[Bug optimization/13552] New: gcc 'optimizes' position of label

[Bug optimization/13552] New: gcc 'optimizes' position of label

[jbemmel at zonnet dot nl]

Compile this code, with or without '-Os' flag:

#include <string.h>

static int initialStack[1024];

void f()
{
   memcpy( initialStack, &&stackcode, 16 );
   __asm__ volatile ( "jmp *%0" : : "r"(initialStack) : "memory" );
stackcode:
   __asm__ volatile ( "movl %0, %%cr3" :  : "a"(0) : "memory" );
}

In the assembly listing generated with '-Os' the stackcode label (L2) is moved 
to the beginning of the function, instead of the 'movl %0, %%cr3' instruction.
Without '-Os' it works as expected

-- 
           Summary: gcc 'optimizes' position of label
           Product: gcc
           Version: 3.3.1
            Status: UNCONFIRMED
          Severity: normal
          Priority: P2
         Component: optimization
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: jbemmel at zonnet dot nl
                CC: gcc-bugs at gcc dot gnu dot org
  GCC host triplet: 3.3.1 (mingw32 special 20030804-1)
GCC target triplet: 3.3.1 (mingw32 special 20030804-1)


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=13552

[Bug optimization/13552] gcc 'optimizes' position of label

[pinskia at gcc dot gnu dot org]

------- Additional Comments From pinskia at gcc dot gnu dot org  2004-01-03 01:56 -------
The code is invalid as you cannot jump out of an asm.
Also you cannot depend on the optimizing compilers not moving labels.

-- 
           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |RESOLVED
         Resolution|                            |INVALID


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=13552

[Bug optimization/13552] gcc 'optimizes' position of label

[jbemmel at zonnet dot nl]

------- Additional Comments From jbemmel at zonnet dot nl  2004-01-03 11:15 -------
Subject: Re:  gcc 'optimizes' position of label

> ------- Additional Comments From pinskia at gcc dot gnu dot org
2004-01-03 01:56 -------
> The code is invalid as you cannot jump out of an asm.

OK, but the case is also valid without the 'jmp' instruction. For the sake
of discussion let's assume valid ASM

> Also you cannot depend on the optimizing compilers not moving labels.

Well, then perhaps this is a feature request and not a bug: I would like gcc
to not move user-defined labels beyond 'asm volatile' statements, especially
ones of which the address is taken





-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=13552