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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/CodeGen/SelectionDAG/TargetLowering.cpp
+11 -14
View File
@@ -1244,7 +1244,7 @@ bool TargetLowering::SimplifyDemandedBits(SDValue Op,
if (Depth != 0) {
// If not at the root, Just compute the KnownZero/KnownOne bits to
// simplify things downstream.
TLO.DAG.ComputeMaskedBits(Op, DemandedMask, KnownZero, KnownOne, Depth);
TLO.DAG.ComputeMaskedBits(Op, KnownZero, KnownOne, Depth);
return false;
}
// If this is the root being simplified, allow it to have multiple uses,
@@ -1263,8 +1263,8 @@ bool TargetLowering::SimplifyDemandedBits(SDValue Op,
switch (Op.getOpcode()) {
case ISD::Constant:
// We know all of the bits for a constant!
KnownOne = cast<ConstantSDNode>(Op)->getAPIntValue() & NewMask;
KnownZero = ~KnownOne & NewMask;
KnownOne = cast<ConstantSDNode>(Op)->getAPIntValue();
KnownZero = ~KnownOne;
return false; // Don't fall through, will infinitely loop.
case ISD::AND:
// If the RHS is a constant, check to see if the LHS would be zero without
@@ -1274,8 +1274,7 @@ bool TargetLowering::SimplifyDemandedBits(SDValue Op,
if (ConstantSDNode *RHSC = dyn_cast<ConstantSDNode>(Op.getOperand(1))) {
APInt LHSZero, LHSOne;
// Do not increment Depth here; that can cause an infinite loop.
TLO.DAG.ComputeMaskedBits(Op.getOperand(0), NewMask,
LHSZero, LHSOne, Depth);
TLO.DAG.ComputeMaskedBits(Op.getOperand(0), LHSZero, LHSOne, Depth);
// If the LHS already has zeros where RHSC does, this and is dead.
if ((LHSZero & NewMask) == (~RHSC->getAPIntValue() & NewMask))
return TLO.CombineTo(Op, Op.getOperand(0));
@@ -1725,11 +1724,11 @@ bool TargetLowering::SimplifyDemandedBits(SDValue Op,
// If the sign bit is known one, the top bits match.
if (KnownOne.intersects(InSignBit)) {
KnownOne |= NewBits;
KnownZero &= ~NewBits;
KnownOne |= NewBits;
assert((KnownZero & NewBits) == 0);
} else { // Otherwise, top bits aren't known.
KnownOne &= ~NewBits;
KnownZero &= ~NewBits;
assert((KnownOne & NewBits) == 0);
assert((KnownZero & NewBits) == 0);
}
break;
}
@@ -1863,7 +1862,7 @@ bool TargetLowering::SimplifyDemandedBits(SDValue Op,
// FALL THROUGH
default:
// Just use ComputeMaskedBits to compute output bits.
TLO.DAG.ComputeMaskedBits(Op, NewMask, KnownZero, KnownOne, Depth);
TLO.DAG.ComputeMaskedBits(Op, KnownZero, KnownOne, Depth);
break;
}
@@ -1879,7 +1878,6 @@ bool TargetLowering::SimplifyDemandedBits(SDValue Op,
/// in Mask are known to be either zero or one and return them in the
/// KnownZero/KnownOne bitsets.
void TargetLowering::computeMaskedBitsForTargetNode(const SDValue Op,
const APInt &Mask,
APInt &KnownZero,
APInt &KnownOne,
const SelectionDAG &DAG,
@@ -1890,7 +1888,7 @@ void TargetLowering::computeMaskedBitsForTargetNode(const SDValue Op,
Op.getOpcode() == ISD::INTRINSIC_VOID) &&
"Should use MaskedValueIsZero if you don't know whether Op"
" is a target node!");
KnownZero = KnownOne = APInt(Mask.getBitWidth(), 0);
KnownZero = KnownOne = APInt(KnownOne.getBitWidth(), 0);
}
/// ComputeNumSignBitsForTargetNode - This method can be implemented by
@@ -1934,9 +1932,8 @@ static bool ValueHasExactlyOneBitSet(SDValue Val, const SelectionDAG &DAG) {
// Fall back to ComputeMaskedBits to catch other known cases.
EVT OpVT = Val.getValueType();
unsigned BitWidth = OpVT.getScalarType().getSizeInBits();
APInt Mask = APInt::getAllOnesValue(BitWidth);
APInt KnownZero, KnownOne;
DAG.ComputeMaskedBits(Val, Mask, KnownZero, KnownOne);
DAG.ComputeMaskedBits(Val, KnownZero, KnownOne);
return (KnownZero.countPopulation() == BitWidth - 1) &&
(KnownOne.countPopulation() == 1);
}