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teach the truncation optimization that an entire chain of

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computation can be truncated if it is fed by a sext/zext that doesn't
have to be exactly equal to the truncation result type.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@112285 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Chris Lattner
2010-08-27 20:32:06 +00:00
parent e8ac3f3be4
commit f9d05ab007
2 changed files with 26 additions and 4 deletions
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5
lib/Transforms/InstCombine/InstCombineCasts.cpp
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@ -396,6 +396,11 @@ static bool CanEvaluateTruncated(Value *V, const Type *Ty) {
case Instruction::Trunc:
// trunc(trunc(x)) -> trunc(x)
return true;
case Instruction::ZExt:
case Instruction::SExt:
// trunc(ext(x)) -> ext(x) if the source type is smaller than the new dest
// trunc(ext(x)) -> trunc(x) if the source type is larger than the new dest
return true;
case Instruction::Select: {
SelectInst *SI = cast<SelectInst>(I);
return CanEvaluateTruncated(SI->getTrueValue(), Ty) &&