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Subzero: Improve effectiveness of local register availability peephole. · f531931fJim Stichnoth authored
X86 only. The register availability peephole optimization during lowering disallows available register substitution when the variable is pre-colored. This is for good reasons (too complex to be discussed here). However, that leaves some potential substitutions on the table. Specifically, this happens a lot around register arguments to function calls, both at the call site and in the prolog. The simplest solution seems to be to launder the pre-colored variable through a separate infinite-weight variable, as implemented in this CL through a combination of such copies and extra legalize() calls. There are other situations where this technique can also work, which may be handled in a separate CL. This CL also fixes a problem where the stack pointer adjustment in the prolog is subject to dead-code elimination if the function has no epilog. This would only happen in asm-verbose mode, in the final liveness analysis pass prior to code emission. BUG= none R=eholk@chromium.org Review URL: https://codereview.chromium.org/2052683003 .
f531931f
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