[SelectionDAGBuilder] Restrict vector reduction check to types with a power of 2 number of elements.

The check for the shuffles usages probably isn't correct for non power of 2 vectors.

llvm-svn: 337651

lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp

@@ -2668,6 +2668,10 @@ static bool isVectorReductionOp(const User *I) {
   }
 
   unsigned ElemNum = Inst->getType()->getVectorNumElements();
+  // Ensure the reduction size is a power of 2.
+  if (!isPowerOf2_32(ElemNum))
+    return false;
+
   unsigned ElemNumToReduce = ElemNum;
 
   // Do DFS search on the def-use chain from the given instruction. We only