https://gcc.gnu.org/bugzilla/show_bug.cgi?id=96888
Richard Biener <rguenth at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
Blocks| |53947
Status|UNCONFIRMED |NEW
Last reconfirmed| |2020-09-02
Ever confirmed|0 |1
--- Comment #2 from Richard Biener <rguenth at gcc dot gnu.org> ---
Confirmed. We currently do not support promoting/demoting the shift amount
vector operand when vectorizing shifts. Note the fact that we
turn word & (1ul<<j) into word >> j likely triggers this issue - this
does not happen when you write word & (1u<<j).
Still AVX2 is needed for the 1<<j induction. Note the generated code
doesn't exactly look good ...
It seems we should be able to use outer loop vectorization here, but
after fixing some things we still run into dependence analysis issues
there:
t.ii:4:46: note: === vect_analyze_data_ref_dependences ===
t.ii:4:46: note: dependence distance = 0.
t.ii:4:46: note: dependence distance == 0 between *_8 and *_8
t.ii:4:46: note: dependence distance = 1.
t.ii:7:23: missed: not vectorized, possible dependence between data-refs *_8
and *_8
t.ii:4:46: missed: bad data dependence.
that's the v[i*16+j] read/write.
Referenced Bugs:
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=53947
[Bug 53947] [meta-bug] vectorizer missed-optimizations
