[ARM] Don't abort on variable-idx extractelt in ReconstructShuffle.

The code introduced in r244314 assumed that EXTRACT_VECTOR_ELT only
takes constant indices, but it does accept variables.
Bail out for those: we can't use them, as the shuffles we want to
reconstruct do require constant masks.

llvm-svn: 246594

1 files changed, 4 insertions, 0 deletions

diff --git a/llvm/lib/Target/ARM/ARMISelLowering.cpp b/llvm/lib/Target/ARM/ARMISelLowering.cpp
index 17c48287f05..f2915a4ab15 100644
--- a/llvm/lib/Target/ARM/ARMISelLowering.cpp
+++ b/llvm/lib/Target/ARM/ARMISelLowering.cpp
@@ -5554,6 +5554,10 @@ SDValue ARMTargetLowering::ReconstructShuffle(SDValue Op,
       // A shuffle can only come from building a vector from various
       // elements of other vectors.
       return SDValue();
+    } else if (!isa<ConstantSDNode>(V.getOperand(1))) {
+      // Furthermore, shuffles require a constant mask, whereas extractelts
+      // accept variable indices.
+      return SDValue();
     }
 
     // Add this element source to the list if it's not already there.