Some really strange GIMPLE

Some really strange GIMPLE

[Gary Oblock]

I'm chasing a bug and I used Creduce to produce a
reduced test case. However, that's really beside to
point.

I this file:
--------------------------------
typedef struct basket {
} a;
long b;
a *basket;
int d, c, e;
a *flake[2];
void primal_bea_mpp();
void primal_net_simplex() {
  flake[1] = &basket[1];
  primal_bea_mpp(d, d, d, b, flake, 0, e, c, c, d);
}
--------------------------------
Produces this GIMPLE:
---------------------------------
;; Function primal_net_simplex (primal_net_simplex, funcdef_no=3, decl_uid=4447, cgraph_uid=16, symbol_order=41) (executed once)

primal_net_simplex ()
{
  <bb 2> [local count: 1073741824]:
  _1 = basket;
  static struct a * flake[2];
struct a *[2]
  flake[1] = _1;
  _2 = d;
  _3 = c;
  _4 = e;
  _5 = b;
  primal_bea_mpp (_2, _2, _2, _5, &flake, 0, _4, _3, _3, _2);
  return;

}
--------------------------------------
These standard calls were used to dump this:

  FOR_EACH_FUNCTION_WITH_GIMPLE_BODY ( node)
  {
    struct function *func = DECL_STRUCT_FUNCTION ( node->decl);
    dump_function_header ( file, func->decl, (dump_flags_t)0);
    dump_function_to_file ( func->decl, file, (dump_flags_t)0);
  }

The GIMPLE above looks malformed to me. Is that the case
or am I not grasping what's going on here?

Note, I wouldn't be asking this question if this wasn't at the start of
my pass and looking at stuff I hadn't modified.

Thanks,

Gary


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Re: Some really strange GIMPLE

[David Malcolm]

On Tue, 2021-04-27 at 20:10 +0000, Gary Oblock via Gcc wrote:
> I'm chasing a bug and I used Creduce to produce a
> reduced test case. However, that's really beside to
> point.
> 
> I this file:
> --------------------------------
> typedef struct basket {
> } a;
> long b;
> a *basket;
> int d, c, e;
> a *flake[2];
> void primal_bea_mpp();
> void primal_net_simplex() {
>   flake[1] = &basket[1];
>   primal_bea_mpp(d, d, d, b, flake, 0, e, c, c, d);
> }
> --------------------------------
> Produces this GIMPLE:
> ---------------------------------
> ;; Function primal_net_simplex (primal_net_simplex, funcdef_no=3,
> decl_uid=4447, cgraph_uid=16, symbol_order=41) (executed once)
> 
> primal_net_simplex ()
> {
>   <bb 2> [local count: 1073741824]:
>   _1 = basket;
>   static struct a * flake[2];
> struct a *[2]
>   flake[1] = _1;
>   _2 = d;
>   _3 = c;
>   _4 = e;
>   _5 = b;
>   primal_bea_mpp (_2, _2, _2, _5, &flake, 0, _4, _3, _3, _2);
>   return;
> 
> }
> --------------------------------------
> These standard calls were used to dump this:
> 
>   FOR_EACH_FUNCTION_WITH_GIMPLE_BODY ( node)
>   {
>     struct function *func = DECL_STRUCT_FUNCTION ( node->decl);
>     dump_function_header ( file, func->decl, (dump_flags_t)0);
>     dump_function_to_file ( func->decl, file, (dump_flags_t)0);
>   }
> 
> The GIMPLE above looks malformed to me. Is that the case
> or am I not grasping what's going on here?

What about it looks malformed to you?

The declaration of primal_bea_mpp and primal_net_simplex could probably
use some parameters, rather than being empty, which might make things
look more sane [1].  I think -Wstrict-prototypes will catch this.

Dave

[1] https://wiki.sei.cmu.edu/confluence/display/c/DCL20-C.+Explicitly+specify+void+when+a+function+accepts+no+arguments

Re: Some really strange GIMPLE

[Andrew Pinski]

On Tue, Apr 27, 2021 at 3:51 PM Gary Oblock via Gcc <gcc@gcc.gnu.org> wrote:
>
> I'm chasing a bug and I used Creduce to produce a
> reduced test case. However, that's really beside to
> point.
>
> I this file:
> --------------------------------
> typedef struct basket {
> } a;
> long b;
> a *basket;
> int d, c, e;
> a *flake[2];
> void primal_bea_mpp();
> void primal_net_simplex() {
>   flake[1] = &basket[1];
>   primal_bea_mpp(d, d, d, b, flake, 0, e, c, c, d);
> }
> --------------------------------
> Produces this GIMPLE:
> ---------------------------------
> ;; Function primal_net_simplex (primal_net_simplex, funcdef_no=3, decl_uid=4447, cgraph_uid=16, symbol_order=41) (executed once)
>
> primal_net_simplex ()
> {
>   <bb 2> [local count: 1073741824]:
>   _1 = basket;
>   static struct a * flake[2];
> struct a *[2]
>   flake[1] = _1;
>   _2 = d;
>   _3 = c;
>   _4 = e;
>   _5 = b;
>   primal_bea_mpp (_2, _2, _2, _5, &flake, 0, _4, _3, _3, _2);
>   return;
>
> }
> --------------------------------------
> These standard calls were used to dump this:
>
>   FOR_EACH_FUNCTION_WITH_GIMPLE_BODY ( node)
>   {
>     struct function *func = DECL_STRUCT_FUNCTION ( node->decl);
>     dump_function_header ( file, func->decl, (dump_flags_t)0);
>     dump_function_to_file ( func->decl, file, (dump_flags_t)0);
>   }
>
> The GIMPLE above looks malformed to me. Is that the case
> or am I not grasping what's going on here?

The above gimple looks correct.
_1 should be of type a*. _2, _3, _4, and _5 are of type int.
Reading from globals (non-local) requires an assignment which is why
you get _1, _2, _3, _4, and _5.
There have already been optimizations going on before your pass so the
loads from d and c have been only done once.
&flake is considered a constant during the execution of the function
is it is propagated into the function call.

What is the exact thing you think is incorrect about the gimple here?

Thanks,
Andrew


>
> Note, I wouldn't be asking this question if this wasn't at the start of
> my pass and looking at stuff I hadn't modified.
>
> Thanks,
>
> Gary
>
>
> CONFIDENTIALITY NOTICE: This e-mail message, including any attachments, is for the sole use of the intended recipient(s) and contains information that is confidential and proprietary to Ampere Computing or its subsidiaries. It is to be used solely for the purpose of furthering the parties' business relationship. Any unauthorized review, copying, or distribution of this email (or any attachments thereto) is strictly prohibited. If you are not the intended recipient, please contact the sender immediately and permanently delete the original and any copies of this email and any attachments thereto.

Re: Some really strange GIMPLE

[Aaron Gyes]

> CONFIDENTIALITY NOTICE: This e-mail message, including any attachments, is for the sole use of the intended recipient(s) and contains information that is confidential and proprietary to Ampere Computing or its subsidiaries. It is to be used solely for the purpose of furthering the parties' business relationship. Any unauthorized review, copying, or distribution of this email (or any attachments thereto) is strictly prohibited. If you are not the intended recipient, please contact the sender immediately and permanently delete the original and any copies of this email and any attachments thereto.

This confidential message is going to be archived on the Internet publicly, likely forever. I would not send proprietary information to a public mailing list.

Aaron