X86: Don't crash if we can't decode the pshufb mask

Constant pool entries are uniqued by their contents regardless of their
type.  This means that a pshufb can have a shuffle mask which isn't a
simple array of bytes.

The code path which attempts to decode the mask didn't check for
failure, causing PR22559.

llvm-svn: 228979

1 files changed, 2 insertions, 0 deletions

diff --git a/llvm/lib/Target/X86/X86ISelLowering.cpp b/llvm/lib/Target/X86/X86ISelLowering.cpp
index c11c8e3febd..3c2e27af8f2 100644
--- a/llvm/lib/Target/X86/X86ISelLowering.cpp
+++ b/llvm/lib/Target/X86/X86ISelLowering.cpp
@@ -5480,6 +5480,8 @@ static bool getTargetShuffleMask(SDNode *N, MVT VT,
 
     if (auto *C = dyn_cast<Constant>(MaskCP->getConstVal())) {
       DecodePSHUFBMask(C, Mask);
+      if (Mask.empty())
+        return false;
       break;
     }