Re: [patch] Fix PR tree-optimization/49318

[Richard Guenther <richard.guenther@gmail.com>]

On Fri, Jun 10, 2011 at 9:19 AM, Ira Rosen <ira.rosen@linaro.org> wrote:
> Hi,
>
> The test in PR 49318 fails because the vectorizer recognizes address
> computation sequence as a widening-multiplication pattern, while such
> sequence is not relevant to vectorization. The problem is that the
> vectorizer doesn't check if a statement is going to be vectorized
> before replacing it with a pattern. Moreover, the vectorizer first
> detects the patterns and only after that looks for relevant
> statements. Changing the order is not a good option, since statements
> relevance is defined also by their belonging to a pattern.
>
> This patch solves the problem by removing pattern statements that were
> created for statements that are not supposed to be vectorized.
>
> Bootstrapped with vectorization enabled on powerpc64-suse-linux and
> tested on powerpc64-suse-linux and x86_64-suse-linux.
> Committed.

Ick, yeah.  I remember running into this ordering issue when doing the
multi-vector size reorgs...

In the end I think we should not generate the pattern stmt during
pattern matching but only mark the relevant statements with a
pattern kind.  Say, for each pattern we have a "main" statement
that has related stmts belonging to the pattern that define uses
of the "main" statement - mark those to refer to that "main" statement.
For that "main" statement simply record an enum value, like,
widening_mult.  Then only at vectorized statement
generation time actually generate the vectorized form of the
pattern statement.

Thus, the non-vectorized pattern statements would never be generated.

So, separate analysis and transform more properly.

Of course I didn't get around to implement the above ... (we'd have
a new vectorizable_pattern worker).

Richard.

> Ira
>
> ChangeLog:
>
>     PR tree-optimization/49318
>     * tree-vect-loop.c (vect_determine_vectorization_factor):
>     Remove irrelevant pattern statements.
>
> testsuite/ChangeLog:
>
>     PR tree-optimization/49318
>     * gcc.dg/vect/pr49318.c: New test.
>