameterIndices` to
-    // take `CaptureInfo` into account.
-    if (originalFnTy->getNumParameters() >
-        desiredParameterIndices->getCapacity()) {
-      desiredParameterIndices = desiredParameterIndices->extendingCapacity(
-          context.getASTContext(), originalFnTy->getNumParameters());
-    }
-    // Look up a differentiability witness with the exact configuration.
-    auto *minimalWitness = getExactDifferentiabilityWitness(
-        context.getModule(), originalFn, desiredParameterIndices,
-        desiredResultIndices);
-    // Otherwise, look up a differentiability witness with a minimal superset
-    // configuration.
+
+    auto *minimalWitness = getOrCreateMinimalDifferentiabilitywitness(
+        originalFnTy, originalFn, desiredConfig.parameterIndices,
+        desiredConfig.resultIndices, original, invoker);
+
+    // All non-differentiability cases should be diagnosted
    if (!minimalWitness)
-      minimalWitness = getOrCreateMinimalASTDifferentiabilityWitness(
-          context.getModule(), originalFn, DifferentiabilityKind::Reverse,
-          desiredParameterIndices, desiredResultIndices);
-    // If no minimal witness exists, check non-differentiable cases before
-    // creating a new private differentiability witness.
-    if (!minimalWitness) {
-      // If the function is intentionally marked as being opaque to
-      // differentiation, then we should not create a task for it.
-      if (originalFn->hasSemanticsAttr("autodiff.opaque")) {
-        context.emitNondifferentiabilityError(
-            original, invoker,
-            diag::autodiff_opaque_function_not_differentiable);
-        return std::nullopt;
-      }
-      // Check and diagnose non-differentiable arguments.
-      auto originalFnTy = originalFn->getLoweredFunctionType();
-      for (unsigned paramIndex : range(originalFnTy->getNumParameters())) {
-        if (desiredConfig.isWrtParameter(paramIndex) &&
-            !originalFnTy->getParameters()[paramIndex]
-                 .getSILStorageInterfaceType()
-                 .isDifferentiable(context.getModule())) {
-          auto diag = context.emitNondifferentiabilityError(
-              original, invoker, diag::autodiff_nondifferentiable_argument);
-          return std::nullopt;
-        }
-      }
-      // Check and diagnose non-differentiable results.
-      unsigned firstSemanticParamResultIdx = originalFnTy->getNumResults();
-      unsigned firstYieldResultIndex = originalFnTy->getNumResults() +
-        originalFnTy->getNumAutoDiffSemanticResultsParameters();
-      for (auto resultIndex : desiredResultIndices->getIndices()) {
-        SILType resultType;
-        if (resultIndex >= firstYieldResultIndex) {
-          auto yieldResultIndex = resultIndex - firstYieldResultIndex;
-          auto yield = originalFnTy->getYields()[yieldResultIndex];
-          // We can only differentiate indirect yields. This should be diagnosed
-          // earlier in VJPCloner.
-          assert(yield.isAutoDiffSemanticResult() && "unsupported result");
-          resultType = yield.getSILStorageInterfaceType();
-        } else if (resultIndex >= firstSemanticParamResultIdx) {
-          auto semanticResultParamIdx = resultIndex - firstSemanticParamResultIdx;
-          auto semanticResultParam =
-              *std::next(originalFnTy->getAutoDiffSemanticResultsParameters().begin(),
-                         semanticResultParamIdx);
-          resultType = semanticResultParam.getSILStorageInterfaceType();
-        } else {
-          resultType = originalFnTy->getResults()[resultIndex]
-                           .getSILStorageInterfaceType();
-        }
-        if (!resultType || !resultType.isDifferentiable(context.getModule())) {
-          context.emitNondifferentiabilityError(
-              original, invoker, diag::autodiff_nondifferentiable_result);
-          return std::nullopt;
-        }
-      }
-      // Check and diagnose external declarations.
-      if (originalFn->isExternalDeclaration()) {
-        context.emitNondifferentiabilityError(
-            original, invoker,
-            diag::autodiff_external_nondifferentiable_function);
-        return std::nullopt;
-      }
-      // Soundness check passed. Create a new differentiability witness and
-      // canonicalize it.
-      GenericSignature contextualDerivativeGenSig = GenericSignature();
-      if (invoker.getKind() ==
-          DifferentiationInvoker::Kind::IndirectDifferentiation)
-        contextualDerivativeGenSig =
-            invoker.getIndirectDifferentiation()
-                .second->getDerivativeGenericSignature();
-      auto derivativeConstrainedGenSig =
-          autodiff::getConstrainedDerivativeGenericSignature(
-              originalFn->getLoweredFunctionType(),
-              desiredParameterIndices, desiredResultIndices,
-              contextualDerivativeGenSig,
-              LookUpConformanceInModule());
-      minimalWitness = SILDifferentiabilityWitness::createDefinition(
-          context.getModule(), SILLinkage::Private, originalFn,
-          DifferentiabilityKind::Reverse, desiredParameterIndices,
-          desiredResultIndices, derivativeConstrainedGenSig, /*jvp*/ nullptr,
-          /*vjp*/ nullptr, /*isSerialized*/ false);
-      if (canonicalizeDifferentiabilityWitness(minimalWitness, invoker,
-                                               IsNotSerialized))
-        return std::nullopt;
-    }
-    assert(minimalWitness);
-    if (original->getFunction()->isSerialized()) {
+      return std::nullopt;
+
+    if (parentFn->isSerialized()) {
      bool isWitnessPublic;
      if (SILFunction *unwrappedFn =
              getUnwrappedCurryThunkFunction(originalFn)) {
@@ -691,15 +745,12 @@ DifferentiationTransformer::emitDerivativeFunctionReference(
        // private linkage.
        isWitnessPublic = hasPublicVisibility(unwrappedFn->getLinkage());
      } else if (originalFn->getDeclRef().getAbstractClosureExpr() &&
-                 originalFRI->getFunction()
-                     ->getDeclRef()
-                     .isDefaultArgGenerator()) {
+                 parentFn->getDeclRef().isDefaultArgGenerator()) {
        // If we reference a closure from inside default argument generator,
        // check against generator's visibility. If the function having this
        // default argument has public visibility, it's OK to have a closure
        // (which always has private visibility) as its default value.
-        isWitnessPublic =
-            hasPublicVisibility(originalFRI->getFunction()->getLinkage());
+        isWitnessPublic = hasPublicVisibility(parentFn->getLinkage());
      } else {
        isWitnessPublic = hasPublicVisibility(minimalWitness->getLinkage());
      }
@@ -709,16 +760,16 @@ DifferentiationTransformer::emitDerivativeFunctionReference(
        // FIXME: This is not a very robust way of determining if the function
        // is a default argument. Also, we have not exhaustively listed all the
        // kinds of fragility.
-        if (original->getFunction()->getLinkage() == SILLinkage::PublicNonABI)
+        if (parentFn->getLinkage() == SILLinkage::PublicNonABI)
          fragileKind = DefaultArgument;
        context.emitNondifferentiabilityError(
            original, invoker, diag::autodiff_private_derivative_from_fragile,
            fragileKind,
-            isa_and_nonnull<AbstractClosureExpr>(
-                originalFRI->getLoc().getAsASTNode<Expr>()));
+            isa_and_nonnull<AbstractClosureExpr>(loc.getAsASTNode<Expr>()));
        return std::nullopt;
      }
    }
+
    // TODO(TF-482): Move generic requirement checking logic to
    // `getExactDifferentiabilityWitness` and
    // `getOrCreateMinimalASTDifferentiabilityWitness`.
@@ -726,18 +777,17 @@ DifferentiationTransformer::emitDerivativeFunctionReference(
    // By default, use the forwarding substitution map of the original function.
    // If the original callee is a `partial_apply` or `apply` instruction, use
    // its substitution map instead.
-    auto substMap = original->getFunction()->getForwardingSubstitutionMap();
-    if (auto *pai =
-            peerThroughFunctionConversions<PartialApplyInst>(original)) {
+    auto substMap = parentFn->getForwardingSubstitutionMap();
+    if (auto *pai = peerThroughFunctionConversions<PartialApplyInst>(original))
      substMap = pai->getSubstitutionMap();
-    } else if (auto *ai = peerThroughFunctionConversions<ApplyInst>(original)) {
+    else if (auto *ai = peerThroughFunctionConversions<ApplyInst>(original))
      substMap = ai->getSubstitutionMap();
-    }
    if (diagnoseUnsatisfiedRequirements(
            context, original->getType().castTo<SILFunctionType>(),
            minimalWitness->getDerivativeGenericSignature(), substMap, invoker,
            original.getLoc().getSourceLoc()))
      return std::nullopt;
+
    DifferentiabilityWitnessFunctionKind witnessKind;
    switch (kind) {
    case AutoDiffDerivativeFunctionKind::JVP:
@@ -764,6 +814,79 @@ DifferentiationTransformer::emitDerivativeFunctionReference(
  if (auto *witnessMethod =
          peerThroughFunctionConversions<WitnessMethodInst>(original)) {
    auto loc = witnessMethod->getLoc();
+    // See if we can derive derivatives for a method statically
+    auto [method, table] = lookUpFunctionInWitnessTable(
+        witnessMethod, SILModule::LinkingMode::LinkNormal);
+    if (method) {
+      auto *originalFn = method;
+      auto originalFnTy = method->getLoweredFunctionTypeInContext(
+          TypeExpansionContext(*original->getFunction()));
+
+      auto *minimalWitness = getOrCreateMinimalDifferentiabilitywitness(
+          originalFnTy, originalFn, desiredConfig.parameterIndices,
+          desiredConfig.resultIndices, original, invoker);
+
+      // All non-differentiability cases should be diagnosted
+      if (!minimalWitness)
+        return std::nullopt;
+
+      if (parentFn->isSerialized() &&
+          !hasPublicVisibility(minimalWitness->getLinkage())) {
+        enum { Inlinable = 0, DefaultArgument = 1 };
+        unsigned fragileKind = Inlinable;
+        // FIXME: This is not a very robust way of determining if the function
+        // is a default argument. Also, we have not exhaustively listed all the
+        // kinds of fragility.
+        if (parentFn->getLinkage() == SILLinkage::PublicNonABI)
+          fragileKind = DefaultArgument;
+        context.emitNondifferentiabilityError(
+            original, invoker, diag::autodiff_private_derivative_from_fragile,
+            fragileKind,
+            isa_and_nonnull<AbstractClosureExpr>(loc.getAsASTNode<Expr>()));
+        return std::nullopt;
+      }
+
+      auto substMap = parentFn->getForwardingSubstitutionMap();
+      if (auto *pai =
+              peerThroughFunctionConversions<PartialApplyInst>(original))
+        substMap =
+            getWitnessMethodSubstitutions(context.getModule(), pai, originalFn,
+                                          witnessMethod->getConformance());
+      else if (auto *ai = peerThroughFunctionConversions<ApplyInst>(original))
+        substMap =
+            getWitnessMethodSubstitutions(context.getModule(), ai, originalFn,
+                                          witnessMethod->getConformance());
+      if (diagnoseUnsatisfiedRequirements(
+              context, original->getType().castTo<SILFunctionType>(),
+              minimalWitness->getDerivativeGenericSignature(), substMap,
+              invoker, original.getLoc().getSourceLoc()))
+        return std::nullopt;
+
+      DifferentiabilityWitnessFunctionKind witnessKind;
+      switch (kind) {
+      case AutoDiffDerivativeFunctionKind::JVP:
+        witnessKind = DifferentiabilityWitnessFunctionKind::JVP;
+        break;
+      case AutoDiffDerivativeFunctionKind::VJP:
+        witnessKind = DifferentiabilityWitnessFunctionKind::VJP;
+        break;
+      }
+
+      auto *derivativeFnRef = builder.createDifferentiabilityWitnessFunction(
+          loc, witnessKind, minimalWitness);
+
+      auto convertedRef = reapplyFunctionConversion(
+          context, derivativeFnRef, witnessMethod, original, builder, loc,
+          newBuffersToDealloc, desiredConfig.parameterIndices,
+          desiredConfig.resultIndices,
+          derivativeFnRef->getType()
+              .getASTType()
+              ->castTo<SILFunctionType>()
+              ->getSubstGenericSignature());
+
+      return std::make_pair(convertedRef, minimalWitness->getConfig());
+    }
+
    auto requirementDeclRef = witnessMethod->getMember();
    auto *requirementDecl = requirementDeclRef.getAbstractFunctionDecl();
    // If requirement declaration does not have any derivative function
--- a/lib/Sema/CSApply.cpp
+++ b/lib/Sema/CSApply.cpp
@@ -588,66 +588,6 @@ namespace {
      }
    }

-    // Returns None if the AST does not contain enough information to recover
-    // substitutions; this is different from an Optional(SubstitutionMap()),
-    // indicating a valid call to a non-generic operator.
-    std::optional<SubstitutionMap> getOperatorSubstitutions(ValueDecl *witness,
-                                                            Type refType) {
-      // We have to recover substitutions in this hacky way because
-      // the AST does not retain enough information to devirtualize
-      // calls like this.
-      auto witnessType = witness->getInterfaceType();
-
-      // Compute the substitutions.
-      auto *gft = witnessType->getAs<GenericFunctionType>();
-      if (gft == nullptr) {
-        if (refType->isEqual(witnessType))
-          return SubstitutionMap();
-        return std::nullopt;
-      }
-
-      auto sig = gft->getGenericSignature();
-      auto *env = sig.getGenericEnvironment();
-
-      witnessType = FunctionType::get(gft->getParams(),
-                                      gft->getResult(),
-                                      gft->getExtInfo());
-      witnessType = env->mapTypeIntoContext(witnessType);
-
-      TypeSubstitutionMap subs;
-      auto substType = witnessType->substituteBindingsTo(
-        refType,
-        [&](ArchetypeType *origType, CanType substType) -> CanType {
-          if (auto gpType = dyn_cast<GenericTypeParamType>(
-                origType->getInterfaceType()->getCanonicalType()))
-            subs[gpType] = substType;
-
-          return substType;
-        });
-
-      // If substitution failed, it means that the protocol requirement type
-      // and the witness type did not match up. The only time that this
-      // should happen is when the witness is defined in a base class and
-      // the actual call uses a derived class. For example,
-      //
-      // protocol P { func +(lhs: Self, rhs: Self) }
-      // class Base : P { func +(lhs: Base, rhs: Base) {} }
-      // class Derived : Base {}
-      //
-      // If we enter this code path with two operands of type Derived,
-      // we know we're calling the protocol requirement P.+, with a
-      // substituted type of (Derived, Derived) -> (). But the type of
-      // the witness is (Base, Base) -> (). Just bail out and make a
-      // witness method call in this rare case; SIL mandatory optimizations
-      // will likely devirtualize it anyway.
-      if (!substType)
-        return std::nullopt;
-
-      return SubstitutionMap::get(sig,
-                                  QueryTypeSubstitutionMap{subs},
-                                  LookUpConformanceInModule());
-    }
-
    /// Determine whether the given reference is to a method on
    /// a remote distributed actor in the given context.
    bool isDistributedThunk(ConcreteDeclRef ref, Expr *context);
@@ -674,65 +614,6 @@ namespace {

        auto baseTy = getBaseType(adjustedFullType->castTo<FunctionType>());

-        // Handle operator requirements found in protocols.
-        if (auto proto = dyn_cast<ProtocolDecl>(decl->getDeclContext())) {
-          bool isCurried = shouldBuildCurryThunk(choice, /*baseIsInstance=*/false);
-
-          // If we have a concrete conformance, build a call to the witness.
-          //
-          // FIXME: This is awful. We should be able to handle this as a call to
-          // the protocol requirement with Self == the concrete type, and SILGen
-          // (or later) can devirtualize as appropriate.
-          auto conformance = checkConformance(baseTy, proto);
-          if (conformance.isConcrete()) {
-            if (auto witness = conformance.getConcrete()->getWitnessDecl(decl)) {
-              bool isMemberOperator = witness->getDeclContext()->isTypeContext();
-
-              if (!isMemberOperator || !isCurried) {
-                // The fullType was computed by substituting the protocol
-                // requirement so it always has a (Self) -> ... curried
-                // application. Strip it off if the witness was a top-level
-                // function.
-                Type refType;
-                if (isMemberOperator)
-                  refType = adjustedFullType;
-                else
-                  refType = adjustedFullType->castTo<AnyFunctionType>()->getResult();
-
-                // Build the AST for the call to the witness.
-                auto subMap = getOperatorSubstitutions(witness, refType);
-                if (subMap) {
-                  ConcreteDeclRef witnessRef(witness, *subMap);
-                  auto declRefExpr =  new (ctx) DeclRefExpr(witnessRef, loc,
-                                                            /*Implicit=*/false);
-                  declRefExpr->setFunctionRefInfo(choice.getFunctionRefInfo());
-                  cs.setType(declRefExpr, refType);
-
-                  Expr *refExpr;
-                  if (isMemberOperator) {
-                    // If the operator is a type member, add the implicit
-                    // (Self) -> ... call.
-                    Expr *base =
-                      TypeExpr::createImplicitHack(loc.getBaseNameLoc(), baseTy,
-                                                   ctx);
-                    cs.setType(base, MetatypeType::get(baseTy));
-
-                    refExpr =
-                        DotSyntaxCallExpr::create(ctx, declRefExpr, SourceLoc(),
-                                                  Argument::unlabeled(base));
-                    auto refType = adjustedFullType->castTo<FunctionType>()->getResult();
-                    cs.setType(refExpr, refType);
-                  } else {
-                    refExpr = declRefExpr;
-                  }
-
-                  return forceUnwrapIfExpected(refExpr, locator);
-                }
-              }
-            }
-          }
-        }
-
        // Build a reference to the member.
        Expr *base =
          TypeExpr::createImplicitHack(loc.getBaseNameLoc(), baseTy, ctx);
--- a/test/AutoDiff/stdlib/simd.swift
+++ b/test/AutoDiff/stdlib/simd.swift
@@ -2,6 +2,9 @@
 // REQUIRES: executable_test

 // Would fail due to unavailability of swift_autoDiffCreateLinearMapContext.
+/* Temporary disabled until https://github.com/swiftlang/swift/issues/84840 is fixed
+   We cannot use `SIMD` :( */
+// XFAIL: *

 import _Differentiation
 import StdlibUnittest
--- a/test/AutoDiff/validation-test/class_differentiation.swift
+++ b/test/AutoDiff/validation-test/class_differentiation.swift
@@ -2,6 +2,9 @@
 // NOTE: Verify whether forward-mode differentiation crashes. It currently does.
 // RUN: not --crash %target-swift-frontend -enable-experimental-forward-mode-differentiation -emit-sil %s
 // REQUIRES: executable_test
+/* Temporary disabled until https://github.com/swiftlang/swift/issues/84840 is fixed
+   We cannot use `Tracked<T>` :( */
+// XFAIL: *

 import StdlibUnittest
 import DifferentiationUnittest
--- a/test/AutoDiff/validation-test/differentiable_property.swift
+++ b/test/AutoDiff/validation-test/differentiable_property.swift
@@ -9,6 +9,144 @@ import DifferentiationUnittest

 var E2EDifferentiablePropertyTests = TestSuite("E2EDifferentiableProperty")

+struct TangentSpace : AdditiveArithmetic {
+  let x, y: Float
+}
+
+extension TangentSpace : Differentiable {
+  typealias TangentVector = TangentSpace
+}
+
+struct Space {
+  /// `x` is a computed property with a custom vjp.
+  var x: Float {
+    @differentiable(reverse)
+    get { storedX }
+    set { storedX = newValue }
+  }
+
+  @derivative(of: x)
+  func vjpX() -> (value: Float, pullback: (Float) -> TangentSpace) {
+    return (x, { v in TangentSpace(x: v, y: 0) } )
+  }
+
+  private var storedX: Float
+
+  @differentiable(reverse)
+  var y: Float
+
+  init(x: Float, y: Float) {
+    self.storedX = x
+    self.y = y
+  }
+}
+
+extension Space : Differentiable {
+  typealias TangentVector = TangentSpace
+  mutating func move(by offset: TangentSpace) {
+    x.move(by: offset.x)
+    y.move(by: offset.y)
+  }
+}
+
+E2EDifferentiablePropertyTests.test("computed property") {
+  let actualGrad = gradient(at: Space(x: 0, y: 0)) { (point: Space) -> Float in
+    return 2 * point.x
+  }
+  let expectedGrad = TangentSpace(x: 2, y: 0)
+  expectEqual(expectedGrad, actualGrad)
+}
+
+E2EDifferentiablePropertyTests.test("stored property") {
+  let actualGrad = gradient(at: Space(x: 0, y: 0)) { (point: Space) -> Float in
+    return 3 * point.y
+  }
+  let expectedGrad = TangentSpace(x: 0, y: 3)
+  expectEqual(expectedGrad, actualGrad)
+}
+
+struct GenericMemberWrapper<T : Differentiable> : Differentiable {
+  // Stored property.
+  @differentiable(reverse)
+  var x: T
+
+  func vjpX() -> (T, (T.TangentVector) -> GenericMemberWrapper.TangentVector) {
+    return (x, { TangentVector(x: $0) })
+  }
+}
+
+E2EDifferentiablePropertyTests.test("generic stored property") {
+  let actualGrad = gradient(at: GenericMemberWrapper<Float>(x: 1)) { point in
+    return 2 * point.x
+  }
+  let expectedGrad = GenericMemberWrapper<Float>.TangentVector(x: 2)
+  expectEqual(expectedGrad, actualGrad)
+}
+
+struct ProductSpaceSelfTangent : AdditiveArithmetic {
+  let x, y: Float
+}
+
+extension ProductSpaceSelfTangent : Differentiable {
+  typealias TangentVector = ProductSpaceSelfTangent
+}
+
+E2EDifferentiablePropertyTests.test("fieldwise product space, self tangent") {
+  let actualGrad = gradient(at: ProductSpaceSelfTangent(x: 0, y: 0)) { (point: ProductSpaceSelfTangent) -> Float in
+    return 5 * point.y
+  }
+  let expectedGrad = ProductSpaceSelfTangent(x: 0, y: 5)
+  expectEqual(expectedGrad, actualGrad)
+}
+
+struct ProductSpaceOtherTangentTangentSpace : AdditiveArithmetic {
+  let x, y: Float
+}
+
+extension ProductSpaceOtherTangentTangentSpace : Differentiable {
+  typealias TangentVector = ProductSpaceOtherTangentTangentSpace
+}
+
+struct ProductSpaceOtherTangent {
+  var x, y: Float
+}
+
+extension ProductSpaceOtherTangent : Differentiable {
+  typealias TangentVector = ProductSpaceOtherTangentTangentSpace
+  mutating func move(by offset: ProductSpaceOtherTangentTangentSpace) {
+    x.move(by: offset.x)
+    y.move(by: offset.y)
+  }
+}
+
+E2EDifferentiablePropertyTests.test("fieldwise product space, other tangent") {
+  let actualGrad = gradient(
+    at: ProductSpaceOtherTangent(x: 0, y: 0)
+  ) { (point: ProductSpaceOtherTangent) -> Float in
+    return 7 * point.y
+  }
+  let expectedGrad = ProductSpaceOtherTangentTangentSpace(x: 0, y: 7)
+  expectEqual(expectedGrad, actualGrad)
+}
+
+E2EDifferentiablePropertyTests.test("computed property") {
+  struct TF_544 : Differentiable {
+    var value: Float
+    @differentiable(reverse)
+    var computed: Float {
+      get { value }
+      set { value = newValue }
+    }
+  }
+  let actualGrad = gradient(at: TF_544(value: 2.4)) { x in
+    return x.computed * x.computed
+  }
+  let expectedGrad = TF_544.TangentVector(value: 4.8)
+  expectEqual(expectedGrad, actualGrad)
+}
+
+/* Temporary disabled until https://github.com/swiftlang/swift/issues/84840 is fixed
+   We cannot use `Tracked<T>` :(
 struct TangentSpace : AdditiveArithmetic {
  let x, y: Tracked<Float>
 }
@@ -144,5 +282,6 @@ E2EDifferentiablePropertyTests.testWithLeakChecking("computed property") {
  let expectedGrad = TF_544.TangentVector(value: 4.8)
  expectEqual(expectedGrad, actualGrad)
 }
+*/

 runAllTests()
--- a/test/AutoDiff/validation-test/existential.swift
+++ b/test/AutoDiff/validation-test/existential.swift
@@ -8,19 +8,39 @@ var ExistentialTests = TestSuite("Existential")

 protocol A {
  @differentiable(reverse, wrt: x)
-  func a(_ x: Tracked<Float>) -> Tracked<Float>
+  func a(_ x: Float) -> Float
 }
-func b(g: A) -> Tracked<Float> {
+func b(g: A) -> Float {
  return gradient(at: 3) { x in g.a(x) }
 }

 struct B : A {
  @differentiable(reverse, wrt: x)
-  func a(_ x: Tracked<Float>) -> Tracked<Float> { return x * 5 }
+  func a(_ x: Float) -> Float { return x * 5 }
 }

-ExistentialTests.testWithLeakChecking("Existential method VJP") {
+ExistentialTests.test("Existential method VJP-Tracked") {
  expectEqual(5.0, b(g: B()))
 }

+/* Temporary disabled until https://github.com/swiftlang/swift/issues/84840 is fixed
+   We cannot use `Tracked<T>` :(
+protocol ATracked {
+  @differentiable(reverse, wrt: x)
+  func a(_ x: Tracked<Float>) -> Tracked<Float>
+}
+func b(g: ATracked) -> Tracked<Float> {
+  return gradient(at: 3) { x in g.a(x) }
+}
+
+struct BTracked : ATracked {
+  @differentiable(reverse, wrt: x)
+  func a(_ x: Tracked<Float>) -> Tracked<Float> { return x * 5 }
+}
+
+ExistentialTests.testWithLeakChecking("Existential method VJP-Tracked") {
+  expectEqual(5.0, b(g: BTracked()))
+}
+*/
+
 runAllTests()
--- a/test/AutoDiff/validation-test/forward_mode_simd.swift
+++ b/test/AutoDiff/validation-test/forward_mode_simd.swift
@@ -1,5 +1,8 @@
 // RUN: %target-run-simple-swift(-Xfrontend -enable-experimental-forward-mode-differentiation)
 // REQUIRES: executable_test
+/* Temporary disabled until https://github.com/swiftlang/swift/issues/84840 is fixed
+   We cannot use `SIMD` :( */
+// XFAIL: *

 import StdlibUnittest
 import DifferentiationUnittest
--- a/test/AutoDiff/validation-test/forward_mode_simple.swift
+++ b/test/AutoDiff/validation-test/forward_mode_simple.swift
@@ -1,5 +1,8 @@
 // RUN: %target-run-simple-swift(-Xfrontend -enable-experimental-forward-mode-differentiation)
 // REQUIRES: executable_test
+/* Temporary disabled until https://github.com/swiftlang/swift/issues/84840 is fixed
+   We cannot use `Tracked<T>` :( */
+// XFAIL: *

 import StdlibUnittest
 import DifferentiationUnittest
--- a/test/AutoDiff/validation-test/method.swift
+++ b/test/AutoDiff/validation-test/method.swift
@@ -9,50 +9,50 @@ var MethodTests = TestSuite("Method")
 // ==== Tests with generated adjoint ====

 struct Parameter : Equatable {
-  private let storedX: Tracked<Float>
+  private let storedX: Float
  @differentiable(reverse, wrt: (self))
-  var x: Tracked<Float> {
+  var x: Float {
      return storedX
  }

-  init(x: Tracked<Float>) {
+  init(x: Float) {
    storedX = x
  }

  @derivative(of: x)
-  func vjpX() -> (value: Tracked<Float>, pullback: (Tracked<Float>) -> Parameter) {
+  func vjpX() -> (value: Float, pullback: (Float) -> Parameter) {
    return (x, { dx in Parameter(x: dx) } )
  }

  @derivative(of: x)
-  func jvpX() -> (value: Tracked<Float>, differential: (Parameter) -> Tracked<Float>) {
+  func jvpX() -> (value: Float, differential: (Parameter) -> Float) {
    return (x, { $0.x })
  }
 }

 extension Parameter {
-  func squared() -> Tracked<Float> {
+  func squared() -> Float {
    return x * x
  }

-  static func squared(p: Parameter) -> Tracked<Float> {
+  static func squared(p: Parameter) -> Float {
    return p.x * p.x
  }

-  func multiplied(with other: Tracked<Float>) -> Tracked<Float> {
+  func multiplied(with other: Float) -> Float {
    return x * other
  }

-  static func * (_ a: Parameter, _ b: Parameter) -> Tracked<Float> {
+  static func * (_ a: Parameter, _ b: Parameter) -> Float {
    return a.x * b.x
  }
 }

 extension Parameter : Differentiable, AdditiveArithmetic {
  typealias TangentVector = Parameter
-  typealias Scalar = Tracked<Float>
+  typealias Scalar = Float
  typealias Shape = ()
-  init(repeating repeatedValue: Tracked<Float>, shape: ()) {
+  init(repeating repeatedValue: Float, shape: ()) {
    self.init(x: repeatedValue)
  }
  static func + (lhs: Parameter, rhs: Parameter) -> Parameter {
@@ -67,37 +67,185 @@ extension Parameter : Differentiable, AdditiveArithmetic {
  static var zero: Parameter { return Parameter(x: 0) }
 }

-MethodTests.testWithLeakChecking(
+MethodTests.test(
  "instance method with generated adjoint, called from differentiated func"
 ) {
-  func f(_ p: Parameter) -> Tracked<Float> {
+  func f(_ p: Parameter) -> Float {
    return 100 * p.squared()
  }
  expectEqual(Parameter(x: 4 * 100), gradient(at: Parameter(x: 2), of: f))
  expectEqual(Parameter(x: 40 * 100), gradient(at: Parameter(x: 20), of: f))
 }

+MethodTests.test(
+  "instance method with generated adjoint, differentiated directly"
+) {
+  // This is our current syntax for taking gradients of instance methods
+  // directly. If/when we develop nicer syntax for this, change this test.
+  func g(p: Parameter) -> Float { p.squared() }
+  expectEqual(Parameter(x: 4), gradient(at: Parameter(x: 2), of: g))
+  expectEqual(Parameter(x: 40), gradient(at: Parameter(x: 20), of: g))
+}
+
+MethodTests.test("instance method with generated adjoint, wrt only self") {
+  func f(_ p: Parameter) -> Float {
+    return 100 * p.multiplied(with: 200)
+  }
+  expectEqual(Parameter(x: 100 * 200), gradient(at: Parameter(x: 1), of: f))
+  expectEqual(Parameter(x: 100 * 200), gradient(at: Parameter(x: 2), of: f))
+}
+
+MethodTests.test("instance method with generated adjoint, wrt only non-self") {
+  func f(_ other: Float) -> Float {
+    return 100 * Parameter(x: 200).multiplied(with: other)
+  }
+  expectEqual(100 * 200, gradient(at: 1, of: f))
+  expectEqual(100 * 200, gradient(at: 2, of: f))
+}
+
+MethodTests.test(
+  "instance method with generated adjoint, wrt self and non-self"
+) {
+  expectEqual(
+    (Parameter(x: 100), 200), gradient(at: Parameter(x: 200), 100) { $0.multiplied(with: $1) })
+  expectEqual(
+    (Parameter(x: 200), 100), gradient(at: Parameter(x: 100), 200) { $0.multiplied(with: $1) })
+}
+
+MethodTests.test(
+  "static method with generated adjoint, called from differentiated func"
+) {
+  func f(_ p: Parameter) -> Float {
+    return 100 * Parameter.squared(p: p)
+  }
+  expectEqual(Parameter(x: 4 * 100), gradient(at: Parameter(x: 2), of: f))
+  expectEqual(Parameter(x: 40 * 100), gradient(at: Parameter(x: 20), of: f))
+}
+
+MethodTests.test(
+  "static method with generated adjoint, differentiated directly"
+) {
+  expectEqual(Parameter(x: 4), gradient(at: Parameter(x: 2), of: Parameter.squared))
+  expectEqual(Parameter(x: 40), gradient(at: Parameter(x: 20), of: Parameter.squared))
+}
+
+MethodTests.test("static method with generated adjoint, wrt only first param") {
+  func f(_ p: Parameter) -> Float {
+    return 100 * (p * Parameter(x: 200))
+  }
+  expectEqual(Parameter(x: 100 * 200), gradient(at: Parameter(x: 1), of: f))
+  expectEqual(Parameter(x: 100 * 200), gradient(at: Parameter(x: 2), of: f))
+}
+
+MethodTests.test("static method with generated adjoint, wrt only second param") {
+  func f(_ p: Parameter) -> Float {
+    return 100 * (Parameter(x: 200) * p)
+  }
+  expectEqual(Parameter(x: 100 * 200), gradient(at: Parameter(x: 1), of: f))
+  expectEqual(Parameter(x: 100 * 200), gradient(at: Parameter(x: 2), of: f))
+}
+
+MethodTests.test("static method with generated adjoint, wrt all params") {
+  func g(a: Parameter, b: Parameter) -> Float { a * b }
+  expectEqual((Parameter(x: 100), Parameter(x: 200)),
+              gradient(at: Parameter(x: 200), Parameter(x: 100), of: g))
+  expectEqual((Parameter(x: 200), Parameter(x: 100)),
+              gradient(at: Parameter(x: 100), Parameter(x: 200), of: g))
+}
+
+
+/* Temporary disabled until https://github.com/swiftlang/swift/issues/84840 is fixed
+   We cannot use `Tracked<T>` :(
+struct ParameterTracked : Equatable {
+  private let storedX: Tracked<Float>
+  @differentiable(reverse, wrt: (self))
+  var x: Tracked<Float> {
+      return storedX
+  }
+
+  init(x: Tracked<Float>) {
+    storedX = x
+  }
+
+  @derivative(of: x)
+  func vjpX() -> (value: Tracked<Float>, pullback: (Tracked<Float>) -> ParameterTracked) {
+    return (x, { dx in ParameterTracked(x: dx) } )
+  }
+
+  @derivative(of: x)
+  func jvpX() -> (value: Tracked<Float>, differential: (ParameterTracked) -> Tracked<Float>) {
+    return (x, { $0.x })
+  }
+}
+
+extension ParameterTracked {
+  func squared() -> Tracked<Float> {
+    return x * x
+  }
+
+  static func squared(p: ParameterTracked) -> Tracked<Float> {
+    return p.x * p.x
+  }
+
+  func multiplied(with other: Tracked<Float>) -> Tracked<Float> {
+    return x * other
+  }
+
+  static func * (_ a: ParameterTracked, _ b: ParameterTracked) -> Tracked<Float> {
+    return a.x * b.x
+  }
+}
+
+extension ParameterTracked : Differentiable, AdditiveArithmetic {
+  typealias TangentVector = ParameterTracked
+  typealias Scalar = Tracked<Float>
+  typealias Shape = ()
+  init(repeating repeatedValue: Tracked<Float>, shape: ()) {
+    self.init(x: repeatedValue)
+  }
+  static func + (lhs: ParameterTracked, rhs: ParameterTracked) -> ParameterTracked {
+    return ParameterTracked(x: lhs.x + rhs.x)
+  }
+  static func - (lhs: ParameterTracked, rhs: ParameterTracked) -> ParameterTracked {
+    return ParameterTracked(x: lhs.x - rhs.x)
+  }
+  static func * (lhs: Scalar, rhs: ParameterTracked) -> ParameterTracked {
+    return ParameterTracked(x: lhs * rhs.x)
+  }
+  static var zero: ParameterTracked { return ParameterTracked(x: 0) }
+}
+
+MethodTests.testWithLeakChecking(
+  "instance method with generated adjoint, called from differentiated func"
+) {
+  func f(_ p: ParameterTracked) -> Tracked<Float> {
+    return 100 * p.squared()
+  }
+  expectEqual(ParameterTracked(x: 4 * 100), gradient(at: ParameterTracked(x: 2), of: f))
+  expectEqual(ParameterTracked(x: 40 * 100), gradient(at: ParameterTracked(x: 20), of: f))
+}
+
 MethodTests.testWithLeakChecking(
  "instance method with generated adjoint, differentiated directly"
 ) {
  // This is our current syntax for taking gradients of instance methods
  // directly. If/when we develop nicer syntax for this, change this test.
-  func g(p: Parameter) -> Tracked<Float> { p.squared() }
-  expectEqual(Parameter(x: 4), gradient(at: Parameter(x: 2), of: g))
-  expectEqual(Parameter(x: 40), gradient(at: Parameter(x: 20), of: g))
+  func g(p: ParameterTracked) -> Tracked<Float> { p.squared() }
+  expectEqual(ParameterTracked(x: 4), gradient(at: ParameterTracked(x: 2), of: g))
+  expectEqual(ParameterTracked(x: 40), gradient(at: ParameterTracked(x: 20), of: g))
 }

 MethodTests.testWithLeakChecking("instance method with generated adjoint, wrt only self") {
-  func f(_ p: Parameter) -> Tracked<Float> {
+  func f(_ p: ParameterTracked) -> Tracked<Float> {
    return 100 * p.multiplied(with: 200)
  }
-  expectEqual(Parameter(x: 100 * 200), gradient(at: Parameter(x: 1), of: f))
-  expectEqual(Parameter(x: 100 * 200), gradient(at: Parameter(x: 2), of: f))
+  expectEqual(ParameterTracked(x: 100 * 200), gradient(at: ParameterTracked(x: 1), of: f))
+  expectEqual(ParameterTracked(x: 100 * 200), gradient(at: ParameterTracked(x: 2), of: f))
 }

 MethodTests.testWithLeakChecking("instance method with generated adjoint, wrt only non-self") {
  func f(_ other: Tracked<Float>) -> Tracked<Float> {
-    return 100 * Parameter(x: 200).multiplied(with: other)
+    return 100 * ParameterTracked(x: 200).multiplied(with: other)
  }
  expectEqual(100 * 200, gradient(at: 1, of: f))
  expectEqual(100 * 200, gradient(at: 2, of: f))
@@ -107,51 +255,52 @@ MethodTests.testWithLeakChecking(
  "instance method with generated adjoint, wrt self and non-self"
 ) {
  expectEqual(
-    (Parameter(x: 100), 200), gradient(at: Parameter(x: 200), 100) { $0.multiplied(with: $1) })
+    (ParameterTracked(x: 100), 200), gradient(at: ParameterTracked(x: 200), 100) { $0.multiplied(with: $1) })
  expectEqual(
-    (Parameter(x: 200), 100), gradient(at: Parameter(x: 100), 200) { $0.multiplied(with: $1) })
+    (ParameterTracked(x: 200), 100), gradient(at: ParameterTracked(x: 100), 200) { $0.multiplied(with: $1) })
 }

 MethodTests.testWithLeakChecking(
  "static method with generated adjoint, called from differentiated func"
 ) {
-  func f(_ p: Parameter) -> Tracked<Float> {
-    return 100 * Parameter.squared(p: p)
+  func f(_ p: ParameterTracked) -> Tracked<Float> {
+    return 100 * ParameterTracked.squared(p: p)
  }
-  expectEqual(Parameter(x: 4 * 100), gradient(at: Parameter(x: 2), of: f))
-  expectEqual(Parameter(x: 40 * 100), gradient(at: Parameter(x: 20), of: f))
+  expectEqual(ParameterTracked(x: 4 * 100), gradient(at: ParameterTracked(x: 2), of: f))
+  expectEqual(ParameterTracked(x: 40 * 100), gradient(at: ParameterTracked(x: 20), of: f))
 }

 MethodTests.testWithLeakChecking(
  "static method with generated adjoint, differentiated directly"
 ) {
-  expectEqual(Parameter(x: 4), gradient(at: Parameter(x: 2), of: Parameter.squared))
-  expectEqual(Parameter(x: 40), gradient(at: Parameter(x: 20), of: Parameter.squared))
+  expectEqual(ParameterTracked(x: 4), gradient(at: ParameterTracked(x: 2), of: ParameterTracked.squared))
+  expectEqual(ParameterTracked(x: 40), gradient(at: ParameterTracked(x: 20), of: ParameterTracked.squared))
 }

 MethodTests.testWithLeakChecking("static method with generated adjoint, wrt only first param") {
-  func f(_ p: Parameter) -> Tracked<Float> {
-    return 100 * (p * Parameter(x: 200))
+  func f(_ p: ParameterTracked) -> Tracked<Float> {
+    return 100 * (p * ParameterTracked(x: 200))
  }
-  expectEqual(Parameter(x: 100 * 200), gradient(at: Parameter(x: 1), of: f))
-  expectEqual(Parameter(x: 100 * 200), gradient(at: Parameter(x: 2), of: f))
+  expectEqual(ParameterTracked(x: 100 * 200), gradient(at: ParameterTracked(x: 1), of: f))
+  expectEqual(ParameterTracked(x: 100 * 200), gradient(at: ParameterTracked(x: 2), of: f))
 }

 MethodTests.testWithLeakChecking("static method with generated adjoint, wrt only second param") {
-  func f(_ p: Parameter) -> Tracked<Float> {
-    return 100 * (Parameter(x: 200) * p)
+  func f(_ p: ParameterTracked) -> Tracked<Float> {
+    return 100 * (ParameterTracked(x: 200) * p)
  }
-  expectEqual(Parameter(x: 100 * 200), gradient(at: Parameter(x: 1), of: f))
-  expectEqual(Parameter(x: 100 * 200), gradient(at: Parameter(x: 2), of: f))
+  expectEqual(ParameterTracked(x: 100 * 200), gradient(at: ParameterTracked(x: 1), of: f))
+  expectEqual(ParameterTracked(x: 100 * 200), gradient(at: ParameterTracked(x: 2), of: f))
 }

 MethodTests.testWithLeakChecking("static method with generated adjoint, wrt all params") {
-  func g(a: Parameter, b: Parameter) -> Tracked<Float> { a * b }
-  expectEqual((Parameter(x: 100), Parameter(x: 200)),
-              gradient(at: Parameter(x: 200), Parameter(x: 100), of: g))
-  expectEqual((Parameter(x: 200), Parameter(x: 100)),
-              gradient(at: Parameter(x: 100), Parameter(x: 200), of: g))
+  func g(a: ParameterTracked, b: ParameterTracked) -> Tracked<Float> { a * b }
+  expectEqual((ParameterTracked(x: 100), ParameterTracked(x: 200)),
+              gradient(at: ParameterTracked(x: 200), ParameterTracked(x: 100), of: g))
+  expectEqual((ParameterTracked(x: 200), ParameterTracked(x: 100)),
+              gradient(at: ParameterTracked(x: 100), ParameterTracked(x: 200), of: g))
 }
+*/

 // ==== Tests with custom adjoint ====

@@ -174,27 +323,27 @@ struct DiffWrtSelf : Differentiable {
 }

 struct CustomParameter : Equatable {
-  let storedX: Tracked<Float>
+  let storedX: Float
  @differentiable(reverse, wrt: (self))
-  var x: Tracked<Float> {
+  var x: Float {
      return storedX
  }

-  init(x: Tracked<Float>) {
+  init(x: Float) {
    storedX = x
  }

  @derivative(of: x)
-  func vjpX() -> (value: Tracked<Float>, pullback: (Tracked<Float>) -> CustomParameter) {
+  func vjpX() -> (value: Float, pullback: (Float) -> CustomParameter) {
    return (x, { dx in CustomParameter(x: dx) })
  }
 }

 extension CustomParameter : Differentiable, AdditiveArithmetic {
  typealias TangentVector = CustomParameter
-  typealias Scalar = Tracked<Float>
+  typealias Scalar = Float
  typealias Shape = ()
-  init(repeating repeatedValue: Tracked<Float>, shape: ()) {
+  init(repeating repeatedValue: Float, shape: ()) {
    self.init(x: repeatedValue)
  }
  static func + (lhs: CustomParameter, rhs: CustomParameter) -> CustomParameter {
@@ -209,38 +358,256 @@ extension CustomParameter : Differentiable, AdditiveArithmetic {
  static var zero: CustomParameter { return CustomParameter(x: 0) }
 }

-extension Tracked where T : FloatingPoint {
-  func clamped(to limits: ClosedRange<Tracked<T>>) -> Tracked<T> {
+extension Float {
+  func clamped(to limits: ClosedRange<Float>) -> Float {
    return min(max(self, limits.lowerBound), limits.upperBound)
  }
 }

 extension CustomParameter {
  @differentiable(reverse, wrt: (self))
-  func squared() -> Tracked<Float> {
+  func squared() -> Float {
    return x * x
  }

  @derivative(of: squared)
-  func dSquared() -> (value: Tracked<Float>, pullback: (Tracked<Float>) -> CustomParameter) {
+  func dSquared() -> (value: Float, pullback: (Float) -> CustomParameter) {
    return (squared(), { [x] v in CustomParameter(x: (2 * x).clamped(to: -10.0...10.0) * v) })
  }

  @differentiable(reverse)
-  static func squared(p: CustomParameter) -> Tracked<Float> {
+  static func squared(p: CustomParameter) -> Float {
    return p.x * p.x
  }

  @derivative(of: squared)
  static func dSquared(
    _ p: CustomParameter
-  ) -> (value: Tracked<Float>, pullback: (Tracked<Float>) -> CustomParameter) {
+  ) -> (value: Float, pullback: (Float) -> CustomParameter) {
    return (p.x * p.x, { v in CustomParameter(x: (2 * p.x).clamped(to: -10.0...10.0) * v) })
  }

  // There is currently no way to define multiple custom VJPs wrt different
  // parameters on the same func, so we define a copy of this func per adjoint.

+  @differentiable(reverse, wrt: (self, other))
+  func multiplied(with other: Float) -> Float {
+    return x * other
+  }
+
+  @differentiable(reverse, wrt: (other))
+  func multiplied_constSelf(with other: Float) -> Float {
+    return x * other
+  }
+
+  @differentiable(reverse, wrt: (self))
+  func multiplied_constOther(with other: Float) -> Float {
+    return x * other
+  }
+
+  @derivative(of: multiplied)
+  func dMultiplied_wrtAll(
+    with other: Float
+  ) -> (value: Float, pullback: (Float) -> (CustomParameter, Float)) {
+    return (multiplied(with: other),
+      { [x] v in (CustomParameter(x: other.clamped(to: -10.0...10.0) * v),
+                  x.clamped(to: -10.0...10.0) * v) })
+  }
+
+  @derivative(of: multiplied_constSelf, wrt: other)
+  func dMultiplied_wrtOther(
+    with other: Float
+  ) -> (value: Float, pullback: (Float) -> Float) {
+    let (r, pb) = dMultiplied_wrtAll(with: other)
+    return (r, { v in pb(v).1 })
+  }
+
+  @derivative(of: multiplied_constOther, wrt: self)
+  func dMultiplied_wrtSelf(
+    with other: Float
+  ) -> (value: Float, pullback: (Float) -> CustomParameter) {
+    let (r, pb) = dMultiplied_wrtAll(with: other)
+    return (r, { v in pb(v).0 })
+  }
+
+  @differentiable(reverse)
+  static func multiply(_ lhs: CustomParameter, _ rhs: CustomParameter)
+      -> Float {
+    return lhs.x * rhs.x
+  }
+
+  @differentiable(reverse, wrt: (rhs))
+  static func multiply_constLhs(_ lhs: CustomParameter, _ rhs: CustomParameter) -> Float {
+    return lhs.x * rhs.x
+  }
+
+  @derivative(of: multiply)
+  static func dMultiply_wrtAll(_ lhs: CustomParameter,_ rhs: CustomParameter)
+      -> (value: Float, pullback: (Float) -> (CustomParameter, CustomParameter)) {
+    let result = multiply(lhs, rhs)
+    return (result, { v in (CustomParameter(x: rhs.x.clamped(to: -10.0...10.0) * v),
+                            CustomParameter(x: lhs.x.clamped(to: -10.0...10.0) * v)) })
+  }
+
+  @derivative(of: multiply_constLhs, wrt: rhs)
+  static func dMultiply_wrtRhs(_ lhs: CustomParameter, _ rhs: CustomParameter)
+      -> (value: Float, pullback: (Float) -> CustomParameter) {
+    let (r, pb) = dMultiply_wrtAll(lhs, rhs)
+    return (r, { v in pb(v).1 })
+  }
+}
+
+MethodTests.test(
+  "instance method with custom adjoint, called from differentiated func"
+) {
+  func f(_ p: CustomParameter) -> Float {
+    return 100 * p.squared()
+  }
+  expectEqual(CustomParameter(x: 4 * 100), gradient(at: CustomParameter(x: 2), of: f))
+  expectEqual(CustomParameter(x: 10 * 100), gradient(at: CustomParameter(x: 20), of: f))
+}
+
+MethodTests.test("instance method with generated adjoint, differentiated directly") {
+  // This is our current syntax for taking gradients of instance methods
+  // directly. If/when we develop nicer syntax for this, change this test.
+  func g(p: CustomParameter) -> Float { p.squared() }
+  expectEqual(CustomParameter(x: 4), gradient(at: CustomParameter(x: 2), of: g))
+  expectEqual(CustomParameter(x: 10), gradient(at: CustomParameter(x: 20), of: g))
+}
+
+MethodTests.test("static method with custom adjoint, called from differentiated func") {
+  func f(_ p: CustomParameter) -> Float {
+    return 100 * CustomParameter.squared(p: p)
+  }
+  expectEqual(CustomParameter(x: 4 * 100), gradient(at: CustomParameter(x: 2), of: f))
+  expectEqual(CustomParameter(x: 10 * 100), gradient(at: CustomParameter(x: 20), of: f))
+}
+
+MethodTests.test("static method with custom adjoint, differentiated directly") {
+  expectEqual(
+    CustomParameter(x: 4), gradient(at: CustomParameter(x: 2), of: CustomParameter.squared))
+  expectEqual(
+    CustomParameter(x: 10), gradient(at: CustomParameter(x: 20), of: CustomParameter.squared))
+}
+
+MethodTests.test("instance method with custom adjoint, wrt only self") {
+  func f(_ p: CustomParameter) -> Float {
+    return 100 * p.multiplied_constOther(with: 200)
+  }
+  expectEqual(CustomParameter(x: 100 * 10), gradient(at: CustomParameter(x: 1), of: f))
+  expectEqual(CustomParameter(x: 100 * 10), gradient(at: CustomParameter(x: 2), of: f))
+}
+
+MethodTests.test("instance method with custom adjoint, wrt only non-self") {
+  func f(_ other: Float) -> Float {
+    return 100 * CustomParameter(x: 200).multiplied_constSelf(with: other)
+  }
+  expectEqual(100 * 10, gradient(at: 1, of: f))
+  expectEqual(100 * 10, gradient(at: 2, of: f))
+}
+
+MethodTests.test("instance method with custom adjoint, wrt self and non-self") {
+  func g(p: CustomParameter, o: Float) -> Float { p.multiplied(with: o) }
+  expectEqual((CustomParameter(x: 5), 10), gradient(at: CustomParameter(x: 100), 5, of: g))
+  expectEqual((CustomParameter(x: 10), 5), gradient(at: CustomParameter(x: 5), 100, of: g))
+}
+
+MethodTests.test("static method with custom adjoint, wrt only lhs") {
+  func f(_ p: CustomParameter) -> Float {
+    return 100 * CustomParameter.multiply_constLhs(CustomParameter(x: 200), p)
+  }
+  expectEqual(CustomParameter(x: 100 * 10), gradient(at: CustomParameter(x: 1), of: f))
+  expectEqual(CustomParameter(x: 100 * 10), gradient(at: CustomParameter(x: 2), of: f))
+}
+
+MethodTests.test("static method with custom adjoint, wrt only rhs") {
+  func f(_ p: CustomParameter) -> Float {
+    return 100 * CustomParameter.multiply_constLhs(CustomParameter(x: 200), p)
+  }
+  expectEqual(CustomParameter(x: 100 * 10), gradient(at: CustomParameter(x: 1), of: f))
+  expectEqual(CustomParameter(x: 100 * 10), gradient(at: CustomParameter(x: 2), of: f))
+}
+
+MethodTests.test("static method with custom adjoint, wrt all") {
+  func f(_ a: CustomParameter, _ b: CustomParameter) -> Float {
+    return CustomParameter.multiply(a, b)
+  }
+  expectEqual((CustomParameter(x: 5), CustomParameter(x: 10)),
+              gradient(at: CustomParameter(x: 100), CustomParameter(x: 5), of: f))
+  expectEqual((CustomParameter(x: 10), CustomParameter(x: 5)),
+              gradient(at: CustomParameter(x: 5), CustomParameter(x: 100), of: f))
+}
+
+/* Temporary disabled until https://github.com/swiftlang/swift/issues/84840 is fixed
+   We cannot use `Tracked<T>` :(
+struct CustomParameterTracked : Equatable {
+  let storedX: Tracked<Float>
+  @differentiable(reverse, wrt: (self))
+  var x: Tracked<Float> {
+      return storedX
+  }
+
+  init(x: Tracked<Float>) {
+    storedX = x
+  }
+
+  @derivative(of: x)
+  func vjpX() -> (value: Tracked<Float>, pullback: (Tracked<Float>) -> CustomParameterTracked) {
+    return (x, { dx in CustomParameterTracked(x: dx) })
+  }
+}
+
+extension CustomParameterTracked : Differentiable, AdditiveArithmetic {
+  typealias TangentVector = CustomParameterTracked
+  typealias Scalar = Tracked<Float>
+  typealias Shape = ()
+  init(repeating repeatedValue: Tracked<Float>, shape: ()) {
+    self.init(x: repeatedValue)
+  }
+  static func + (lhs: CustomParameterTracked, rhs: CustomParameterTracked) -> CustomParameterTracked {
+    return CustomParameterTracked(x: lhs.x + rhs.x)
+  }
+  static func - (lhs: CustomParameterTracked, rhs: CustomParameterTracked) -> CustomParameterTracked {
+    return CustomParameterTracked(x: lhs.x - rhs.x)
+  }
+  static func * (lhs: Scalar, rhs: CustomParameterTracked) -> CustomParameterTracked {
+    return CustomParameterTracked(x: lhs * rhs.x)
+  }
+  static var zero: CustomParameterTracked { return CustomParameterTracked(x: 0) }
+}
+
+extension Tracked where T : FloatingPoint {
+  func clamped(to limits: ClosedRange<Tracked<T>>) -> Tracked<T> {
+    return min(max(self, limits.lowerBound), limits.upperBound)
+  }
+}
+
+extension CustomParameterTracked {
+  @differentiable(reverse, wrt: (self))
+  func squared() -> Tracked<Float> {
+    return x * x
+  }
+
+  @derivative(of: squared)
+  func dSquared() -> (value: Tracked<Float>, pullback: (Tracked<Float>) -> CustomParameterTracked) {
+    return (squared(), { [x] v in CustomParameterTracked(x: (2 * x).clamped(to: -10.0...10.0) * v) })
+  }
+
+  @differentiable(reverse)
+  static func squared(p: CustomParameterTracked) -> Tracked<Float> {
+    return p.x * p.x
+  }
+
+  @derivative(of: squared)
+  static func dSquared(
+    _ p: CustomParameterTracked
+  ) -> (value: Tracked<Float>, pullback: (Tracked<Float>) -> CustomParameterTracked) {
+    return (p.x * p.x, { v in CustomParameterTracked(x: (2 * p.x).clamped(to: -10.0...10.0) * v) })
+  }
+
+  // There is currently no way to define multiple custom VJPs wrt different
+  // parameters on the same func, so we define a copy of this func per adjoint.
+
  @differentiable(reverse, wrt: (self, other))
  func multiplied(with other: Tracked<Float>) -> Tracked<Float> {
    return x * other
@@ -259,9 +626,9 @@ extension CustomParameter {
  @derivative(of: multiplied)
  func dMultiplied_wrtAll(
    with other: Tracked<Float>
-  ) -> (value: Tracked<Float>, pullback: (Tracked<Float>) -> (CustomParameter, Tracked<Float>)) {
+  ) -> (value: Tracked<Float>, pullback: (Tracked<Float>) -> (CustomParameterTracked, Tracked<Float>)) {
    return (multiplied(with: other),
-      { [x] v in (CustomParameter(x: other.clamped(to: -10.0...10.0) * v),
+      { [x] v in (CustomParameterTracked(x: other.clamped(to: -10.0...10.0) * v),
                  x.clamped(to: -10.0...10.0) * v) })
  }

@@ -276,33 +643,33 @@ extension CustomParameter {
  @derivative(of: multiplied_constOther, wrt: self)
  func dMultiplied_wrtSelf(
    with other: Tracked<Float>
-  ) -> (value: Tracked<Float>, pullback: (Tracked<Float>) -> CustomParameter) {
+  ) -> (value: Tracked<Float>, pullback: (Tracked<Float>) -> CustomParameterTracked) {
    let (r, pb) = dMultiplied_wrtAll(with: other)
    return (r, { v in pb(v).0 })
  }

  @differentiable(reverse)
-  static func multiply(_ lhs: CustomParameter, _ rhs: CustomParameter)
+  static func multiply(_ lhs: CustomParameterTracked, _ rhs: CustomParameterTracked)
      -> Tracked<Float> {
    return lhs.x * rhs.x
  }

  @differentiable(reverse, wrt: (rhs))
-  static func multiply_constLhs(_ lhs: CustomParameter, _ rhs: CustomParameter) -> Tracked<Float> {
+  static func multiply_constLhs(_ lhs: CustomParameterTracked, _ rhs: CustomParameterTracked) -> Tracked<Float> {
    return lhs.x * rhs.x
  }

  @derivative(of: multiply)
-  static func dMultiply_wrtAll(_ lhs: CustomParameter,_ rhs: CustomParameter)
-      -> (value: Tracked<Float>, pullback: (Tracked<Float>) -> (CustomParameter, CustomParameter)) {
+  static func dMultiply_wrtAll(_ lhs: CustomParameterTracked,_ rhs: CustomParameterTracked)
+      -> (value: Tracked<Float>, pullback: (Tracked<Float>) -> (CustomParameterTracked, CustomParameterTracked)) {
    let result = multiply(lhs, rhs)
-    return (result, { v in (CustomParameter(x: rhs.x.clamped(to: -10.0...10.0) * v),
-                            CustomParameter(x: lhs.x.clamped(to: -10.0...10.0) * v)) })
+    return (result, { v in (CustomParameterTracked(x: rhs.x.clamped(to: -10.0...10.0) * v),
+                            CustomParameterTracked(x: lhs.x.clamped(to: -10.0...10.0) * v)) })
  }

  @derivative(of: multiply_constLhs, wrt: rhs)
-  static func dMultiply_wrtRhs(_ lhs: CustomParameter, _ rhs: CustomParameter)
-      -> (value: Tracked<Float>, pullback: (Tracked<Float>) -> CustomParameter) {
+  static func dMultiply_wrtRhs(_ lhs: CustomParameterTracked, _ rhs: CustomParameterTracked)
+      -> (value: Tracked<Float>, pullback: (Tracked<Float>) -> CustomParameterTracked) {
    let (r, pb) = dMultiply_wrtAll(lhs, rhs)
    return (r, { v in pb(v).1 })
  }
@@ -311,82 +678,83 @@ extension CustomParameter {
 MethodTests.testWithLeakChecking(
  "instance method with custom adjoint, called from differentiated func"
 ) {
-  func f(_ p: CustomParameter) -> Tracked<Float> {
+  func f(_ p: CustomParameterTracked) -> Tracked<Float> {
    return 100 * p.squared()
  }
-  expectEqual(CustomParameter(x: 4 * 100), gradient(at: CustomParameter(x: 2), of: f))
-  expectEqual(CustomParameter(x: 10 * 100), gradient(at: CustomParameter(x: 20), of: f))
+  expectEqual(CustomParameterTracked(x: 4 * 100), gradient(at: CustomParameterTracked(x: 2), of: f))
+  expectEqual(CustomParameterTracked(x: 10 * 100), gradient(at: CustomParameterTracked(x: 20), of: f))
 }

 MethodTests.testWithLeakChecking("instance method with generated adjoint, differentiated directly") {
  // This is our current syntax for taking gradients of instance methods
  // directly. If/when we develop nicer syntax for this, change this test.
-  func g(p: CustomParameter) -> Tracked<Float> { p.squared() }
-  expectEqual(CustomParameter(x: 4), gradient(at: CustomParameter(x: 2), of: g))
-  expectEqual(CustomParameter(x: 10), gradient(at: CustomParameter(x: 20), of: g))
+  func g(p: CustomParameterTracked) -> Tracked<Float> { p.squared() }
+  expectEqual(CustomParameterTracked(x: 4), gradient(at: CustomParameterTracked(x: 2), of: g))
+  expectEqual(CustomParameterTracked(x: 10), gradient(at: CustomParameterTracked(x: 20), of: g))
 }

 MethodTests.testWithLeakChecking("static method with custom adjoint, called from differentiated func") {
-  func f(_ p: CustomParameter) -> Tracked<Float> {
-    return 100 * CustomParameter.squared(p: p)
+  func f(_ p: CustomParameterTracked) -> Tracked<Float> {
+    return 100 * CustomParameterTracked.squared(p: p)
  }
-  expectEqual(CustomParameter(x: 4 * 100), gradient(at: CustomParameter(x: 2), of: f))
-  expectEqual(CustomParameter(x: 10 * 100), gradient(at: CustomParameter(x: 20), of: f))
+  expectEqual(CustomParameterTracked(x: 4 * 100), gradient(at: CustomParameterTracked(x: 2), of: f))
+  expectEqual(CustomParameterTracked(x: 10 * 100), gradient(at: CustomParameterTracked(x: 20), of: f))
 }

 MethodTests.testWithLeakChecking("static method with custom adjoint, differentiated directly") {
  expectEqual(
-    CustomParameter(x: 4), gradient(at: CustomParameter(x: 2), of: CustomParameter.squared))
+    CustomParameterTracked(x: 4), gradient(at: CustomParameterTracked(x: 2), of: CustomParameterTracked.squared))
  expectEqual(
-    CustomParameter(x: 10), gradient(at: CustomParameter(x: 20), of: CustomParameter.squared))
+    CustomParameterTracked(x: 10), gradient(at: CustomParameterTracked(x: 20), of: CustomParameterTracked.squared))
 }

 MethodTests.testWithLeakChecking("instance method with custom adjoint, wrt only self") {
-  func f(_ p: CustomParameter) -> Tracked<Float> {
+  func f(_ p: CustomParameterTracked) -> Tracked<Float> {
    return 100 * p.multiplied_constOther(with: 200)
  }
-  expectEqual(CustomParameter(x: 100 * 10), gradient(at: CustomParameter(x: 1), of: f))
-  expectEqual(CustomParameter(x: 100 * 10), gradient(at: CustomParameter(x: 2), of: f))
+  expectEqual(CustomParameterTracked(x: 100 * 10), gradient(at: CustomParameterTracked(x: 1), of: f))
+  expectEqual(CustomParameterTracked(x: 100 * 10), gradient(at: CustomParameterTracked(x: 2), of: f))
 }

 MethodTests.testWithLeakChecking("instance method with custom adjoint, wrt only non-self") {
  func f(_ other: Tracked<Float>) -> Tracked<Float> {
-    return 100 * CustomParameter(x: 200).multiplied_constSelf(with: other)
+    return 100 * CustomParameterTracked(x: 200).multiplied_constSelf(with: other)
  }
  expectEqual(100 * 10, gradient(at: 1, of: f))
  expectEqual(100 * 10, gradient(at: 2, of: f))
 }

 MethodTests.testWithLeakChecking("instance method with custom adjoint, wrt self and non-self") {
-  func g(p: CustomParameter, o: Tracked<Float>) -> Tracked<Float> { p.multiplied(with: o) }
-  expectEqual((CustomParameter(x: 5), 10), gradient(at: CustomParameter(x: 100), 5, of: g))
-  expectEqual((CustomParameter(x: 10), 5), gradient(at: CustomParameter(x: 5), 100, of: g))
+  func g(p: CustomParameterTracked, o: Tracked<Float>) -> Tracked<Float> { p.multiplied(with: o) }
+  expectEqual((CustomParameterTracked(x: 5), 10), gradient(at: CustomParameterTracked(x: 100), 5, of: g))
+  expectEqual((CustomParameterTracked(x: 10), 5), gradient(at: CustomParameterTracked(x: 5), 100, of: g))
 }

 MethodTests.testWithLeakChecking("static method with custom adjoint, wrt only lhs") {
-  func f(_ p: CustomParameter) -> Tracked<Float> {
-    return 100 * CustomParameter.multiply_constLhs(CustomParameter(x: 200), p)
+  func f(_ p: CustomParameterTracked) -> Tracked<Float> {
+    return 100 * CustomParameterTracked.multiply_constLhs(CustomParameterTracked(x: 200), p)
  }
-  expectEqual(CustomParameter(x: 100 * 10), gradient(at: CustomParameter(x: 1), of: f))
-  expectEqual(CustomParameter(x: 100 * 10), gradient(at: CustomParameter(x: 2), of: f))
+  expectEqual(CustomParameterTracked(x: 100 * 10), gradient(at: CustomParameterTracked(x: 1), of: f))
+  expectEqual(CustomParameterTracked(x: 100 * 10), gradient(at: CustomParameterTracked(x: 2), of: f))
 }

 MethodTests.testWithLeakChecking("static method with custom adjoint, wrt only rhs") {
-  func f(_ p: CustomParameter) -> Tracked<Float> {
-    return 100 * CustomParameter.multiply_constLhs(CustomParameter(x: 200), p)
+  func f(_ p: CustomParameterTracked) -> Tracked<Float> {
+    return 100 * CustomParameterTracked.multiply_constLhs(CustomParameterTracked(x: 200), p)
  }
-  expectEqual(CustomParameter(x: 100 * 10), gradient(at: CustomParameter(x: 1), of: f))
-  expectEqual(CustomParameter(x: 100 * 10), gradient(at: CustomParameter(x: 2), of: f))
+  expectEqual(CustomParameterTracked(x: 100 * 10), gradient(at: CustomParameterTracked(x: 1), of: f))
+  expectEqual(CustomParameterTracked(x: 100 * 10), gradient(at: CustomParameterTracked(x: 2), of: f))
 }

 MethodTests.testWithLeakChecking("static method with custom adjoint, wrt all") {
-  func f(_ a: CustomParameter, _ b: CustomParameter) -> Tracked<Float> {
-    return CustomParameter.multiply(a, b)
+  func f(_ a: CustomParameterTracked, _ b: CustomParameterTracked) -> Tracked<Float> {
+    return CustomParameterTracked.multiply(a, b)
  }
-  expectEqual((CustomParameter(x: 5), CustomParameter(x: 10)),
-              gradient(at: CustomParameter(x: 100), CustomParameter(x: 5), of: f))
-  expectEqual((CustomParameter(x: 10), CustomParameter(x: 5)),
-              gradient(at: CustomParameter(x: 5), CustomParameter(x: 100), of: f))
+  expectEqual((CustomParameterTracked(x: 5), CustomParameterTracked(x: 10)),
+              gradient(at: CustomParameterTracked(x: 100), CustomParameterTracked(x: 5), of: f))
+  expectEqual((CustomParameterTracked(x: 10), CustomParameterTracked(x: 5)),
+              gradient(at: CustomParameterTracked(x: 5), CustomParameterTracked(x: 100), of: f))
 }
+*/

 runAllTests()
--- a/test/AutoDiff/validation-test/repeated_calls.swift
+++ b/test/AutoDiff/validation-test/repeated_calls.swift
@@ -1,4 +1,4 @@
-// RUN: %target-run-simple-swift
+1// RUN: %target-run-simple-swift
 // REQUIRES: executable_test

 import StdlibUnittest
@@ -6,7 +6,19 @@ import DifferentiationUnittest

 var RepeatedCallsTests = TestSuite("RepeatedCalls")

-RepeatedCallsTests.testWithLeakChecking("Repeat") {
+RepeatedCallsTests.test("Repeat") {
+  func mul2(_ x: Float) -> Float {
+    return 2 * x
+  }
+  func mul4(_ x: Float) -> Float {
+    return mul2(mul2(x))
+  }
+  expectEqual(4, gradient(at: 0, of: mul4))
+}
+
+/* Temporary disabled until https://github.com/swiftlang/swift/issues/84840 is fixed
+   We cannot use `Tracked<T>` :(
+RepeatedCallsTests.testWithLeakChecking("Repeat-Tracked") {
  func mul2(_ x: Tracked<Float>) -> Tracked<Float> {
    return 2 * x
  }
@@ -15,5 +27,6 @@ RepeatedCallsTests.testWithLeakChecking("Repeat") {
  }
  expectEqual(4, gradient(at: 0, of: mul4))
 }
+*/

 runAllTests()
--- a/test/AutoDiff/validation-test/simple_math.swift
+++ b/test/AutoDiff/validation-test/simple_math.swift
@@ -266,6 +266,9 @@ SimpleMathTests.test("TupleMutation") {
 }

 // Tests TF-321.
+
+/* Temporary disabled until https://github.com/swiftlang/swift/issues/84840 is fixed
+   We cannot use `Tracked<T>` :(
 SimpleMathTests.test("TupleNonDifferentiableElements") {
  // TF-964: Test tuple with non-tuple-typed adjoint value.
  func tupleLet(_ x: Tracked<Float>) -> Tracked<Float> {
@@ -309,6 +312,51 @@ SimpleMathTests.test("TupleNonDifferentiableElements") {
  }
  expectEqual((3, 1), valueWithGradient(at: 3, of: wrapper))
 }
+*/
+
+SimpleMathTests.test("TupleNonDifferentiableElementsNotTracked") {
+  // TF-964: Test tuple with non-tuple-typed adjoint value.
+  func tupleLet(_ x: Float) -> Float {
+    let tuple = (2 * x, 1)
+    return tuple.0
+  }
+  expectEqual((8, 2), valueWithGradient(at: 4, of: tupleLet))
+
+  func tupleVar(_ x: Float) -> Float {
+    var tuple = (x, 1)
+    tuple.0 = x
+    tuple.1 = 1
+    return tuple.0
+  }
+  expectEqual((3, 1), valueWithGradient(at: 3, of: tupleVar))
+
+  func nested(_ x: Float) -> Float {
+    // Convoluted function computing `x * x`.
+    var tuple: (Int, (Int, Float), Float) = (1, (1, 0), 0)
+    tuple.0 = 1
+    tuple.1.0 = 1
+    tuple.1.1 = x
+    tuple.2 = x
+    return tuple.1.1 * tuple.2
+  }
+  expectEqual((16, 8), valueWithGradient(at: 4, of: nested))
+
+  struct Wrapper<T> {
+    @differentiable(reverse where T : Differentiable)
+    func baz(_ x: T) -> T {
+      var tuple = (1, 1, x, 1)
+      tuple.0 = 1
+      tuple.2 = x
+      tuple.3 = 1
+      return tuple.2
+    }
+  }
+  func wrapper(_ x: Float) -> Float {
+    let w = Wrapper<Float>()
+    return w.baz(x)
+  }
+  expectEqual((3, 1), valueWithGradient(at: 3, of: wrapper))
+}

 // Tests TF-21.
 SimpleMathTests.test("StructMemberwiseInitializer") {
--- a/test/Constraints/anyhashable_and_operator_filtering.swift
+++ b/test/Constraints/anyhashable_and_operator_filtering.swift
@@ -21,9 +21,10 @@ func test(arr: [any P]) {
  }
 }

+// Make sure that we don't pick a concrete `(AnyHashable, AnyHashable) -> Bool` overload.
+
 // CHECK: sil private [ossa] @$s34anyhashable_and_operator_filtering4test3arrySayAA1P_pG_tFyAaD_pXEfU_
 // CHECK: [[LHS_ARG:%.*]] = alloc_stack $E
 // CHECK: [[RHS_ARG:%.*]] = alloc_stack $E
-// CHECK: function_ref == infix<A>(_:_:)
-// CHECK-NEXT: [[GENERIC_OP:%.*]] = function_ref @$ss2eeoiySbx_xtSYRzSQ8RawValueRpzlF : $@convention(thin) <τ_0_0 where τ_0_0 : RawRepresentable, τ_0_0.RawValue : Equatable> (@in_guaranteed τ_0_0, @in_guaranteed τ_0_0) -> Bool
-// CHECK-NEXT: apply [[GENERIC_OP]]<E>([[LHS_ARG]], [[RHS_ARG]])
+// CHECK: [[GENERIC_OP:%.*]] = witness_method $E, #Equatable."==" : <Self where Self : Equatable> (Self.Type) -> (Self, Self) -> Bool
+// CHECK-NEXT: apply [[GENERIC_OP]]<E>([[LHS_ARG]], [[RHS_ARG]], {{.*}})
--- a/test/Constraints/rdar158063151.swift
+++ b/test/Constraints/rdar158063151.swift
@@ -8,9 +8,8 @@ struct Value: Equatable, ExpressibleByNilLiteral {
 }

 // CHECK-LABEL: sil hidden [ossa] @$s13rdar1580631514test1vyAA5ValueV_tF : $@convention(thin) (Value) -> ()
-// function_ref static Value.__derived_struct_equals(_:_:)
-// CHECK: [[EQUALS_REF:%.*]] = function_ref @$s13rdar1580631515ValueV23__derived_struct_equalsySbAC_ACtFZ
-// CHECK-NEXT: apply [[EQUALS_REF]](%0, {{.*}})
+// CHECK: [[EQUALS_REF:%.*]] = witness_method $Value, #Equatable."==" : <Self where Self : Equatable> (Self.Type) -> (Self, Self) -> Bool
+// CHECK-NEXT: apply [[EQUALS_REF]]<Value>({{.*}})
 func test(v: Value) {
  _ = v == nil
 }
--- a/test/Index/index_refs_to_synthesized_decls.swift
+++ b/test/Index/index_refs_to_synthesized_decls.swift
@@ -12,6 +12,6 @@ func testFoo() {
    // CHECK: [[@LINE+1]]:7 | instance-method/Swift | hash(into:) | s:14swift_ide_test9CustomFooV4hash4intoys6HasherVz_tF | {{.*}}Ref
    f.hash(into: &hasher)
    hasher.finalize()
-    // CHECK: [[@LINE+1]]:11 | static-method/Swift | __derived_struct_equals(_:_:) | s:14swift_ide_test9CustomFooV23__derived_struct_equalsySbAC_ACtFZ | {{.*}}Ref
+    // CHECK: [[@LINE+1]]:11 | static-method/infix-operator/Swift | ==(_:_:) | s:SQ2eeoiySbx_xtFZ | {{.*}}Ref
    _ = f == CustomFoo(a: 0, b: "b")
 }
--- a/test/SILGen/enum_equatable_witness.swift
+++ b/test/SILGen/enum_equatable_witness.swift
@@ -48,15 +48,15 @@ public enum Alphabet : String {

 // CHECK-LABEL: sil [ossa] @$s4main14check_alphabetySiAA8AlphabetOF : $@convention(thin) (Alphabet) -> Int {
 public func check_alphabet(_ state : Alphabet) -> Int {
-  // FRAGILE: function_ref @$ss2eeoiySbx_xtSYRzSQ8RawValueRpzlF
-  // RESILIENT: function_ref @$ss2eeoiySbx_xtSYRzSQ8RawValueRpzlF
+  // FRAGILE: witness_method $Alphabet, #Equatable."==" : <Self where Self : Equatable> (Self.Type) -> (Self, Self) -> Bool
+  // RESILIENT: witness_method $Alphabet, #Equatable."==" : <Self where Self : Equatable> (Self.Type) -> (Self, Self) -> Bool
  return state == .E ? 1 : 0
 }

 // CHECK-LABEL: sil [ossa] @$s4main9compareItySbAA8AlphabetO_ADtF : $@convention(thin) (Alphabet, Alphabet) -> Bool {
 public func compareIt(_ state : Alphabet, _ rhs: Alphabet) -> Bool {
-  // FRAGILE: function_ref @$ss2eeoiySbx_xtSYRzSQ8RawValueRpzlF
-  // RESILIENT: function_ref @$ss2eeoiySbx_xtSYRzSQ8RawValueRpzlF
+  // FRAGILE: witness_method $Alphabet, #Equatable."==" : <Self where Self : Equatable> (Self.Type) -> (Self, Self) -> Bool
+  // RESILIENT: witness_method $Alphabet, #Equatable."==" : <Self where Self : Equatable> (Self.Type) -> (Self, Self) -> Bool
  return state == rhs
 }

@@ -67,14 +67,14 @@ public enum AlphabetInt : Int {

 // CHECK-LABEL: sil [ossa] @$s4main18check_alphabet_intySiAA11AlphabetIntOF : $@convention(thin) (AlphabetInt) -> Int {
 public func check_alphabet_int(_ state : AlphabetInt) -> Int {
-  // FRAGILE: function_ref @$ss2eeoiySbx_xtSYRzSQ8RawValueRpzlF
-  // RESILIENT: function_ref @$ss2eeoiySbx_xtSYRzSQ8RawValueRpzlF
+  // FRAGILE: witness_method $AlphabetInt, #Equatable."==" : <Self where Self : Equatable> (Self.Type) -> (Self, Self) -> Bool
+  // RESILIENT: witness_method $AlphabetInt, #Equatable."==" : <Self where Self : Equatable> (Self.Type) -> (Self, Self) -> Bool
  return state == .E ? 1 : 0
 }

 // CHECK-LABEL: sil [ossa] @$s4main9compareItySbAA11AlphabetIntO_ADtF : $@convention(thin) (AlphabetInt, AlphabetInt) -> Bool {
 public func compareIt(_ state : AlphabetInt, _ rhs: AlphabetInt) -> Bool {
-  // FRAGILE: function_ref @$ss2eeoiySbx_xtSYRzSQ8RawValueRpzlF
-  // RESILIENT: function_ref @$ss2eeoiySbx_xtSYRzSQ8RawValueRpzlF
+  // FRAGILE: witness_method $AlphabetInt, #Equatable."==" : <Self where Self : Equatable> (Self.Type) -> (Self, Self) -> Bool
+  // RESILIENT: witness_method $AlphabetInt, #Equatable."==" : <Self where Self : Equatable> (Self.Type) -> (Self, Self) -> Bool
  return state == rhs
 }
--- a/test/SILGen/protocol_operators.swift
+++ b/test/SILGen/protocol_operators.swift
@@ -1,4 +1,7 @@
-// RUN: %target-swift-frontend -emit-silgen %s | %FileCheck %s
+// RUN: %target-swift-frontend -emit-silgen %s | %FileCheck %s --check-prefix=SILGEN
+// RUN: %target-swift-frontend -emit-sil %s | %FileCheck %s --check-prefix=OPTIMIZED
+
+// Operators are no longer devirtualized at AST level, it's done during SIL optimization.

 infix operator +++

@@ -11,9 +14,13 @@ struct Branch : Twig {
  static func doIt(_: Branch, _: Branch) {}
 }

-// CHECK-LABEL: sil hidden [ossa] @$s18protocol_operators9useBranchyyAA0D0VF : $@convention(thin) (Branch) -> () {
-// CHECK: function_ref @$s18protocol_operators6BranchV4doItyyAC_ACtFZ : $@convention(method) (Branch, Branch, @thin Branch.Type) -> ()
-// CHECK: return
+// SILGEN-LABEL: sil hidden [ossa] @$s18protocol_operators9useBranchyyAA0D0VF : $@convention(thin) (Branch) -> () {
+// SILGEN: witness_method $Branch, #Twig."+++" : <Self where Self : Twig> (Self.Type) -> (Self, Self) -> ()
+// SILGEN: return
+
+// OPTIMIZED-LABEL: sil hidden @$s18protocol_operators9useBranchyyAA0D0VF : $@convention(thin) (Branch) -> () {
+// OPTIMIZED: function_ref @$s18protocol_operators6BranchV4doItyyAC_ACtFZ
+// OPTIMIZED: return
 func useBranch(_ b: Branch) {
  b +++ b
 }
@@ -28,11 +35,17 @@ class Stuck : Stick, ExpressibleByIntegerLiteral {
  required init(integerLiteral: Int) {}
 }

-// CHECK-LABEL: sil hidden [ossa] @$s18protocol_operators8useStickyyAA5StuckC_AA0D0CtF : $@convention(thin) (@guaranteed Stuck, @guaranteed Stick) -> () {
-// CHECK: function_ref @$s18protocol_operators5StickC3pppoiyyAC_ACtFZ : $@convention(method) (@guaranteed Stick, @guaranteed Stick, @thick Stick.Type) -> ()
-// CHECK: function_ref @$s18protocol_operators5StickC3pppoiyyAC_ACtFZ : $@convention(method) (@guaranteed Stick, @guaranteed Stick, @thick Stick.Type) -> ()
-// CHECK: witness_method $Stuck, #Twig."+++" : <Self where Self : Twig> (Self.Type) -> (Self, Self) -> () : $@convention(witness_method: Twig) <τ_0_0 where τ_0_0 : Twig> (@in_guaranteed τ_0_0, @in_guaranteed τ_0_0, @thick τ_0_0.Type) -> ()
-// CHECK: return
+// SILGEN-LABEL: sil hidden [ossa] @$s18protocol_operators8useStickyyAA5StuckC_AA0D0CtF : $@convention(thin) (@guaranteed Stuck, @guaranteed Stick) -> () {
+// SILGEN: function_ref @$s18protocol_operators5StickC3pppoiyyAC_ACtFZ : $@convention(method) (@guaranteed Stick, @guaranteed Stick, @thick Stick.Type) -> ()
+// SILGEN: function_ref @$s18protocol_operators5StickC3pppoiyyAC_ACtFZ : $@convention(method) (@guaranteed Stick, @guaranteed Stick, @thick Stick.Type) -> ()
+// SILGEN: witness_method $Stuck, #Twig."+++" : <Self where Self : Twig> (Self.Type) -> (Self, Self) -> () : $@convention(witness_method: Twig) <τ_0_0 where τ_0_0 : Twig> (@in_guaranteed τ_0_0, @in_guaranteed τ_0_0, @thick τ_0_0.Type) -> ()
+// SILGEN: return
+
+// OPTIMIZED-LABEL: sil hidden @$s18protocol_operators8useStickyyAA5StuckC_AA0D0CtF : $@convention(thin) (@guaranteed Stuck, @guaranteed Stick) -> () {
+// OPTIMIZED: function_ref @$s18protocol_operators5StickC3pppoiyyAC_ACtFZ : $@convention(method) (@guaranteed Stick, @guaranteed Stick, @thick Stick.Type) -> ()
+// OPTIMIZED: function_ref @$s18protocol_operators5StickC3pppoiyyAC_ACtFZ : $@convention(method) (@guaranteed Stick, @guaranteed Stick, @thick Stick.Type) -> ()
+// OPTIMIZED: function_ref @$s18protocol_operators5StickC3pppoiyyAC_ACtFZ : $@convention(method) (@guaranteed Stick, @guaranteed Stick, @thick Stick.Type) -> ()
+// OPTIMIZED: return
 func useStick(_ a: Stuck, _ b: Stick) {
  _ = a +++ b
  _ = b +++ b
@@ -49,10 +62,15 @@ class Rope : Twine<Int>, ExpressibleByIntegerLiteral {
  required init(integerLiteral: Int) {}
 }

-// CHECK-LABEL: sil hidden [ossa] @$s18protocol_operators7useRopeyyAA0D0C_ADtF : $@convention(thin) (@guaranteed Rope, @guaranteed Rope) -> () {
-// CHECK: function_ref @$s18protocol_operators5TwineC3pppoiyyACyxG_AEtFZ : $@convention(method) <τ_0_0> (@guaranteed Twine<τ_0_0>, @guaranteed Twine<τ_0_0>, @thick Twine<τ_0_0>.Type) -> ()
-// CHECK: function_ref @$s18protocol_operators5TwineC3pppoiyyACyxG_AEtFZ : $@convention(method) <τ_0_0> (@guaranteed Twine<τ_0_0>, @guaranteed Twine<τ_0_0>, @thick Twine<τ_0_0>.Type) -> ()
-// CHECK: witness_method $Rope, #Twig."+++" : <Self where Self : Twig> (Self.Type) -> (Self, Self) -> () : $@convention(witness_method: Twig) <τ_0_0 where τ_0_0 : Twig> (@in_guaranteed τ_0_0, @in_guaranteed τ_0_0, @thick τ_0_0.Type) -> ()
+// SILGEN-LABEL: sil hidden [ossa] @$s18protocol_operators7useRopeyyAA0D0C_ADtF : $@convention(thin) (@guaranteed Rope, @guaranteed Rope) -> () {
+// SILGEN: function_ref @$s18protocol_operators5TwineC3pppoiyyACyxG_AEtFZ : $@convention(method) <τ_0_0> (@guaranteed Twine<τ_0_0>, @guaranteed Twine<τ_0_0>, @thick Twine<τ_0_0>.Type) -> ()
+// SILGEN: function_ref @$s18protocol_operators5TwineC3pppoiyyACyxG_AEtFZ : $@convention(method) <τ_0_0> (@guaranteed Twine<τ_0_0>, @guaranteed Twine<τ_0_0>, @thick Twine<τ_0_0>.Type) -> ()
+// SILGEN: witness_method $Rope, #Twig."+++" : <Self where Self : Twig> (Self.Type) -> (Self, Self) -> () : $@convention(witness_method: Twig) <τ_0_0 where τ_0_0 : Twig> (@in_guaranteed τ_0_0, @in_guaranteed τ_0_0, @thick τ_0_0.Type) -> ()
+
+// OPTIMIZED-LABEL: sil hidden @$s18protocol_operators7useRopeyyAA0D0C_ADtF : $@convention(thin) (@guaranteed Rope, @guaranteed Rope) -> () {
+// OPTIMIZED: function_ref @$s18protocol_operators5TwineC3pppoiyyACyxG_AEtFZ : $@convention(method) <τ_0_0> (@guaranteed Twine<τ_0_0>, @guaranteed Twine<τ_0_0>, @thick Twine<τ_0_0>.Type) -> ()
+// OPTIMIZED: function_ref @$s18protocol_operators5TwineC3pppoiyyACyxG_AEtFZ : $@convention(method) <τ_0_0> (@guaranteed Twine<τ_0_0>, @guaranteed Twine<τ_0_0>, @thick Twine<τ_0_0>.Type) -> ()
+// OPTIMIZED: function_ref @$s18protocol_operators5TwineC3pppoiyyACyxG_AEtFZ : $@convention(method) <τ_0_0> (@guaranteed Twine<τ_0_0>, @guaranteed Twine<τ_0_0>, @thick Twine<τ_0_0>.Type) -> ()
 func useRope(_ r: Rope, _ s: Rope) {
  _ = r +++ s
  _ = s +++ s