[Bug tree-optimization/41464] vector loads are unnecessarily split into high and low loads

["irar at il dot ibm dot com" <gcc-bugzilla@gcc.gnu.org>]

------- Comment #4 from irar at il dot ibm dot com  2009-09-27 08:06 -------
(In reply to comment #1)
> The interesting thing is that data-ref analysis sees 128bit alignment but
> the vectorizer still produces
>   vect_var_.24_59 = M*vect_p.20_57{misalignment: 0};
>   D.2564_12 = *D.2563_11;
>   vect_var_.25_61 = vect_var_.24_59 * vect_cst_.26_60;
>   D.2565_13 = D.2564_12 * 2.2999999523162841796875e+0;
>   M*vect_p.27_64{misalignment: 0} = vect_var_.25_61;
> thus, unknown misalignment.
> (instantiate_scev
>   (instantiate_below = 3)
>   (evolution_loop = 1)
>   (chrec = {i_10(D), +, 4}_1)
>   (res = {i_10(D), +, 4}_1))
>         base_address: i_10(D)
>         offset from base address: 0
>         constant offset from base address: 0
>         step: 4
>         aligned to: 128
>         base_object: *i_10(D)
> Creating dr for *D.2562_7
>   (res = {f_6(D), +, 4}_1))
>         base_address: f_6(D)
>         offset from base address: 0
>         constant offset from base address: 0
>         step: 4
>         aligned to: 128
>         base_object: *f_6(D)
> t2.i:5: note: === vect_enhance_data_refs_alignment ===
> t2.i:5: note: Vectorizing an unaligned access.
> t2.i:5: note: Vectorizing an unaligned access.

"aligned to" refers to the offset misalignment and not to the misalignment of
base.
attribute aligned works only for arrays, i.e., declarations, and not for
pointer arguments. For pointers the vectorizer only checks TYPE_ALIGN_UNIT of
the base type.

Ira


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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=41464