http://gcc.gnu.org/bugzilla/show_bug.cgi?id=59470
--- Comment #6 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
CXXFLAGS='-fstack-protector ...' ../configure ...
(at least I believe so, we override a bunch of other variables in the gcc.spec
file).
Anyway, I've instrumented gcc so that based on env var it used the r205708 way
of TER for some functions and r205709 for others and it seems for this testcase
the only problematic one is
_ZNKSt7num_putIcSt19ostreambuf_iteratorIcSt11char_traitsIcEEE13_M_insert_intIlEES3_S3_RSt8ios_basecT_
On that function, I see that the r205709 change made _46, _47, _114, _119 and
_126 not TERable.
That's:
_46 = MEM[(const struct __cache_type *)prephitmp_130]._M_grouping_size;
_47 = MEM[(const struct __cache_type *)prephitmp_130]._M_grouping;
std::num_put<char>::_M_group_int (this_48(D), _47, _46, _45, __io_10(D),
__cs_43, __cs_36, &__len);
...
_114 = MEM[(const struct locale &)__io_10(D) + 108]._M_impl;
std::locale::_Impl::_M_install_cache (_114, __tmp_113, __i_107);
...
_119 = MEM[(int (*__vtbl_ptr_type) () *)_118 + 4B];
OBJ_TYPE_REF(_119;__tmp_113->1) (__tmp_113);
...
_126 = MEM[(int (*__vtbl_ptr_type) () *)_125 + 48B];
_127 = OBJ_TYPE_REF(_126;__s$_M_sbuf_106->12) (__s$_M_sbuf_106, __cs_3,
prephitmp_175);
All of these single use SSA_NAMEs. I don't see why these shouldn't be TERable,
function arguments necessarily are evaluated before the function is called and
the aliasing stmt_may_clobber_ref_p talks about are either the side-effects of
the call itself, or storing to the lhs.
So, for calls, can't we do only the first part of stmt_may_clobber_ref_p_1
handling and not the rest (i.e. the gimple_call_lhs handling there only),
unless the SSA_NAME is used somewhere in the lhs of the call?
Similarly for ASMs, IMHO terring into inline asm is especially important, while
your change pretty much disables it always:
else if (gimple_code (stmt) == GIMPLE_ASM)
return true;
What should be avoided is if SSA_NAME is used in some output operand (say as
part of a reference), that I can understand why we shouldn't ter. But
otherwise?
Note, this of course doesn't explain why this PR breaks.
