The following works with PARALLEL but not with TARGET.
OpenMP states the following is supposed to work:
A = 5; // == this->A
B = 6; // == this->B
C[44] = 7; // == this->C; assume 'int C[100]'
#pragma <parallel|target> firstprivate(A,C) private(B)
{
A += 5; // Now: A is 10.
B = 7;
C[44] += 7; // Now C is 14
// It is unspecified what value this->{A,B,C} has
}
// {A,B,C[44]} == this->{A,B,C[44]} are still {5,6,7}
* * *
In the C++ FE, that's handled by creating a temporary variable:
v = create_temporary_var (TREE_TYPE (m));
with
SET_DECL_VALUE_EXPR (v, m);
DECL_OMP_PRIVATIZED_MEMBER(v)
where 'm' is, e.g., 'this->A' - and a bunch of
'if (DECL_OMP_PRIVATIZED_MEMBER(decl))'
in the g++ FE, only.
For PARALLEL, the VALUE_EXPR survives until omp-low.cc, which handles
this for (first)privatizing.
But for TARGET, in gimplify.cc, after the following call in
gimplify_omp_workshare
16813 gimple *g = gimplify_and_return_first (OMP_BODY (expr), &body);
the 'A' in the body will be turned into 'this->A'.
* * *
Thus, while there is after omplower the expected
#pragma omp target ... firstprivate(A)
and also
D.3081 = .omp_data_i->A; A= ...;
what actually gets used is
D.3084 = .omp_data_i->D.3046;
this = D.3084;
D.2996 = this->A;
which unsurprisingly breaks.
* * *
This can be "fixed" by using the following patch.
With that patch, the -fdump-tree-omplower looks fine. But it does then
fail with:
during RTL pass: expand
g2.cpp:11:7: internal compiler error: in make_decl_rtl, at varasm.cc:1443
for the 'A' with 'B = A' (where B is a non-member var) and 'A' is still
as the value expr 'this->A'.
--- a/gcc/gimplify.cc
+++ b/gcc/gimplify.cc
@@ -3285,12 +3285,15 @@ gimplify_var_or_parm_decl (tree *expr_p)
if (gimplify_omp_ctxp && omp_notice_variable (gimplify_omp_ctxp,
decl, true))
return GS_ALL_DONE;
+ if (!flag_openmp) // Assume: C++'s DECL_OMP_PRIVATIZED_MEMBER (decl)
+ {
/* If the decl is an alias for another expression, substitute it. */
if (DECL_HAS_VALUE_EXPR_P (decl))
{
*expr_p = unshare_expr (DECL_VALUE_EXPR (decl));
return GS_OK;
}
+ }
return GS_ALL_DONE;
}
* * *
Any idea / suggestion how to handle this best?
One way I see would be to add a lang-hook here to check for
DECL_OMP_PRIVATIZED_MEMBER, similar to the hack above. And
then ensure that the DECL_VALUE_EXPR points to the var decl
in the target region (i.e. some hacking in omp-low.cc).
I have no idea whether that would - nor whether that would be
the way forward. - Thoughts?
Tobias
#if TEMPL
template <typename T>
#else
#define T int
#endif
#if PRIVATE
#define firstprivate private
#endif
struct t {
T A;
void f()
{
T B = 49;
A = 7;
#pragma omp parallel firstprivate(A) if(0) shared(B) default(none)
{
if (A != 7) __builtin_printf("ERROR 1b: %d (!= 7) inside omp parallel\n", A);
A = 5;
B = A;
}
if (A != 7) __builtin_printf("ERROR 1: %d (!= 7) omp parallel\n", A);
if (B != 5) __builtin_printf("ERROR 1a: %d\n", B);
A = 8; B = 49;
#pragma omp parallel firstprivate(A)if(0) shared(B) default(none)
{
if (A != 8) __builtin_printf("ERROR 1b: %d (!= 8) inside omp parallel\n", A);
A = 6;
B = A;
}
if (A != 8) __builtin_printf("ERROR 2: %d (!= 8) omp parallel\n", A);
if (B != 6) __builtin_printf("ERROR 2a: %d\n", B);
A = 8; B = 49;
#pragma omp target firstprivate(A) map(from:B) defaultmap(none)
{
if (A != 7) __builtin_printf("ERROR 2b: %d (!= 7) inside omp target\n", A);
A = 7;
B = A;
}
if (A != 8) __builtin_printf("ERROR 3: %d (!= 8) omp target\n", A);
if (B != 7) __builtin_printf("ERROR 3a: %d\n", B);
A = 9; B = 49;
#pragma omp target firstprivate(A) map(from:B) defaultmap(none)
{
if (A != 7) __builtin_printf("ERROR 3b: %d (!= 7) inside omp target\n", A);
A = 8;
B = A;
}
if (A != 9) __builtin_printf("ERROR 4: %d (!= 9) omp target\n", A); else __builtin_printf("OK\n");
if (B != 8) __builtin_printf("ERROR 4a: %d\n", B);
}
};
void bar() {
#if TEMPL
struct t<int> x;
#else
struct t x;
#endif
x.f();
}
int main()
{
bar();
}
