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rearrange two transforms, since one subsumes the other. Make the shift-exactness

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xform recurse.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@131888 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Chris Lattner 2011-05-23 00:32:19 +00:00
parent 05cd886561
commit 613f1a3994
1 changed files with 26 additions and 19 deletions
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45
lib/Transforms/InstCombine/InstCombineMulDivRem.cpp
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@ -29,23 +29,8 @@ 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;
}
}
bool MadeChange = false;
// ((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;
@ -57,12 +42,34 @@ static Value *simplifyValueKnownNonZero(Value *V, InstCombiner &IC) {
return IC.Builder->CreateShl(PowerOf2, A);
}
// (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())) {
// We know that this is an exact/nuw shift and that the input is a
// non-zero context as well.
if (Value *V2 = simplifyValueKnownNonZero(I->getOperand(0), IC)) {
I->setOperand(0, V2);
MadeChange = true;
}
if (I->getOpcode() == Instruction::LShr && !I->isExact()) {
I->setIsExact();
MadeChange = true;
}
if (I->getOpcode() == Instruction::Shl && !I->hasNoUnsignedWrap()) {
I->setHasNoUnsignedWrap();
MadeChange = true;
}
}
// TODO: Lots more we could do here:
// "1 >> X" could get an "isexact" bit.
// If V is a phi node, we can call this on each of its operands.
// "select cond, X, 0" can simplify to "X".
return 0;
return MadeChange ? V : 0;
}