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[SelectionDAG] Don't subject ConstantSDNodes to the depth limit in computeKnownBits and ComputeNumSignBits.

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We don't need to do any additional recursion, we just need to analyze the APInt stored in the node. This matches what the ValueTracking versions do for IR.

llvm-svn: 316256
This commit is contained in:
Craig Topper 2017-10-21 03:22:13 +00:00
parent bd7165ec1f
commit 722fe7b374
1 changed files with 13 additions and 10 deletions
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23
lib/CodeGen/SelectionDAG/SelectionDAG.cpp
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@ -2089,6 +2089,14 @@ void SelectionDAG::computeKnownBits(SDValue Op, KnownBits &Known,
unsigned BitWidth = Op.getScalarValueSizeInBits();
Known = KnownBits(BitWidth); // Don't know anything.
if (auto *C = dyn_cast<ConstantSDNode>(Op)) {
// We know all of the bits for a constant!
Known.One = C->getAPIntValue();
Known.Zero = ~Known.One;
return;
}
if (Depth == 6)
return; // Limit search depth.
@ -2100,11 +2108,6 @@ void SelectionDAG::computeKnownBits(SDValue Op, KnownBits &Known,
unsigned Opcode = Op.getOpcode();
switch (Opcode) {
case ISD::Constant:
// We know all of the bits for a constant!
Known.One = cast<ConstantSDNode>(Op)->getAPIntValue();
Known.Zero = ~Known.One;
break;
case ISD::BUILD_VECTOR:
// Collect the known bits that are shared by every demanded vector element.
assert(NumElts == Op.getValueType().getVectorNumElements() &&
@ -2963,6 +2966,11 @@ unsigned SelectionDAG::ComputeNumSignBits(SDValue Op, const APInt &DemandedElts,
unsigned Tmp, Tmp2;
unsigned FirstAnswer = 1;
if (auto *C = dyn_cast<ConstantSDNode>(Op)) {
const APInt &Val = cast<ConstantSDNode>(Op)->getAPIntValue();
return Val.getNumSignBits();
}
if (Depth == 6)
return 1; // Limit search depth.
@ -2978,11 +2986,6 @@ unsigned SelectionDAG::ComputeNumSignBits(SDValue Op, const APInt &DemandedElts,
Tmp = cast<VTSDNode>(Op.getOperand(1))->getVT().getSizeInBits();
return VTBits-Tmp;
case ISD::Constant: {
const APInt &Val = cast<ConstantSDNode>(Op)->getAPIntValue();
return Val.getNumSignBits();
}
case ISD::BUILD_VECTOR:
Tmp = VTBits;
for (unsigned i = 0, e = Op.getNumOperands(); (i < e) && (Tmp > 1); ++i) {