c/2243: Misplacement of label at start of function.

[voel@diku.dk]

>Number:         2243
>Category:       c
>Synopsis:       Misplacement of label at start of function.
>Confidential:   no
>Severity:       serious
>Priority:       medium
>Responsible:    unassigned
>State:          open
>Class:          wrong-code
>Submitter-Id:   net
>Arrival-Date:   Fri Mar 09 07:56:03 PST 2001
>Closed-Date:
>Last-Modified:
>Originator:     Rasmus Erik Voel Jensen
>Release:        gcc version 2.95.2 19991024 (release) (andalso CodeSourcery's Online Test Compilation)
>Organization:
>Environment:
Linux 2.2.16-3, i686
>Description:
Labels in the start of a function is placed at the function
entry instead of inside the function if the following 
conditions hold:
 * the source is compiled on the i386-platform.
 * optimization is enabled (not run with -O0).
 * there is no goto's to the label.
>How-To-Repeat:
Compile the following code with ``gcc -O1 labelerr.c''. If
you then look at the objectcode it is clear that the prelude-
size > 0 (ebp is pushed on the stack, and the stackpointer
is saved).

labelerr.c:
/*
 * The label should be after the prelude, such that a jump 
 * to it would not inflect a new stackframe.
 * It is misplaced if the code is optimized end there is no 
 * goto to the label. It is only observed on the ia-32 arch.
 */
int 
main(argv, argc) 
    char      **argv;
    int         argc;
{
  label:
  printf("Preludesize = %x\n", &&label-((void *)main));
  return 1;
}
>Fix:

>Release-Note:
>Audit-Trail:
>Unformatted: