[Bug rtl-optimization/64895] RA picks the wrong register for -fipa-ra

["renlin at gcc dot gnu.org" <gcc-bugzilla at gcc dot gnu dot org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=64895

Renlin Li <renlin at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |renlin at gcc dot gnu.org

--- Comment #12 from Renlin Li <renlin at gcc dot gnu.org> ---
The same happens for aarch64.

> [hjl@gnu-tools-1 gcc]$ cat /tmp/x.c 
> static int __attribute__((noinline))
> bar (int x)
> {
>   if (x > 4)
>     return bar (x - 3);
>   return 0;
> }
> 
> int __attribute__((noinline))
> foo (int y)
> {
>   return y + bar (y);
> }
> 

There is another problem here actually.

In this particular case, bar() is a static function which is not exported.
Although -fpic option is provided, pic_offset_table_rtx is not used at all in
function foo().

In this case, pic_offset_table_rtx may not be initialized at all. The target
hook TARGET_INIT_PIC_REG can be improved to initialize pic register only when
necessary.


On the other hand, if pic_offset_table_rtx is not used at all,
lra_risky_transformations_p should not be true. Does it make sensible?

diff --git a/gcc/lra-constraints.c b/gcc/lra-constraints.c
index a78edd8..d4a950f 100644
--- a/gcc/lra-constraints.c
+++ b/gcc/lra-constraints.c
@@ -4221,7 +4221,8 @@ lra_constraints (bool first_p)
             lra_constraint_iter);
   changed_p = false;
   if (pic_offset_table_rtx
-      && REGNO (pic_offset_table_rtx) >= FIRST_PSEUDO_REGISTER)
+      && (i = REGNO (pic_offset_table_rtx)) >= FIRST_PSEUDO_REGISTER
+      && lra_reg_info[i].nrefs > 0)
     lra_risky_transformations_p = true;
   else
     lra_risky_transformations_p = false;