Insert a sanity check on the combining of x86 truncing-store nodes. This comes to replace the problematic check that was removed in r139995.

llvm-svn: 140246

llvm/lib/Target/X86/X86ISelLowering.cpp

@@ -13563,6 +13563,9 @@ static SDValue PerformSTORECombine(SDNode *N, SelectionDAG &DAG,
 
     // From, To sizes and ElemCount must be pow of two
     if (!isPowerOf2_32(NumElems * FromSz * ToSz)) return SDValue();
+    // We are going to use the original vector elt for storing.
+    // accumulated smaller vector elements must be a multiple of the store size.
+    if (0 != (NumElems * FromSz) % ToSz) return SDValue();
 
     unsigned SizeRatio  = FromSz / ToSz;