[PATCH] D63640: [clang] Improve Serialization/Imporing/Dumping of APValues

[Tyker via Phabricator via cfe-commits]

Tyker marked an inline comment as done.
Tyker added inline comments.


================
Comment at: clang/lib/Serialization/ASTReader.cpp:9635
+        if (IsExpr) {
+          Base = APValue::LValueBase(ReadExpr(F), CallIndex, Version);
+          ElemTy = Base.get<const Expr *>()->getType();
----------------
Tyker wrote:
> rsmith wrote:
> > This is problematic.
> > 
> > `ReadExpr` will read a new copy of the expression, creating a distinct object. But in the case where we reach this when deserializing (for a `MaterializeTemporaryExpr`), we need to refer to the existing `MaterializeTemporaryExpr` in the initializer of its lifetime-extending declaration. We will also need to serialize the `ASTContext`'s `MaterializedTemporaryValues` collection so that the temporaries lifetime-extended in a constant initializer get properly handled.
> > 
> > That all sounds very messy, so I think we should reconsider the model that we use for lifetime-extended materialized temporaries. As a half-baked idea:
> > 
> >  * When we lifetime-extend a temporary, create a `MaterializedTemporaryDecl` to hold its value, and modify `MaterializeTemporaryExpr` to refer to the `MaterializedTemporaryDecl` rather than to just hold the subexpression for the temporary.
> >  * Change the `LValueBase` representation to denote the declaration rather than the expression.
> >  * Store the constant evaluated value for a materialized temporary on the `MaterializedTemporaryDecl` rather than on a side-table in the `ASTContext`.
> > 
> > With that done, we should verify that all remaining `Expr*`s used as `LValueBase`s are either only transiently used during evaluation or don't have these kinds of identity problems.
> Would it be possible to adapt serialization/deserialization so that they make sure that `MaterializeTemporaryExpr` are unique.
> by:
> 
>   - When serializing `MaterializeTemporaryExpr` serialize a key obtained from the pointer to the expression as it is unique.
>   - When deserializing `MaterializeTemporaryExpr` deserializing the key, and than have a cache for previously deserialized expression that need to be unique.
> 
> This would make easier adding new `Expr` that require uniqueness and seem less complicated.
> What do you think ?
i added a review that does the refactoring https://reviews.llvm.org/D69360.


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https://reviews.llvm.org/D63640