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    X87: [turbofan]: Support using push instructions for setting up tail call parameters. · c140a90c
    zhengxing.li authored
      port bd0d9e7d (r37477)
    
      original commit message:
      This optimizes the passing of stack parameters in function calls.
    
      For some architectures (ia32/x64), using pushes when possible instead
      of bumping the stack and then storing parameters generates much
      smaller code, and in some cases is faster (e.g. when a push of a memory
      location can implement a memory-to-memory copy and thus elide an
      intermediate load. On others (e.g. ARM), the benefit is smaller, where
      it's only possible to elide direct stack pointer adjustment in certain cases
      or combine multiple register stores into a single instruction in other limited
      situations. On yet other platforms (ARM64, MIPS), there are no push instructions,
      and this optimization isn't used at all.
    
      Ideally, this mechanism would be used for both tail calls and normal calls,
      but "normal" calls are currently pretty efficient, and tail calls are very
      inefficient, so this CL sets the bar low for building a new mechanism to
      handle parameter pushing that only needs to raise the bar on tail calls for now.
    
      The key aspect of this change is that adjustment to the stack pointer
      for tail calls (and perhaps later real calls) is an explicit step separate from
      instruction selection and gap resolution, but aware of both, making it possible
      to safely recognize gap moves that are actually pushes.
    
    BUG=
    
    Review-Url: https://codereview.chromium.org/2120413002
    Cr-Commit-Position: refs/heads/master@{#37508}
    c140a90c
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