https://gcc.gnu.org/bugzilla/show_bug.cgi?id=101642
Jakub Jelinek <jakub at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
CC| |jakub at gcc dot gnu.org
--- Comment #7 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
I think better testcase would be
int x;
unsigned short
foo (void)
{
return __builtin_bswap16 (x) ? : x;
}
because otherwise you're asking for it to be DCEd.
The problem is that for __builtin_bswap16 like for many other builtins with 8
or 16-bit argument(s) the operand is promoted to int.
So, many of the match.pd rules just don't trigger for it at all, like:
(simplify
(bswap (bswap @0))
@0)
(simplify
(bswap (bit_not (bswap @0)))
(bit_not @0))
(for bitop (bit_xor bit_ior bit_and)
(simplify
(bswap (bitop:c (bswap @0) @1))
(bitop @0 (bswap @1))))
because there are casts it doesn't take into account for bswap16, others are
just incorrect, like:
(for cmp (eq ne)
(simplify
(cmp (bswap @0) (bswap @1))
(cmp @0 @1))
- it needs to convert @0 and @1 to the type of one of the bswaps, otherwise it
could be comparing even the upper bits, and others are both incorrect and cause
ICE, like
(simplify
(cmp (bswap @0) INTEGER_CST@1)
(cmp @0 (bswap @1))))
Let me deal with just those now and the rest that just don't match can be dealt
with later on.
