lildmh added inline comments.
================
Comment at: lib/AST/DeclOpenMP.cpp:164
+ if (NumClauses) {
+ Clauses = (OMPClause **)C.Allocate(sizeof(OMPClause *) * NumClauses);
+ setClauses(CL);
----------------
ABataev wrote:
> lildmh wrote:
> > ABataev wrote:
> > > lildmh wrote:
> > > > ABataev wrote:
> > > > > lildmh wrote:
> > > > > > ABataev wrote:
> > > > > > > lildmh wrote:
> > > > > > > > ABataev wrote:
> > > > > > > > > No, bad idea. Use tail allocation for the clauses. Check the
> > > > > > > > > implementation of `OMPRequiresDecl`
> > > > > > > > I think it is possible to use TrailingObjects for clause
> > > > > > > > storage when the number of clauses are known before creating
> > > > > > > > the directive (e.g., for OMPRequiresDecl and
> > > > > > > > OMPExecutableDirective).
> > > > > > > >
> > > > > > > > The reason that I had to create OMPDeclareMapperDecl before
> > > > > > > > parsing map clauses, is the mapper variable (AA in the example
> > > > > > > > below) needs to be declared within OMPDeclareMapperDecl,
> > > > > > > > because the following map clauses will use it.
> > > > > > > >
> > > > > > > > ```
> > > > > > > > #pragma omp declare mapper(struct S AA) map(AA.field1)
> > > > > > > > ```
> > > > > > > >
> > > > > > > > A possible way to get around this is to count the number of map
> > > > > > > > clauses before hand. But this solution is not trivial since the
> > > > > > > > normal method for parsing map clauses cannot be used (e.g., it
> > > > > > > > does not know AA when parsing map(AA.field1)). A customized and
> > > > > > > > complex (because it needs to handle all possible situations)
> > > > > > > > parsing method needs to be created, just for counting clause
> > > > > > > > number. I think it's not worthy to do this compared with
> > > > > > > > allocating map clause space later.
> > > > > > > >
> > > > > > > > I checked the code for OMPDeclareReductionDecl that you wrote.
> > > > > > > > It also has to be created before parsing the combiner and
> > > > > > > > initializer. It does not have a variable number of clauses
> > > > > > > > though.
> > > > > > > >
> > > > > > > > Any suggestions?
> > > > > > > Instead, you can introduce special DeclContext-based declaration
> > > > > > > and keep the reference to this declaration inside of the
> > > > > > > `OMPDeclareMapperDecl`.
> > > > > > Hi Alexey,
> > > > > >
> > > > > > Thanks a lot for your quick response! I don't think I understand
> > > > > > your idea. Can you establish more on that?
> > > > > >
> > > > > > In my current implementation, OMPDeclareMapperDecl is used as the
> > > > > > DeclConext of the variable AA in the above example, and it already
> > > > > > includes the reference to AA's declaration.
> > > > > >
> > > > > > My problem is, I need to create OMPDeclareMapperDecl before parsing
> > > > > > map clauses. But before parsing map clauses, I don't know the
> > > > > > number of clauses. Using TrailingObject requires to know how many
> > > > > > clauses there are when creating OMPDeclareMapperDecl. So I couldn't
> > > > > > use TrailingObject.
> > > > > >
> > > > > > My current solution is to create OMPDeclareMapperDecl before
> > > > > > parsing map clauses, and to create the clause storage after parsing
> > > > > > finishes.
> > > > > What I meant, that you don't need to use `OMPDeclareMapperDecl` for
> > > > > this, instead you can add another (very simple) special declaration
> > > > > based on `DeclContext` to use it as the parent declaration for the
> > > > > variable. In the `OMPDeclareMapperDecl` you can keep the reference to
> > > > > this special declaration.
> > > > Thanks for your response! Please let me know if my understanding below
> > > > is correct:
> > > >
> > > > `OMPDeclareMapperDecl` no longer inherits from `DeclContext`. Instead,
> > > > we create something like `OMPDeclareMapperDeclContext` which inherits
> > > > from `DeclContext`, and `OMPDeclareMapperDecl` keeps a pointer that
> > > > points to this `OMPDeclareMapperDeclContext`. AA and map clauses are
> > > > parsed within `OMPDeclareMapperDeclContext`.
> > > >
> > > > This sounds a bit more complex, but if you believe it's better, I can
> > > > change the code. Please share your thoughts.
> > > Yes, something like this.
> > Hi Alexey,
> >
> > Sorry for the late response. I was working on something else last week.
> >
> > When I tried to modify the code based on your suggestions, I found out that
> > `DeclContext` is only meant to be used for a `Decl` (please see the
> > comments before `class DeclContext {...}` in include/clang/AST/DeclBase.h).
> >
> > It means, if I create a `OMPDeclareMapperDeclContext ` which is a
> > `DeclContext ` but not a `Decl`, the code cannot work correctly. Therefore
> > `OMPDeclareMapperDeclContext` must be a `Decl` itself. If I do it this way,
> > a lot of useless information (all inherited from `Decl`) will exist within
> > `OMPDeclareMapperDeclContext`, which is very inefficient.
> >
> > An alternative way is to have something called `OMPDeclareMapperClauses`
> > that inherits from `TrailingObject` to store clause information, and
> > `OMPDeclareMapperDecl` keeps a pointer that points to
> > `OMPDeclareMapperClauses`. But I don't think this is better than just
> > having a `OMPClause **Clauses`, which is my current implementation.
> >
> > What do you think?
> I don't think the Decl requires a lot of memory. Seems to me, it requires ~32
> bytes.
Hi Alexey,
Thanks for the quick response! In the case we discussed earlier, we'll have 2
entities for a mapper:
```
class OMPDeclareMapperDeclContext : public Decl, public DeclContext {...};
class OMPDeclareMapperDecl : public ValueDecl, private TrailingObjects {
OMPDeclareMapperDeclContext *DC;
...
};
```
To me, the `Decl` within `OMPDeclareMapperDeclContext` is useless and confusing
to people. If you insist to get rid of `OMPClause **Clauses` in the current
implementation, I propose something below:
We still have 2 entities for a mapper:
```
class OMPDeclareMapperClauses : private TrailingObjects {...}
class OMPDeclareMapperDecl : public ValueDecl, public DeclContext {
OMPDeclareMapperClauses *Clauses;
...
};
```
This seems to be better than the above case. Do you like it?
CHANGES SINCE LAST ACTION
https://reviews.llvm.org/D56326/new/
https://reviews.llvm.org/D56326
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