https://gcc.gnu.org/bugzilla/show_bug.cgi?id=104943
Bug ID: 104943
Summary: Analyzer fails to purge state for local structs
Product: gcc
Version: 12.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: analyzer
Assignee: dmalcolm at gcc dot gnu.org
Reporter: dmalcolm at gcc dot gnu.org
Target Milestone: ---
State purging only happens for SSA names, and locals of struct type aren't SSA
names.
Given e.g.:
struct boxed {
int value;
};
extern struct boxed boxed_add (struct boxed a, struct boxed b);
extern struct boxed boxed_mul (struct boxed a, struct boxed b);
struct boxed
test (struct boxed a, struct boxed b)
{
struct boxed result = boxed_add (boxed_mul (a, a),
boxed_mul (b, b));
return result;
}
without optimization we have this gimple:
struct boxed test (struct boxed a, struct boxed b)
{
struct boxed result;
struct boxed D.1994;
struct boxed D.1993;
struct boxed D.1992;
<bb 2> :
D.1992 = boxed_mul (b, b);
D.1993 = boxed_mul (a, a);
result = boxed_add (D.1993, D.1992);
D.1994 = result;
result ={v} {CLOBBER(eol)};
<bb 3> :
<L1>:
return D.1994;
}
and this final exploded node:
EN 11:
preds: EN: 10
succs:
callstring: []
after SN: 3
rmodel:
stack depth: 1
frame (index 0): frame: ‘test’@1
clusters within frame: ‘test’@1
cluster for: <anonymous>: CONJURED(D.1992 = boxed_mul (b, b);, <anonymous>)
cluster for: <anonymous>: CONJURED(D.1993 = boxed_mul (a, a);, <anonymous>)
cluster for: <anonymous>: CONJURED(result = boxed_add (D.1993, D.1992);,
result)
cluster for: <anonymous>: CONJURED(result = boxed_add (D.1993, D.1992);,
result)
m_called_unknown_fn: TRUE
constraint_manager:
equiv classes:
constraints:
where the various <anonymous> are the values of the local temporaries of struct
type, which ought to be purged; they don't matter anymore.
Seen on linux kernel: drivers/gpu/drm/amd/display/dc/calcs/dce_calcs.c which
amongst other things has:
struct bw_fixed {
int64_t value;
};
with numerous calls to manipulate values; the states get bloated with bindings
for temporaries that persist far longer than they are needed.
