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| author | Evan Cheng <evan.cheng@apple.com> | 2010-01-18 21:38:44 +0000 |
|---|---|---|
| committer | Evan Cheng <evan.cheng@apple.com> | 2010-01-18 21:38:44 +0000 |
| commit | 1ad0e8b5769f25ca442f3d77bf374d03469010bc (patch) | |
| tree | a4413ab41fe7bc56f036ec89728f80bde599b205 /lib/CodeGen | |
| parent | 2d53c21eca34b77bbe12a5208af9da780d6465c8 (diff) | |
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.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@93773 91177308-0d34-0410-b5e6-96231b3b80d8
Diffstat (limited to 'lib/CodeGen')
| -rw-r--r-- | lib/CodeGen/SelectionDAG/DAGCombiner.cpp | 3 |
1 files changed, 3 insertions, 0 deletions
diff --git a/lib/CodeGen/SelectionDAG/DAGCombiner.cpp b/lib/CodeGen/SelectionDAG/DAGCombiner.cpp index 549527c1a3..7fe908c730 100644 --- a/lib/CodeGen/SelectionDAG/DAGCombiner.cpp +++ b/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); |