[DAGCombiner] rearrange extract_element+bitcast fold; NFC

  
I want to add another pattern here that includes scalar_to_vector,
so this makes that patch smaller. I was hoping to remove the
hasOneUse() check because it shouldn't be necessary for common
codegen, but an AMDGPU test has a comment suggesting that the
extra check makes things better on one of those targets.

llvm-svn: 344320

1 files changed, 8 insertions, 6 deletions

diff --git a/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp b/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
index 16834dc1a26..7ec5fac390b 100644
--- a/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
+++ b/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
@@ -15499,13 +15499,15 @@ SDValue DAGCombiner::visitEXTRACT_VECTOR_ELT(SDNode *N) {
     // converts.
   }
 
-  // extract_vector_elt (v2i32 (bitcast i64:x)), EltTrunc -> i32 (trunc i64:x)
-  bool isLE = DAG.getDataLayout().isLittleEndian();
-  unsigned EltTrunc = isLE ? 0 : VT.getVectorNumElements() - 1;
-  if (ConstEltNo && InVec.getOpcode() == ISD::BITCAST && InVec.hasOneUse() &&
-      ConstEltNo->getZExtValue() == EltTrunc && VT.isInteger()) {
+  if (ConstEltNo && InVec.getOpcode() == ISD::BITCAST) {
+    // The vector index of the LSBs of the source depend on the endian-ness.
+    bool IsLE = DAG.getDataLayout().isLittleEndian();
+
+    // extract_elt (v2i32 (bitcast i64:x)), BCTruncElt -> i32 (trunc i64:x)
+    unsigned BCTruncElt = IsLE ? 0 : VT.getVectorNumElements() - 1;
     SDValue BCSrc = InVec.getOperand(0);
-    if (BCSrc.getValueType().isScalarInteger())
+    if (InVec.hasOneUse() && ConstEltNo->getZExtValue() == BCTruncElt &&
+        VT.isInteger() && BCSrc.getValueType().isScalarInteger())
       return DAG.getNode(ISD::TRUNCATE, SDLoc(N), NVT, BCSrc);
   }