[cfe-dev] why does clang re-evaluate the target info for each input file?

Ted Kremenek kremenek at apple.com
Fri Feb 29 11:19:59 PST 2008

On Feb 29, 2008, at 10:50 AM, Sam Bishop wrote:

> The subject line says it all, I suppose.  It seems to me that the  
> target
> would be a per-invocation constant.  Is state modified that needs to  
> be
> refreshed?
> clang.cpp:main():
>  for (unsigned i = 0, e = InputFilenames.size(); i != e; ++i) {
>    const std::string &InFile = InputFilenames[i];
>    ...
>    <if not a serialized file> {
>      Target = TargetInfo::CreateTargetInfo(&triples[0],
>                                            &triples[0]+triples.size(),
>                                            &Diags);
>    }
>    ...
>  }
> If we want to optimize for the serialized case, perhaps we could  
> allocate
> the target information lazily?

Hi Sam,

Originally the Target was computed only once, prior to adding  
serialization support.  Because the changes I made to the driver when  
I added serialization support were fairly invasive, small  
inefficiencies like this were (deliberately) introduced.  The desired  
tradeoff at the time was to have my changes be more readable and  
understandable at the cost of a few things in the driver being  
slightly less efficient.  The hope was that this would help shake out  
bugs introduced by my changes (of which there were several that we  
encountered).  Certainly some of these inefficiencies can (and should)  
be fixed.  I am fine with introducing optimizations like the one you  
suggest as long as we also aim to keep the driver readable and  


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