[libc-commits] [libc] [libc] Proof of concept of aliasing long double math functions. (PR #132627)

[via libc-commits]

================
@@ -37,21 +37,47 @@
 
 #define LLVM_LIBC_ATTR(name) EXPAND_THEN_SECOND(LLVM_LIBC_FUNCTION_ATTR_##name)
 
-// MacOS needs to be excluded because it does not support aliasing.
-#if defined(LIBC_COPT_PUBLIC_PACKAGING) && (!defined(__APPLE__))
-#define LLVM_LIBC_FUNCTION_IMPL(type, name, arglist)                           \
+// MacOS needs to be excluded because it does not support [[gnu::aliasing]].
+#ifndef __APPLE__
+
+#if defined(LIBC_COPT_PUBLIC_PACKAGING)
+#define LLVM_LIBC_FUNCTION(type, name, arglist)                                \
   LLVM_LIBC_ATTR(name)                                                         \
   LLVM_LIBC_FUNCTION_ATTR decltype(LIBC_NAMESPACE::name)                       \
-      __##name##_impl__ __asm__(#name);                                        \
+      __##name##_impl__ asm(#name);                                            \
   decltype(LIBC_NAMESPACE::name) name [[gnu::alias(#name)]];                   \
   type __##name##_impl__ arglist
-#else
-#define LLVM_LIBC_FUNCTION_IMPL(type, name, arglist) type name arglist
-#endif
 
-// This extra layer of macro allows `name` to be a macro to rename a function.
+#define LLVM_LIBC_ALIASING_FUNCTION(name, func)                                \
+  namespace LIBC_NAMESPACE_DECL {                                              \
----------------
lntue wrote:

it's because when adding aliases for `copysignl`, we will need to include `copysignl.h` header.  So to keep them in just one `#if ... #endif` block for ease of use, it's cleaner to add the namespace to the macro than having 1 line macro in the namespace all the time, like:
```
#if ...
#include "copysignl.h"

namespace LIBC_NAMESPACE_DECL {
  LLVM_LIBC_ALIASING_FUNCTION(copysignl, copysignf128);
}
#endif
```
vs
```
#if ...
#include "copysignl.h"

LLVM_LIBC_ALIASING_FUNCTION(copysignl, copysignf128);
#endif

https://github.com/llvm/llvm-project/pull/132627