https://gcc.gnu.org/bugzilla/show_bug.cgi?id=126130
Bug ID: 126130
Summary: IPA PTA: Points-to sets shouldn't contain
function-name.{clobber, use, result}
Product: gcc
Version: 17.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: tree-optimization
Assignee: unassigned at gcc dot gnu.org
Reporter: pheeck at gcc dot gnu.org
Target Milestone: ---
Host: x86_64-pc-linux-gnu
Target: x86_64-pc-linux-gnu
Compile this testcase with -O2 -fipa-pta -fdump-tree-pta2-details with trunk
GCC
---- testcase.c ----
enum vlc_module_properties { VLC_MODULE_CB_OPEN };
char ParseNALBlock_p_frag_0;
int vlc_entry__0_9_0f_p_submodule;
void Open();
void vlc_module_set(int *, enum vlc_module_properties, void *);
void vlc_entry__0_9_0f() {
vlc_module_set(&vlc_entry__0_9_0f_p_submodule, VLC_MODULE_CB_OPEN, Open);
}
void ParseNALBlock();
void Open() { ParseNALBlock(); }
void bs_read_ue();
void ParseNALBlock() {
if (ParseNALBlock_p_frag_0)
bs_read_ue();
}
---- ----
In the pta2 dump you'll see
vlc_entry__0_9_0f_p_submodule = { NULL ESCAPED NONLOCAL Open
vlc_entry__0_9_0f_p_submodule Open.clobber Open.use Open.result }
callarg(36) = { NULL ESCAPED NONLOCAL Open vlc_entry__0_9_0f_p_submodule
Open.clobber Open.use Open.result }
callarg(38) = { ESCAPED Open Open.clobber Open.use Open.result }
and more points-to sets containing .clobber .use, and .result points-to
subvariables of the function Open. As far as I know, this is meaningless. A
pointer cannot point to Open.clobber nor .use nor .result. Therefore it
shouldn't be possible for them to be elements of points-to sets.
The fact that this currently happens possibly makes IPA PTA less precise.
The problem stems from these two constraints:
callarg(38) = &Open
callarg(38) = callarg(38) + UNKNOWN
The first one ensures that the points-to set of callarg(38) contains Open. The
second one is responsible for Open being expanded into Open.clobber, Open.use
and Open.result (this is done in pta-andersen.cc:solution_set_expand()).
While the constraints themselves make sense, we should ensure that
solution_set_expand() doesn't expand Open into .clobber, .use and .result
(perhaps by somehow specialcasing these kinds of subvariables).
