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Add a new pass on machine instructions to optimize away PHI cycles that

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reduce down to a single value.  InstCombine already does this transformation
but DAG legalization may introduce new opportunities.  This has turned out to
be important for ARM where 64-bit values are split up during type legalization:
InstCombine is not able to remove the PHI cycles on the 64-bit values but
the separate 32-bit values can be optimized.  I measured the compile time 
impact of this (running llc on 176.gcc) and it was not significant.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@95951 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Bob Wilson
2010-02-12 01:30:21 +00:00
parent ccfa1db538
commit fe61fb1e10
5 changed files with 181 additions and 0 deletions
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lib/CodeGen/LLVMTargetMachine.cpp
+1
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@@ -299,6 +299,7 @@ bool LLVMTargetMachine::addCommonCodeGenPasses(PassManagerBase &PM,
if (OptLevel != CodeGenOpt::None) {
PM.add(createOptimizeExtsPass());
PM.add(createOptimizePHIsPass());
if (!DisableMachineLICM)
PM.add(createMachineLICMPass());
if (!DisableMachineSink)