https://gcc.gnu.org/bugzilla/show_bug.cgi?id=81502
Marc Glisse <glisse at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
Keywords| |missed-optimization
Status|UNCONFIRMED |NEW
Last reconfirmed| |2017-07-21
Ever confirmed|0 |1
--- Comment #1 from Marc Glisse <glisse at gcc dot gnu.org> ---
.optimized dump:
int bar(void*) (void * ptr)
{
int res;
__m128i word;
long unsigned int _2;
vector(2) long long int word.3_3;
unsigned int _4;
<bb 2> [100.00%] [count: INV]:
_2 = (long unsigned int) ptr_9(D);
word = { 0, 0 };
MEM[(char * {ref-all})&word] = _2;
word.3_3 = word;
word ={v} {CLOBBER};
_4 = BIT_FIELD_REF <word.3_3, 32, 0>;
res_5 = (int) _4;
return res_5;
}
We missed turning the memory write into a BIT_INSERT_EXPR, and passes like PRE
missed following the bit_field_expr all the way to _2.
.combine dump:
[...]
(insn 8 3 10 2 (set (reg/v:V2DI 90 [ word ])
(vec_concat:V2DI (reg/v/f:DI 92 [ ptr ])
(const_int 0 [0]))) "b.c":16 3712 {vec_concatv2di}
(expr_list:REG_DEAD (reg/v/f:DI 92 [ ptr ])
(nil)))
(insn 10 8 15 2 (set (reg:SI 94 [ res ])
(vec_select:SI (subreg:V4SI (reg/v:V2DI 90 [ word ]) 0)
(parallel [
(const_int 0 [0])
]))) "b.c":20 3697 {*vec_extractv4si_0}
(expr_list:REG_DEAD (reg/v:V2DI 90 [ word ])
(nil)))
[...]
combine tries
(set (reg:SI 94 [ res ])
(vec_select:SI (subreg:V4SI (vec_concat:V2DI (reg/v/f:DI 92 [ ptr ])
(const_int 0 [0])) 0)
(parallel [
(const_int 0 [0])
])))
which we fail to simplify. The xmm1-xmm0 mov is not considered a mov by the
compiler but concatenation with 0, so not a RA problem.
The change of mode (64-bit pointer to 32-bit int) seems to play a big role in
confusing things here.
