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[TTI] Improved cost heuristic for cttz/ctlz calls.

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This patch is a follow-up of r228826 (see code-review: D7506).

Now that SimplifyCFG uses TargetTransformInfo for cost analysis, we 
have to fix the cost heuristic for intrinsic calls to cttz/ctlz.

This patch defines method 'getIntrinsicCost' in BasicTTIImpl: now, BasicTTIImpl
queries TLI to check if a call to cttz/ctlz is cheap for the target.

Added test cases in Transforms/SimplifyCFG/X86 to verify that on x86,
SimplifyCFG only speculates a call to cttz/ctlz if it is cheap.

Differential Revision: http://reviews.llvm.org/D7554


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@228829 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Andrea Di Biagio
2015-02-11 14:22:18 +00:00
parent 1777ae7a05
commit f033db57e9
3 changed files with 163 additions and 16 deletions
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22
include/llvm/CodeGen/BasicTTIImpl.h
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@@ -150,6 +150,28 @@ public:
return getTLI()->isTypeLegal(VT);
}
unsigned getIntrinsicCost(Intrinsic::ID IID, Type *RetTy,
ArrayRef<const Value *> Arguments) {
return BaseT::getIntrinsicCost(IID, RetTy, Arguments);
}
unsigned getIntrinsicCost(Intrinsic::ID IID, Type *RetTy,
ArrayRef<Type *> ParamTys) {
if (IID == Intrinsic::cttz) {
if (getTLI()->isCheapToSpeculateCttz())
return TargetTransformInfo::TCC_Basic;
return TargetTransformInfo::TCC_Expensive;
}
if (IID == Intrinsic::ctlz) {
if (getTLI()->isCheapToSpeculateCtlz())
return TargetTransformInfo::TCC_Basic;
return TargetTransformInfo::TCC_Expensive;
}
return BaseT::getIntrinsicCost(IID, RetTy, ParamTys);
}
unsigned getJumpBufAlignment() { return getTLI()->getJumpBufAlignment(); }
unsigned getJumpBufSize() { return getTLI()->getJumpBufSize(); }