[PATCH] Remove redundent register mov by improving TwoAddressInstructionPass

[Wei Mi]

I rewrite the code to expand the cases that can be handled.

Now for %reg103 = ADD %reg102, %reg101;  I check whether there is a reversed copy chain from %reg102 to %reg103 or from %reg101 to %reg103. If there is a reversed copy chain from a src operand to a dest oeprand, that src operand will be choosen to be merged with the dest operand.  In this way, the case Quentin suggested like the following will be handled.

// %reg101 = MOV %reg100
// %reg102 = ...
// %reg103 = ADD %reg102, %reg101
// %reg104 = <something> %reg103
// %reg100 = MOV %reg103

I still don't use getUniqueVRegDef to replace getSingleDef because getSingleDef can find out the def inside current BB when a use has multiple defs (one in current BB and one in predecessor BB). This is common because the IR in TwoAddrInstruction pass is already out-of-ssa form. getUniqueVRegDef will return NULL for that case.

Thanks,
Wei.


REPOSITORY
  rL LLVM

http://reviews.llvm.org/D7806

Files:
  lib/CodeGen/TwoAddressInstructionPass.cpp
  test/CodeGen/X86/twoaddr-coalesce-3.ll

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