IZ95943: INCORRECT OUTPUT WITH -O3 -Q64

Fixes are available

APAR status

Closed as program error.

Error description

compiling the following test case with -O3 -q64 in V11.1, code
geneneration for pop_stack is not generated even though the
conditions are met.

The lines in questions are here:

   if (pushed)
      if ((ele != 0) && (ele) && (ele->flags & 0x2))
        stack_pop(ele, 0);      /* Expect a POP here */

Adding printf statements between if (pushed) and stack_pop()
call, the code gen is correct again.



===== TESTCASE:

$cat t.c
#include <stdio.h>
#include <setjmp.h>

typedef struct ele_t
{
  unsigned int flags;
} ele_t;

int stack[64];
int nstack;

void stack_pop(ele_t *ele_p, int *xptr)
{
  printf("stack_pop \n");
  nstack--;
  if (xptr)
    *xptr = stack[nstack];
}

void stack_push(ele_t *elep , int x)
{
  printf("stack_push \n");
  stack[nstack] = x;
  nstack++;
}

void func(ele_t *ele)
{
  int     some_flag;
  int     vfalse = 0;
  int     pushed = 0;
  jmp_buf buf;

  stack_push(ele, 1);                        /* PUSH */
  pushed = 1;

  if ((setjmp(buf)) == 0) ;
  else          /* block never reached for test case */
  {
    if (!(some_flag & (unsigned int) 0x8))
      some_flag |= (unsigned int) 0x8;

    if ((ele != 0) && (ele) && (ele->flags & 0x2))
      stack_pop(ele, 0);
  }

  if (vfalse)
  {
    if ((ele != 0) && (ele) && (ele->flags & 0x2))
      stack_pop(ele, &vfalse);
  }
  else
  {
    printf("line# %d is reachable, but not rest of block when
compiled with -O3\n", __LINE__);
    if (pushed)
      if ((ele != 0) && (ele) && (ele->flags & 0x2))
        stack_pop(ele, 0);      /* Expect a POP here */
  }

  if ((ele != 0) && (ele) && (ele->flags & 0x2))
    do { { } } while(0);
}

int main()
{
  ele_t ele = { 2 };;
  func(&ele);
}






===== ACTUAL OUTPUT:


$xlc -O3 -q64 t.c && ./a.out
stack_push
line# 54 is reachable, but not rest of block when compiled with
-O3


===== EXPECTED OUTPUT:
stack_push
line# 54 is reachable, but not rest of block when compiled with
-O3
stack_pop

Local fix

```
Use -O2 -q64 or use -q32
```

Problem summary

PROBLEM DESCRIPTION: incorrect output from program optimized
with O3

USERS AFFECTED: all who use -O3

Problem conclusion

The problem is fixed. Apply recommended PTF level.

Temporary fix

Comments

APAR Information

APAR number
IZ95943
Reported component name
XL C/C++ AIX
Reported component ID
5724X1300
Reported release
B10
Status
CLOSED PER
PE
NoPE
HIPER
NoHIPER
Special Attention
NoSpecatt
Submitted date
2011-03-02
Closed date
2011-04-20
Last modified date
2011-04-20

APAR is sysrouted FROM one or more of the following:
APAR is sysrouted TO one or more of the following:

LI76265

Fix information

Fixed component name
XL C FOR AIX
Fixed component ID
5724X1200

Applicable component levels

[{"Line of Business":{"code":"LOB57","label":"Power"},"Business Unit":{"code":"BU058","label":"IBM Infrastructure w\/TPS"},"Product":{"code":"SSGH2K","label":"XL C for AIX"},"Platform":[{"code":"PF025","label":"Platform Independent"}],"Version":"11.1"}]

Document Information

Modified date:
06 October 2021

Tips

IZ95943: INCORRECT OUTPUT WITH -O3 -Q64

Fixes are available

Subscribe

APAR status

Closed as program error.

Error description

Local fix

Problem summary

Problem conclusion

Temporary fix

Comments

APAR Information

APAR number

Reported component name

Reported component ID

Reported release

Status

PE

HIPER

Special Attention

Submitted date

Closed date

Last modified date

APAR is sysrouted FROM one or more of the following:

APAR is sysrouted TO one or more of the following:

Fix information

Fixed component name

Fixed component ID

Applicable component levels

Document Information

Share your feedback

Need support?