Revision 107218 changed addressing mode generation

[Bernd Schmidt]

Richard Guenther wrote:
> I think CSE added/removed by either canoncial form is less important
> than things like SCEV analysis being unaffected and IVOPTs still
> creating proper induction variables on the tree level.
> 
> Of course a canonical form should minimize the number of operations,
> so folding i * 4 + j * 4 to (i + j) * 4 should still be done.  But
> folding i * 4 + j * 2 to (i * 2 + j) * 2 and not i * 4 + 4 to (i + 1) * 4
> looks strange.
> 
> I have been resistant to change this canonicalization simply because
> the current one seems to work well with the tree loop optimizers and
> date-dependence analysis nowadays, thus also my hint at doing
> such change during stage1 instead of stage4 (after all this "problem"
> now exists since 4.1 ...?)
> 
> Implementing the change should be straight-forward (we should
> make sure the tree reassociation pass agrees with it).

So, how do we proceed?  IMO the canonical form should be that addition 
of a constant is always the outermost operation.  That seems to be what 
the EXPAND_SUM machinery expects, and what extract_muldiv wants to do. 
It's also IMO most likely to be helpful when generating addressing modes.

The patch below should do that, but unfortunately:
+FAIL: gcc.dg/vect/vect-103.c scan-tree-dump-times vect "dependence 
distance modulo vf == 0" 1
+FAIL: gcc.dg/vect/no-vfa-vect-102.c scan-tree-dump-times vect "possible 
dependence between data-refs" 1

I'm not really familiar with the vectorizer.

Still - would someone like to benchmark this patch on i686-linux, maybe 
with a SPEC run?  I don't have that available.


Bernd
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