ping
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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