[Bug driver/50740] CPUID leaf 7 for BMI/BMI2/AVX2 feature detection not qualified with max_level and doesn't use subleaf

["warnerme at ptd dot net" <gcc-bugzilla at gcc dot gnu dot org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=50740

Mark Warner <warnerme at ptd dot net> changed:

           What    |Removed                     |Added
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                 CC|                            |warnerme at ptd dot net

--- Comment #4 from Mark Warner <warnerme at ptd dot net> ---
In the file cpuid.h, there is a problem with the definition:

#define __cpuid(level, a, b, c, d)                      \
  __asm__ ("cpuid\n\t"                                  \
           : "=a" (a), "=b" (b), "=c" (c), "=d" (d)     \
           : "0" (level))

With the ecx undefined, the leaf 7 (Extended Features %eax == 7) can not be
accessed.  Leaf 7 (%eax) can only be accessed when sub-leaf (%ecx) is 0

I suggest instead:
#define __cpuid(level, a, b, c, d)                      \
  __asm__ ("cpuid\n\t"                                  \
           : "=a" (a), "=b" (b), "=c" (c), "=d" (d)     \
           : "0" (level), "2" (0))