[llvm] r312253 - [DAGCombiner] Do a better job of ensuring we don't split elements when combining an extract_subvector of a bitcasted build_vector.

[Craig Topper via llvm-commits]

Author: ctopper
Date: Thu Aug 31 10:02:22 2017
New Revision: 312253

URL: http://llvm.org/viewvc/llvm-project?rev=312253&view=rev
Log:
[DAGCombiner] Do a better job of ensuring we don't split elements when combining an extract_subvector of a bitcasted build_vector.

Modified:
    llvm/trunk/lib/CodeGen/SelectionDAG/DAGCombiner.cpp

Modified: llvm/trunk/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/CodeGen/SelectionDAG/DAGCombiner.cpp?rev=312253&r1=312252&r2=312253&view=diff
==============================================================================
--- llvm/trunk/lib/CodeGen/SelectionDAG/DAGCombiner.cpp (original)
+++ llvm/trunk/lib/CodeGen/SelectionDAG/DAGCombiner.cpp Thu Aug 31 10:02:22 2017
@@ -15173,14 +15173,17 @@ SDValue DAGCombiner::visitEXTRACT_SUBVEC
   if (V->getOpcode() == ISD::BUILD_VECTOR) {
     if (auto *Idx = dyn_cast<ConstantSDNode>(N->getOperand(1))) {
       EVT InVT = V->getValueType(0);
-      unsigned NumElems = NVT.getSizeInBits() / InVT.getScalarSizeInBits();
-      if (NumElems > 0) {
+      unsigned ExtractSize = NVT.getSizeInBits();
+      unsigned EltSize = InVT.getScalarSizeInBits();
+      // Only do this if we won't split any elements.
+      if (ExtractSize % EltSize == 0) {
+        unsigned NumElems = ExtractSize / EltSize;
         EVT ExtractVT = EVT::getVectorVT(*DAG.getContext(),
                                          InVT.getVectorElementType(), NumElems);
         if (!LegalOperations ||
             TLI.isOperationLegal(ISD::BUILD_VECTOR, ExtractVT)) {
-          unsigned IdxVal = Idx->getZExtValue() * NVT.getScalarSizeInBits() /
-                            InVT.getScalarSizeInBits();
+          unsigned IdxVal = (Idx->getZExtValue() * NVT.getScalarSizeInBits()) /
+                            EltSize;
 
           // Extract the pieces from the original build_vector.
           SDValue BuildVec = DAG.getBuildVector(ExtractVT, SDLoc(N),