https://gcc.gnu.org/bugzilla/show_bug.cgi?id=88823
Richard Biener <rguenth at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
Status|UNCONFIRMED |NEW
Last reconfirmed| |2019-01-14
Ever confirmed|0 |1
--- Comment #1 from Richard Biener <rguenth at gcc dot gnu.org> ---
The flag is usually harmless and might only result in missed optimizations down
the road. At some point it caused VRP to ICE eventually. One -1(OVF) is
built here:
#4 0x000000000137f9d2 in get_computation_aff_1 (loop=0x7ffff6888ee0, at=
<gimple_cond 0x7ffff69cb280>, use=0x31d8e00, cand=0x31d8f90,
aff_inv=0x7fffffffd130, aff_var=0x7fffffffd2f0, prat=0x7fffffffd100)
at /space/rguenther/src/gcc-sccvn/gcc/tree-ssa-loop-ivopts.c:3947
(gdb) l
3942 if (stmt_after_increment (loop, cand, at))
3943 {
3944 aff_tree cstep_aff;
3945
3946 if (common_type != uutype)
3947 cstep_common = fold_convert (common_type, cstep);
where cstep is 4294967295 and common_type is int. That's probably harmless
as we just feed it back to tree-affine. Then there's
#4 0x0000000001383a5a in may_eliminate_iv (data=0x7fffffffd810,
use=0x31d8e00, cand=0x31d90b0, bound=0x7fffffffd638, comp=0x7fffffffd5c4)
at /space/rguenther/src/gcc-sccvn/gcc/tree-ssa-loop-ivopts.c:5147
5147 *bound = fold_convert (TREE_TYPE (cand->iv->base),
(gdb) l
5142 }
5143 }
5144
5145 cand_value_at (loop, cand, use->stmt, desc->niter, &bnd);
5146
5147 *bound = fold_convert (TREE_TYPE (cand->iv->base),
5148 aff_combination_to_tree (&bnd));
where a similar issue happens (unsigned -> signed convert). This is the
one ending up in the IL.
