> If x_2 is a default def then the IL isn't correct in the first place. I doubt
> it is that way, btw. - we have verifiers that would blow up if it would.
Richard,
I'm just sharing this so you can tell me whether or not I'm going
crazy. ;-)
This little function is finding that arr_2 = PHI <arr_12(2), arr_15(5)>
is problematic.
void
wolf_fence (
Info *info // Pass level gobal info (might not use it)
)
{
struct cgraph_node *node;
fprintf( stderr,
"Wolf Fence: Find wolf for default defs with non nop defines\n");
FOR_EACH_FUNCTION_WITH_GIMPLE_BODY ( node)
{
struct function *func = DECL_STRUCT_FUNCTION ( node->decl);
push_cfun ( func);
unsigned int len = SSANAMES ( func)->length ();
for ( unsigned int i = 0; i < len; i++)
{
tree ssa_name = (*SSANAMES ( func))[i];
if ( ssa_name == NULL ) continue;
if ( ssa_defined_default_def_p ( ssa_name) )
{
gimple *def_stmt =
SSA_NAME_DEF_STMT ( ssa_name);
if ( !gimple_nop_p ( def_stmt) )
{
fprintf ( stderr, "Wolf fence caught :");
print_gimple_stmt ( stderr, def_stmt, 0);
gcc_assert (0);
}
}
}
pop_cfun ();
}
fprintf( stderr, "Wolf Fence: Didn't find wolf!\n");
}
This is run at the very start of the structure reorg pass
before any of my code did anything at all (except initiate
the structure info with a few flags and the like.)
Here's C code:
----- aux.h ---------------------------------------------------
#include "stdlib.h"
typedef struct type type_t;
struct type {
double x;
double y;
};
extern type_t *min_of_x( type_t *, size_t);
----- aux.c ---------------------------------------------------
#include "aux.h"
#include "stdlib.h"
type_t *
min_of_x( type_t *arr, size_t len)
{
type_t *end_of = arr + len;
type_t *loc = arr;
double result = arr->x;
arr++;
for( ; arr < end_of ; arr++ ) {
double value = arr->x;
if ( value < result ) {
result = value;
loc = arr;
}
}
return loc;
}
----- main.c --------------------------------------------------
#include "aux.h"
#include "stdio.h"
int
main(void)
{
size_t len = 10000;
type_t *data = (type_t *)malloc( len * sizeof(type_t));
int i;
for( i = 0; i < len; i++ ) {
data[i].x = drand48();
}
type_t *min_x;
min_x = min_of_x( data, len);
if ( min_x == 0 ) {
printf("min_x error\n");
exit(-1);
}
printf("min_x %e\n" , min_x->x);
}
---------------------------------------------------------------
Here's the GIMPLE comining into the structure reoganization pass:
Program:
;; Function min_of_x (min_of_x, funcdef_no=0, decl_uid=4391, cgraph_uid=2,
symbol_order=23) (executed once)
min_of_x (struct type_t * arr, size_t len)
{
double value;
double result;
struct type_t * loc;
struct type_t * end_of;
<bb 2> [local count: 118111600]:
_1 = len_7(D) * 16;
end_of_9 = arr_8(D) + _1;
result_11 = arr_8(D)->x;
arr_12 = arr_8(D) + 16;
goto <bb 6>; [100.00%]
<bb 3> [local count: 955630225]:
value_14 = arr_2->x;
if (result_6 > value_14)
goto <bb 4>; [50.00%]
else
goto <bb 5>; [50.00%]
<bb 4> [local count: 477815112]:
<bb 5> [local count: 955630225]:
# loc_3 = PHI <loc_4(3), arr_2(4)>
# result_5 = PHI <result_6(3), value_14(4)>
arr_15 = arr_2 + 16;
<bb 6> [local count: 1073741824]:
# arr_2 = PHI <arr_12(2), arr_15(5)>
# loc_4 = PHI <arr_8(D)(2), loc_3(5)>
# result_6 = PHI <result_11(2), result_5(5)>
if (arr_2 < end_of_9)
goto <bb 3>; [89.00%]
else
goto <bb 7>; [11.00%]
<bb 7> [local count: 118111600]:
# loc_13 = PHI <loc_4(6)>
return loc_13;
}
;; Function main (main, funcdef_no=1, decl_uid=4389, cgraph_uid=1,
symbol_order=5) (executed once)
main ()
{
struct type_t * min_x;
int i;
struct type_t * data;
<bb 2> [local count: 10737416]:
data_10 = malloc (160000);
goto <bb 4>; [100.00%]
<bb 3> [local count: 1063004409]:
_1 = _4 * 16;
_2 = data_10 + _1;
_3 = drand48 ();
_2->x = _3;
i_18 = i_6 + 1;
<bb 4> [local count: 1073741824]:
# i_6 = PHI <0(2), i_18(3)>
_4 = (long unsigned int) i_6;
if (_4 != 10000)
goto <bb 3>; [99.00%]
else
goto <bb 5>; [1.00%]
<bb 5> [local count: 10737416]:
min_x_12 = min_of_x (data_10, 10000);
if (min_x_12 == 0B)
goto <bb 6>; [0.04%]
else
goto <bb 7>; [99.96%]
<bb 6> [local count: 4295]:
__builtin_puts (&"min_x error"[0]);
exit (-1);
<bb 7> [local count: 10733121]:
_5 = min_x_12->x;
printf ("min_x %e\n", _5);
return 0;
}
Am I crazy?
Thanks,
Gary
________________________________
From: Richard Biener <richard.guent...@gmail.com>
Sent: Thursday, August 27, 2020 2:04 AM
To: Gary Oblock <g...@amperecomputing.com>
Cc: gcc@gcc.gnu.org <gcc@gcc.gnu.org>
Subject: Re: Questions regarding update_stmt and release_ssa_name_fn.
[EXTERNAL EMAIL NOTICE: This email originated from an external sender. Please
be mindful of safe email handling and proprietary information protection
practices.]
On Wed, Aug 26, 2020 at 11:32 PM Gary Oblock via Gcc <gcc@gcc.gnu.org> wrote:
>
> I'm having some major grief with a few related things that I'm try to
> do. The mostly revolve around trying to change the type of an SSA name
> (which I've given up in favor of creating new SSA names and replacing
> the ones I wanted to change.) However, this seems too has its own
> issues.
>
> In one problematic case in particular, I'm seeing a sequence like:
>
> foo_3 = mumble_1 op mumble_2
>
> bar_5 = foo_3 op baz_4
>
> when replace foo_3 with foo_4 the (having the needed new type.)
>
> I'm seeing a later verification phase think
>
> bar_5 = foo_4 op baz_4
>
> is still associated with the foo_3.
>
> Should the transformation above be associated with update_stmt and/or
> release_ssa_name_fn? And if they are both needed is there a proper
> order required. Note, when I try using them, I'm seeing some malformed
> tree operands that die in horrible ways.
>
> By the way, I realize I can probably simply create a new GIMPLE stmt
> from scratch to replace the ones I'm modifying but this will cause
> some significant code bloat and I want to avoid that if at all
> possible.
You need to call update_stmt () if you change SSA operands to
sth else.
> There is an addition wrinkle to this problem with C code like this
>
> void
> whatever ( int x, .. )
> {
> :
> x++;
> :
> }
>
> I'm seeing x_2 being thought of as default definition in the following
> GIMPLE stmt when it's clearly not since it's defined by the statement.
>
> x_2 = X_1 + 4
>
> My approach has been to simply make the SSA name to replace x_2a
> normal SSA name and not a default def. Is this not reasonable and
> correct?
If x_2 is a default def then the IL isn't correct in the first place. I doubt
it is that way, btw. - we have verifiers that would blow up if it would.
Richard.
>
> Thanks,
>
> Gary Oblock
>
> Gary
>
>
>
>
>
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