https://gcc.gnu.org/bugzilla/show_bug.cgi?id=107138
Richard Biener <rguenth at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
Keywords| |missed-optimization
Last reconfirmed| |2022-12-22
Ever confirmed|0 |1
Status|UNCONFIRMED |NEW
Priority|P3 |P2
--- Comment #11 from Richard Biener <rguenth at gcc dot gnu.org> ---
Confirmed. We're diagnosing the read
# VUSE <.MEM_106>
_60 = MEM[(const struct basic_string *)&D.48280]._M_string_length;
which happens conditional after the lifetime of D.48280 starts:
MEM[(struct __as_base &)&D.48280] ={v} {CLOBBER};
MEM[(union _Variadic_union *)&D.48280] ={v} {CLOBBER};
MEM[(union _Variadic_union *)&D.48280] ={v} {CLOBBER};
MEM[(struct _Uninitialized *)&D.48280] ={v} {CLOBBER};
_128 = (void *) ivtmp.494_2;
_19 = MEM[(const type &)_128];
MEM[(struct _Uninitialized *)&D.48280]._M_storage = _19;
MEM[(struct _Variant_storage *)&D.48280]._M_index = 2;
...
the condition chains is
<bb 7> [local count: 668941184]:
MEM[(struct _Variant_storage *)_35]._M_index = 255;
_45 = D.48280.D.48091.D.47570.D.47488.D.47356.D.47242.D.47146._M_index;
_46 = (signed char) _45;
_47 = (long unsigned int) _46;
if (_47 > 4)
goto <bb 40>; [16.67%]
else
goto <bb 8>; [83.33%]
<bb 8> [local count: 557450988]:
switch (_45) <default: <L7> [20.00%], case 1: <L8> [20.00%], case 2: <L9>
[20.00%], case 3: <L10> [20.00%], case 4: <L14> [20.00%]>
<bb 9> [local count: 111490196]:
<L7>:
_57 = &MEM[(struct basic_string *)_35].D.36033._M_local_buf;
MEM[(struct _Alloc_hider *)_35]._M_p = _57;
_58 = MEM[(const struct basic_string *)&D.48280]._M_dataplus._M_p;
if (&MEM[(const struct basic_string *)&D.48280].D.36033._M_local_buf == _58)
goto <bb 10>; [30.00%]
else
goto <bb 12>; [70.00%]
<bb 10> [local count: 33447058]:
_60 = MEM[(const struct basic_string *)&D.48280]._M_string_length;
in this case we have other stores possibly clobbering the _M_index store
so we fail to statically optimize these branches (from the = 2 initializer
which should be still there?).
