6502/llvm-6502
1
0
Fork 0
mirror of https://github.com/c64scene-ar/llvm-6502.git synced 2026-04-25 21:18:19 +00:00
Code Issues Projects Releases Wiki Activity

optimize cttz and ctlz when we can prove something about the

Browse Source 
leading/trailing bits.  Patch by Alastair Lynn!


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@92706 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Chris Lattner
2010-01-05 07:23:56 +00:00
parent f87cd93e0c
commit 16507fe9fd
2 changed files with 58 additions and 2 deletions
Download Patch File Download Diff File Expand all files Collapse all files
lib/Transforms/InstCombine/InstructionCombining.cpp
+34 -1
View File
@@ -3144,7 +3144,40 @@ Instruction *InstCombiner::visitCallInst(CallInst &CI) {
II->getOperand(1));
}
break;
case Intrinsic::cttz: {
// If all bits below the first known one are known zero,
// this value is constant.
const IntegerType *IT = cast<IntegerType>(II->getOperand(1)->getType());
uint32_t BitWidth = IT->getBitWidth();
APInt KnownZero(BitWidth, 0);
APInt KnownOne(BitWidth, 0);
ComputeMaskedBits(II->getOperand(1), APInt::getAllOnesValue(BitWidth),
KnownZero, KnownOne);
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.
const IntegerType *IT = cast<IntegerType>(II->getOperand(1)->getType());
uint32_t BitWidth = IT->getBitWidth();
APInt KnownZero(BitWidth, 0);
APInt KnownOne(BitWidth, 0);
ComputeMaskedBits(II->getOperand(1), APInt::getAllOnesValue(BitWidth),
KnownZero, KnownOne);
unsigned LeadingZeros = KnownOne.countLeadingZeros();
APInt Mask(APInt::getHighBitsSet(BitWidth, LeadingZeros));
if ((Mask & KnownZero) == Mask)
return ReplaceInstUsesWith(CI, ConstantInt::get(IT,
APInt(BitWidth, LeadingZeros)));
}
break;
case Intrinsic::uadd_with_overflow: {
Value *LHS = II->getOperand(1), *RHS = II->getOperand(2);
const IntegerType *IT = cast<IntegerType>(II->getOperand(1)->getType());