https://gcc.gnu.org/bugzilla/show_bug.cgi?id=68640
Bug ID: 68640
Summary: foo restrict propagated to foo._omp_fn.0
Product: gcc
Version: 6.0
Status: UNCONFIRMED
Severity: minor
Priority: P3
Component: tree-optimization
Assignee: unassigned at gcc dot gnu.org
Reporter: vries at gcc dot gnu.org
Target Milestone: ---
I.
Consider parallel-alias.c:
...
#define N 1024
int
foo (int *__restrict__ ap, int *__restrict__ bp)
{
#pragma omp parallel for
for (unsigned int idx = 0; idx < N; idx++)
ap[idx] = bp[idx];
}
...
compile with:
...
$ gcc parallel-alias.c -O2 -fopenmp -S
...
At ealias in foo._omp_fn.0, we have:
...
ap_9 = { PARM_NOALIAS(10) }
_24 = { PARM_NOALIAS(10) }
bp_8 = { PARM_NOALIAS(12) }
_27 = { PARM_NOALIAS(12) }
...
resulting in:
...
# VUSE <.MEM_4>
_28 = MEM[(intD.6 *)_27 clique 1 base 3];
# .MEM_29 = VDEF <.MEM_4>
MEM[(intD.6 *)_24 clique 1 base 2] = _28;
...
So the restrict in foo had an effect in foo._omp_fn.0.
While doing omp-lower, we enter install_var_field with a var with restrict
type:
...
Breakpoint 1, install_var_field (var=0x7ffff61b2080, by_ref=false, mask=3,
ctx=0x2aad910)
at src/gcc/omp-low.c:1374
1374 tree field, type, sfield = NULL_TREE;
(gdb) call debug_generic_expr (var)
bp
(gdb) call debug_generic_expr (var.typed.type)
int * restrict
...
And declare the field with the same type:
...
1389 type = TREE_TYPE (var);
...
1400 field = build_decl (DECL_SOURCE_LOCATION (var),
1401 FIELD_DECL, DECL_NAME (var), type);
...
II.
Now we rewrite the example a bit to introduce aliasing between ap and bp:
...
#define N 1024
int
foo (int *__restrict__ ap)
{
int *bp = ap;
#pragma omp parallel for
for (unsigned int idx = 0; idx < N; idx++)
ap[idx] = bp[idx];
}
...
at ealias, we have:
...
ap_9 = { PARM_NOALIAS(10) }
_24 = { PARM_NOALIAS(10) }
bp_8 = { NONLOCAL }
_27 = { NONLOCAL }
...
Resulting in:
...
# VUSE <.MEM_4>
_28 = *_27;
# .MEM_29 = VDEF <.MEM_4>
MEM[(intD.6 *)_24 clique 1 base 2] = _28;
...
So, atm I cannot find an example where we generate wrong code (but that might
happen when we make compute_dependence_clique more aggressive).
But I do wonder whether the usage of the restrict of foo in foo._omp_fn.0 is
intentional or accidental.
