[Bug target/64458] New: [ARM] Redundant ldr when accessing var inside and outside a loop

[Bug target/64458] New: [ARM] Redundant ldr when accessing var inside and outside a loop

[thopre01 at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=64458

            Bug ID: 64458
           Summary: [ARM] Redundant ldr when accessing var inside and
                    outside a loop
           Product: gcc
           Version: unknown
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: target
          Assignee: unassigned at gcc dot gnu.org
          Reporter: thopre01 at gcc dot gnu.org
            Target: arm-none-eabi

When compiling the below example with -O2, 2 ldr are generated to access the
variable "some": one for the loop and one for the store.

int f (int);

unsigned int glob;

void
g (void)
{
  while (glob);
  glob = 1;
}

The following code is then generated:

0: push
{r4, lr}
4: ldr r4, pc, #32 ; 2c
8: ldr r0, [r4]
c: bl 0 <g>
10: cmp r0, #0
14: ldr r3, pc, #16 ; 2c
18: bne 8
1c: mov r2, #1
20: pop {r4, lr}

24: str r2, [r3]
28: bx lr
2c: .word 0x00000000

Note the redundant load of the address at offset 2c in instructions at offsets
4 and 14.

[Bug target/64458] [ARM] Redundant ldr when accessing var inside and outside a loop

[ramana at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=64458

Ramana Radhakrishnan <ramana at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |WAITING
   Last reconfirmed|                            |2015-01-16
                 CC|                            |ramana at gcc dot gnu.org
     Ever confirmed|0                           |1

--- Comment #1 from Ramana Radhakrishnan <ramana at gcc dot gnu.org> ---
Huh, what arch options ? 

    .arm
    .syntax divided
    .file    "ldr.c"
    .text
    .align    2
    .global    g
    .type    g, %function
g:
    @ Function supports interworking.
    @ args = 0, pretend = 0, frame = 0
    @ frame_needed = 0, uses_anonymous_args = 0
    @ link register save eliminated.
    ldr    r2, .L5
    ldr    r3, [r2]
.L2:
    cmp    r3, #0
    bne    .L2
    mov    r3, #1
    str    r3, [r2]
    bx    lr
.L6:
    .align    2
.L5:
    .word    glob
    .size    g, .-g
    .comm    glob,4,4

[Bug target/64458] [ARM] Redundant ldr when accessing var inside and outside a loop

[thopre01 at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=64458

Thomas Preud'homme <thopre01 at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|WAITING                     |RESOLVED
         Resolution|---                         |DUPLICATE

--- Comment #2 from Thomas Preud'homme <thopre01 at gcc dot gnu.org> ---


*** This bug has been marked as a duplicate of bug 64616 ***

[Bug target/64458] [ARM] Redundant ldr when accessing var inside and outside a loop

[thopre01 at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=64458

--- Comment #3 from Thomas Preud'homme <thopre01 at gcc dot gnu.org> ---
Hi Ramana,

As said in PR64616, this happens with the default cpu selected when configuring
with --with-arch=armv7-a.

Best regards.