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Re: type consistency of gimple

Kenneth Zadeck wrote:
> Nick Clifton wrote:
>> Hi Diego,
>>> Jeff's point about our optimizers is also true.  Nick, remember that
>>> issue with MIPS optimizations you were discussing with Jeff a few days
>>> ago?  I didn't follow most of the details, but it involved ivopts and
>>> sign issues.  Could you send a summary?
>> Sure:
>>   I was looking at how a gcc 4.1 based compiler optimized a fast
>> fourier transform algorithm for the MIPS target.  What I found was the
>> it was producing much worse code than a similarly configured gcc 3.4
>> based compiler, and the culprit was the creation of the induction
>> variables used in the inner loop.
> I think that you are pointing the gun at the wrong suspect.  I believe
> that the true villain is some where down stream in the backend passes
> that cannot see thru the type conversions.  This is one case of us
> having "degraded" the back end because the middle end likes to break
> things up into smaller pieces and the back end has too small of a window
> to look thru to do its work.
> We should be looking at the back end to see where it cannot see what it
> needs to see rather than trying to stop getting the middle end code into
> a reasonable form.

Uh, well, since the backend doesn't have real type information, it would
be hard to make it see through type conversions.

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