[clang][headers][Apple] Don't include_next float.h to avoid an unnecessary module dependency

[ian-twilightcoder]

float.h doesn't define anything in Apple's SDKs that the clang float.h doesn't undefine, so all the include_next does is add an unnecessary module dependency. Skip the include_next and completely shadow the SDK header.

[llvmbot]

@llvm/pr-subscribers-clang

@llvm/pr-subscribers-backend-x86

Author: Ian Anderson (ian-twilightcoder)

Changes

float.h doesn't define anything in Apple's SDKs that the clang float.h doesn't undefine, so all the include_next does is add an unnecessary module dependency. Skip the include_next and completely shadow the SDK header.

---

Full diff: https://github.com/llvm/llvm-project/pull/137432.diff

1 Files Affected:

• (modified) clang/lib/Headers/float.h (+2-11)

diff --git a/clang/lib/Headers/float.h b/clang/lib/Headers/float.h
index e5c439a9d47ae..84551af473b28 100644
--- a/clang/lib/Headers/float.h
+++ b/clang/lib/Headers/float.h
@@ -18,21 +18,12 @@
  * additional definitions provided for Windows.
  * For more details see http://msdn.microsoft.com/en-us/library/y0ybw9fy.aspx
  *
- * Also fall back on Darwin and AIX to allow additional definitions and
+ * Also fall back on AIX to allow additional definitions and
  * implementation-defined values.
  */
-#if (defined(__APPLE__) || defined(__MINGW32__) || defined(_MSC_VER) ||        \
-     defined(_AIX)) &&                                                         \
+#if (defined(__MINGW32__) || defined(_MSC_VER) || defined(_AIX)) &&            \
     __STDC_HOSTED__ && __has_include_next(<float.h>)
 
-/* Prior to Apple's 10.7 SDK, float.h SDK header used to apply an extra level
- * of #include_next<float.h> to keep Metrowerks compilers happy. Avoid this
- * extra indirection.
- */
-#ifdef __APPLE__
-#define _FLOAT_H_
-#endif
-
 #  include_next <float.h>
 
 /* Undefine anything that we'll be redefining below. */

[ian-twilightcoder]

This was originally added in d93779d / d89a1eb (can't find either of these in Phabricator) for _HAS_SUBNORM, but that's since been obsoleted by https://reviews.llvm.org/D37302. So including this header just causes an unnecessary include and module build of Apple's float.h.

[AaronBallman]

LGTM assuming @rjmccall or @ldionne have no concerns

[cyndyishida]

AFAICT this seems like a good cleanup for detangling sdk dependencies where its safe to.

[rjmccall]

Messing around with #include_next is scary, but the problems are always thorny reasons that only come up in intense testing; I don't see anything obviously wrong, and I trust @ian-twilightcoder to have done the investigation properly. LGTM.