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Rename ValueRequiresCast to ShouldOptimizeCast, to better reflect

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what it does.  Enhance it to return false to optimizing vector
sign extensions from vector comparisions, which is the idiom used
to get a splatted vector for a vector comparison.

Doing this breaks vector-casts.ll, add some compensating 
transformations to handle the important case they cover without
depending on this canonicalization.

This fixes rdar://7434900 a serious pessimization of vector compares.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@95855 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Chris Lattner
2010-02-11 06:26:33 +00:00
parent 2e1cdbf92d
commit 8c5ad3a5da
4 changed files with 113 additions and 55 deletions
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23
lib/Transforms/InstCombine/InstCombineCasts.cpp
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@@ -255,17 +255,26 @@ isEliminableCastPair(
return Instruction::CastOps(Res);
}
/// ValueRequiresCast - Return true if the cast from "V to Ty" actually results
/// in any code being generated. It does not require codegen if V is simple
/// enough or if the cast can be folded into other casts.
bool InstCombiner::ValueRequiresCast(Instruction::CastOps opcode,const Value *V,
const Type *Ty) {
/// ShouldOptimizeCast - Return true if the cast from "V to Ty" actually
/// results in any code being generated and is interesting to optimize out. If
/// the cast can be eliminated by some other simple transformation, we prefer
/// to do the simplification first.
bool InstCombiner::ShouldOptimizeCast(Instruction::CastOps opc, const Value *V,
const Type *Ty) {
// Noop casts and casts of constants should be eliminated trivially.
if (V->getType() == Ty || isa<Constant>(V)) return false;
// If this is another cast that can be eliminated, it isn't codegen either.
// If this is another cast that can be eliminated, we prefer to have it
// eliminated.
if (const CastInst *CI = dyn_cast<CastInst>(V))
if (isEliminableCastPair(CI, opcode, Ty, TD))
if (isEliminableCastPair(CI, opc, Ty, TD))
return false;
// If this is a vector sext from a compare, then we don't want to break the
// idiom where each element of the extended vector is either zero or all ones.
if (opc == Instruction::SExt && isa<CmpInst>(V) && isa<VectorType>(Ty))
return false;
return true;
}