https://gcc.gnu.org/bugzilla/show_bug.cgi?id=118795
--- Comment #12 from Richard Biener <rguenth at gcc dot gnu.org> ---
(In reply to Richard Biener from comment #11)
> (In reply to Jakub Jelinek from comment #10)
> > typedef unsigned char V __attribute__((vector_size (16)));
> >
> > V
> > foo (V x)
> > {
> > return __builtin_shuffle (x, x, (V) { 0, 0, 0, 0, 4, 4, 4, 4, 8, 8, 8, 8,
> > 12, 12, 12, 12 });
> > }
> > compiles fine.
>
> Yes, that's lowered then. I suspect sth post veclower introduces this
> (folding, forwprop).
Shows up after FRE5 which does
Value numbering stmt = _242 = VEC_PERM_EXPR <_226, _240, { 0, 1, 16, 17, 2, 3,
18, 19, 4, 5, 20, 21, 6, 7, 22, 23 }>;
Applying pattern match.pd:11067, gimple-match-6.cc:23482
Applying pattern match.pd:11067, gimple-match-6.cc:23482
Applying pattern match.pd:11285, gimple-match-6.cc:23983
Applying pattern match.pd:11067, gimple-match-6.cc:23482
Applying pattern match.pd:11067, gimple-match-6.cc:23482
Applying pattern match.pd:11067, generic-match-9.cc:11623
Setting value number of _242 to _242 (changed)
Applying pattern match.pd:11067, gimple-match-6.cc:23482
Applying pattern match.pd:5352, gimple-match-9.cc:7744
Applying pattern match.pd:11152, gimple-match-6.cc:23690
Applying pattern match.pd:11067, gimple-match-6.cc:23482
Applying pattern match.pd:5352, gimple-match-9.cc:7744
Applying pattern match.pd:11152, gimple-match-6.cc:23690
Applying pattern match.pd:5352, gimple-match-9.cc:7744
Applying pattern match.pd:11152, gimple-match-6.cc:23690
Applying pattern match.pd:11067, gimple-match-6.cc:23482
gimple_simplified to _257 = VEC_PERM_EXPR <vect__13.7476_216,
vect__13.7476_216, { 0, 0, 0, 0, 4, 4, 4, 4, 8, 8, 8, 8, 12, 12, 12, 12 }>;
possibly some intermediate state fools the match.pd logic that formerly
unsupported permutes are OK to be transformed into unsupported permutes.
I'll wait for the reduced testcase before investigating in more detail.
