[PATCH] D77560: [SCEV] don't try to query getSCEV() for incomplete PHIs

[ChenZheng via Phabricator via llvm-commits]

shchenz added inline comments.


================
Comment at: llvm/lib/Transforms/Utils/ScalarEvolutionExpander.cpp:1190
+      // PHI has no meaning at all.
+      if (!PN.getParent()->hasNPredecessors(PN.getNumIncomingValues()))
+        continue;
----------------
lebedev.ri wrote:
> I don't think this is correct fix. It is perfectly legal to have e.g. the following:
> ```
> pred:
>  <...>
>  br label %succ
> succ:
>  %10 = phi i32 [ 0, %pred ], [ 0, %pred ]
> ```
Here we want to identify an incomplete PHI.
The incomplete PHI is like `%10 = phi i32`, `hasNPredecessors` should be set when the PHI node is created, so it is 2.
```
  PHINode *PN = Builder.CreatePHI(ExpandTy, std::distance(HPB, HPE),
                                  Twine(IVName) + ".iv");
```

But its `getNumIncomingValues()` is 0 because it is not populated yet.

Do you have any other ways to identify an incomplete PHI? @lebedev.ri 


Repository:
  rG LLVM Github Monorepo

CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D77560/new/

https://reviews.llvm.org/D77560