https://gcc.gnu.org/bugzilla/show_bug.cgi?id=81876
Richard Biener <rguenth at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
Priority|P3 |P2
Status|UNCONFIRMED |NEW
Known to work| |6.4.0
Keywords| |diagnostic
Last reconfirmed| |2017-08-17
Component|c |middle-end
CC| |rguenth at gcc dot gnu.org
Ever confirmed|0 |1
Summary|[7 Regression] bogus |[7/8 Regression] bogus
|-Wstrict-overflow warning |-Wstrict-overflow warning
|with -O3 |with -O3
Target Milestone|--- |7.3
--- Comment #1 from Richard Biener <rguenth at gcc dot gnu.org> ---
This is the loop distribution generated size argument to memcpy:
<bb 2> [15.00%]:
_1 = ca_7(D)->first_row;
i_8 = _1 * 8;
_13 = _1 + 1;
_14 = _13 * 8;
_17 = (unsigned int) _14;
_2 = (unsigned int) i_8;
_3 = _17 - _2;
_5 = _3 + 4294967295;
_4 = (sizetype) _5;
_12 = _4 + 1;
_11 = _12 * 8;
_18 = i_8 < _14 ? _11 : 8;
_19 = _1 * 8;
_20 = (sizetype) _19;
_21 = _20 * 8;
_22 = ca_7(D) + _21;
__builtin_memset (_22, 0, _18);
which later during forwprop which sees
<bb 2> [15.00%]:
_1 = ca_7(D)->first_row;
i_8 = _1 * 8;
_14 = i_8 + 8;
_18 = i_8 < _14 ? 64 : 8;
_19 = _14 - 8;
_20 = (sizetype) _19;
_21 = _20 * 8;
_22 = ca_7(D) + _21;
__builtin_memset (_22, 0, _18);
is optimized i_8 < i_8 + 8 -> 1 to
<bb 2> [15.00%]:
_1 = ca_7(D)->first_row;
i_8 = _1 * 8;
_14 = i_8 + 8;
_18 = 64;
_19 = i_8;
_20 = (sizetype) i_8;
_21 = _20 * 8;
_22 = ca_7(D) + _21;
__builtin_memset (_22, 0, _18);
this warning is somewhat fragile in that it triggers quite randomly and also
on compiler-generated intermediate code in case it gets a location.
Also warns on trunk.
I suppose we should look into niter analysis why it generates that conditional
and/or make sure niter generated GENERIC ends up with TREE_NO_WARNING set
and/or no location.
