[Modules] Avoid false swift module sharing

When the swiftmodule is built with different clang importer arguments,
they can have the same module hash, causing them to be wrongly re-used even
they contains different interfaces.

Add ReducedExtraArgs to the module hash to disambiguate them.

rdar://131408266
(cherry picked from commit d3adf17)

Author: cachemeifyoucan

lib/Frontend/ModuleInterfaceLoader.cpp

@@ -2035,6 +2035,8 @@ InterfaceSubContextDelegateImpl::getCacheHash(StringRef useInterfacePath,
   auto normalizedTargetTriple =
       getTargetSpecificModuleTriple(genericSubInvocation.getLangOptions().Target);
   std::string sdkBuildVersion = getSDKBuildVersion(sdkPath);
+  const auto ExtraArgs = genericSubInvocation.getClangImporterOptions()
+                             .getReducedExtraArgsForSwiftModuleDependency();
 
   llvm::hash_code H = hash_combine(
       // Start with the compiler version (which will be either tag names or
@@ -2076,6 +2078,10 @@ InterfaceSubContextDelegateImpl::getCacheHash(StringRef useInterfacePath,
       // correctly load the dependencies.
       genericSubInvocation.getCASOptions().getModuleScanningHashComponents(),
 
+      // Clang ExtraArgs that affects how clang types are imported into swift
+      // module.
+      llvm::hash_combine_range(ExtraArgs.begin(), ExtraArgs.end()),
+
       // Whether or not OSSA modules are enabled.
       //
       // If OSSA modules are enabled, we use a separate namespace of modules to

test/ScanDependencies/module_hash.swift

@@ -0,0 +1,46 @@
+// RUN: %empty-directory(%t)
+// RUN: split-file %s %t
+
+// RUN: %target-swift-frontend -scan-dependencies -module-name Test %t/main-1.swift -module-cache-path %t/clang-module-cache \
+// RUN:   -disable-implicit-string-processing-module-import -disable-implicit-concurrency-module-import -O \
+// RUN:   -o %t/deps-1.json -I %t/include
+
+// RUN: %target-swift-frontend -scan-dependencies -module-name Test %t/main-2.swift -module-cache-path %t/clang-module-cache \
+// RUN:   -disable-implicit-string-processing-module-import -disable-implicit-concurrency-module-import -O \
+// RUN:   -o %t/deps-2.json -Xcc -DHAS_FOO=1 -I %t/include
+
+// RUN: %{python} %S/../CAS/Inputs/SwiftDepsExtractor.py %t/deps-1.json Library modulePath > %t/path-1
+// RUN: %{python} %S/../CAS/Inputs/SwiftDepsExtractor.py %t/deps-2.json Library modulePath > %t/path-2
+
+/// Library module should not have the same path.
+// RUN: not diff %t/path-1 %t/path-2
+
+//--- main-1.swift
+import Library
+func test() {
+    bar();
+}
+
+//--- main-2.swift
+import Library
+func test() {
+    foo();
+}
+
+//--- include/Library.swiftinterface
+// swift-interface-format-version: 1.0
+// swift-module-flags: -module-name Library -O -disable-implicit-string-processing-module-import -disable-implicit-concurrency-module-import -user-module-version 1.0
+@_exported import A
+public func test() {}
+
+//--- include/a.h
+#ifdef HAS_FOO
+void foo(void);
+#endif
+void bar(void);
+
+//--- include/module.modulemap
+module A {
+  header "a.h"
+  export *
+}