Re: Redundant malloc in structure optimization? (testsuite/gcc.dg/struct/wo_prof_global_var.c)

[Kenneth Zadeck]

Bingfeng Mei wrote:
Olga,
Yes, I agree the "p" is global. But how p is going to be accessed if
another file uses p?  D.2215 represents the original "p", but it is not
initialized as "p.0.4" and "p.0.3" do. It won't be correct if other file
tried to use it. Am I right? 

Cheers,
Bingfeng
  
I would be surprised if we could remove a dead malloc (assuming that we 
could determine that p was dead, which is another issue). It would not 
be hard to add this but p is the hardest problem.

kenny 
  D.2215 = malloc (8000);
  D.2240 = malloc (4000);
  p.0.3 = (struct struct.0_sub.0 *) D.2240;
  D.2242 = malloc (4000);
  p.0.4 = (struct struct.0_sub.1 *) D.2242;
  p = (struct str_t *) D.2215;
  p.1 = p.0.4;
  p.0 = p.0.3;
    

-----Original Message-----
From: Olga Golovanevsky [mailto:[EMAIL PROTECTED] 
Sent: 01 May 2008 13:19
To: Bingfeng Mei
Cc: gcc@gcc.gnu.org; Kenneth Zadeck
Subject: Re: Redundant malloc in structure optimization?
(testsuite/gcc.dg/struct/wo_prof_global_var.c)



[EMAIL PROTECTED] wrote on 28/04/2008 12:36:44:

  
Hello,
I am looking at a testsuite failure (wo_prof_global_var.c) in my
porting. Somehow, I found GCC 4.3.0 seems to generate unnecessary
    
malloc
  
during structure optimization. In the code, the structure is split
    
into
  
two individual fields (D.2240 and D.2242) and they are allocated
separately. But the original structure (D.2215) is still allocated,
    
and
  
not used afterward.  The following RTL-level optimization cannot
eliminate it.
    

I think that p is global, and in my understanding right now we have no
whole
program dead code elimination optimization in gcc, but may be I am
wrong.

Kenny?

Olga

  
Cheers,
Bingfeng Mei
Broadcom UK

Original C code:

/* { dg-do compile } */
/* { dg-do run } */

#include <stdlib.h>
typedef struct
{
  int a;
  float b;
}str_t;

#define N 1000

str_t *p;

int
main ()
{
  int i, sum;

  p = malloc (N * sizeof (str_t));
  for (i = 0; i < N; i++)
    p[i].a = p[i].b + 1;

  for (i = 0; i < N; i++)
    if (p[i].a != p[i].b + 1)
      abort ();

  return 0;
}

.final_cleanup


    
/*----------------------------------------------------------------------
  
----*/
/* { dg-final { scan-ipa-dump "Number of structures to transform is 1"
"ipa_struct_reorg" } } */
/* { dg-final { cleanup-ipa-dump "*" } } */


;; Function main (main)

main ()
{
  int i.43;
  unsigned int D.2245;
  unsigned int D.2243;
  void * D.2242;
  void * D.2240;
  struct struct.0_sub.1 * p.0.4;
  struct struct.0_sub.0 * p.0.3;
  int i;
  void * D.2215;

<bb 2>:
  D.2215 = malloc (8000);
  D.2240 = malloc (4000);
  p.0.3 = (struct struct.0_sub.0 *) D.2240;
  D.2242 = malloc (4000);
  p.0.4 = (struct struct.0_sub.1 *) D.2242;
  p = (struct str_t *) D.2215;
  p.1 = p.0.4;
  p.0 = p.0.3;
  i = 0;

<bb 3>:
  D.2243 = (unsigned int) i << 2;
  (p.0.4 + D.2243)->a = (int) ((p.0.3 + D.2243)->b + 1.0e+0);
  i = i + 1;
  if (i != 1000)
    goto <bb 3>;
  else
    goto <bb 4>;

<bb 4>:
  i.43 = 0;

<bb 5>:
  D.2245 = (unsigned int) i.43 << 2;
  if ((float) (p.0.4 + D.2245)->a != (p.0.3 + D.2245)->b + 1.0e+0)
    goto <bb 6>;
  else
    goto <bb 7>;

<bb 6>:
  abort ();

<bb 7>:
  i.43 = i.43 + 1;
  if (i.43 != 1000)
    goto <bb 5>;
  else
    goto <bb 8>;

<bb 8>:
  return 0;

}