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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 | 2c94b4201beccbd061fd679ea7e9db1381fe8357 (patch) | |
| tree | c9e4e2e881b416c3a3292e02e138ca76fb48185b /lib/CodeGen/SelectionDAG/DAGCombiner.cpp | |
| parent | 60f5ad46c2147af79035a43e5745e46376124780 (diff) | |
| download | external_llvm-2c94b4201beccbd061fd679ea7e9db1381fe8357.zip external_llvm-2c94b4201beccbd061fd679ea7e9db1381fe8357.tar.gz external_llvm-2c94b4201beccbd061fd679ea7e9db1381fe8357.tar.bz2 | |
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.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@124532 91177308-0d34-0410-b5e6-96231b3b80d8
Diffstat (limited to 'lib/CodeGen/SelectionDAG/DAGCombiner.cpp')
| -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 186f4af..a5b2d95 100644 --- a/lib/CodeGen/SelectionDAG/DAGCombiner.cpp +++ b/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); |