• Zhi An Ng's avatar
    [wasm-simd][x64] Optimize integer splats of constant 0 · 7d7b25d9
    Zhi An Ng authored
    Integer splats (especially for sizes < 32-bits) does not directly
    translate to a single instruction on x64. We can do better for special
    values, like 0, which can be lowered to `xor dst dst`. We do this check
    in the instruction selector, and emit a special opcode kX64S128Zero.
    
    Also change the xor operation for kX64S128Zero from xorps to pxor. This
    can help reduce any potential data bypass delay (search for this on
    agner's microarchitecture manual for more details.). Since integer
    splats are likely to be followed by integer ops, we should remain in the
    integer domain, thus use pxor.
    
    For i64x2.splat the codegen goes from:
    
      xorl rdi,rdi
      vmovq xmm0,rdi
      vmovddup xmm0,xmm0
    
    to:
    
      vpxor xmm0,xmm0,xmm0
    
    Also add a unittest to verify this optimization, and necessary
    raw-assembler methods for the test.
    
    Bug: v8:11093
    Change-Id: I26b092032b6e672f1d5d26e35d79578ebe591cfe
    Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2516299Reviewed-by: 's avatarTobias Tebbi <tebbi@chromium.org>
    Commit-Queue: Zhi An Ng <zhin@chromium.org>
    Cr-Commit-Position: refs/heads/master@{#70977}
    7d7b25d9
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