Fix PR12359
- In addition to undefined, if V2 is zero vector, skip 2nd PSHUFB and POR as
well as PSHUFB will zero elements with negative indices.
Patch by Sriram Murali <sriram.murali@intel.com>
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@163018 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/Target/X86/X86ISelLowering.cpp b/lib/Target/X86/X86ISelLowering.cpp
index f9184f6..f4329d3 100644
--- a/lib/Target/X86/X86ISelLowering.cpp
+++ b/lib/Target/X86/X86ISelLowering.cpp
@@ -5881,8 +5881,6 @@
DebugLoc dl = SVOp->getDebugLoc();
ArrayRef<int> MaskVals = SVOp->getMask();
- bool V2IsUndef = V2.getOpcode() == ISD::UNDEF;
-
// If we have SSSE3, case 1 is generated when all result bytes come from
// one of the inputs. Otherwise, case 2 is generated. If no SSSE3 is
// present, fall back to case 3.
@@ -5906,7 +5904,11 @@
V1 = DAG.getNode(X86ISD::PSHUFB, dl, MVT::v16i8, V1,
DAG.getNode(ISD::BUILD_VECTOR, dl,
MVT::v16i8, &pshufbMask[0], 16));
- if (V2IsUndef)
+
+ // As PSHUFB will zero elements with negative indices, it's safe to ignore
+ // the 2nd operand if it's undefined or zero.
+ if (V2.getOpcode() == ISD::UNDEF ||
+ ISD::isBuildVectorAllZeros(V2.getNode()))
return V1;
// Calculate the shuffle mask for the second input, shuffle it, and