[patch] [PR25413] fix natural-alignment assumption in the vectorizer

[Dorit Nuzman <DORIT at il dot ibm dot com>]

Hi,

This is a slightly revised and updated resubmission of this patch:
http://gcc.gnu.org/ml/gcc-patches/2006-03/msg00167.html
It fixes PR25413, and hopefully also PR32093 and the zlib breakage
mentioned here:
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=32093#c2.

The vectorizer assumes that all data is naturally aligned on the size of
its data-type. This is not always the case. Packed structs are one example.
Another example is 64-bit doubles which, on some targets, are not
guaranteed to be aligned on 64-bit boundary. With this patch, when the
vectorizer cannot prove that a data-reference is naturally aligned it
avoids using loop-peeling as a means to align this data-reference (cause it
cannot work). This is done in a new function - vector_alignment_reachable_p
- which also contains some code that was factored out from
vect_enhance_data_refs_alignment. It adds a new target-builtin, a default
implementation for it in default_builtin_vector_alignment_reachable, and
also an rs6000 implementation for it. Maybe target-specific implementations
for other targets are appropriate as well (*). I'm not 100% sure about the
rs6000 implementation, but even if it's not accurate enough, it is still an
improvement over the current situation.

Bootstrapped on powerpc-linux, passed the vectorizer testcases, and going
through full regression testing.
Also bootstrapped on i386-linux, and passed full regression testing.

(*) Also included in the patch is a suggested implementation of the target
hook for the SPU. If this is approved and applied we'd also need to xfail
the current dg-final checks for spu-*-* in pr25413.c, pr25413a.c,
pr31699.c, because on the SPU longs and doubles are natually aligned
(right?), so we can use peeling there. For the SPU I only tested that the
patch builds with a cross-compile for c only, and checked that the 3 tests
above run ok. So this requires more thorough testing (If someone can help
with this it would be most appreciated...).

OK for mainline?

:ADDPATCH middle-end,rs6000:

thanks,
dorit

2007-07-02  Dorit Nuzman  <dorit@il.ibm.com>
            Devang Patel  <dpatel@apple.com>

        PR tree-optimization/25413
        * targhooks.c (default_builtin_vector_alignment_reachable): New.
        * targhooks.h (default_builtin_vector_alignment_reachable): New.
        * tree.h (contains_packed_reference): New.
        * expr.c (contains_packed_reference): New.
        * tree-vect-analyze.c (vector_alignment_reachable_p): New.
        (vect_enhance_data_refs_alignment): Call
vector_alignment_reachable_p.
        * target.h (vector_alignment_reachable): New builtin.
        * target-def.h (TARGET_VECTOR_ALIGNMENT_REACHABLE): New.
        * config/rs6000/rs6000.c (rs6000_vector_alignment_reachable): New.
        (TARGET_VECTOR_ALIGNMENT_REACHABLE): Define.

2007-07-02  Dorit Nuzman  <dorit@il.ibm.com>
            Devang Patel  <dpatel@apple.com>

        PR tree-optimization/25413
        * gcc.dg/vect/vect-align-1.c: New.
        * gcc.dg/vect/vect-align-2.c: New.
        * gcc.dg/vect/pr25413.c: New.
        * gcc.dg/vect/pr25413a.c: New.
        * gcc.dg/vect/pr31699.c: Fix dg-final check.

(See attached file: pr25413.july2.txt)

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