[LLVMbugs] [Bug 22024] New: Unnecessary vxorps instructions

[bugzilla-daemon at llvm.org]

http://llvm.org/bugs/show_bug.cgi?id=22024

            Bug ID: 22024
           Summary: Unnecessary vxorps instructions
           Product: libraries
           Version: trunk
          Hardware: PC
                OS: Linux
            Status: NEW
          Severity: normal
          Priority: P
         Component: Backend: X86
          Assignee: unassignedbugs at nondot.org
          Reporter: tobias at grosser.es
                CC: llvmbugs at cs.uiuc.edu
    Classification: Unclassified

Created attachment 13590
  --> http://llvm.org/bugs/attachment.cgi?id=13590&action=edit
Test case

For the following code:

void foo(float *A, float *B, long x, long y) {
        *B = y;
    *A = x;
}

gcc -S -o - /tmp/test.c -O3 -mavx

    vcvtsi2ssq    %rcx, %xmm0, %xmm0
    vmovss    %xmm0, (%rsi)
    vcvtsi2ssq    %rdx, %xmm0, %xmm0
    vmovss    %xmm0, (%rdi)
    ret

clang -S -o - /tmp/test.c -O3 -mavx

    vcvtsi2ssq    %rcx, %xmm0, %xmm0
    vmovss    %xmm0, (%rsi)
    vxorps    %xmm0, %xmm0, %xmm0
    vcvtsi2ssq    %rdx, %xmm0, %xmm0
    vmovss    %xmm0, (%rdi)
    retq

The vxorps instruction is unnecessary.

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