maxjhandsome
/
llvm-project
forked from OSchip/llvm-project
1
0
Fork 0
Code Issues Pull Requests Packages Releases Wiki Activity

[InstCombine] refactor ctlz/cttz folds (NFCI) 

Note that this fold really belongs in InstSimplify.
Refactoring here anyway as an intermediate step because
there's a planned addition to this function in D23134.

Differential Revision: https://reviews.llvm.org/D23223

llvm-svn: 277883
This commit is contained in:
Sanjay Patel 2016-08-05 22:42:46 +00:00
parent 0f6aad4ad2
commit 8e3ab17c44
1 changed files with 33 additions and 34 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

67
llvm/lib/Transforms/InstCombine/InstCombineCalls.cpp
View File

@ -1104,6 +1104,35 @@ static Instruction *simplifyMaskedScatter(IntrinsicInst &II, InstCombiner &IC) {
return nullptr;
}
static Value *foldCttzCtlz(IntrinsicInst &II, InstCombiner &IC) {
Value *Op0 = II.getArgOperand(0);
// FIXME: Try to simplify vectors of integers.
auto *IT = dyn_cast<IntegerType>(Op0->getType());
if (!IT)
return nullptr;
unsigned BitWidth = IT->getBitWidth();
APInt KnownZero(BitWidth, 0);
APInt KnownOne(BitWidth, 0);
IC.computeKnownBits(Op0, KnownZero, KnownOne, 0, &II);
// Create a mask for bits above (ctlz) or below (cttz) the first known one.
bool IsTZ = II.getIntrinsicID() == Intrinsic::cttz;
unsigned NumMaskBits = IsTZ ? KnownOne.countTrailingZeros()
: KnownOne.countLeadingZeros();
APInt Mask = IsTZ ? APInt::getLowBitsSet(BitWidth, NumMaskBits)
: APInt::getHighBitsSet(BitWidth, NumMaskBits);
// If all bits above (ctlz) or below (cttz) the first known one are known
// zero, this value is constant.
// FIXME: This should be in InstSimplify because we're replacing an
// instruction with a constant.
if ((Mask & KnownZero) == Mask)
return ConstantInt::get(IT, APInt(BitWidth, NumMaskBits));
return nullptr;
}
// TODO: If the x86 backend knew how to convert a bool vector mask back to an
// XMM register mask efficiently, we could transform all x86 masked intrinsics
// to LLVM masked intrinsics and remove the x86 masked intrinsic defs.
@ -1397,41 +1426,11 @@ Instruction *InstCombiner::visitCallInst(CallInst &CI) {
II->getArgOperand(0));
}
break;
case Intrinsic::cttz: {
// If all bits below the first known one are known zero,
// this value is constant.
IntegerType *IT = dyn_cast<IntegerType>(II->getArgOperand(0)->getType());
// FIXME: Try to simplify vectors of integers.
if (!IT) break;
uint32_t BitWidth = IT->getBitWidth();
APInt KnownZero(BitWidth, 0);
APInt KnownOne(BitWidth, 0);
computeKnownBits(II->getArgOperand(0), KnownZero, KnownOne, 0, II);
unsigned TrailingZeros = KnownOne.countTrailingZeros();
APInt Mask(APInt::getLowBitsSet(BitWidth, TrailingZeros));
if ((Mask & KnownZero) == Mask)
return replaceInstUsesWith(CI, ConstantInt::get(IT,
APInt(BitWidth, TrailingZeros)));
}
break;
case Intrinsic::ctlz: {
// If all bits above the first known one are known zero,
// this value is constant.
IntegerType *IT = dyn_cast<IntegerType>(II->getArgOperand(0)->getType());
// FIXME: Try to simplify vectors of integers.
if (!IT) break;
uint32_t BitWidth = IT->getBitWidth();
APInt KnownZero(BitWidth, 0);
APInt KnownOne(BitWidth, 0);
computeKnownBits(II->getArgOperand(0), KnownZero, KnownOne, 0, II);
unsigned LeadingZeros = KnownOne.countLeadingZeros();
APInt Mask(APInt::getHighBitsSet(BitWidth, LeadingZeros));
if ((Mask & KnownZero) == Mask)
return replaceInstUsesWith(CI, ConstantInt::get(IT,
APInt(BitWidth, LeadingZeros)));
}
case Intrinsic::cttz:
case Intrinsic::ctlz:
if (Value *V = foldCttzCtlz(*II, *this))
return replaceInstUsesWith(*II, V);
break;
case Intrinsic::uadd_with_overflow: