Improve handling of insert_subvector of bitcast values

Fix insert_subvector / extract_subvector merges of bitcast values.

Reviewers: efriedma, craig.topper, RKSimon

Subscribers: RKSimon, llvm-commits

Differential Revision: https://reviews.llvm.org/D34571

llvm-svn: 310711

1 files changed, 35 insertions, 0 deletions

diff --git a/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp b/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
index a247f2656be..2aa8e6382e6 100644
--- a/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
+++ b/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
@@ -15890,12 +15890,47 @@ SDValue DAGCombiner::visitINSERT_SUBVECTOR(SDNode *N) {
   if (N1.isUndef())
     return N0;
 
+  // For nested INSERT_SUBVECTORs, attempt to combine inner node first to allow
+  // us to pull BITCASTs from input to output.
+  if (N0.hasOneUse() && N0->getOpcode() == ISD::INSERT_SUBVECTOR)
+    if (SDValue NN0 = visitINSERT_SUBVECTOR(N0.getNode()))
+      return DAG.getNode(ISD::INSERT_SUBVECTOR, SDLoc(N), VT, NN0, N1, N2);
+
   // If this is an insert of an extracted vector into an undef vector, we can
   // just use the input to the extract.
   if (N0.isUndef() && N1.getOpcode() == ISD::EXTRACT_SUBVECTOR &&
       N1.getOperand(1) == N2 && N1.getOperand(0).getValueType() == VT)
     return N1.getOperand(0);
 
+  // If we are inserting a bitcast value into an undef, with the same
+  // number of elements, just use the bitcast input of the extract.
+  // i.e. INSERT_SUBVECTOR UNDEF (BITCAST N1) N2 ->
+  //        BITCAST (INSERT_SUBVECTOR UNDEF N1 N2)
+  if (N0.isUndef() && N1.getOpcode() == ISD::BITCAST &&
+      N1.getOperand(0).getOpcode() == ISD::EXTRACT_SUBVECTOR &&
+      N1.getOperand(0).getOperand(1) == N2 &&
+      N1.getOperand(0).getOperand(0).getValueType().getVectorNumElements() ==
+          VT.getVectorNumElements()) {
+    return DAG.getBitcast(VT, N1.getOperand(0).getOperand(0));
+  }
+
+  // If both N1 and N2 are bitcast values on which insert_subvector
+  // would makes sense, pull the bitcast through.
+  // i.e. INSERT_SUBVECTOR (BITCAST N0) (BITCAST N1) N2 ->
+  //        BITCAST (INSERT_SUBVECTOR N0 N1 N2)
+  if (N0.getOpcode() == ISD::BITCAST && N1.getOpcode() == ISD::BITCAST) {
+    SDValue CN0 = N0.getOperand(0);
+    SDValue CN1 = N1.getOperand(0);
+    if (CN0.getValueType().getVectorElementType() ==
+            CN1.getValueType().getVectorElementType() &&
+        CN0.getValueType().getVectorNumElements() ==
+            VT.getVectorNumElements()) {
+      SDValue NewINSERT = DAG.getNode(ISD::INSERT_SUBVECTOR, SDLoc(N),
+                                      CN0.getValueType(), CN0, CN1, N2);
+      return DAG.getBitcast(VT, NewINSERT);
+    }
+  }
+
   // Combine INSERT_SUBVECTORs where we are inserting to the same index.
   // INSERT_SUBVECTOR( INSERT_SUBVECTOR( Vec, SubOld, Idx ), SubNew, Idx )
   // --> INSERT_SUBVECTOR( Vec, SubNew, Idx )