match.pd, optabs: Avoid vectorization of {FLOOR,CEIL,ROUND}_{DIV,MOD}_EXPR [PR102860]

match.pd, optabs: Avoid vectorization of {FLOOR,CEIL,ROUND}_{DIV,MOD}_EXPR [PR102860]

power10 has modv4si3 expander and so vectorizes the following testcase
where Fortran modulo is FLOOR_MOD_EXPR.
optabs_for_tree_code indicates that the optab for all the *_MOD_EXPR
variants is umod_optab or smod_optab, but that isn't true, that optab
actually expands just TRUNC_MOD_EXPR.  For the other tree codes expmed.cc
has code how to adjust the TRUNC_MOD_EXPR into those by emitting some
extra comparisons and conditional updates.  Similarly for *_DIV_EXPR,
except in that case it actually needs both division and modulo.

While it would be possible to handle it in expmed.cc for vectors as well,
we'd need to be sure all the vector operations we need for that are
available, and furthermore we wouldn't account for that in the costing.

So, IMHO it is better to stop pretending those non-truncating (and
non-exact) div/mod operations have an optab.  For GCC 13, we should
IMHO pattern match these in tree-vect-patterns.cc and transform them
to truncating div/mod with follow-up adjustments and let the vectorizer
vectorize that.  As written in the PR, for signed operands:
r = x %[fl] y;
is
r = x % y; if (r && (x ^ y) < 0) r += y;
and
d = x /[fl] y;
is
r = x % y; d = x / y; if (r && (x ^ y) < 0) --d;
and
r = x %[cl] y;
is
r = x % y; if (r && (x ^ y) >= 0) r -= y;
and
d = /[cl] y;
is
r = x % y; d = x / y; if (r && (x ^ y) >= 0) ++d;
(too lazy to figure out rounding div/mod now).  I'll create a PR
for that.
The patch also extends a match.pd optimization that floor_mod on
unsigned operands is actually trunc_mod.

2022-01-19  Jakub Jelinek  <jakub@redhat.com>

	PR middle-end/102860
	* match.pd (x %[fl] y -> x % y): New simplification for
	unsigned integral types.
	* optabs-tree.cc (optab_for_tree_code): Return unknown_optab
	for {CEIL,FLOOR,ROUND}_{DIV,MOD}_EXPR with VECTOR_TYPE.

	* gfortran.dg/pr102860.f90: New test.