Fold (add x, shl(0 - y, n)) -> sub(x, shl(y, n)), to simplify some code
that SCEVExpander can produce when running on behalf of LSR.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@93949 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/CodeGen/SelectionDAG/DAGCombiner.cpp b/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
index 7fe908c..8883064 100644
--- a/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
+++ b/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
@@ -1088,6 +1088,26 @@
if (Result.getNode()) return Result;
}
+ // fold (add x, shl(0 - y, n)) -> sub(x, shl(y, n))
+ if (N1.getOpcode() == ISD::SHL &&
+ N1.getOperand(0).getOpcode() == ISD::SUB)
+ if (ConstantSDNode *C =
+ dyn_cast<ConstantSDNode>(N1.getOperand(0).getOperand(0)))
+ if (C->getAPIntValue() == 0)
+ return DAG.getNode(ISD::SUB, N->getDebugLoc(), VT, N0,
+ DAG.getNode(ISD::SHL, N->getDebugLoc(), VT,
+ N1.getOperand(0).getOperand(1),
+ N1.getOperand(1)));
+ if (N0.getOpcode() == ISD::SHL &&
+ N0.getOperand(0).getOpcode() == ISD::SUB)
+ if (ConstantSDNode *C =
+ dyn_cast<ConstantSDNode>(N0.getOperand(0).getOperand(0)))
+ if (C->getAPIntValue() == 0)
+ return DAG.getNode(ISD::SUB, N->getDebugLoc(), VT, N1,
+ DAG.getNode(ISD::SHL, N->getDebugLoc(), VT,
+ N0.getOperand(0).getOperand(1),
+ N0.getOperand(1)));
+
return SDValue();
}