When pattern matching during instruction selection make sure shl x,1 is not
converted to add x,x if x is a undef. add undef, undef does not guarantee
that the resulting low order bit is zero.
Fixes <rdar://problem/9453156> and <rdar://problem/9487392>.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@133022 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/CodeGen/SelectionDAG/DAGCombiner.cpp b/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
index 6f94076..3cf7a2b 100644
--- a/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
+++ b/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
@@ -3030,6 +3030,9 @@
// fold (shl x, 0) -> x
if (N1C && N1C->isNullValue())
return N0;
+ // fold (shl undef, x) -> 0
+ if (N0.getOpcode() == ISD::UNDEF)
+ return DAG.getConstant(0, VT);
// if (shl x, c) is known to be zero, return 0
if (DAG.MaskedValueIsZero(SDValue(N, 0),
APInt::getAllOnesValue(OpSizeInBits)))