[PATCH] D100667: [clang] Fix assert() crash when checking undeduced arg alignment

[Haojian Wu via Phabricator via cfe-commits]

hokein added a comment.

thanks, I think we can simplify a bit more.



================
Comment at: clang/lib/Sema/SemaChecking.cpp:4543
   // getTypeAlignInChars requires complete types
-  if (ParamTy->isIncompleteType() || ArgTy->isIncompleteType() ||
-      ParamTy->isUndeducedType() || ArgTy->isUndeducedType())
+  auto CheckTypeOK = [](QualType Ty) {
+    if (Ty->isIncompleteType() || Ty->isUndeducedType())
----------------
adamcz wrote:
> hokein wrote:
> > The current fix is on top of kadir's fix, now the code becomes more add-hoc, it looks like a smell to me.
> > 
> > 
> > It looks like `CheckArgAlignment` has an implicit invariant (the arg type should never be undeduced), and this invariant was enforced by dropping the invalid AST. Now with `RecoveryExpr`, we might break the invariant -- when the RecoveryExpr preserves an `undeduced` type, like the test case in this patch (which is done via the [code](https://github.com/llvm/llvm-project/blob/main/clang/lib/Sema/SemaExprCXX.cpp#L1420)).
> > 
> > 
> > I think a right fix is to fix in the `RecoveryExpr` side, `RecoveryExpr` should not preserve an undeduced type, we did it for function return type already (https://reviews.llvm.org/D87350), but it didn't cover all places. I think a general fixing place is `Sema::CreateRecoveryExpr`, if the passing `T` is undeduced, fallback to dependent type.
> > 
> Ooh, interesting. Thanks for the info.
> 
> I updated the change to catch this in CreateRecoveryExpr as well. I kept my original changes too, they shouldn't harm anything and it's better than crashing.
> 
> Let me know what you think about this now.
> I kept my original changes too, they shouldn't harm anything and it's better than crashing.

I'm a bit nervous about keeping the change/extending the undeduced-type here, this looks like a defensive programming, it might hide some bugs in the future.  As we have figured out the root cause, I'd also remove the bailout `isUndeducedType` case here.


================
Comment at: clang/lib/Sema/SemaExpr.cpp:19668
     T = Context.DependentTy;
+  else if (const auto *U = T->getUnqualifiedDesugaredType())
+    if (U->isUndeducedType())
----------------
I'm not sure we need this well. I think the above `T->isUndeducedType()` should be enough to fix all known crashes. I'd just remove this one.


Repository:
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  https://reviews.llvm.org/D100667/new/

https://reviews.llvm.org/D100667