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[SelectionDAG] Don't subject ISD:Constant to the depth limit in TargetLowering::SimplifyDemandedBits. 

Summary:
We shouldn't recurse any further but it doesn't mean we shouldn't be able to give the known bits for a constant. The caller would probably like that we always return the right answer for a constant RHS. This matches what InstCombine does in this case.

I don't have a test case because this showed up while trying to revive D31724.

Reviewers: RKSimon, spatel

Reviewed By: RKSimon

Subscribers: arsenm, llvm-commits

Differential Revision: https://reviews.llvm.org/D38967

llvm-svn: 316255
This commit is contained in:
Craig Topper 2017-10-21 02:27:19 +00:00
parent fcf27188d7
commit 195dad4264
1 changed files with 7 additions and 5 deletions
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12
llvm/lib/CodeGen/SelectionDAG/TargetLowering.cpp
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@ -516,6 +516,13 @@ bool TargetLowering::SimplifyDemandedBits(SDValue Op,
// Don't know anything. // Don't know anything.
Known = KnownBits(BitWidth); Known = KnownBits(BitWidth);
if (Op.getOpcode() == ISD::Constant) {
// We know all of the bits for a constant!
Known.One = cast<ConstantSDNode>(Op)->getAPIntValue();
Known.Zero = ~Known.One;
return false;
}
// Other users may use these bits. // Other users may use these bits.
if (!Op.getNode()->hasOneUse() && !AssumeSingleUse) { if (!Op.getNode()->hasOneUse() && !AssumeSingleUse) {
if (Depth != 0) { if (Depth != 0) {
@ -538,11 +545,6 @@ bool TargetLowering::SimplifyDemandedBits(SDValue Op,
KnownBits Known2, KnownOut; KnownBits Known2, KnownOut;
switch (Op.getOpcode()) { switch (Op.getOpcode()) {
case ISD::Constant:
// We know all of the bits for a constant!
Known.One = cast<ConstantSDNode>(Op)->getAPIntValue();
Known.Zero = ~Known.One;
return false; // Don't fall through, will infinitely loop.
case ISD::BUILD_VECTOR: case ISD::BUILD_VECTOR:
// Collect the known bits that are shared by every constant vector element. // Collect the known bits that are shared by every constant vector element.
Known.Zero.setAllBits(); Known.One.setAllBits(); Known.Zero.setAllBits(); Known.One.setAllBits();