https://gcc.gnu.org/bugzilla/show_bug.cgi?id=77550
Bernd Edlinger <bernd.edlinger at hotmail dot de> changed:
What |Removed |Added
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CC| |bernd.edlinger at hotmail dot
de
--- Comment #9 from Bernd Edlinger <bernd.edlinger at hotmail dot de> ---
I'm unable to reduce the test case...
The deque_iterator has these members:
_Elt_pointer _M_cur;
_Elt_pointer _M_first;
_Elt_pointer _M_last;
_Map_pointer _M_node;
the first 3 elements have alias set 12
while _M_node has alias set 13.
when all 4 elements are assigned that becomes
2 vector statements, but all use alias set 12.
but _M_node is read back in the loop using alias set 13.
and thus it seems _M_node is constant.
It can be seen first in expand.
_M_node is read without non-vectorized:
(insn 290 289 291 44 (set (reg/f:DI 117 [ prephitmp_166 ])
(mem/f/c:DI (plus:DI (reg/f:DI 82 virtual-stack-vars)
(const_int -176 [0xffffffffffffff50])) [12 MEM[(struct
_Deque_iterator *)&D.66017]._M_last+0 S8 A128])) -1
(nil))
(insn 291 290 292 44 (set (reg/f:DI 149 [ _215 ])
(mem/f/c:DI (plus:DI (reg/f:DI 82 virtual-stack-vars)
(const_int -168 [0xffffffffffffff58])) [13 MEM[(struct
_Deque_iterator *)&D.66017]._M_node+0 S8 A64]))
/var/tmp/gcc_test/usr/local/include/c++/7.0.0/bits/stl_deque.h:173 -1
(nil))
_M_node is written using _M_last's alias set in insn 307:
(insn 305 304 306 46 (set (mem/c:V2DI (plus:DI (reg/f:DI 82 virtual-stack-vars)
(const_int -192 [0xffffffffffffff40])) [12 MEM[(struct Foo *
*)&D.66017]+0 S16 A128])
(reg:V2DI 237))
/var/tmp/gcc_test/usr/local/include/c++/7.0.0/bits/stl_deque.h:174 -1
(nil))
(insn 306 305 307 46 (set (reg:V2DI 238)
(vec_concat:V2DI (reg/f:DI 117 [ prephitmp_166 ])
(reg:DI 90 [ _25 ])))
/var/tmp/gcc_test/usr/local/include/c++/7.0.0/bits/stl_deque.h:258 -1
(nil))
(insn 307 306 308 46 (set (mem/c:V2DI (plus:DI (reg/f:DI 82 virtual-stack-vars)
(const_int -176 [0xffffffffffffff50])) [12 MEM[(struct Foo *
*)&D.66017 + 16B]+0 S16 A128])
(reg:V2DI 238))
/var/tmp/gcc_test/usr/local/include/c++/7.0.0/bits/stl_deque.h:174 -1
(nil))
