[Bug optimization/12306] New: GOT pointer (r12) reloaded unnecessarily

[tm at kloo dot net]

PLEASE REPLY TO gcc-bugzilla@gcc.gnu.org ONLY, *NOT* gcc-bugs@gcc.gnu.org.

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=12306

           Summary: GOT pointer (r12) reloaded unnecessarily
           Product: gcc
           Version: 3.4
            Status: UNCONFIRMED
          Severity: normal
          Priority: P2
         Component: optimization
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: tm at kloo dot net
                CC: gcc-bugs at gcc dot gnu dot org
 GCC build triplet: i386-linux
  GCC host triplet: i386-linux
GCC target triplet: sh-elf

On the Renesas SH, the register r12 is fixed and reserved for the pointer to the
GOT. However, the code emitted saves r12 and reloads r12.

int a, b; int foo(void) { return a + b; }

compiled with -O2 -m4 -fPIC -S produces:

_foo:
        mov.l   r12,@-r15		<- r12 saved to stack
        mova    .L3,r0
        mov.l   .L3,r12
        mov.l   r14,@-r15
        add     r0,r12			<- r12 (GOT pointer) rebuilt
        mov.l   .L4,r0
        sts.l   pr,@-r15
        mov.l   @(r0,r12),r1
        mov     r12,r0
        mov     r15,r14
        mov.l   @r1,r2
        mov.l   .L5,r1
        mov.l   @(r0,r1),r1
        mov.l   @r1,r1
        add     r1,r2
        mov     r2,r0
        mov     r14,r15
        lds.l   @r15+,pr
        mov.l   @r15+,r14
        rts
        mov.l   @r15+,r12		<- r12 restored