[llvm-commits] CVS: llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp

[Chris Lattner]

Changes in directory llvm/lib/CodeGen/SelectionDAG:

DAGCombiner.cpp updated: 1.216 -> 1.217
---
Log message:

add a minor dag combine noticed when looking at PR945: http://llvm.org/PR945 


---
Diffs of the changes:  (+7 -0)

 DAGCombiner.cpp |    7 +++++++
 1 files changed, 7 insertions(+)


Index: llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
diff -u llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp:1.216 llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp:1.217
--- llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp:1.216	Thu Oct 12 10:22:24 2006
+++ llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp	Thu Oct 12 15:23:19 2006
@@ -1664,6 +1664,13 @@
     return DAG.getNode(ISD::ANY_EXTEND, VT, SmallShift);
   }
   
+  // fold (srl (sra X, Y), 31) -> (srl X, 31).  This srl only looks at the sign
+  // bit, which is unmodified by sra.
+  if (N1C && N1C->getValue()+1 == MVT::getSizeInBits(VT)) {
+    if (N0.getOpcode() == ISD::SRA)
+      return DAG.getNode(ISD::SRL, VT, N0.getOperand(0), N1);
+  }
+  
   // fold (srl (ctlz x), "5") -> x  iff x has one bit set (the low bit).
   if (N1C && N0.getOpcode() == ISD::CTLZ && 
       N1C->getValue() == Log2_32(MVT::getSizeInBits(VT))) {