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Always compute all the bits in ComputeMaskedBits.

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This allows us to keep passing reduced masks to SimplifyDemandedBits, but
know about all the bits if SimplifyDemandedBits fails. This allows instcombine
to simplify cases like the one in the included testcase.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@154011 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Rafael Espindola
2012-04-04 12:51:34 +00:00
parent 00b73a5e44
commit 26c8dcc692
35 changed files with 265 additions and 417 deletions
Download Patch File Download Diff File Expand all files Collapse all files
lib/Transforms/InstCombine/InstCombineSimplifyDemanded.cpp
+10 -16
View File
@@ -142,7 +142,7 @@ Value *InstCombiner::SimplifyDemandedUseBits(Value *V, APInt DemandedMask,
Instruction *I = dyn_cast<Instruction>(V);
if (!I) {
ComputeMaskedBits(V, DemandedMask, KnownZero, KnownOne, Depth);
ComputeMaskedBits(V, KnownZero, KnownOne, Depth);
return 0; // Only analyze instructions.
}
@@ -156,10 +156,8 @@ Value *InstCombiner::SimplifyDemandedUseBits(Value *V, APInt DemandedMask,
// this instruction has a simpler value in that context.
if (I->getOpcode() == Instruction::And) {
// If either the LHS or the RHS are Zero, the result is zero.
ComputeMaskedBits(I->getOperand(1), DemandedMask,
RHSKnownZero, RHSKnownOne, Depth+1);
ComputeMaskedBits(I->getOperand(0), DemandedMask & ~RHSKnownZero,
LHSKnownZero, LHSKnownOne, Depth+1);
ComputeMaskedBits(I->getOperand(1), RHSKnownZero, RHSKnownOne, Depth+1);
ComputeMaskedBits(I->getOperand(0), LHSKnownZero, LHSKnownOne, Depth+1);
// If all of the demanded bits are known 1 on one side, return the other.
// These bits cannot contribute to the result of the 'and' in this
@@ -180,10 +178,8 @@ Value *InstCombiner::SimplifyDemandedUseBits(Value *V, APInt DemandedMask,
// only bits from X or Y are demanded.
// If either the LHS or the RHS are One, the result is One.
ComputeMaskedBits(I->getOperand(1), DemandedMask,
RHSKnownZero, RHSKnownOne, Depth+1);
ComputeMaskedBits(I->getOperand(0), DemandedMask & ~RHSKnownOne,
LHSKnownZero, LHSKnownOne, Depth+1);
ComputeMaskedBits(I->getOperand(1), RHSKnownZero, RHSKnownOne, Depth+1);
ComputeMaskedBits(I->getOperand(0), LHSKnownZero, LHSKnownOne, Depth+1);
// If all of the demanded bits are known zero on one side, return the
// other. These bits cannot contribute to the result of the 'or' in this
@@ -206,7 +202,7 @@ Value *InstCombiner::SimplifyDemandedUseBits(Value *V, APInt DemandedMask,
}
// Compute the KnownZero/KnownOne bits to simplify things downstream.
ComputeMaskedBits(I, DemandedMask, KnownZero, KnownOne, Depth);
ComputeMaskedBits(I, KnownZero, KnownOne, Depth);
return 0;
}
@@ -219,7 +215,7 @@ Value *InstCombiner::SimplifyDemandedUseBits(Value *V, APInt DemandedMask,
switch (I->getOpcode()) {
default:
ComputeMaskedBits(I, DemandedMask, KnownZero, KnownOne, Depth);
ComputeMaskedBits(I, KnownZero, KnownOne, Depth);
break;
case Instruction::And:
// If either the LHS or the RHS are Zero, the result is zero.
@@ -570,7 +566,7 @@ Value *InstCombiner::SimplifyDemandedUseBits(Value *V, APInt DemandedMask,
// Otherwise just hand the sub off to ComputeMaskedBits to fill in
// the known zeros and ones.
ComputeMaskedBits(V, DemandedMask, KnownZero, KnownOne, Depth);
ComputeMaskedBits(V, KnownZero, KnownOne, Depth);
// Turn this into a xor if LHS is 2^n-1 and the remaining bits are known
// zero.
@@ -729,10 +725,8 @@ Value *InstCombiner::SimplifyDemandedUseBits(Value *V, APInt DemandedMask,
// The sign bit is the LHS's sign bit, except when the result of the
// remainder is zero.
if (DemandedMask.isNegative() && KnownZero.isNonNegative()) {
APInt Mask2 = APInt::getSignBit(BitWidth);
APInt LHSKnownZero(BitWidth, 0), LHSKnownOne(BitWidth, 0);
ComputeMaskedBits(I->getOperand(0), Mask2, LHSKnownZero, LHSKnownOne,
Depth+1);
ComputeMaskedBits(I->getOperand(0), LHSKnownZero, LHSKnownOne, Depth+1);
// If it's known zero, our sign bit is also zero.
if (LHSKnownZero.isNegative())
KnownZero |= LHSKnownZero;
@@ -795,7 +789,7 @@ Value *InstCombiner::SimplifyDemandedUseBits(Value *V, APInt DemandedMask,
return 0;
}
}
ComputeMaskedBits(V, DemandedMask, KnownZero, KnownOne, Depth);
ComputeMaskedBits(V, KnownZero, KnownOne, Depth);
break;
}