https://gcc.gnu.org/bugzilla/show_bug.cgi?id=98658
Richard Biener <rguenth at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
Resolution|--- |INVALID
Status|UNCONFIRMED |RESOLVED
--- Comment #2 from Richard Biener <rguenth at gcc dot gnu.org> ---
it's because
(gdb) p debug_data_dependence_relation (ddr)
(Data Dep:
#(Data Ref:
# bb: 3
# stmt: _1 = *s_19;
# ref: *s_19;
# base_object: *s_7(D);
# Access function 0: {0B, +, 4}_1
#)
#(Data Ref:
# bb: 3
# stmt: *d_18 = _1;
# ref: *d_18;
# base_object: *d_6(D);
# Access function 0: {0B, +, 4}_1
#)
(don't know)
)
and we say
/* Can't do memmove in case of unknown dependence or dependence without
classical distance vector. */
if (DDR_ARE_DEPENDENT (ddr) == chrec_dont_know
|| DDR_NUM_DIST_VECTS (ddr) == 0)
return;
which is because we need to check the depdenence is not backwards
(*s++ loads an earlier stored value). I don't see how that is
guaranteed in the 'copy' case and ICC either miscompiles this
or has a runtime check doing the memcpy only conditionally.
