Don't use certain attributes in shims or stubs if the attribute doesn't exist

Author: hughbe

stdlib/public/SwiftShims/LibcShims.h

@@ -60,13 +60,13 @@ __swift_size_t _swift_stdlib_fwrite_stdout(const void *ptr, __swift_size_t size,
                                            __swift_size_t nitems);
 
 // String handling <string.h>
-__attribute__((__pure__)) SWIFT_RUNTIME_STDLIB_INTERFACE __swift_size_t
+SWIFT_READONLY SWIFT_RUNTIME_STDLIB_INTERFACE __swift_size_t
 _swift_stdlib_strlen(const char *s);
 
-__attribute__((__pure__)) SWIFT_RUNTIME_STDLIB_INTERFACE __swift_size_t
+SWIFT_READONLY SWIFT_RUNTIME_STDLIB_INTERFACE __swift_size_t
 _swift_stdlib_strlen_unsigned(const unsigned char *s);
 
-__attribute__((__pure__))
+SWIFT_READONLY
 SWIFT_RUNTIME_STDLIB_INTERFACE
 int _swift_stdlib_memcmp(const void *s1, const void *s2, __swift_size_t n);
 
@@ -80,7 +80,7 @@ SWIFT_RUNTIME_STDLIB_INTERFACE
 int _swift_stdlib_close(int fd);
 
 // Non-standard extensions
-__attribute__((__const__)) SWIFT_RUNTIME_STDLIB_INTERFACE __swift_size_t
+SWIFT_READNONE SWIFT_RUNTIME_STDLIB_INTERFACE __swift_size_t
 _swift_stdlib_malloc_size(const void *ptr);
 
 // Random number <random>

stdlib/public/SwiftShims/Visibility.h

@@ -19,7 +19,11 @@
 #define SWIFT_STDLIB_SHIMS_VISIBILITY_H
 
 #if !defined(__has_feature)
-#define __has_feature(x) false
+#define __has_feature(x) 0
+#endif
+
+#if !defined(__has_attribute)
+#define __has_attribute(x) 0
 #endif
 
 #if __has_feature(nullability)
@@ -40,6 +44,18 @@
 # define SWIFT_END_NULLABILITY_ANNOTATIONS
 #endif
 
+#if __has_attribute(pure)
+#define SWIFT_READONLY __attribute__((__pure__))
+#else
+#define SWIFT_READONLY
+#endif
+
+#if __has_attribute(const)
+#define SWIFT_READNONE __attribute__((__const__))
+#else
+#define SWIFT_READNONE
+#endif
+
 // TODO: support using shims headers in overlays by parameterizing
 // SWIFT_RUNTIME_EXPORT on the library it's exported from, then setting
 // protected vs. default based on the current value of __SWIFT_CURRENT_DYLIB.

stdlib/public/stubs/Stubs.cpp

@@ -65,6 +65,7 @@ static long double swift_strtold_l(const char *nptr,
 #endif
 #include <limits>
 #include "llvm/ADT/StringExtras.h"
+#include "llvm/Support/Compiler.h"
 #include "swift/Runtime/Debug.h"
 #include "swift/Basic/Lazy.h"
 
@@ -394,7 +395,13 @@ __muloti4(ti_int a, ti_int b, int* overflow)
 // some other lower-level architecture issue that I'm
 // missing.  Perhaps relevant bug report:
 // FIXME: https://llvm.org/bugs/show_bug.cgi?id=14469
-typedef int di_int __attribute__((__mode__(DI)));
+#if __has_attribute(__mode__(DI))
+#define SWIFT_MODE_DI __attribute__((__mode__(DI)))
+#else
+#define SWIFT_MODE_DI
+#endif
+
+typedef int di_int SWIFT_MODE_DI;
 SWIFT_RUNTIME_STDLIB_INTERFACE
 di_int
 __mulodi4(di_int a, di_int b, int* overflow)