[PATCH, tree-optimization]: Fix PR 40550

[Uros Bizjak]

Hello!

The problem here is with generic vectorizer which produces vector 
operations in wider mode than original mode. In this particular example, 
where generic v2sf mode addition is disabled due to problems with 
[f]emms, type_for_widest_vector_mode () returns v4sf mode. 
Unfortunately, this is not in line with the comment that says:

  /* For very wide vectors, try using a smaller vector mode.  */

- since v4sf mode is obviously wider than v2sf mode. Operating in wider 
mode leads to all sort of problems with uninitialized values (NaNs, 
subnormals, etc...) and overwritten stack slots.

The solution is to reject all modes, wider than the original mode.

2009-06-28  Uros Bizjak <ubizjak@gmail.com>

     PR tree-optimization/40550
     * tree-vect-generic.c (expand_vector_operations_1): Compute in
     vector_compute_type only when the size of vector_compute_type is
     less or equal to the size of type.

testsuite/ChangeLog:

2009-06-28  Uros Bizjak <ubizjak@gmail.com>

     PR tree-optimization/40550
     * gcc.dg/pr40550.c: New test.

Patch was bootstrapped and regression tested on 4.4 branch, where the 
testcase breaks for unpatched gcc on i686 and x86_64 targets. There is 
the same problem present on 4.3 and earlier branches. The problem is 
also present on mainline, but masked by different stack layout.

I have also checked, that v8sf mode still gets decomposed to v4sf mode 
on SSE targets (FWIW, when mmx_addv2sf3 is renamed to addv2sf3 gcc 
generates expected pfadd with -m3dnow).

OK for 4.3, 4.4 and mainline?

Uros.
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