[PATCH] D57921: [DAG] Cleanup unused node in SimplifySelectCC.

[Simon Pilgrim via Phabricator via llvm-commits]

RKSimon added inline comments.


================
Comment at: llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp:18677
   SDValue SCC = SimplifySetCC(getSetCCResultType(CmpOpVT), N0, N1, CC, DL,
                               false);
+  if (SCC.getNode()) {
----------------
RKSimon wrote:
> RKSimon wrote:
> > Could we replace this with a call to SelectionDAG::FoldSetCC()? That should only ever constant fold which AFAICT is what we're after.
> Actually it looks like there's a tiny bit of commutation code (moves single constant to RHS) that probably needs pulling out of FoldSetCC into getNode - but that's trivial compared to the TLI.SimplifySetCC monster.
Confirmed, this gives the same result and is a lot cleaner:
```
  // Determine if the condition we're dealing with is constant.
  if (SDValue SCC = DAG.FoldSetCC(VT, N0, N1, CC, DL)) {
    if (auto *SCCC = dyn_cast<ConstantSDNode>(SCC)) {
      // fold select_cc true, x, y -> x
      // fold select_cc false, x, y -> y
      return !SCCC->isNullValue() ? N2 : N3;
    }
  }
```


Repository:
  rL LLVM

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  https://reviews.llvm.org/D57921/new/

https://reviews.llvm.org/D57921