Cherry-pick fixes for availability-checks.

lib/SILOptimizer/Utils/ConstantFolding.cpp

@@ -1408,6 +1408,11 @@ static bool isApplyOfBuiltin(SILInstruction &I, BuiltinValueKind kind) {
 }
 
 static bool isApplyOfKnownAvailability(SILInstruction &I) {
+  // Inlinable functions can be deserialized in other modules which can be
+  // compiled with a different deployment target.
+  if (I.getFunction()->getResilienceExpansion() != ResilienceExpansion::Maximal)
+    return false;
+
   auto apply = FullApplySite::isa(&I);
   if (!apply)
     return false;

lib/SILOptimizer/Utils/Generics.cpp

@@ -2496,7 +2496,20 @@ usePrespecialized(SILOptFunctionBuilder &funcBuilder, ApplySite apply,
     auto specializationAvail = SA->getAvailability();
     auto &ctxt = funcBuilder.getModule().getSwiftModule()->getASTContext();
     auto deploymentAvail = AvailabilityContext::forDeploymentTarget(ctxt);
-    auto currentFnAvailability = apply.getFunction()->getAvailabilityForLinkage();
+    auto currentFn = apply.getFunction();
+    auto isInlinableCtxt = (currentFn->getResilienceExpansion()
+                             == ResilienceExpansion::Minimal);
+    auto currentFnAvailability = currentFn->getAvailabilityForLinkage();
+
+    // If we are in an inlineable function we can't use the specialization except
+    // the inlinable function itself has availability we can use.
+    if (currentFnAvailability.isAlwaysAvailable() && isInlinableCtxt) {
+      continue;
+    }
+    else if (isInlinableCtxt) {
+      deploymentAvail = currentFnAvailability;
+    }
+
     if (!currentFnAvailability.isAlwaysAvailable() &&
         !deploymentAvail.isContainedIn(currentFnAvailability))
       deploymentAvail = currentFnAvailability;

test/SILOptimizer/constant_propagation_availability.swift

@@ -1,8 +1,12 @@
 // RUN: %target-swift-frontend -target %target-cpu-apple-macos10.15 -emit-sil %s | %FileCheck --check-prefix=CHECK-macosx10_15 %s
 // RUN: %target-swift-frontend -target %target-cpu-apple-macos10.14 -emit-sil %s | %FileCheck --check-prefix=CHECK-macosx10_14 %s
-// RUN: %target-swift-frontend -O -target %target-cpu-apple-macos10.15 -emit-sil %s | %FileCheck --check-prefix=CHECK-macosx10_15 %s
+// RUN: %target-swift-frontend -O -target %target-cpu-apple-macos10.15 -emit-sil %s | %FileCheck --check-prefix=CHECK-macosx10_15 --check-prefix=CHECK-macosx10_15_opt %s
 // RUN: %target-swift-frontend -O -target %target-cpu-apple-macos10.14 -emit-sil %s | %FileCheck --check-prefix=CHECK-macosx10_14 %s
 
+// RUN: %empty-directory(%t) 
+// RUN: %target-swift-frontend -O -target %target-cpu-apple-macos10.15 -module-name=Test -emit-module -emit-module-path %t/Test.swiftmodule %s
+// RUN: %sil-opt -target %target-cpu-apple-macos10.15 %t/Test.swiftmodule | %FileCheck --check-prefix=CHECK-inlinable %s
+
 // REQUIRES: OS=macosx
 
 @available(macOS 10.15, *)
@@ -24,13 +28,31 @@ public func testAvailabilityPropagation() -> Int {
   }
 }
 
+@inlinable
+public func testInlinable() -> Int {
+  if #available(macOS 10.15, *) {
+    return newFunction()
+  } else {
+    return 0
+  }
+}
+
 // CHECK-macosx10_15-LABEL: sil @$s33constant_propagation_availability27testAvailabilityPropagationSiyF : $@convention(thin) () -> Int {
 // CHECK-macosx10_15-NOT: apply
 // CHECK-macosx10_15:  [[F:%.*]] = function_ref @$s33constant_propagation_availability11newFunctionSiyF
 // CHECK-macosx10_15:  apply [[F]]() : $@convention(thin) () -> Int
 // CHECK-macosx10_15-NOT: apply
 // CHECK-macosx10_15: } // end sil function '$s33constant_propagation_availability27testAvailabilityPropagationSiyF'
 
+// After serialization, availability checks can be constant folded.
+
+// CHECK-macosx10_15_opt-LABEL: sil @$s33constant_propagation_availability13testInlinableSiyF : $@convention(thin) () -> Int {
+// CHECK-macosx10_15_opt-NOT: apply
+// CHECK-macosx10_15_opt:  [[F:%.*]] = function_ref @$s33constant_propagation_availability11newFunctionSiyF
+// CHECK-macosx10_15_opt:  apply [[F]]() : $@convention(thin) () -> Int
+// CHECK-macosx10_15_opt-NOT: apply
+// CHECK-macosx10_15_opt: } // end sil function '$s33constant_propagation_availability13testInlinableSiyF'
+
 // CHECK-macosx10_14-LABEL: sil @$s33constant_propagation_availability27testAvailabilityPropagationSiyF : $@convention(thin) () -> Int {
 // CHECK-macosx10_14:  [[F:%.*]] = function_ref @$ss26_stdlib_isOSVersionAtLeastyBi1_Bw_BwBwtF
 // CHECK-macosx10_14:  apply [[F]]
@@ -41,3 +63,10 @@ public func testAvailabilityPropagation() -> Int {
 // CHECK-macosx10_14: } // end sil function '$s33constant_propagation_availability27testAvailabilityPropagationSiyF'
 
 // CHECK-macosx10_14: sil [readnone] [_semantics "availability.osversion"] @$ss26_stdlib_isOSVersionAtLeastyBi1_Bw_BwBwtF
+
+// CHECK-inlinable-LABEL: sil {{.*}} @$s4Test13testInlinableSiyF  : $@convention(thin) () -> Int {
+// CHECK-inlinable:  [[F:%.*]] = function_ref @$ss26_stdlib_isOSVersionAtLeastyBi1_Bw_BwBwtF
+// CHECK-inlinable:  apply [[F]]
+// CHECK-inlinable:  [[F:%.*]] = function_ref @$s4Test11newFunctionSiyF
+// CHECK-inlinable:  apply [[F]]() : $@convention(thin) () -> Int
+// CHECK-inlinable: } // end sil function '$s4Test13testInlinableSiyF'