stdlib/SILGen: Emit SIL for Swift runtime availability queries.

When emitting SIL for `if #available(Swift ..., *)` queries, call the new
`_isSwiftRuntimeVersionAtLeast()` function in the stdlib to check the
condition. To support back deployment, the implementation of
`_isSwiftRuntimeVersionAtLeast()` is `@_alwaysEmitIntoClient` and performs its
comparison against the result of `_SwiftStdlibVersion.current`, which is
pre-existing ABI that the stdlib exposes for querying the Swift runtime
version.

Resolves rdar://162726037.

include/swift/AST/ASTContext.h

@@ -801,6 +801,9 @@ public:
   // Swift._stdlib_isOSVersionAtLeastOrVariantVersionAtLeast.
   FuncDecl *getIsOSVersionAtLeastOrVariantVersionAtLeast() const;
 
+  /// Retrieve the declaration of Swift._isSwiftRuntimeVersionAtLeast.
+  FuncDecl *getIsSwiftRuntimeVersionAtLeast() const;
+
   /// Look for the declaration with the given name within the
   /// passed in module.
   void lookupInModule(ModuleDecl *M, StringRef name,

include/swift/AST/AvailabilityQuery.h

@@ -47,9 +47,7 @@ class AvailabilityQuery final {
 
   AvailabilityQuery(AvailabilityDomain domain, ResultKind kind,
                     const std::optional<AvailabilityRange> &primaryRange,
-                    const std::optional<AvailabilityRange> &variantRange)
-      : domain(domain), primaryRange(primaryRange), variantRange(variantRange),
-        kind(kind), unavailable(false) {};
+                    const std::optional<AvailabilityRange> &variantRange);
 
 public:
   /// Returns an `AvailabilityQuery` for a query that evaluates to true or

lib/AST/ASTContext.cpp

@@ -425,6 +425,13 @@ struct ASTContext::Implementation {
   ///  -> Builtin.Int1
   FuncDecl *IsOSVersionAtLeastOrVariantVersionAtLeastDecl = nullptr;
 
+  /// func _isSwiftRuntimeVersionAtLeast(
+  ///   Builtin.Word,
+  ///   Builtin.Word,
+  ///   Builtin.word)
+  ///  -> Builtin.Int1
+  FuncDecl *IsSwiftRuntimeVersionAtLeastDecl = nullptr;
+
   /// The set of known protocols, lazily populated as needed.
   ProtocolDecl *KnownProtocols[NumKnownProtocols] = { };
 
@@ -1946,6 +1953,18 @@ if (getImpl().IsOSVersionAtLeastOrVariantVersionAtLeastDecl)
   return decl;
 }
 
+FuncDecl *ASTContext::getIsSwiftRuntimeVersionAtLeast() const {
+  if (getImpl().IsSwiftRuntimeVersionAtLeastDecl)
+    return getImpl().IsSwiftRuntimeVersionAtLeastDecl;
+
+  auto decl = findLibraryIntrinsic(*this, "_isSwiftRuntimeVersionAtLeast");
+  if (!decl)
+    return nullptr;
+
+  getImpl().IsSwiftRuntimeVersionAtLeastDecl = decl;
+  return decl;
+}
+
 static bool isHigherPrecedenceThan(PrecedenceGroupDecl *a,
                                    PrecedenceGroupDecl *b) {
   assert(a != b && "exact match should already have been filtered");

lib/AST/AvailabilityQuery.cpp

@@ -17,6 +17,54 @@
 
 using namespace swift;
 
+AvailabilityQuery::AvailabilityQuery(
+    AvailabilityDomain domain, ResultKind kind,
+    const std::optional<AvailabilityRange> &primaryRange,
+    const std::optional<AvailabilityRange> &variantRange)
+    : domain(domain), primaryRange(primaryRange), variantRange(variantRange),
+      kind(kind), unavailable(false) {
+  // Check invariants.
+  switch (domain.getKind()) {
+  case AvailabilityDomain::Kind::SwiftLanguageMode:
+  case AvailabilityDomain::Kind::PackageDescription:
+  case AvailabilityDomain::Kind::Embedded:
+    // These domains don't support queries at all.
+    DEBUG_ASSERT(false);
+    break;
+
+  case AvailabilityDomain::Kind::Universal:
+    // The universal domain can only support constant queries.
+    DEBUG_ASSERT(kind != ResultKind::Dynamic);
+    break;
+
+  case AvailabilityDomain::Kind::SwiftRuntime:
+    // Dynamic Swift runtime queries take just a primary version argument.
+    if (kind == ResultKind::Dynamic) {
+      DEBUG_ASSERT(primaryRange);
+      DEBUG_ASSERT(!variantRange);
+    }
+    break;
+
+  case AvailabilityDomain::Kind::Platform:
+    // Dynamic platform version queries must have either a primary version
+    // argument or a variant version argument (or both).
+    if (kind == ResultKind::Dynamic) {
+      DEBUG_ASSERT(primaryRange || variantRange);
+    }
+    break;
+
+  case AvailabilityDomain::Kind::Custom:
+    // Custom availability domains do not support versioned queries at all yet.
+    DEBUG_ASSERT(!primaryRange);
+    DEBUG_ASSERT(!variantRange);
+
+    // A valid custom domain object is required.
+    auto customDomain = domain.getCustomDomain();
+    ASSERT(customDomain);
+    break;
+  }
+}
+
 static void unpackVersion(const llvm::VersionTuple &version,
                           llvm::SmallVectorImpl<unsigned> &arguments) {
   arguments.push_back(version.getMajor());
@@ -133,16 +181,17 @@ FuncDecl *AvailabilityQuery::getDynamicQueryDeclAndArguments(
   switch (domain.getKind()) {
   case AvailabilityDomain::Kind::Universal:
   case AvailabilityDomain::Kind::SwiftLanguageMode:
-  case AvailabilityDomain::Kind::SwiftRuntime:
   case AvailabilityDomain::Kind::PackageDescription:
   case AvailabilityDomain::Kind::Embedded:
+    // These domains don't support dynamic queries.
     return nullptr;
+
+  case AvailabilityDomain::Kind::SwiftRuntime:
+    unpackVersion(getPrimaryArgument().value(), arguments);
+    return ctx.getIsSwiftRuntimeVersionAtLeast();
   case AvailabilityDomain::Kind::Platform:
     return getOSAvailabilityDeclAndArguments(*this, arguments, ctx);
   case AvailabilityDomain::Kind::Custom:
-    auto customDomain = domain.getCustomDomain();
-    ASSERT(customDomain);
-
-    return customDomain->getPredicateFunc();
+    return domain.getCustomDomain()->getPredicateFunc();
   }
 }

lib/AST/AvailabilityScopeBuilder.cpp

@@ -870,6 +870,8 @@ private:
                                         variantRange);
 
     case AvailabilityDomain::Kind::SwiftRuntime:
+      return AvailabilityQuery::dynamic(domain, primaryRange, std::nullopt);
+
     case AvailabilityDomain::Kind::Platform:
       // Platform and Swift runtime checks are always dynamic. The SIL optimizer
       // is responsible eliminating these checks when it can prove that they can

stdlib/public/core/Availability.swift

@@ -197,6 +197,22 @@ public func _stdlib_isOSVersionAtLeastOrVariantVersionAtLeast(
 
 public typealias _SwiftStdlibVersion = SwiftShims._SwiftStdlibVersion
 
+/// This is a magic entry point known to the compiler. It is called in
+/// generated code for Swift runtime availability checking, e.g.
+///
+///     if #available(Swift 6.2, *) { }
+///
+@available(SwiftStdlib 5.7, *)
+@_alwaysEmitIntoClient
+internal func _isSwiftRuntimeVersionAtLeast(
+  _ major: Builtin.Word,
+  _ minor: Builtin.Word,
+  _ patch: Builtin.Word
+) -> Builtin.Int1 {
+  let version = _SwiftStdlibVersion(major, minor, patch)
+  return (_SwiftStdlibVersion.current._value <= version._value)._value
+}
+
 /// Return true if the main executable was linked with an SDK version
 /// corresponding to the given Swift Stdlib release, or later. Otherwise, return
 /// false.
@@ -243,8 +259,36 @@ extension _SwiftStdlibVersion {
   @_alwaysEmitIntoClient
   public static var v6_3_0: Self { Self(_value: 0x060300) }
 
+  private static var _current: Self { .v6_3_0 }
+
+#if hasFeature(Macros)
   @available(SwiftStdlib 5.7, *)
-  public static var current: Self { .v6_3_0 }
+  public static var current: Self {
+    @_noLocks
+    @_effects(readnone)
+    get { ._current }
+  }
+#else
+  @available(SwiftStdlib 5.7, *)
+  public static var current: Self {
+    @_effects(readnone)
+    get { ._current }
+  }
+#endif
+
+  @_alwaysEmitIntoClient
+  internal init(
+    _ major: Builtin.Word,
+    _ minor: Builtin.Word,
+    _ patch: Builtin.Word
+  ) {
+    let version = (Int(major), Int(minor), Int(patch))
+    var value: UInt32 = 0x0
+    value |= ((UInt32(truncatingIfNeeded: version.0) & 0xffff) << 16)
+    value |= ((UInt32(truncatingIfNeeded: version.1) & 0xff) << 8)
+    value |= ((UInt32(truncatingIfNeeded: version.2) & 0xff))
+    self = Self(_value: value)
+  }
 }
 
 @available(SwiftStdlib 5.7, *)

test/IRGen/availability_swift_runtime.swift

@@ -0,0 +1,46 @@
+// RUN: %target-swift-emit-ir %s -min-swift-runtime-version 5.0 -O -enable-experimental-feature SwiftRuntimeAvailability | %FileCheck %s
+
+// REQUIRES: swift_feature_SwiftRuntimeAvailability
+
+@_silgen_name("callMeMaybe")
+public func callMeMaybe()
+
+// Verify that optimized IR for "if #available(Swift X.Y, *)" is composed of a
+// call to the stdlib ABI that returns the current runtime version and an
+// integer comparison of that version and the predicate version.
+
+// CHECK-LABEL: define {{.*}}swiftcc void @"$s26availability_swift_runtime15testIfAvailableyyF"()
+// CHECK:         [[CURRENT_VERS:%.*]] = tail call swiftcc i32 @"$sSo19_SwiftStdlibVersionasE7currentABvgZ"()
+// CHECK:         [[ICMP:%.*]] = icmp {{.*}}
+// CHECK:         br i1 [[ICMP]], label %[[TRUE_LABEL:.*]], label %[[FALSE_LABEL:.*]]
+// CHECK:       [[TRUE_LABEL]]:
+// CHECK:         call {{.*}} @callMeMaybe()
+// CHECK:       [[FALSE_LABEL]]:
+// CHECK:         ret void
+public func testIfAvailable() {
+  if #available(Swift 6.2, *) {
+    callMeMaybe()
+  }
+}
+
+// In optimized IR multiple "if #available" checks for the same version should
+// only generate a single call to the getter for _SwiftStdlibVersion.current.
+
+// CHECK-LABEL: define {{.*}}swiftcc void @"$s26availability_swift_runtime23testIfAvailableMultipleyyF"()
+// CHECK:         call {{.*}} @"$sSo19_SwiftStdlibVersionasE7currentABvgZ"()
+// CHECK-NOT:     call {{.*}} @"$sSo19_SwiftStdlibVersionasE7currentABvgZ"()
+// CHECK:         icmp
+// CHECK:         call {{.*}} @callMeMaybe()
+// CHECK:         call {{.*}} @callMeMaybe()
+// CHECK:         call {{.*}} @callMeMaybe()
+public func testIfAvailableMultiple() {
+  if #available(Swift 5.10, *) {
+    callMeMaybe()
+  }
+  if #available(Swift 5.10, *) {
+    callMeMaybe()
+  }
+  if #available(Swift 5.10, *) {
+    callMeMaybe()
+  }
+}

test/SILGen/availability_query_swift_runtime.swift

@@ -0,0 +1,26 @@
+// RUN: %target-swift-emit-sil %s -min-swift-runtime-version 5.0 -verify -enable-experimental-feature SwiftRuntimeAvailability
+// RUN: %target-swift-emit-silgen %s -min-swift-runtime-version 5.0 -enable-experimental-feature SwiftRuntimeAvailability | %FileCheck %s
+
+// REQUIRES: swift_feature_SwiftRuntimeAvailability
+
+// CHECK-LABEL: sil [ossa] @$s32availability_query_swift_runtime15testIfAvailableyyF : $@convention(thin) () -> () {
+// CHECK:         [[MAJOR:%.*]] = integer_literal $Builtin.Word, 6
+// CHECK:         [[MINOR:%.*]] = integer_literal $Builtin.Word, 2
+// CHECK:         [[PATCH:%.*]] = integer_literal $Builtin.Word, 0
+// CHECK:         [[FUNC:%.*]] = function_ref @$ss29_isSwiftRuntimeVersionAtLeastyBi1_Bw_BwBwtF : $@convention(thin) (Builtin.Word, Builtin.Word, Builtin.Word) -> Builtin.Int1
+// CHECK:         [[QUERY_RESULT:%.*]] = apply [[FUNC]]([[MAJOR]], [[MINOR]], [[PATCH]]) : $@convention(thin) (Builtin.Word, Builtin.Word, Builtin.Word) -> Builtin.Int1
+public func testIfAvailable() {
+  if #available(Swift 6.2, *) { }
+}
+
+// CHECK-LABEL: sil [ossa] @$s32availability_query_swift_runtime17testIfUnavailableyyF : $@convention(thin) () -> () {
+// CHECK:         [[MAJOR:%.*]] = integer_literal $Builtin.Word, 5
+// CHECK:         [[MINOR:%.*]] = integer_literal $Builtin.Word, 10
+// CHECK:         [[PATCH:%.*]] = integer_literal $Builtin.Word, 1
+// CHECK:         [[FUNC:%.*]] = function_ref @$ss29_isSwiftRuntimeVersionAtLeastyBi1_Bw_BwBwtF : $@convention(thin) (Builtin.Word, Builtin.Word, Builtin.Word) -> Builtin.Int1
+// CHECK:         [[QUERY_RESULT:%.*]] = apply [[FUNC]]([[MAJOR]], [[MINOR]], [[PATCH]]) : $@convention(thin) (Builtin.Word, Builtin.Word, Builtin.Word) -> Builtin.Int1
+// CHECK:         [[MINUSONE:%.*]] = integer_literal $Builtin.Int1, -1
+// CHECK:         [[QUERY_INVERSION:%.*]] = builtin "xor_Int1"([[QUERY_RESULT]], [[MINUSONE]]) : $Builtin.Int1
+public func testIfUnavailable() {
+  if #unavailable(Swift 5.10.1) { }
+}

test/SILGen/availability_query_swift_runtime_maccatalyst_zippered.swift

@@ -0,0 +1,27 @@
+// RUN: %target-swift-emit-sil %s -target %target-cpu-apple-macosx11 -target-variant %target-cpu-apple-ios14-macabi -min-swift-runtime-version 5.0 -verify -enable-experimental-feature SwiftRuntimeAvailability
+// RUN: %target-swift-emit-silgen %s -target %target-cpu-apple-macosx11 -target-variant %target-cpu-apple-ios14-macabi -min-swift-runtime-version 5.0 -enable-experimental-feature SwiftRuntimeAvailability | %FileCheck %s
+
+// REQUIRES: OS=macosx || OS=maccatalyst
+// REQUIRES: swift_feature_SwiftRuntimeAvailability
+
+// CHECK-LABEL: sil [ossa] @$s53availability_query_swift_runtime_maccatalyst_zippered15testIfAvailableyyF : $@convention(thin) () -> () {
+// CHECK:         [[MAJOR:%.*]] = integer_literal $Builtin.Word, 6
+// CHECK:         [[MINOR:%.*]] = integer_literal $Builtin.Word, 2
+// CHECK:         [[PATCH:%.*]] = integer_literal $Builtin.Word, 0
+// CHECK:         [[FUNC:%.*]] = function_ref @$ss29_isSwiftRuntimeVersionAtLeastyBi1_Bw_BwBwtF : $@convention(thin) (Builtin.Word, Builtin.Word, Builtin.Word) -> Builtin.Int1
+// CHECK:         [[QUERY_RESULT:%.*]] = apply [[FUNC]]([[MAJOR]], [[MINOR]], [[PATCH]]) : $@convention(thin) (Builtin.Word, Builtin.Word, Builtin.Word) -> Builtin.Int1
+public func testIfAvailable() {
+  if #available(Swift 6.2, *) { }
+}
+
+// CHECK-LABEL: sil [ossa] @$s53availability_query_swift_runtime_maccatalyst_zippered17testIfUnavailableyyF : $@convention(thin) () -> () {
+// CHECK:         [[MAJOR:%.*]] = integer_literal $Builtin.Word, 5
+// CHECK:         [[MINOR:%.*]] = integer_literal $Builtin.Word, 10
+// CHECK:         [[PATCH:%.*]] = integer_literal $Builtin.Word, 1
+// CHECK:         [[FUNC:%.*]] = function_ref @$ss29_isSwiftRuntimeVersionAtLeastyBi1_Bw_BwBwtF : $@convention(thin) (Builtin.Word, Builtin.Word, Builtin.Word) -> Builtin.Int1
+// CHECK:         [[QUERY_RESULT:%.*]] = apply [[FUNC]]([[MAJOR]], [[MINOR]], [[PATCH]]) : $@convention(thin) (Builtin.Word, Builtin.Word, Builtin.Word) -> Builtin.Int1
+// CHECK:         [[MINUSONE:%.*]] = integer_literal $Builtin.Int1, -1
+// CHECK:         [[QUERY_INVERSION:%.*]] = builtin "xor_Int1"([[QUERY_RESULT]], [[MINUSONE]]) : $Builtin.Int1
+public func testIfUnavailable() {
+  if #unavailable(Swift 5.10.1) { }
+}