[Bug rtl-optimization/19560] New: Adding -g disables -foptimize-sibling-calls optimization in some cases

[gcc-bugzilla at gcc dot gnu dot org]

        With the option -foptimize-sibling-calls tail recursion is
        performed. Adding -g destroys this optimization. In my opinion,
        adding compiler option -g should not change the behaviour of
        the compiled program.

Environment:
System: SunOS rungner.nada.kth.se 5.9 Generic_117171-07 sun4u sparc 
SUNW,Sun-Fire-280R
Architecture: sun4

        
host: sparc-sun-solaris2.9
build: sparc-sun-solaris2.9
target: sparc-sun-solaris2.9
configured with: /afs/.nada.kth.se/pkg/gcc/src/3.4.2/gcc-3.4.2/configure 
--prefix=/pkg/gcc/3.4.2/os

How-To-Repeat:
        Compile the following program:

/*
 * In this function, it seems that tail recursion is performed both with
 *
 *   gcc -foptimize-sibling-calls -S tail.c 
 *
 * and with
 *
 *   gcc -g -foptimize-sibling-calls -S tail.c 
 *
 * using gcc 3.4.2 on a SPARC.
 */
void f(int n)
{
    if(n > 0)
        f(--n);
}

/*
 * In this function, it seems that tail recursion is performed with
 *
 *   gcc -foptimize-sibling-calls -S tail.c 
 *
 * but not with
 *
 *   gcc -g -foptimize-sibling-calls -S tail.c 
 *
 * using gcc 3.4.2 on a SPARC.
 */
void g(int n)
{
    if(n > 0)
        f(--n);
    return;
}

int main(int argc, char **argv)
{
    f(10);
    g(10);
}



        (Preprocessor output is included below.)
        For the function f(), the assembler output ends with


        call    f, 0
         restore
.LL1:
        nop
        ret
        restore
.LLFE2:
        .size   f, .-f


        both with and without compiler option -g. For the function
        g(), however, the assembler output ends with


        call    f, 0
         restore
.LL3:
        nop
        ret
        restore
        .size   g, .-g


        if "-g" is *not* used, and with


        call    f, 0
         nop
.LL3:
        nop
        ret
        restore
.LLFE3:
        .size   g, .-g


        if "-g" *is* used. And now the preprocessor output:

# 1 "tail.c"
# 1 "<built-in>"
# 1 "<command line>"
# 1 "tail.c"
# 27 "tail.c"
void f(int n)
{
    if(n > 0)
 f(--n);
}
# 44 "tail.c"
void g(int n)
{
    if(n > 0)
 f(--n);
    return;
}

int main(int argc, char **argv)
{
    f(10);
    g(10);
}
------- Additional Comments From enge at nada dot kth dot se  2005-01-21 10:12 
-------
Fix:
        I do not know of a fix.

-- 
           Summary: Adding -g disables -foptimize-sibling-calls optimization
                    in some cases
           Product: gcc
           Version: 3.4.2
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: rtl-optimization
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: enge at nada dot kth dot se
                CC: gcc-bugs at gcc dot gnu dot org
 GCC build triplet: sparc-sun-solaris2.9
  GCC host triplet: sparc-sun-solaris2.9
GCC target triplet: sparc-sun-solaris2.9


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=19560