[PATCH] D119654: [SDAG] enable binop identity constant folds for add/sub

[LuoYuanke via Phabricator via llvm-commits]

LuoYuanke added inline comments.


================
Comment at: llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp:3333
 
+  if (N0->getOpcode() == ISD::FREEZE && N0.hasOneUse())
+    N0 = N0->getOperand(0);
----------------
xbolva00 wrote:
> Some general solution? FREEZE should be dropped much sooner, no?
It is not dropped soon, because compiler can't guarantee it is NOT undef or poison value.

```
13469 SDValue DAGCombiner::visitFREEZE(SDNode *N) {
13470   SDValue N0 = N->getOperand(0);
13471
13472   if (DAG.isGuaranteedNotToBeUndefOrPoison(N0, /*PoisonOnly*/ false))
13473     return N0;
13474
13475   return SDValue();
13476 }

```
The freeze node live until instruction selection.

```
ISEL: Starting selection on root node: t40: v4i32 = freeze t2
```


Repository:
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  https://reviews.llvm.org/D119654/new/

https://reviews.llvm.org/D119654