https://gcc.gnu.org/bugzilla/show_bug.cgi?id=108688
--- Comment #4 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
I think the bug is in the match.pd
/* Simplify a bit extraction from a bit insertion for the cases with
the inserted element fully covering the extraction or the insertion
not touching the extraction. */
(simplify
(BIT_FIELD_REF (bit_insert @0 @1 @ipos) @rsize @rpos)
(with
{
unsigned HOST_WIDE_INT isize;
if (INTEGRAL_TYPE_P (TREE_TYPE (@1)))
isize = TYPE_PRECISION (TREE_TYPE (@1));
else
isize = tree_to_uhwi (TYPE_SIZE (TREE_TYPE (@1)));
}
(switch
(if (wi::leu_p (wi::to_wide (@ipos), wi::to_wide (@rpos))
&& wi::leu_p (wi::to_wide (@rpos) + wi::to_wide (@rsize),
wi::to_wide (@ipos) + isize))
(BIT_FIELD_REF @1 @rsize { wide_int_to_tree (bitsizetype,
wi::to_wide (@rpos)
- wi::to_wide (@ipos)); }))
(if (wi::geu_p (wi::to_wide (@ipos),
wi::to_wide (@rpos) + wi::to_wide (@rsize))
|| wi::geu_p (wi::to_wide (@rpos),
wi::to_wide (@ipos) + isize))
(BIT_FIELD_REF @0 @rsize @rpos)))))
which folds
_ifc__35 = BIT_INSERT_EXPR <_ifc__34, _2, 0 (7 bits)>;
_ifc__31 = BIT_FIELD_REF <_ifc__35, 2, 0>;
where 34/35 have unsigned char type, 31 signed:2 and 2 signed:7.
So, in this case it wants to extract low 2 bits out of the 7 bits _2 which is
invalid
because _2 doesn't have mode precision. If it tried to extract 7 bits out of
it, we have:
(simplify
(BIT_FIELD_REF @0 @1 integer_zerop)
(if (tree_int_cst_equal (@1, TYPE_SIZE (TREE_TYPE (@0))))
(view_convert @0)))
simplification but that one wouldn't trigger, because those signed:2 types have
TYPE_SIZE 8 rather than 7, only TYPE_PRECISION of 7.
