Increase opportunities to optimize (brcond (srl (and c1), c2)).

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@91717 91177308-0d34-0410-b5e6-96231b3b80d8

1 files changed, 28 insertions, 1 deletions

diff --git a/lib/CodeGen/SelectionDAG/DAGCombiner.cpp b/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
index 6cef239..e6aa14c 100644
--- a/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
+++ b/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
@@ -2755,7 +2755,34 @@ SDValue DAGCombiner::visitSRL(SDNode *N) {
   if (N1C && SimplifyDemandedBits(SDValue(N, 0)))
     return SDValue(N, 0);
 
-  return N1C ? visitShiftByConstant(N, N1C->getZExtValue()) : SDValue();
+  if (N1C) {
+    SDValue NewSRL = visitShiftByConstant(N, N1C->getZExtValue());
+    if (NewSRL.getNode())
+      return NewSRL;
+  }
+
+  // Here is a common situation. We want to optimize:
+  //
+  //   %a = ...
+  //   %b = and i32 %a, 2
+  //   %c = srl i32 %b, 1
+  //   brcond i32 %c ...
+  //
+  // into
+  // 
+  //   %a = ...
+  //   %b = and %a, 2
+  //   %c = setcc eq %b, 0
+  //   brcond %c ...
+  //
+  // However when after the source operand of SRL is optimized into AND, the SRL
+  // itself may not be optimized further. Look for it and add the BRCOND into
+  // the worklist.
+  if (N->hasOneUse() &&
+      N->use_begin()->getOpcode() == ISD::BRCOND)
+    AddToWorkList(*N->use_begin());
+
+  return SDValue();
 }
 
 SDValue DAGCombiner::visitCTLZ(SDNode *N) {