From 954f49014dd45e806e5459d3ed67b0681d4fb63c Mon Sep 17 00:00:00 2001 From: Dan Gohman Date: Tue, 19 Jan 2010 23:30:49 +0000 Subject: 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. llvm-svn: 93949 --- llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp | 20 ++++++++++++++++++++ 1 file changed, 20 insertions(+) (limited to 'llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp') diff --git a/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp b/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp index 7fe908c7302..8883064df99 100644 --- a/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp +++ b/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp @@ -1088,6 +1088,26 @@ SDValue DAGCombiner::visitADD(SDNode *N) { 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(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(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(); } -- cgit v1.2.3