[PATCH] D86689: [DAGCombine] Don't delete the node if it has uses immediately

[Sanjay Patel via Phabricator via llvm-commits]

spatel added inline comments.


================
Comment at: llvm/lib/CodeGen/SelectionDAG/TargetLowering.cpp:5823
       Cost = CostX;
+      SDValue N = DAG.getNode(ISD::FSUB, DL, VT, NegX, Y, Flags);
       RemoveDeadNode(NegY);
----------------
I think it would be clearer and less code duplication to put the 'if' check into the lambda, so something like:
  auto RemoveDeadNode = [&](SDValue N, SDValue Other) {
    if (N && N.getNode()->use_empty() && N != Other)
      DAG.RemoveDeadNode(N.getNode());
  };

Then call it with something like this:
      RemoveDeadNode(NegX, NegY);



================
Comment at: llvm/test/CodeGen/PowerPC/fneg.ll:56-62
+  %_val_rw_ = load float, float* undef, align 4
+  %_val_w_ = load float, float* undef, align 4
+  %_sub_tmp = fsub fast float 1.000000e+00, %_val_w_
+  %_conv25 = fpext float %_sub_tmp to double
+  %_expi_result = call fast double @llvm.powi.f64(double %_conv25, i32 3)
+  %_conv26 = fptrunc double %_expi_result to float
+  store float %_conv26, float* undef, align 4
----------------
We should reduce the test to avoid UB and extra operations, so something like this should work?

```
define double @fneg_no_ice(float %x) {
  %y = fsub fast float 1.0, %x
  %e = fpext float %y to double
  %e2 = fmul double %e, %e
  %e3 = fmul double %e, %e2
  ret double %e3
}

```


Repository:
  rG LLVM Github Monorepo

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  https://reviews.llvm.org/D86689/new/

https://reviews.llvm.org/D86689