[DAGCombiner][X86][SystemZ][AArch64] Combine some cases of (bitcast (build_vector constants)) between legalize types and legalize dag.

This patch enables combining integer bitcasts of integer build vectors when the new scalar type is legal. I've avoided floating point because the implementation bitcasts float to int along the way and we would need to check the intermediate types for legality

Differential Revision: https://reviews.llvm.org/D58884

llvm-svn: 355324

1 files changed, 9 insertions, 6 deletions

diff --git a/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp b/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
index 18fe03fa468..a53219aa357 100644
--- a/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
+++ b/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
@@ -10206,14 +10206,17 @@ SDValue DAGCombiner::visitBITCAST(SDNode *N) {
     return DAG.getUNDEF(VT);
 
   // If the input is a BUILD_VECTOR with all constant elements, fold this now.
-  // Only do this before legalize types, since we might create an illegal
-  // scalar type. Even if we knew we wouldn't create an illegal scalar type
-  // we can only do this before legalize ops, since the target maybe
-  // depending on the bitcast.
+  // Only do this before legalize types, unless both types are integer and the
+  // scalar type is legal. Only do this before legalize ops, since the target
+  // maybe depending on the bitcast.
   // First check to see if this is all constant.
-  if (!LegalTypes &&
+  // TODO: Support FP bitcasts after legalize types.
+  if (VT.isVector() &&
+      (!LegalTypes ||
+       (!LegalOperations && VT.isInteger() && N0.getValueType().isInteger() &&
+        TLI.isTypeLegal(VT.getVectorElementType()))) &&
       N0.getOpcode() == ISD::BUILD_VECTOR && N0.getNode()->hasOneUse() &&
-      VT.isVector() && cast<BuildVectorSDNode>(N0)->isConstant())
+      cast<BuildVectorSDNode>(N0)->isConstant())
     return ConstantFoldBITCASTofBUILD_VECTOR(N0.getNode(),
                                              VT.getVectorElementType());