[LegalizeTypes] Teach PromoteIntRes_BITCAST to better handle a bitcast with vector output type and a vector input type that needs to be widened

Summary: Previously if we had a bitcast vector output type that needs promotion and a vector input type that needs widening we would just do a stack store and load to handle the conversion. We can do a little better if we can widen the bitcast to a legal vector type the same size as the widened input type. Then we can do the bitcast between this widened type and the widened input type. Afterwards we can extract_subvector back to the original output and any_extend that. Type legalization will then circle back and handle promotion of the extract_subvector and the any_extend will just be removed. This will avoid going through the stack and allows us to remove a custom version of this legalization from X86.

Reviewers: efriedma, RKSimon

Reviewed By: efriedma

Subscribers: javed.absar, llvm-commits

Differential Revision: https://reviews.llvm.org/D53229

llvm-svn: 345567

1 files changed, 20 insertions, 0 deletions

diff --git a/llvm/lib/CodeGen/SelectionDAG/LegalizeIntegerTypes.cpp b/llvm/lib/CodeGen/SelectionDAG/LegalizeIntegerTypes.cpp
index f24659ac274..2b1df0165d3 100644
--- a/llvm/lib/CodeGen/SelectionDAG/LegalizeIntegerTypes.cpp
+++ b/llvm/lib/CodeGen/SelectionDAG/LegalizeIntegerTypes.cpp
@@ -310,6 +310,26 @@ SDValue DAGTypeLegalizer::PromoteIntRes_BITCAST(SDNode *N) {
     // make us bitcast between two vectors which are legalized in different ways.
     if (NOutVT.bitsEq(NInVT) && !NOutVT.isVector())
       return DAG.getNode(ISD::BITCAST, dl, NOutVT, GetWidenedVector(InOp));
+    // If the output type is also a vector and widening it to the same size
+    // as the widened input type would be a legal type, we can widen the bitcast
+    // and handle the promotion after.
+    if (NOutVT.isVector()) {
+      unsigned WidenInSize = NInVT.getSizeInBits();
+      unsigned OutSize = OutVT.getSizeInBits();
+      if (WidenInSize % OutSize == 0) {
+        unsigned Scale = WidenInSize / OutSize;
+        EVT WideOutVT = EVT::getVectorVT(*DAG.getContext(),
+                                         OutVT.getVectorElementType(),
+                                         OutVT.getVectorNumElements() * Scale);
+        if (isTypeLegal(WideOutVT)) {
+          InOp = DAG.getBitcast(WideOutVT, GetWidenedVector(InOp));
+          MVT IdxTy = TLI.getVectorIdxTy(DAG.getDataLayout());
+          InOp = DAG.getNode(ISD::EXTRACT_SUBVECTOR, dl, OutVT, InOp,
+                             DAG.getConstant(0, dl, IdxTy));
+          return DAG.getNode(ISD::ANY_EXTEND, dl, NOutVT, InOp);
+        }
+      }
+    }
   }
 
   return DAG.getNode(ISD::ANY_EXTEND, dl, NOutVT,