[PATCH] D39282: DAG: Fold fma (fneg x), K, y -> fma x, -K, y

[Simon Pilgrim via Phabricator via llvm-commits]

RKSimon added inline comments.


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Comment at: lib/CodeGen/SelectionDAG/DAGCombiner.cpp:10128
+    // fma (fneg x), K, y -> fma x -K, y
+    if (N0.getOpcode() == ISD::FNEG) {
+      return DAG.getNode(ISD::FMA, DL, VT, N0.getOperand(0),
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arsenm wrote:
> RKSimon wrote:
> > Do we need a OneUse test on FNEG(N0)?
> I don't think so because this eliminates a use of fneg.
>> Do we need a OneUse test on FNEG(N0)?
> I don't think so because this eliminates a use of fneg.

OK - what about permitting negations of FpImmLegal constants if the negated value is FpImmLegal too?






https://reviews.llvm.org/D39282