• Andreas Haas's avatar
    [turbofan] For Word32Shl optimizations only consider the last 5 bits of the shift · 5f1661aa
    Andreas Haas authored
    One optimization in the machine-operator-reducer did not consider that
    that word32 shift left instructions only consider the last 5 bits of
    the shift input.
    
    The issue only occurs for WebAssembly because in JavaScript we always
    add a "& 0xf" on the shift value to the TurboFan graph.
    
    For additional background: The JavaScript and WebAssembly spec both
    say that only the last 5 bits of the shift value are used in the
    word32-shift-left operation. This means that an "x << 0x29", in the
    code is actually executed as "x << 0x09". Therefore the changes in
    this CL are okay because they mask the last 5 bit of the shift value.
    
    BUG=chromium:689450
    
    Change-Id: Id92f298ed6d7f1714b109b3f4fbcecd5ac6d30f7
    Reviewed-on: https://chromium-review.googlesource.com/439312Reviewed-by: 's avatarBen Titzer <titzer@chromium.org>
    Commit-Queue: Andreas Haas <ahaas@chromium.org>
    Cr-Commit-Position: refs/heads/master@{#43245}
    5f1661aa
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