[LLVMbugs] [Bug 16391] New: __cpuid_count() not implemented in cpuid.h

[bugzilla-daemon at llvm.org]

http://llvm.org/bugs/show_bug.cgi?id=16391

            Bug ID: 16391
           Summary: __cpuid_count()  not implemented in cpuid.h
           Product: clang
           Version: trunk
          Hardware: PC
                OS: All
            Status: NEW
          Severity: normal
          Priority: P
         Component: Headers
          Assignee: unassignedclangbugs at nondot.org
          Reporter: mark.charney at intel.com
                CC: llvmbugs at cs.uiuc.edu
    Classification: Unclassified

GCC provides a mechanism to query leaf/subleaf of cpuid using the __cpuid_count
function which is a macro in the cpuid.h header file.

(MS provides another) From what I can see, there is
now way in clang to query the cpuid output using both the leaf and subleaf
inputs.


This is required for checking for the presence of newer features on x86 cpus.

One can do ones own inline asm, but it is very error prone considering the
complexity fo the instruction and the registers it clobbers (which have
predefined uses on some systems or compilation styles). 


This is related to issue 12719 from 2012-05-01.

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