http://gcc.gnu.org/bugzilla/show_bug.cgi?id=54200
Jakub Jelinek <jakub at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
CC| |jakub at gcc dot gnu.org
--- Comment #12 from Jakub Jelinek <jakub at gcc dot gnu.org> 2013-03-29
15:36:15 UTC ---
This patch regressed code quality on find_vma function in Linux kernel on
s390x:
struct rb_node
{
unsigned long __rb_parent_color;
struct rb_node *rb_right;
struct rb_node *rb_left;
} __attribute__ ((aligned (sizeof (long))));
struct rb_root {
struct rb_node *rb_node;
};
struct vm_area_struct
{
unsigned long vm_start;
unsigned long vm_end;
struct vm_area_struct *vm_next, *vm_prev;
struct rb_node vm_rb;
};
struct mm_struct
{
struct vm_area_struct *mmap;
struct rb_root mm_rb;
struct vm_area_struct *mmap_cache;
};
struct vm_area_struct *
find_vma (struct mm_struct *mm, unsigned long addr)
{
struct vm_area_struct *vma = ((void *) 0);
static _Bool __attribute__ ((__section__ (".data.unlikely"))) __warned;
int __ret_warn_once = !!(!mm);
if (__builtin_expect (!!(__ret_warn_once), 0))
{
int __ret_warn_on = !!(!__warned);
if (__builtin_expect (!!(__ret_warn_on), 0))
asm volatile ("": :"i" (1920), "i" (((1 << 0) | ((9) << 8))), "i" (64));
if (__builtin_expect (!!(__ret_warn_on), 0))
__warned = 1;
}
if (__builtin_expect (!!(__ret_warn_once), 0))
return ((void *) 0);
vma = mm->mmap_cache;
if (!(vma && vma->vm_end > addr && vma->vm_start <= addr))
{
struct rb_node *rb_node;
rb_node = mm->mm_rb.rb_node;
vma = ((void *) 0);
while (rb_node)
{
struct vm_area_struct *vma_tmp;
const typeof (((struct vm_area_struct *)0)->vm_rb) *__mptr = rb_node;
vma_tmp = (struct vm_area_struct *) ((char *) __mptr - __builtin_offsetof
(struct vm_area_struct, vm_rb));
if (vma_tmp->vm_end > addr)
{
vma = vma_tmp;
if (vma_tmp->vm_start <= addr)
break;
rb_node = rb_node->rb_left;
}
else
rb_node = rb_node->rb_right;
}
if (vma)
mm->mmap_cache = vma;
}
return vma;
}
with:
-fno-strict-aliasing -fno-common -fno-delete-null-pointer-checks -O2 -m64
-mbackchain -msoft-float -march=z9-109 -mpacked-stack -mstack-size=16384
-fno-strength-reduce -fno-stack-protector -fomit-frame-pointer
-fno-inline-functions-called-once -fconserve-stack
The difference in *.optimized is just:
- # vma_5 = PHI <0B(18), vma_2(15), vma_20(6), vma_2(16), 0B(7)>
- return vma_5;
+ # _5 = PHI <0B(18), vma_2(15), vma_20(6), vma_2(16), 0B(7)>
+ return _5;
but later on CSE2 decides to use REG_EQUAL somewhere for some reason, and we
end up reading mm->mmap_cache twice, first into a register to do the
comparisons of it, and then when we know it is the value we actually want to
return, we just forget we have it in a pseudo and read it again from memory.
