[PATCH] Consider error-reporting calls cold in BPI

[Hal Finkel]

----- Original Message -----
> 
> Actually looking at this patch, why not do this in the pass which
> adds function attributes by adding the cold attribute to error
> reporting library functions? Then the existing BPI code will
> trigger.
> 
> 
> Also, I would sink the logic for determining if a particular library
> call to write to a stream is writing to 'stderr' into
> TargetLibraryInfo itself. Essentially, make a boolean query for
> 'isLikelyErrorReportingFn' or something.

Make sense.

> 
> 
> Finally, why not also bias against write() calls with a numeric
> argument pointing to the typical stderr file descriptor?

I could do that too.

> 
> 
> With all of these heuristics, it would be useful to clarify that this
> isn't a *guarantee* that this is an error reporting function (you
> can rearrange stderr if you want, etc), but it's a strong signal
> that we can do stuff like synthesizing the cold attribute from.

Yes, exactly.

Thanks again,
Hal

> 
> 
> 
> On Sun, Oct 27, 2013 at 4:23 PM, Hal Finkel < hfinkel at anl.gov >
> wrote:
> 
> 
> Hello,
> 
> BranchProbabilityInfo, which is used by the SDAG builder to assign
> branch weights, contains a number of well-known heuristics for
> statically predicting branch outcomes. One of these heuristics
> assigns low probabilities to paths post-dominated by cold calls
> (calls with the cold attribute). This patch enhances that heuristic
> to consider 'error reporting' calls to also be cold. An 'error
> reporting' call is a call to perror or a call to fprintf, fwrite,
> etc. where stderr is the stream.
> 
> This is one of the suggested heuristics from:
> http://impact.crhc.illinois.edu/shared/papers/pact-98-branchpred.pdf
> 
> I don't see any significant test-suite changes.
> 
> Please review.
> 
> Thanks again,
> Hal
> 
> --
> Hal Finkel
> Assistant Computational Scientist
> Leadership Computing Facility
> Argonne National Laboratory
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> 
> 
> 

-- 
Hal Finkel
Assistant Computational Scientist
Leadership Computing Facility
Argonne National Laboratory