SILGen: Bitcast indirect returns that differ only in concurrency annotations.

A call to a `@preconcurrency` function goes through a function conversion
that removes `Sendable` from existentials among other things. Implement
support for this by bitcasting indirect return slots whose type differs
from the formal indirect return type in concurrency markings only.

Fixes rdar://154240007

include/swift/SIL/SILType.h

@@ -754,6 +754,13 @@ public:
   SILType subst(SILModule &M, SubstitutionMap subs,
                 TypeExpansionContext context) const;
 
+  /// Strip concurrency annotations from the representation type.
+  SILType stripConcurrency(bool recursive, bool dropGlobalActor) {
+    auto strippedASTTy = getASTType()->stripConcurrency(recursive, dropGlobalActor);
+    return SILType::getPrimitiveType(strippedASTTy->getCanonicalType(),
+                                     getCategory());
+  }
+
   /// Return true if this type references a "ref" type that has a single pointer
   /// representation. Class existentials do not always qualify.
   bool isHeapObjectReferenceType() const;

lib/SILGen/SILGenApply.cpp

@@ -1966,15 +1966,21 @@ static void emitRawApply(SILGenFunction &SGF,
   SmallVector<SILValue, 4> argValues;
 
   // Add the buffers for the indirect results if needed.
-#ifndef NDEBUG
-  assert(indirectResultAddrs.size() == substFnConv.getNumIndirectSILResults());
   unsigned resultIdx = 0;
-  for (auto indResultTy :
-       substFnConv.getIndirectSILResultTypes(SGF.getTypeExpansionContext())) {
-    assert(indResultTy == indirectResultAddrs[resultIdx++]->getType());
+  for (auto indResultTy : substFnConv.getIndirectSILResultTypes(SGF.getTypeExpansionContext())) {
+    auto indResultAddr = indirectResultAddrs[resultIdx++];
+
+    if (indResultAddr->getType() != indResultTy) {
+      // Bitcast away differences in Sendable, global actor, etc.
+      if (indResultAddr->getType().stripConcurrency(/*recursive*/ true, /*dropGlobalActor*/ true)
+          == indResultTy.stripConcurrency(/*recursive*/ true, /*dropGlobalActor*/ true)) {
+        indResultAddr = SGF.B.createUncheckedAddrCast(loc, indResultAddr, indResultTy);
+      }
+    }
+    assert(indResultTy == indResultAddr->getType());
+
+    argValues.push_back(indResultAddr);
   }
-#endif
-  argValues.append(indirectResultAddrs.begin(), indirectResultAddrs.end());
 
   assert(!!indirectErrorAddr == substFnConv.hasIndirectSILErrorResults());
   if (indirectErrorAddr)

test/SILGen/preconcurrency_indirect_return.swift

@@ -0,0 +1,10 @@
+// RUN: %target-swift-emit-silgen %s | %FileCheck %s
+
+@preconcurrency
+func test() -> (any Sendable)? { nil }
+
+// CHECK-LABEL: sil {{.*}} @$s{{.*}}callWithPreconcurrency
+func callWithPreconcurrency() {
+	// CHECK: unchecked_addr_cast {{.*}} to $*Optional<any Sendable>
+	let x = test()
+}