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SPECjbb X86 validation failures


Boehm, Hans writes:
 > I'm unfortunately still seeing problems with SPECjbb on X86 with gcc3.1.
 > These are apparently optimization failures.  They don't seem to be
 > correlated with the reload1.c ICEs that I mentioned earlier.
 > 
 > I know that:
 > 
 > - They occur at -O1 and -O2, but not at -O0.
 > 
 > - The result is incorrect code, which is detected by the SPECjbb validation
 > test.
 > 
 > - More than one file in SPECjbb is misoptimized as a result.
 > 
 > - They do not occur on IA64.
 > 
 > I've identified one file that's definitely being misoptimized (by binary
 > search).  Are there known techniques for systematically narrowing this down
 > further?  I'm looking for something like a list of optimization flags
 > implied by -O1 that I can toggle individually, 

Use -fverbose-asm.  A list of all the optimizations applies is in the
asm file.

 > and ideally a flag to turn off optimization in all functions past
 > line N, or something similar.

Ah, that's much harder.  I guess you have a licence for SPECjbb and we
don't, so I can't look at it?

 > The underying problem here is that this is a fairly large body of code,
 > which I don't understand well.  Thus tracking down a bug is hard, and
 > tracking down a misoptimization is harder.

It is, and it takes time to understand how to fix optimizer bugs.

Andrew.


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