[PATCH] D77453: [GlobalISel] Simplify G_ADD when it has (0-X) on the LHS or RHS

[Jessica Paquette via Phabricator via llvm-commits]

paquette marked an inline comment as done.
paquette added inline comments.


================
Comment at: llvm/lib/CodeGen/GlobalISel/CombinerHelper.cpp:1634
+  std::tie(SubLHS, SubRHS) = MatchInfo;
+  Builder.buildSub(MI.getOperand(0).getReg(), SubLHS, SubRHS);
+  MI.eraseFromParent();
----------------
arsenm wrote:
> Should this preserve any flags?
In the DAGCombiner, it doesn't seem to:

```
  // fold ((0-A) + B) -> B-A
  if (N0.getOpcode() == ISD::SUB && isNullOrNullSplat(N0.getOperand(0)))
    return DAG.getNode(ISD::SUB, DL, VT, N1, N0.getOperand(1));
```

but maybe we should? It would make sense.




CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D77453/new/

https://reviews.llvm.org/D77453