From 88b65bc835444e4cac27fa8032948f7bb51781fa Mon Sep 17 00:00:00 2001 From: Evan Cheng Date: Mon, 18 Jan 2010 21:38:44 +0000 Subject: Canonicalize -1 - x to ~x. Instcombine does this but apparently there are situations where this pattern will escape the optimizer and / or created by isel. Here is a case that's seen in JavaScriptCore: %t1 = sub i32 0, %a %t2 = add i32 %t1, -1 The dag combiner pattern: ((c1-A)+c2) -> (c1+c2)-A will fold it to -1 - %a. llvm-svn: 93773 --- llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp | 3 +++ 1 file changed, 3 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 549527c1a3f..7fe908c7302 100644 --- a/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp +++ b/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp @@ -1176,6 +1176,9 @@ SDValue DAGCombiner::visitSUB(SDNode *N) { if (N1C) return DAG.getNode(ISD::ADD, N->getDebugLoc(), VT, N0, DAG.getConstant(-N1C->getAPIntValue(), VT)); + // Canonicalize (sub -1, x) -> ~x, i.e. (xor x, -1) + if (N0C && N0C->isAllOnesValue()) + return DAG.getNode(ISD::XOR, N->getDebugLoc(), VT, N1, N0); // fold (A+B)-A -> B if (N0.getOpcode() == ISD::ADD && N0.getOperand(0) == N1) return N0.getOperand(1); -- cgit v1.2.3