[SystemZ] Add check VT.isSimple() in canTreateAsByteVector()

Since BB-vectorizer can produce vectors of for example 3 elements,
this check is needed.

Review: Ulrich Weigand
llvm-svn: 297136
diff --git a/llvm/lib/Target/SystemZ/SystemZISelLowering.cpp b/llvm/lib/Target/SystemZ/SystemZISelLowering.cpp
index afc9e60..6322098 100644
--- a/llvm/lib/Target/SystemZ/SystemZISelLowering.cpp
+++ b/llvm/lib/Target/SystemZ/SystemZISelLowering.cpp
@@ -4737,7 +4737,7 @@
 // Return true if VT is a vector whose elements are a whole number of bytes
 // in width.
 static bool canTreatAsByteVector(EVT VT) {
-  return VT.isVector() && VT.getScalarSizeInBits() % 8 == 0;
+  return VT.isVector() && VT.getScalarSizeInBits() % 8 == 0 && VT.isSimple();
 }
 
 // Try to simplify an EXTRACT_VECTOR_ELT from a vector of type VecVT