[llvm] [WPD] Dereference `GlobalAlias` targets (PR #215880)

[Teresa Johnson via llvm-commits]

================
@@ -1147,6 +1147,10 @@ bool DevirtModule::tryFindVirtualCallTargets(
     // target.
     auto *GV = dyn_cast<GlobalValue>(C);
     assert(GV);
+    if (!GV->isInterposable())
+      if (auto *GA = dyn_cast<GlobalAlias>(GV))
+        if (!GA->isInterposable())
----------------
teresajohnson wrote:

This is effectively doing the same check as the one 2 lines up, since GA = GV. I think you meant to check the aliasee object (which you are doing correctly in the ThinLTO case further down). Might make sense to do the check in a single if statement like you are doing there too. I.e.:

```
    assert(GV);
    if (auto *GA = dyn_cast<GlobalAlias>(GV))
        if (!GA->isInterposable() && !GA->getAliaseeObject()->isInterposable())
          GV = GA->getAliaseeObject();
```

I guess all the tests in the PR so far are for the ThinLTO case. You could presumably test this one in llvm/test/Transforms/WholeProgramDevirt/.

https://github.com/llvm/llvm-project/pull/215880