[DAGCombiner] allow hoisting vector bitwise logic ahead of truncates

The transform performs a bitwise logic op in a wider type followed by
truncate when both inputs are truncated from the same source type:
logic_op (truncate x), (truncate y) --> truncate (logic_op x, y)

There are a bunch of other checks that should prevent doing this when 
it might be harmful.

We already do this transform for scalars in this spot. The vector 
limitation was shared with a check for the case when the operands are 
extended. I'm not sure if that limit is needed either, but that would 
be a separate patch.

Differential Revision: https://reviews.llvm.org/D55448

llvm-svn: 349303

1 files changed, 2 insertions, 5 deletions

diff --git a/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp b/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
index 93a1ab1dcff..7a22caf9c8b 100644
--- a/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
+++ b/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
@@ -3755,11 +3755,8 @@ SDValue DAGCombiner::hoistLogicOpWithSameOpcodeHands(SDNode *N) {
     // instructions without eliminating anything.
     if (!N0.hasOneUse() && !N1.hasOneUse())
       return SDValue();
-    // We need matching integer source types.
-    // Do not hoist logic op inside of a vector extend, since it may combine
-    // into a vsetcc.
-    // TODO: Should the vector check apply to truncate though?
-    if (VT.isVector() || XVT != Y.getValueType())
+    // We need matching source types.
+    if (XVT != Y.getValueType())
       return SDValue();
     // Don't create an illegal op during or after legalization.
     if (LegalOperations && !TLI.isOperationLegal(LogicOpcode, XVT))