[cfe-dev] Determining macros used in a function or SourceRange (using clang plugin)

Eric Bayer via cfe-dev cfe-dev at lists.llvm.org
Wed Sep 28 11:59:03 PDT 2016

Thanks Richard,

Question/comment inline.

On 9/28/2016 11:50 AM, Richard Smith wrote:
> On Wed, Sep 28, 2016 at 11:29 AM, Eric Bayer via cfe-dev 
> <cfe-dev at lists.llvm.org <mailto:cfe-dev at lists.llvm.org>> wrote:
>     Oh, one follow on question... If I persist a MacroDefinition* or
>     MacroInfo* in a datastructure, will this still exist when
>     processing the AST tree or will these have been deleted out from
>     under me?  Just trying to understand how much info I need to copy
>     in a few cases.
> MacroInfo, MacroDirective and ModuleMacro objects should persist until 
> the Preprocessor object is destroyed. You can hold onto them until 
> that happens.

That had been my guess, unfortunately as I'm a plugin I am not creating 
that myself.  I guess my real question is then, at what stage is the 
default preprocessor object destroyed in the compiler.

> MacroDefinition has value semantics, so if you want to persist a 
> MacroDefinition* it's up to you to store the MacroDefinition object 
> somewhere. But you should probably just be passing it around by value.

Ohhh, gotcha!  Thanks for the tip.

>        -Eric
>     On 9/27/2016 6:59 PM, Eric Bayer wrote:
>         Hi Alex,
>         Thanks again for all your help.  Actually I did manage to make
>         this eventually work with a huge amount of Lexer/Token magic.
>         Unfortunately I could not actually follow it past 1 level, so
>         it looks like an unworkable solution for what I have in mind.
>         I had thought the macro definitons were expanded from other
>         macros. After digging though the SLocEntries, this is clearly
>         not the case and they are expanded at their final uses.  This
>         means I'm going back to the PPCallbacks and digging in there. 
>         I think I can get the whole tree without annotating every
>         macro I meet. Apparently MacroExpands gets called repeatedly
>         at the point the macro gets used.
>         Kind Regards,
>            -Eric
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