SILOptimizer: Allow inlining of transparent functions in @backDeployed thunks

include/swift/SIL/SILFunction.h

@@ -56,7 +56,8 @@ enum IsThunk_t {
   IsNotThunk,
   IsThunk,
   IsReabstractionThunk,
-  IsSignatureOptimizedThunk
+  IsSignatureOptimizedThunk,
+  IsBackDeployedThunk,
 };
 enum IsDynamicallyReplaceable_t {
   IsNotDynamic,
@@ -368,7 +369,7 @@ class SILFunction
   ///
   /// The inliner uses this information to avoid inlining (non-trivial)
   /// functions into the thunk.
-  unsigned Thunk : 2;
+  unsigned Thunk : 3;
 
   /// The scope in which the parent class can be subclassed, if this is a method
   /// which is contained in the vtable of that class.
@@ -486,6 +487,7 @@ class SILFunction
       break;
     case IsThunk:
     case IsReabstractionThunk:
+    case IsBackDeployedThunk:
       thunkCanHaveSubclassScope = false;
       break;
     }

lib/SIL/IR/SILPrinter.cpp

@@ -3387,6 +3387,7 @@ void SILFunction::print(SILPrintContext &PrintCtx) const {
 
   switch (isThunk()) {
   case IsNotThunk: break;
+  case IsBackDeployedThunk: // FIXME: Give this a distinct label
   case IsThunk: OS << "[thunk] "; break;
   case IsSignatureOptimizedThunk:
     OS << "[signature_optimized_thunk] ";

lib/SILGen/SILGen.cpp

@@ -906,7 +906,7 @@ void SILGenModule::emitFunctionDefinition(SILDeclRef constant, SILFunction *f) {
     preEmitFunction(constant, f, loc);
     PrettyStackTraceSILFunction X("silgen emitBackDeploymentThunk", f);
     f->setBare(IsBare);
-    f->setThunk(IsThunk);
+    f->setThunk(IsBackDeployedThunk);
 
     SILGenFunction(*this, *f, dc).emitBackDeploymentThunk(constant);
 

lib/SILOptimizer/Mandatory/MandatoryInlining.cpp

@@ -1030,10 +1030,22 @@ class MandatoryInlining : public SILModuleTransform {
 
     SILOptFunctionBuilder FuncBuilder(*this);
     for (auto &F : *M) {
-      // Don't inline into thunks, even transparent callees.
-      if (F.isThunk())
+      switch (F.isThunk()) {
+      case IsThunk_t::IsThunk:
+      case IsThunk_t::IsReabstractionThunk:
+      case IsThunk_t::IsSignatureOptimizedThunk:
+        // Don't inline into most thunks, even transparent callees.
         continue;
 
+      case IsThunk_t::IsNotThunk:
+      case IsThunk_t::IsBackDeployedThunk:
+        // For correctness, inlining _stdlib_isOSVersionAtLeast() when it is
+        // declared transparent is mandatory in the thunks of @backDeployed
+        // functions. These thunks will not contain calls to other transparent
+        // functions.
+        break;
+      }
+
       // Skip deserialized functions.
       if (F.wasDeserializedCanonical())
         continue;

lib/Serialization/ModuleFormat.h

@@ -58,7 +58,7 @@ const uint16_t SWIFTMODULE_VERSION_MAJOR = 0;
 /// describe what change you made. The content of this comment isn't important;
 /// it just ensures a conflict if two people change the module format.
 /// Don't worry about adhering to the 80-column limit for this line.
-const uint16_t SWIFTMODULE_VERSION_MINOR = 885; // opened existentials
+const uint16_t SWIFTMODULE_VERSION_MINOR = 886; // SIL function thunk kind
 
 /// A standard hash seed used for all string hashes in a serialized module.
 ///

lib/Serialization/SILFormat.h

@@ -292,7 +292,7 @@ namespace sil_block {
       BCRecordLayout<SIL_FUNCTION, SILLinkageField,
                      BCFixed<1>,  // transparent
                      BCFixed<2>,  // serializedKind
-                     BCFixed<2>,  // thunks: signature optimized/reabstraction
+                     BCFixed<3>,  // thunk kind
                      BCFixed<1>,  // without_actually_escaping
                      BCFixed<3>,  // specialPurpose
                      BCFixed<2>,  // inlineStrategy

stdlib/public/core/Availability.swift

@@ -17,25 +17,73 @@ import SwiftShims
 ///
 /// This is a magic entry point known to the compiler. It is called in
 /// generated code for API availability checking.
+///
+/// This is marked @_transparent on iOS to work around broken availability
+/// checking for iOS apps running on macOS (rdar://83378814). libswiftCore uses
+/// the macOS platform identifier for its version check in that scenario,
+/// causing all queries to return true. When this function is inlined into the
+/// caller, the compiler embeds the correct platform identifier in the client
+/// code, and we get the right answer.
+///
+/// @_transparent breaks the optimizer's ability to remove availability checks
+/// that are unnecessary due to the current deployment target. We call through
+/// to the _stdlib_isOSVersionAtLeast_AEIC function below to work around this,
+/// as the optimizer is able to perform this optimization for a
+/// @_alwaysEmitIntoClient function. We can't use @_alwaysEmitIntoClient
+/// directly on this call because it would break ABI for existing apps.
+///
+/// `@_transparent` breaks the interpreter mode on macOS, as it creates a direct
+/// reference to ___isPlatformVersionAtLeast from compiler-rt, and the
+/// interpreter doesn't currently know how to load symbols from compiler-rt.
+/// Since `@_transparent` is only necessary for iOS apps, we only apply it on
+/// iOS, not any other which would inherit/remap iOS availability.
+#if os(iOS) && !os(xrOS)
+@_effects(readnone)
+@_transparent
+public func _stdlib_isOSVersionAtLeast(
+  _ major: Builtin.Word,
+  _ minor: Builtin.Word,
+  _ patch: Builtin.Word
+) -> Builtin.Int1 {
+  return _stdlib_isOSVersionAtLeast_AEIC(major, minor, patch)
+}
+#else
 @_semantics("availability.osversion")
 @_effects(readnone)
 @_unavailableInEmbedded
 public func _stdlib_isOSVersionAtLeast(
   _ major: Builtin.Word,
   _ minor: Builtin.Word,
   _ patch: Builtin.Word
+) -> Builtin.Int1 {
+  return _stdlib_isOSVersionAtLeast_AEIC(major, minor, patch)
+}
+#endif
+
+@_semantics("availability.osversion")
+@_effects(readnone)
+@_alwaysEmitIntoClient
+public func _stdlib_isOSVersionAtLeast_AEIC(
+  _ major: Builtin.Word,
+  _ minor: Builtin.Word,
+  _ patch: Builtin.Word
 ) -> Builtin.Int1 {
 #if (os(macOS) || os(iOS) || os(tvOS) || os(watchOS) || os(visionOS)) && SWIFT_RUNTIME_OS_VERSIONING
   if Int(major) == 9999 {
     return true._value
   }
-  let runningVersion = _swift_stdlib_operatingSystemVersion()
-
-  let result =
-    (runningVersion.majorVersion,runningVersion.minorVersion,runningVersion.patchVersion)
-    >= (Int(major),Int(minor),Int(patch))
 
-  return result._value
+  let queryVersion = (Int(major), Int(minor), Int(patch))
+  let major32 = Int32(truncatingIfNeeded:Int(queryVersion.0))
+  let minor32 = Int32(truncatingIfNeeded:Int(queryVersion.1))
+  let patch32 = Int32(truncatingIfNeeded:Int(queryVersion.2))
+
+  // Defer to a builtin that calls clang's version checking builtin from
+  // compiler-rt.
+  let result32 = Int32(Builtin.targetOSVersionAtLeast(major32._value,
+                                                      minor32._value,
+                                                      patch32._value))
+  return (result32 != (0 as Int32))._value
 #else
   // FIXME: As yet, there is no obvious versioning standard for platforms other
   // than Darwin-based OSes, so we just assume false for now. 

test/IRGen/Inputs/back_deployed.swift

@@ -0,0 +1,6 @@
+@backDeployed(before: SwiftStdlib 6.0)
+public func backDeployedFunc() {
+  otherFunc()
+}
+
+@usableFromInline internal func otherFunc() {}

test/IRGen/availability.swift

@@ -1,7 +1,8 @@
 // RUN: %target-swift-frontend -primary-file %s -emit-ir | %FileCheck %s
 // RUN: %target-swift-frontend -primary-file %s -O -emit-ir | %FileCheck %s --check-prefix=OPT
 
-// REQUIRES: objc_interop
+// On iOS stdlib_isOSVersionAtLeast() is @_transparent, which affects optimization.
+// REQUIRES: OS=macosx || OS=tvos || OS=watchos || OS=xros
 
 import Foundation
 

test/IRGen/availability_ios.swift

@@ -0,0 +1,64 @@
+// RUN: %target-swift-frontend -primary-file %s -emit-ir | %FileCheck %s
+// RUN: %target-swift-frontend -primary-file %s -O -emit-ir | %FileCheck %s --check-prefix=OPT
+
+// On iOS _stdlib_isOSVersionAtLeast() is @_transparent, which affects optimization.
+// See IRGen/availability.swift for other Apple platforms.
+// REQUIRES: OS=ios
+
+import Foundation
+
+// We mustn't hoist the alloc_stack for measurement out of the availability
+// guard.
+
+// CHECK-LABEL: define{{.*}} @{{.*}}dontHoist
+// CHECK-NOT: s10Foundation11MeasurementVySo17NSUnitTemperature
+// CHECK: call swiftcc i1 @"$ss31_stdlib_isOSVersionAtLeast_AEICyBi1_Bw_BwBwtF"(
+// CHECK: s10Foundation11MeasurementVySo17NSUnitTemperature
+
+// OPT-LABEL: define{{.*}} @{{.*}}dontHoist
+// OPT-NOT: S10Foundation11MeasurementVySo17NSUnitTemperature
+// OPT: call {{.*}} @__isPlatformVersionAtLeast(
+// OPT: s10Foundation11MeasurementVySo17NSUnitTemperature
+
+public func dontHoist() {
+  if #available(macOS 51.0, iOS 54.0, watchOS 57.0, tvOS 54.0, visionOS 51.1, *) {
+      let measurement = Measurement<UnitTemperature>(value: Double(42), unit: .celsius)
+      print("\(measurement)")
+  } else {
+      print("Not measurement")
+  }
+}
+
+
+// Now that _isOSVersionAtLeast is no longer inlinable, we do still
+// mark it as _effects(readnone).
+// This means that unlike in the past the optimizer can now only coalesce
+// availability checks with the same availability. It does not determine,
+// for example, that a check for iOS 10 is sufficient to guarantee that a check
+// for iOS 9 will also succeed.
+
+// With optimizations on, multiple #availability checks should generate only
+// a single call into _isOSVersionAtLeast, which after inlining will be a
+// call to __isPlatformVersionAtLeast.
+
+// CHECK-LABEL: define{{.*}} @{{.*}}multipleAvailabilityChecks
+// CHECK: call swiftcc i1 @"$ss31_stdlib_isOSVersionAtLeast_AEICyBi1_Bw_BwBwtF"(
+// CHECK: call swiftcc i1 @"$ss31_stdlib_isOSVersionAtLeast_AEICyBi1_Bw_BwBwtF"(
+// CHECK: call swiftcc i1 @"$ss31_stdlib_isOSVersionAtLeast_AEICyBi1_Bw_BwBwtF"(
+// CHECK: ret void
+
+// OPT-LABEL: define{{.*}} @{{.*}}multipleAvailabilityChecks
+// OPT: call {{.*}} @__isPlatformVersionAtLeast
+// OPT-NOT: call {{.*}} @$__isPlatformVersionAtLeast
+// OPT: ret void
+public func multipleAvailabilityChecks() {
+  if #available(macOS 51.0, iOS 54.0, watchOS 57.0, tvOS 54.0, visionOS 51.1, *) {
+    print("test one")
+  }
+  if #available(macOS 51.0, iOS 54.0, watchOS 57.0, tvOS 54.0, visionOS 51.1, *) {
+    print("test two")
+  }
+  if #available(macOS 51.0, iOS 54.0, watchOS 57.0, tvOS 54.0, visionOS 51.1, *) {
+    print("test three")
+  }
+}

test/IRGen/back_deployed_Onone.swift

@@ -0,0 +1,17 @@
+// RUN: %empty-directory(%t)
+// RUN: %target-swift-frontend -emit-module %S/Inputs/back_deployed.swift -o %t/ -swift-version 5 -enable-library-evolution
+// RUN: %target-swift-frontend -emit-ir %s -I %t -Onone | %FileCheck %s
+
+// _stdlib_isOSVersionAtLeast() is not @_transparent on macOS, watchOS, and tvOS
+// REQUIRES: OS=macosx || OS=watchos || OS=tvos
+
+import back_deployed
+
+public func test() {
+  backDeployedFunc()
+}
+
+// CHECK: define{{.*}} hidden swiftcc void @"$s13back_deployed0A12DeployedFuncyyFTwb"
+// CHECK:   call swiftcc i1 @"$ss26_stdlib_isOSVersionAtLeastyBi1_Bw_BwBwtF"
+// CHECK:   call swiftcc void @"$s13back_deployed0A12DeployedFuncyyFTwB"
+// CHECK:   call swiftcc void @"$s13back_deployed0A12DeployedFuncyyF"

test/IRGen/back_deployed_Onone_transparent.swift

@@ -0,0 +1,20 @@
+// RUN: %empty-directory(%t)
+// RUN: %target-swift-frontend -emit-module %S/Inputs/back_deployed.swift -o %t/ -swift-version 5 -enable-library-evolution
+// RUN: %target-swift-frontend -emit-ir %s -I %t -Onone | %FileCheck %s
+
+// _stdlib_isOSVersionAtLeast() is @_transparent on iOS
+// REQUIRES: OS=ios
+
+import back_deployed
+
+public func test() {
+  backDeployedFunc()
+}
+
+// CHECK: define{{.*}} hidden swiftcc void @"$s13back_deployed0A12DeployedFuncyyFTwb"
+// CHECK:   call swiftcc i1 @"$ss31_stdlib_isOSVersionAtLeast_AEICyBi1_Bw_BwBwtF"
+// CHECK:   call swiftcc void @"$s13back_deployed0A12DeployedFuncyyFTwB"
+// CHECK:   call swiftcc void @"$s13back_deployed0A12DeployedFuncyyF"
+
+// CHECK: define{{.*}} hidden swiftcc i1 @"$ss31_stdlib_isOSVersionAtLeast_AEICyBi1_Bw_BwBwtF"
+// CHECK:   call i32 @__isPlatformVersionAtLeast

test/IRGen/temporary_allocation/codegen_very_large_allocation.swift

@@ -7,6 +7,9 @@
 // this function.
 // UNSUPPORTED: OS=xros
 
+// On iOS _stdlib_isOSVersionAtLeast() is @_transparent, which affects codegen.
+// UNSUPPORTED: OS=ios
+
 @_silgen_name("blackHole")
 func blackHole(_ value: UnsafeMutableRawPointer?) -> Void
 

test/SILGen/availability_query_maccatalyst_zippered.swift

@@ -1,11 +1,11 @@
-// RUN: %target-swift-emit-silgen %s -target x86_64-apple-macosx10.52 -target-variant x86_64-apple-ios50.0-macabi | %FileCheck %s
-// RUN: %target-swift-emit-silgen %s -target x86_64-apple-ios50.0-macabi -target-variant x86_64-apple-macosx10.52 | %FileCheck %s
+// RUN: %target-swift-emit-silgen %s -target %target-cpu-apple-macosx10.52 -target-variant %target-cpu-apple-ios50.0-macabi | %FileCheck %s
+// RUN: %target-swift-emit-silgen %s -target %target-cpu-apple-ios50.0-macabi -target-variant %target-cpu-apple-macosx10.52 | %FileCheck %s
 
-// RUN: %target-swift-emit-silgen %s -target x86_64-apple-macosx10.14.4 -target-variant x86_64-apple-ios50.0-macabi | %FileCheck %s --check-prefix=CHECK-BACKDEPLOY-MAC
-// RUN: %target-swift-emit-silgen %s -target x86_64-apple-ios50.0-macabi -target-variant x86_64-apple-macosx10.14.4 | %FileCheck %s --check-prefix=CHECK-BACKDEPLOY-MAC
+// RUN: %target-swift-emit-silgen %s -target %target-cpu-apple-macosx10.14.4 -target-variant %target-cpu-apple-ios50.0-macabi | %FileCheck %s --check-prefix=CHECK-BACKDEPLOY-MAC
+// RUN: %target-swift-emit-silgen %s -target %target-cpu-apple-ios50.0-macabi -target-variant %target-cpu-apple-macosx10.14.4 | %FileCheck %s --check-prefix=CHECK-BACKDEPLOY-MAC
 
-// RUN: %target-swift-emit-silgen %s -target x86_64-apple-macosx10.15 -target-variant x86_64-apple-ios50.0-macabi | %FileCheck %s --check-prefix=CHECK-DEPLOY10_15-MAC
-// RUN: %target-swift-emit-silgen %s -target x86_64-apple-ios50.0-macabi -target-variant x86_64-apple-macosx10.15 | %FileCheck %s --check-prefix=CHECK-DEPLOY10_15-MAC
+// RUN: %target-swift-emit-silgen %s -target %target-cpu-apple-macosx10.15 -target-variant %target-cpu-apple-ios50.0-macabi | %FileCheck %s --check-prefix=CHECK-DEPLOY10_15-MAC
+// RUN: %target-swift-emit-silgen %s -target %target-cpu-apple-ios50.0-macabi -target-variant %target-cpu-apple-macosx10.15 | %FileCheck %s --check-prefix=CHECK-DEPLOY10_15-MAC
 
 // REQUIRES: OS=macosx || OS=maccatalyst