Fix a bug in the code which determines when it's safe to use the
bt instruction, which was exposed by r106263.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@106718 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/Target/X86/X86ISelLowering.cpp b/lib/Target/X86/X86ISelLowering.cpp
index bd95c85..d64ac6c 100644
--- a/lib/Target/X86/X86ISelLowering.cpp
+++ b/lib/Target/X86/X86ISelLowering.cpp
@@ -6175,15 +6175,21 @@
Op1 = Op1.getOperand(0);
SDValue LHS, RHS;
- if (Op1.getOpcode() == ISD::SHL) {
- if (ConstantSDNode *And10C = dyn_cast<ConstantSDNode>(Op1.getOperand(0)))
- if (And10C->getZExtValue() == 1) {
- LHS = Op0;
- RHS = Op1.getOperand(1);
- }
- } else if (Op0.getOpcode() == ISD::SHL) {
+ if (Op1.getOpcode() == ISD::SHL)
+ std::swap(Op0, Op1);
+ if (Op0.getOpcode() == ISD::SHL) {
if (ConstantSDNode *And00C = dyn_cast<ConstantSDNode>(Op0.getOperand(0)))
if (And00C->getZExtValue() == 1) {
+ // If we looked past a truncate, check that it's only truncating away
+ // known zeros.
+ unsigned BitWidth = Op0.getValueSizeInBits();
+ unsigned AndBitWidth = And.getValueSizeInBits();
+ if (BitWidth > AndBitWidth) {
+ APInt Mask = APInt::getAllOnesValue(BitWidth), Zeros, Ones;
+ DAG.ComputeMaskedBits(Op0, Mask, Zeros, Ones);
+ if (Zeros.countLeadingOnes() < BitWidth - AndBitWidth)
+ return SDValue();
+ }
LHS = Op1;
RHS = Op0.getOperand(1);
}