[PATCH] D106907: [clang] fix concepts crash on substitution failure during normalization

[Matheus Izvekov via Phabricator via cfe-commits]

mizvekov added inline comments.


================
Comment at: clang/lib/Sema/SemaConcept.cpp:744
                                           ArrayRef<const Expr *> E) {
-  assert(E.size() != 0);
-  auto First = fromConstraintExpr(S, D, E[0]);
----------------
rsmith wrote:
> Might be useful to keep this assert; it will make it clearer to future readers that this function isn't intended to handle this case.
Yeah you are right, the assert makes it obvious this is intended.


================
Comment at: clang/lib/Sema/SemaConcept.cpp:751
+      return None;
+    Conjunction.emplace(S.Context, std::move(*Conjunction), std::move(*Next),
+                        CCK_Conjunction);
----------------
rsmith wrote:
> Doesn't this have a use-after-destruction bug? I'd expect `emplace` to first destroy its contained value and then construct a new one; in this case the second constructor argument looks like it'll be a reference to a destroyed object. I assume that's why the old code did the two-step construct and assign dance.
The constructor used here takes both constraints by value:
```
  NormalizedConstraint(ASTContext &C, NormalizedConstraint LHS,
                       NormalizedConstraint RHS, CompoundConstraintKind Kind)
      : Constraint{CompoundConstraint{
            new (C) std::pair<NormalizedConstraint, NormalizedConstraint>{
                std::move(LHS), std::move(RHS)}, Kind}} { };
```


Repository:
  rG LLVM Github Monorepo

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  https://reviews.llvm.org/D106907/new/

https://reviews.llvm.org/D106907