[PATCH] [X86] Memory folding for commutative instructions.

[Simon Pilgrim]

Hi nadav, andreadb, spatel,

This patch improves support for commutative instructions in the x86 memory folding implementation by attempting to fold a commuted version of the instruction if the original folding fails - if that folding fails as well the instruction is 're-commuted' back to its original order before returning.

This mainly helps the stack inliner better fold reloads of 3 (or more) operand instructions (VEX encoded SSE etc.) but by performing this in the lowest foldMemoryOperandImpl implementation it also replaces the X86InstrInfo::optimizeLoadInstr version and is now used by FastISel too.

Unlike the X86InstrInfo::optimizeLoadInstr implementation it uses findCommutedOpIndices instead of hard coded commute operand indices.

http://reviews.llvm.org/D5701

Files:
  lib/Target/X86/X86FastISel.cpp
  lib/Target/X86/X86InstrInfo.cpp
  lib/Target/X86/X86InstrInfo.h
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