https://gcc.gnu.org/bugzilla/show_bug.cgi?id=110228
Sergei Trofimovich <slyfox at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
CC| |rguenth at gcc dot gnu.org
--- Comment #24 from Sergei Trofimovich <slyfox at gcc dot gnu.org> ---
Trying to understand the failure mode here:
In bug.c.033t.early_objsz I still see the explicit stores to LocalFlags:
<bb 4> :
LookupFlags_15 = 0;
goto <bb 7>; [INV]
<bb 5> :
if (v_13 == 1)
goto <bb 6>; [INV]
else
goto <bb 7>; [INV]
<bb 6> :
LookupFlags_14 = 1;
<bb 7> :
# LookupFlags_4 = PHI <LookupFlags_15(4), LookupFlags_5(5),
LookupFlags_14(6)>
*p_16(D) = LookupFlags_4;
But in bug.c.034t.ccp1 I see no stores at all:
if (v_13 == 0)
goto <bb 6>; [INV]
else
goto <bb 4>; [INV]
<bb 4> :
if (v_13 == 1)
goto <bb 5>; [INV]
else
goto <bb 6>; [INV]
<bb 5> :
<bb 6> :
# LookupFlags_4 = PHI <0(3), LookupFlags_5(4), 1(5)>
Specifically '# LookupFlags_4 = PHI <0(3), LookupFlags_5(4), 1(5)>' claims that
somehow gets values '0' and '1' into a PHI node.
AFAIU PHI is an equivalent of a mutable variable in an otherwise immutable SSA
form. It has to be a write it needed value is not there yet. Why the store of
'1' was removed? Is it because variable 'v_13' already happens to have 0 or 1
value?
I wonder why PHI does not look like something below:
# LookupFlags_4 = PHI <v_13(3), LookupFlags_5(4), v_13(5)>
