http://gcc.gnu.org/bugzilla/show_bug.cgi?id=46032
Richard Guenther <rguenth at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
Status|UNCONFIRMED |NEW
Last reconfirmed| |2010.10.15 10:08:39
CC| |jakub at gcc dot gnu.org,
| |rguenth at gcc dot gnu.org
Ever Confirmed|0 |1
--- Comment #1 from Richard Guenther <rguenth at gcc dot gnu.org> 2010-10-15
10:08:39 UTC ---
The problem is that local variables are accessed indirectly via the
.omp_data_i pointer and alias analysis is unable to hoist the load of
.omp_data_i_12(D)->coeff across the store to *pretmp.5_27[idx_1].
A fix is to make the argument DECL_BY_REFERENCE and the
type restrict qualified. This will make alias analysis assume that
the pointed-to object is not aliased unless later somebody takes its
address.
<bb 3>:
pretmp.5_23 = .omp_data_i_12(D)->pData;
pretmp.5_27 = .omp_data_i_12(D)->results;
<bb 4>:
# idx_1 = PHI <idx_8(3), idx_18(5)>
D.2142_14 = *pretmp.5_23[idx_1];
D.2143_15 = .omp_data_i_12(D)->coeff;
D.2144_16 = D.2142_14 * D.2143_15;
*pretmp.5_27[idx_1] = D.2144_16;
idx_18 = idx_1 + 1;
if (D.2139_10 > idx_18)
goto <bb 5>;
else
goto <bb 6>;
<bb 5>:
goto <bb 4>;
Not completely enough though, as we consider *.omp_data_i escaped
(and thus reachable by NONLOCAL).
The following fixes that (with unknown consequences, I think fortran
array descriptors are the only other user):
Index: gcc/omp-low.c
===================================================================
--- gcc/omp-low.c (revision 165474)
+++ gcc/omp-low.c (working copy)
@@ -1349,7 +1349,8 @@ fixup_child_record_type (omp_context *ct
layout_type (type);
}
- TREE_TYPE (ctx->receiver_decl) = build_pointer_type (type);
+ TREE_TYPE (ctx->receiver_decl) = build_qualified_type (build_pointer_type
(type),
+ TYPE_QUAL_RESTRICT);
}
/* Instantiate decls as necessary in CTX to satisfy the data sharing
@@ -1584,6 +1585,7 @@ create_omp_child_function (omp_context *
DECL_NAMELESS (t) = 1;
DECL_ARG_TYPE (t) = ptr_type_node;
DECL_CONTEXT (t) = current_function_decl;
+ DECL_BY_REFERENCE (t) = 1;
TREE_USED (t) = 1;
DECL_ARGUMENTS (decl) = t;
if (!task_copy)
Index: gcc/tree-ssa-structalias.c
===================================================================
--- gcc/tree-ssa-structalias.c (revision 165474)
+++ gcc/tree-ssa-structalias.c (working copy)
@@ -5575,7 +5575,6 @@ intra_create_variable_infos (void)
var_ann_t ann;
heapvar = create_tmp_var_raw (TREE_TYPE (TREE_TYPE (t)),
"PARM_NOALIAS");
- DECL_EXTERNAL (heapvar) = 1;
heapvar_insert (t, 0, heapvar);
ann = get_var_ann (heapvar);
ann->is_heapvar = 1;
@@ -5590,6 +5589,12 @@ intra_create_variable_infos (void)
rhsc.offset = 0;
process_constraint (new_constraint (lhsc, rhsc));
vi->is_restrict_var = 1;
+ do
+ {
+ make_constraint_from (vi, nonlocal_id);
+ vi = vi->next;
+ }
+ while (vi);
continue;
}
it means that stores to *.omp_data_i in the omp fn are considered not
escaping to the caller (and thus can be DSEd). With the above patch
the loop is vectorized with a runtime alias check, as we can't
see that results and pData do not alias. Not even with IPA-PTA as
the OMP function escapes through __builtin_GOMP_parallel_start.
