[PATCH] D128461: [X86] Simplify __cpuid_count

[Fangrui Song via Phabricator via cfe-commits]

MaskRay created this revision.
Herald added subscribers: jsji, StephenFan, pengfei.
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MaskRay requested review of this revision.
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Use the x86-32 implementation for x86-64, i.e. replace =r plus xchgq with =b.
Using =r seems like a workaround when RBX as a base register did not
work well =b (2014-09 416efb5f909e45f67ee81d382a708fc41666c5c6), likely
no longer relevant today.


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D128461

Files:
  clang/lib/Headers/cpuid.h


Index: clang/lib/Headers/cpuid.h
===================================================================
--- clang/lib/Headers/cpuid.h
+++ clang/lib/Headers/cpuid.h
@@ -235,7 +235,6 @@
 #define bit_WBNOINVD    0x00000200
 
 
-#if __i386__
 #define __cpuid(__leaf, __eax, __ebx, __ecx, __edx) \
     __asm("cpuid" : "=a"(__eax), "=b" (__ebx), "=c"(__ecx), "=d"(__edx) \
                   : "0"(__leaf))
@@ -243,22 +242,6 @@
 #define __cpuid_count(__leaf, __count, __eax, __ebx, __ecx, __edx) \
     __asm("cpuid" : "=a"(__eax), "=b" (__ebx), "=c"(__ecx), "=d"(__edx) \
                   : "0"(__leaf), "2"(__count))
-#else
-/* x86-64 uses %rbx as the base register, so preserve it. */
-#define __cpuid(__leaf, __eax, __ebx, __ecx, __edx) \
-    __asm("  xchgq  %%rbx,%q1\n" \
-          "  cpuid\n" \
-          "  xchgq  %%rbx,%q1" \
-        : "=a"(__eax), "=r" (__ebx), "=c"(__ecx), "=d"(__edx) \
-        : "0"(__leaf))
-
-#define __cpuid_count(__leaf, __count, __eax, __ebx, __ecx, __edx) \
-    __asm("  xchgq  %%rbx,%q1\n" \
-          "  cpuid\n" \
-          "  xchgq  %%rbx,%q1" \
-        : "=a"(__eax), "=r" (__ebx), "=c"(__ecx), "=d"(__edx) \
-        : "0"(__leaf), "2"(__count))
-#endif
 
 static __inline int __get_cpuid_max (unsigned int __leaf, unsigned int *__sig)
 {


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