[Bug regression/38674] New: optimization bug.

[Bug regression/38674] New: optimization bug.

[gilles dot chanteperdrix at xenomai dot org]

When compiling the following code with -O2:

#include <stdio.h>

static unsigned long long __attribute__((noinline)) f(void *ptr, unsigned long
long ull)
{
        register unsigned long __r2 __asm__ ("r2") = (unsigned long) (&ull);
        __asm__ __volatile__ ("" : "+r" (__r2));
        return * (unsigned long long *) __r2;
}

int main(void)
{
        fprintf(stderr, "f(NULL, 0): %Lu\n", f(NULL, 0));
        return 0;
}

we get the following warning:
/tmp/ccJNzMaH.s: Assembler messages:
/tmp/ccJNzMaH.s:21: Warning: source register same as write-back base

And when running the program on target, the printed return value of f is not 0.

A disassembly of f:
000083f4 <f>:
    83f4:       e24dd008        sub     sp, sp, #8      ; 0x8
    83f8:       e28d2008        add     r2, sp, #8      ; 0x8
    83fc:       e16220f8        strd    r2, [r2, #-8]!
    8400:       e8920003        ldm     r2, {r0, r1}
    8404:       e28dd008        add     sp, sp, #8      ; 0x8
    8408:       e12fff1e        bx      lr

shows that r2 seems to be clobbered before its value is saved on stack.


-- 
           Summary: optimization bug.
           Product: gcc
           Version: 4.3.2
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: regression
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: gilles dot chanteperdrix at xenomai dot org
GCC target triplet: armeb-unknown-linux-gnueabi


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=38674

[Bug middle-end/38674] When storing in a register the address of a value contained in the same register, gcc 4.3.2 on ARM clobbers the register before saving its content on the stack.

[gilles dot chanteperdrix at xenomai dot org]

------- Comment #1 from gilles dot chanteperdrix at xenomai dot org  2009-01-05 15:21 -------
The following, even simpler test case:

unsigned long long f(unsigned long long ull)
{
        register unsigned long long *__r0 __asm__ ("r0") = &ull;
        __asm__ __volatile__ ("" : "+r" (__r0));
        return * __r0;
}

gives the same warning, and the following assembly code:

00000000 <f>:
   0:   e24dd008        sub     sp, sp, #8      ; 0x8
   4:   e28d0008        add     r0, sp, #8      ; 0x8
   8:   e16000f8        strd    r0, [r0, #-8]!
   c:   e8900003        ldm     r0, {r0, r1}
  10:   e28dd008        add     sp, sp, #8      ; 0x8
  14:   e12fff1e        bx      lr


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=38674

[Bug middle-end/38674] When storing in a register the address of a value contained in the same register, gcc 4.3.2 on ARM clobbers the register before saving its content on the stack.

[rearnsha at gcc dot gnu dot org]

------- Comment #2 from rearnsha at gcc dot gnu dot org  2009-03-16 23:38 -------
Confirmed.  We need a way to represent an early-clobber between a register and
a memory-address with side-effects.


-- 

rearnsha at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |rearnsha at gcc dot gnu dot
                   |                            |org, ramana dot r at gmail
                   |                            |dot com
             Status|UNCONFIRMED                 |NEW
     Ever Confirmed|0                           |1
   Last reconfirmed|0000-00-00 00:00:00         |2009-03-16 23:38:45
               date|                            |


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=38674

[Bug middle-end/38674] When storing in a register the address of a value contained in the same register, gcc 4.3.2 on ARM clobbers the register before saving its content on the stack.

[rearnsha at gcc dot gnu dot org]

-- 

rearnsha at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Keywords|                            |wrong-code
           Priority|P3                          |P2


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=38674

[Bug middle-end/38674] When storing in a register the address of a value contained in the same register, gcc 4.3.2 on ARM clobbers the register before saving its content on the stack.

[cbaylis at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=38674

cbaylis at gcc dot gnu.org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|NEW                         |RESOLVED
                 CC|                            |cbaylis at gcc dot gnu.org
         Resolution|---                         |DUPLICATE

--- Comment #3 from cbaylis at gcc dot gnu.org ---
This appears to have been fixed by r161920

2010-07-07  Bernd Schmidt  <bernds@codesourcery.com>

        PR rtl-optimization/44404
        * auto-inc-dec.c (find_inc): Avoid calling count_occurrences if
        possible, use reg_overlap_mentioned_p instead.

*** This bug has been marked as a duplicate of bug 44404 ***