[Bug middle-end/26187] New: computed goto code does not produce jumps

[Bug middle-end/26187] New: computed goto code does not produce jumps

[bje at gcc dot gnu dot org]

When compiling the test case below, the assembly output shows jmps through eax
to the destination pointer, p, for the functions goto0 and goto2 (which contain
zero and two expressions that take the address of a label).  In function goto1,
which only takes the address of one label, there is no jmp instruction
generated.  The test case originally assigned the label addresses to void *
auto variables, but I removed those while simplifying the test.

I've been able to reproduce this problem on powerpc-linux-gnu also, so it
appears to be target independent.

Compile with gcc -S foo.c and examine foo.s.

extern int printf (const char *format, ...);
int x;

void goto0 (void *p)
{
  goto *p;
}

void goto1 (void *p)
{
  &&label;
  goto *p;
 label:
  x = 0;
}

void goto2 (void *p)
{
  &&label1;
  &&label2;
  goto *p;
 label1:
 label2:
  x = 0;
}


-- 
           Summary: computed goto code does not produce jumps
           Product: gcc
           Version: 4.2.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: middle-end
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: bje at gcc dot gnu dot org
  GCC host triplet: i686-pc-linux-gnu
GCC target triplet: i686-pc-linux-gnu


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=26187

[Bug middle-end/26187] computed goto code does not produce jumps

[pinskia at gcc dot gnu dot org]

------- Comment #1 from pinskia at gcc dot gnu dot org  2006-02-09 00:32 -------
computed goto's can only goto local labels or gotos in the contained functions.
 I don't see the bug here really.


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=26187

[Bug middle-end/26187] computed goto code does not produce jumps

[bje at gcc dot gnu dot org]

------- Comment #2 from bje at gcc dot gnu dot org  2006-02-09 00:38 -------
Thanks; I guess I misunderstood the semantics of computed gotos.  On closer
inspection of the GCC manual,

  "You may not use this mechanism to jump to code in a different function.
   If you do that, totally unpredictable things will happen.  The best way
   to avoid this is to store the label address only in automatic variables
   and never pass it as an argument."


-- 

bje at gcc dot gnu dot org changed:

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


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=26187

[Bug middle-end/26187] computed goto code does not produce jumps

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=26187

Andrew Pinski <pinskia at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |rakdver at gcc dot gnu.org

--- Comment #3 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
*** Bug 31727 has been marked as a duplicate of this bug. ***