gcc-ow...@gcc.gnu.org wrote on 11/12/2009 20:25:33:
> Allan Sandfeld Jensen <li...@carewolf.com>
> Hi
>
> I hope someone can help me. I've been trying to write some tight
> integer loops
> in way that could be auto-vectorized, saving me to write assembler or
using
> specific vectorization extensions. Unfortunately I've not yet managed to
make
> gcc vectorize any of them.
>
> I've simplified the case to just perform the very first operation inthe
loop;
> converting from two's complement to sign-and-magnitude.
>
> I've then used -ftree-vectorizer-verbose to examine if and if not,
> why not the
> loops were not vectorized, but I am afraid I don't understand the output.
>
> The simplest version of the loop is here (it appears the branch is not a
> problem, but I have another version without).
>
> inline uint16_t transsign(int16_t v) {
> if (v<0) {
> return 0x8000U | (1-v);
> } else {
> return v;
> }
> }
>
> It very simply converts in a fashion that maintains the full effective
bit-
> width.
>
> The error from the vectorizer is:
> vectorizesign.cpp:42: note: not vectorized: relevant stmt not supported:
> v.1_16 = (uint16_t) D.2157_11;
>
> It appears the unsupported operation in vectorization is the typecast
from
> int16_t to uint16_t, can this really be the case, or is the output
misleading?
Yes, the problem is in signed->unsigned cast. I think it is related to PR
26128.
Ira
>
> If it is the case, then is there good reason for it, or can I fix
itmyself by
> adding additional vectorizable operations?
>
> I've attached both test case and full output of
ftree-vectorized-verbose=9
>
> Best regards
> `Allan
>
> [attachment "vectorizesign.cpp" deleted by Ira Rosen/Haifa/IBM]
> [attachment "vectorizesign-debug.txt" deleted by Ira Rosen/Haifa/IBM]
