[Bug rtl-optimization/64616] New: 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=64616

            Bug ID: 64616
           Summary: Redundant ldr when accessing var inside and outside a
                    loop
           Product: gcc
           Version: 5.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: rtl-optimization
          Assignee: unassigned at gcc dot gnu.org
          Reporter: thopre01 at gcc dot gnu.org

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 g (int);

unsigned int glob;

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

The following code is then generated:

f:
push    {r3, r4, r5, lr}
ldr     r5, .L6
.L2:
ldr     r0, [r5]
ldr     r4, .L6
bl      g
cmp     r0, #0
bne     .L2
movs    r3, #1
str     r3, [r4]
pop     {r3, r4, r5, pc}

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