[llvm-bugs] [Bug 42538] New: vzeroupper elimination

[via llvm-bugs]

https://bugs.llvm.org/show_bug.cgi?id=42538

            Bug ID: 42538
           Summary: vzeroupper elimination
           Product: libraries
           Version: trunk
          Hardware: PC
                OS: Linux
            Status: NEW
          Severity: enhancement
          Priority: P
         Component: Backend: X86
          Assignee: unassignedbugs at nondot.org
          Reporter: david.bolvansky at gmail.com
                CC: craig.topper at gmail.com, llvm-bugs at lists.llvm.org,
                    llvm-dev at redking.me.uk, spatel+llvm at rotateright.com

#include <immintrin.h>

Since GCC 9+, GCC can eliminate vzeroupper in various cases, e.g.:

long long get_elem2(__m256i v) {
    return v[2];
}

Clang -O3 -march=skylake-avx512
get_elem2:
        vextracti128    xmm0, ymm0, 1
        vmovq   rax, xmm0
        vzeroupper
        ret

GCC  -O3 -march=skylake-avx512
get_elem2:
        vextracti64x2   xmm0, ymm0, 0x1
        vmovq   rax, xmm0
        ret

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