[Bug target/114847] New: arm: epilogue in _Unwind_RaiseException corrupts return value due to __builtin_eh_return

[Bug target/114847] New: arm: epilogue in _Unwind_RaiseException corrupts return value due to __builtin_eh_return

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=114847

            Bug ID: 114847
           Summary: arm: epilogue in _Unwind_RaiseException corrupts
                    return value due to __builtin_eh_return
           Product: gcc
           Version: 14.0
            Status: UNCONFIRMED
          Keywords: wrong-code
          Severity: normal
          Priority: P3
         Component: target
          Assignee: unassigned at gcc dot gnu.org
          Reporter: pinskia at gcc dot gnu.org
  Target Milestone: ---
            Target: arm-linux-gnueabi

I reduced an miscompile for aarch64 inside _Unwind_RaiseException and I noticed
the same issue can be reproduced on arm-linux-gnueabi also.

Reduced testcase:
```
__attribute__((noipa,noinline))
int f(int *a, long offset, void *handler)
{
  if (*a == 5)
    return 5;
  __builtin_eh_return (offset, handler);
}

int main()
{
  int t = 5;
  if (f(&t, 0, 0) != 5)
    __builtin_abort();
}
```

This produces a load in the epilogue part for the `return 5` path (which is
reduced from the end of stack path inside _Unwind_RaiseException).

```
        ldr     r0, [r0]
        cmp     r0, #5
        bne     .L2
        movs    r2, #0
.L4:
        pop     {r0, r1}
        @ r2 needed
        add     sp, sp, r2
        bx      lr
```

r0 is clobbered by the pop.