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| author | Benjamin Kramer <benny.kra@googlemail.com> | 2011-01-29 12:34:05 +0000 |
|---|---|---|
| committer | Benjamin Kramer <benny.kra@googlemail.com> | 2011-01-29 12:34:05 +0000 |
| commit | 65bb14d3683e64cc50ae9004367f664f9c9b368c (patch) | |
| tree | a8f36317a446d0df9a7f5d47987b25a683d73a23 /llvm/lib/CodeGen/SelectionDAG | |
| parent | e1af156bdf4cfe02621a68aef58167b371fa9d90 (diff) | |
| download | bcm5719-llvm-65bb14d3683e64cc50ae9004367f664f9c9b368c.tar.gz bcm5719-llvm-65bb14d3683e64cc50ae9004367f664f9c9b368c.zip | |
Add the missing sub identity "A-(A-B) -> B" to DAGCombine.
This happens e.g. for code like "X - X%10" where we lower the modulo operation
to a series of multiplies and shifts that are then subtracted from X, leading to
this missed optimization.
llvm-svn: 124532
Diffstat (limited to 'llvm/lib/CodeGen/SelectionDAG')
| -rw-r--r-- | llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp | 3 |
1 files changed, 3 insertions, 0 deletions
diff --git a/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp b/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp index 186f4afc3d0..a5b2d9594d5 100644 --- a/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp +++ b/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp @@ -1542,6 +1542,9 @@ SDValue DAGCombiner::visitSUB(SDNode *N) { // 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-(A-B) -> B + if (N1.getOpcode() == ISD::SUB && N0 == N1.getOperand(0)) + return N1.getOperand(1); // fold (A+B)-A -> B if (N0.getOpcode() == ISD::ADD && N0.getOperand(0) == N1) return N0.getOperand(1); |
