[LLVMbugs] [Bug 15946] New: Poor code generated for double conditional

[bugzilla-daemon at llvm.org]

http://llvm.org/bugs/show_bug.cgi?id=15946

            Bug ID: 15946
           Summary: Poor code generated for double conditional
           Product: libraries
           Version: trunk
          Hardware: PC
                OS: All
            Status: NEW
          Severity: normal
          Priority: P
         Component: Backend: X86
          Assignee: unassignedbugs at nondot.org
          Reporter: jmuizelaar at mozilla.com
                CC: llvmbugs at cs.uiuc.edu
    Classification: Unclassified

gcc gives:
        xor    %eax,%eax
        ucomisd %xmm0,%xmm1
        seta   %al
        retq

clang gives:
    ucomisd    %xmm0,%xmm1
    seta    %al
    movzbl    %al,%eax
    ret

https://bugzilla.mozilla.org/show_bug.cgi?id=869525#c6 gives some more
justification for this optimization.

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