Add arm64 -> arm64e fallback

If we are building for ARM64 but we try to import a module with only an ARM64e interface, fall back to importing said interface.

This is the reverse of a similar fallback briefly introduced last year, but removed in #31196.

Author: beccadax

lib/Serialization/SerializedModuleLoader.cpp

@@ -46,8 +46,23 @@ namespace {
 void forEachTargetModuleBasename(const ASTContext &Ctx,
                                  llvm::function_ref<void(StringRef)> body) {
   auto normalizedTarget = getTargetSpecificModuleTriple(Ctx.LangOpts.Target);
+
+  // An arm64 module can import an arm64e module.
+  Optional<llvm::Triple> normalizedAltTarget;
+  if ((normalizedTarget.getArch() == llvm::Triple::ArchType::aarch64) &&
+      (normalizedTarget.getSubArch() !=
+       llvm::Triple::SubArchType::AArch64SubArch_arm64e)) {
+    auto altTarget = normalizedTarget;
+    altTarget.setArchName("arm64e");
+    normalizedAltTarget = getTargetSpecificModuleTriple(altTarget);
+  }
+
   body(normalizedTarget.str());
 
+  if (normalizedAltTarget) {
+    body(normalizedAltTarget->str());
+  }
+
   // We used the un-normalized architecture as a target-specific
   // module name. Fall back to that behavior.
   body(Ctx.LangOpts.Target.getArchName());
@@ -61,6 +76,10 @@ void forEachTargetModuleBasename(const ASTContext &Ctx,
   if (Ctx.LangOpts.Target.getArch() == llvm::Triple::ArchType::arm) {
     body("arm");
   }
+
+  if (normalizedAltTarget) {
+    body(normalizedAltTarget->getArchName());
+  }
 }
 
 enum class SearchPathKind {

test/ModuleInterface/Inputs/DummyFramework.framework/Modules/DummyFramework.swiftmodule/arm64-apple-ios.swiftinterface

@@ -0,0 +1,10 @@
+// swift-interface-format-version: 1.0
+// swift-compiler-version: Apple Swift version 5.2
+// swift-module-flags: -target arm64e-apple-ios13.0 -enable-library-evolution -swift-version 5 -module-name PtrAuthFramework
+import Swift
+
+#if _ptrauth(_arm64e)
+public let iOSPtrAuth: Bool = true
+#else
+public let iOSNotPtrAuth: Bool = true
+#endif

test/ModuleInterface/Inputs/DummyFramework.framework/Modules/DummyFramework.swiftmodule/arm64.swiftinterface

@@ -0,0 +1,10 @@
+// swift-interface-format-version: 1.0
+// swift-compiler-version: Apple Swift version 5.2
+// swift-module-flags: -target arm64e-apple-macos10.13 -enable-library-evolution -swift-version 5 -module-name PtrAuthFramework
+import Swift
+
+#if _ptrauth(_arm64e)
+public let macOSPtrAuth: Bool = true
+#else
+public let macOSNotPtrAuth: Bool = true
+#endif

test/ModuleInterface/Inputs/DummyFramework.framework/Modules/DummyFramework.swiftmodule/arm64e.swiftinterface

@@ -0,0 +1,11 @@
+// swift-interface-format-version: 1.0
+// swift-compiler-version: Apple Swift version 5.2
+// swift-module-flags: -target arm64e-apple-tvos13.0 -enable-library-evolution -swift-version 5 -module-name PtrAuthFramework
+import Swift
+
+// Intentionally incompatible
+#if _ptrauth(_arm64e)
+public let tvOSPtrAuth: Bool = true
+#else
+public let tvOSNotPtrAuth: Bool = true
+#endif

test/ModuleInterface/Inputs/PtrAuthFramework.framework/Modules/PtrAuthFramework.swiftmodule/arm64e-apple-ios.swiftinterface

@@ -1,7 +1,42 @@
-// RUN: not %target-typecheck-verify-swift -target arm64e-apple-ios13.0 -F %S/Inputs 2>&1 | %FileCheck %s
+// RUN: %empty-directory(%t)
+// RUN: %target-typecheck-verify-swift -F %S/Inputs -module-cache-path %t -verify-ignore-unknown -Rmodule-interface-rebuild
 
-// REQUIRES: OS=ios
-// UNSUPPORTED: OS=maccatalyst
+// PtrAuthFramework only supports these OSes.
+//
+// REQUIRES: OS=tvos || OS=macosx || OS=ios
 
-import DummyFramework
-// CHECK: no such module 'DummyFramework'
+// When run on arm64, this tests that we fall back to the arm64e interface, but
+// build it with `#if _ptrauth(_arm64e)` off.
+//
+// When run on arm64e, this tests that we build the same interface with
+// `#if _ptrauth(_arm64e)` on.
+//
+// REQUIRES: CPU=arm64 || CPU=arm64e
+
+import PtrAuthFramework // expected-remark{{rebuilding module 'PtrAuthFramework' from interface}}
+
+#if os(iOS)
+
+#if _ptrauth(_arm64e)
+public let x: Bool = iOSPtrAuth
+#else
+public let x: Bool = iOSNotPtrAuth
+#endif
+
+#elseif os(macOS)
+
+#if _ptrauth(_arm64e)
+public let x: Bool = macOSPtrAuth
+#else
+public let x: Bool = macOSNotPtrAuth
+#endif
+
+#else
+
+#if _ptrauth(_arm64e)
+public let x: Bool = tvOSPtrAuth
+#else
+public let x: Bool = tvOSNotPtrAuth
+#endif
+
+#endif