https://gcc.gnu.org/bugzilla/show_bug.cgi?id=104151
Jakub Jelinek <jakub at gcc dot gnu.org> changed:
What |Removed |Added
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CC| |jakub at gcc dot gnu.org
--- Comment #11 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
With -O3 it regresses with
r7-2009-g8d4fc2d3d0c8f87bb3e182be1a618a511f8f9465
__uint128_t bswap(__uint128_t a) { return __builtin_bswap128 (a); }
emits the optimal code but is only in GCC 11.1 and later.
One fix for this might be to handle
_8 = BIT_FIELD_REF <a_3(D), 64, 64>;
_1 = __builtin_bswap64 (_8);
y[0] = _1;
_10 = BIT_FIELD_REF <a_3(D), 64, 0>;
_2 = __builtin_bswap64 (_10);
y[1] = _2;
_7 = MEM <uint128_t> [(char * {ref-all})&y];
in bswap or store merging.
Though, current bswap infrastructure I'm afraid limits it to 64-bit size,
because it tracks the bytes in uint64_t vars and uses 8 bits to determine which
byte it is (0 value of zero, 1-8 byte index and 0xff unknown).
While that is 10 different values right now, if we handled uint128_t we'd need
18 different values times 16.
Note, even:
unsigned long long
bswap (unsigned long long a)
{
unsigned int x[2];
__builtin_memcpy (x, &a, 8);
unsigned int y[2];
y[0] = __builtin_bswap32 (x[1]);
y[1] = __builtin_bswap32 (x[0]);
__builtin_memcpy (&a, y, 8);
return a;
}
unsigned long long
bswap2 (unsigned long long a)
{
return __builtin_bswap64 (a);
}
emits better code in the latter function rather than former store-merging
isn't able to handle even that.
So we want to handle it in store-merging, we should start with handling
_8 = BIT_FIELD_REF <a_3(D), 32, 32>;
_1 = __builtin_bswap32 (_8);
_10 = (unsigned int) a_3(D);
_2 = __builtin_bswap32 (_10);
_11 = {_1, _2};
_5 = VIEW_CONVERT_EXPR<unsigned long>(_11);
and
_8 = BIT_FIELD_REF <a_3(D), 32, 32>;
_1 = __builtin_bswap32 (_8);
y[0] = _1;
_10 = (unsigned int) a_3(D);
_2 = __builtin_bswap32 (_10);
y[1] = _2;
_7 = MEM <unsigned long> [(char * {ref-all})&y];
and only once that is handled try
_8 = BIT_FIELD_REF <a_3(D), 64, 64>;
_1 = __builtin_bswap64 (_8);
_10 = (long long unsigned int) a_3(D);
_2 = __builtin_bswap64 (_10);
_11 = {_1, _2};
_5 = VIEW_CONVERT_EXPR<uint128_t>(_11);
Doesn't look like stage4 material though.
So in the meantime perhaps some other improvements.
