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Transform any logical shift of a power of two into an exact/NUW shift when

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in a known-non-zero context.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@131887 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Chris Lattner
2011-05-23 00:21:50 +00:00
parent f415d8b646
commit 05cd886561
2 changed files with 38 additions and 0 deletions
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17
lib/Transforms/InstCombine/InstCombineMulDivRem.cpp
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@ -29,6 +29,23 @@ static Value *simplifyValueKnownNonZero(Value *V, InstCombiner &IC) {
// code.
if (!V->hasOneUse()) return 0;
// (PowerOfTwo >>u B) --> isExact since shifting out the result would make it
// inexact. Similarly for <<.
if (BinaryOperator *I = dyn_cast<BinaryOperator>(V))
if (I->isLogicalShift() &&
isPowerOfTwo(I->getOperand(0), IC.getTargetData())) {
if (I->getOpcode() == Instruction::LShr && !I->isExact()) {
I->setIsExact();
return I;
}
if (I->getOpcode() == Instruction::Shl && !I->hasNoUnsignedWrap()) {
I->setHasNoUnsignedWrap();
return I;
}
}
// ((1 << A) >>u B) --> (1 << (A-B))
// Because V cannot be zero, we know that B is less than A.
Value *A = 0, *B = 0, *PowerOf2 = 0;