Merge pull request #78099 from xymus/optional-memcmp-6.1

[6.1] SwiftShims: memcmp should accept optional pointers on Darwin

Author: xymus

stdlib/public/SwiftShims/swift/shims/LibcShims.h

@@ -60,8 +60,11 @@ static inline __swift_size_t _swift_stdlib_strlen_unsigned(const unsigned char *
 SWIFT_READONLY
 static inline int _swift_stdlib_memcmp(const void *s1, const void *s2,
                                        __swift_size_t n) {
+#if defined(__APPLE__)
+  // Darwin defines memcmp with optional pointers, preserve the same type here.
+  extern int memcmp(const void * _Nullable, const void * _Nullable, __swift_size_t);
 // FIXME: Is there a way to identify Glibc specifically?
-#if (defined(__gnu_linux__) || defined(__ANDROID__)) && !defined(__musl__)
+#elif (defined(__gnu_linux__) || defined(__ANDROID__)) && !defined(__musl__)
   extern int memcmp(const void * _Nonnull, const void * _Nonnull, __swift_size_t);
 #else
   extern int memcmp(const void * _Null_unspecified, const void * _Null_unspecified, __swift_size_t);

validation-test/ClangImporter/memcmp-definitions.swift

@@ -1,4 +1,5 @@
-/// rdar://69876253
+/// Darwin's memcmp accepts nullable pointers, make sure the SwiftShims one
+/// preserves the same type.
 // REQUIRES: VENDOR=apple
 // RUN: %target-build-swift %s -o %t.out
 
@@ -9,4 +10,6 @@ func foo () {
   let a = UnsafeMutableRawPointer.allocate(byteCount: 4, alignment: 4)
   let b = UnsafeMutableRawPointer.allocate(byteCount: 4, alignment: 4)
   memcmp(a, b, 4)
+
+  memcmp(nil, nil, 0)
 }