[cfe-commits] Separate semantic checking of EnumConstantDecl from the action

Vassil Vassilev vasil.georgiev.vasilev at cern.ch
Tue Dec 13 11:35:22 PST 2011

On 04.12.2011 г. 11:34, Vassil Vassilev wrote:
> Hi Doug,
>     Sorry I didn't give the use case. I thought that this will be only
> benefit for the compiler.
>     So in our use case (in cling) we want to allow stmts "on the global
> scope" like:
>     [cling$] int i =0;
>     [cling$] for(...) {
>     ...
>     There is no easy way how we can understand whether the user input was
> declaration or stmt.
> So we wrap the input internally into void cling_unique_name { body of
> stmts and decls}
> For non declstmts it's all fine. However, when we have declaration the
> user expects to be visible
> from the other stmts (internally wrappers).
>     In that case we create a SemaConsumer that extract the declarations
> on the global scope, i.e.
> change the linkage and visibility and the declaration context and we
> re-register it in the as resolver
> chain if needed. Before pulling the decl out we need to make sure that
> all the c/c++ semantic rules
> for that decl hold at the new position. For example, are there clashing
> names etc. If there is
> something wrong we want proper diagnostic for that. In that case,
> ideally, we don't want to create yet
> another AST node, which will be dangling.
>     Even if we create a new node directly at the new position the old
> node will shadow the new one. Eg:
> [cling$] int i; i = 15; // transformed into void cling_unique_name{int
> i; i=15;}
>     I really liked the interface Sema::CheckVariableDeclaration,
> Sema::CheckFunctionDeclaration and I maybe
> concluded wrongly that's the idea of all the CheckXXX functions.
> I think no AST node creating CheckXXX will be reused by the template
> instantiation subsystem.
> Correct me if I am wrong but right now in
> TemplateDeclInstantiator::VisitEnumDecl clang
> creates redundant EnumConstantDecl because the node is created by
> Sema::CheckEnumConstant.
>     Maybe I am missing something but I don't understand how this could
> make it easier to create broken AST nodes.
> I guess you say that because some of the node properties are determined
> only after semantic analysis.
> Can't we work this around somehow? I am willing to do the rest of the work.
> Vassil
> On 12/03/2011 08:43 PM, Douglas Gregor wrote:
>> On Nov 30, 2011, at 6:22 AM, Vassil Vassilev wrote:
>>> Hi,
>>>    The attached patch tries to split the semantic checking from the AST node creation.
>>>    I think it is useful one to be able to check already created AST node. Do you think that
>>> makes sense? Can that patch end up in clang's mainline?
>> I don't understand why you want to split this. Within Sema, we often combine semantic analysis with AST building so that there is just one place in the code that is responsible for making sure that the AST node is built with all of its invariants satisfied. Splitting semantic analysis from AST building makes it easier to create broken nodes that will cause problems downstream.
>> 	- Doug
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