[Bug target/84626] New: powerpc toc register is reloaded unnecessarily

[npiggin at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=84626

            Bug ID: 84626
           Summary: powerpc toc register is reloaded unnecessarily
           Product: gcc
           Version: 8.0.1
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: target
          Assignee: unassigned at gcc dot gnu.org
          Reporter: npiggin at gmail dot com
  Target Milestone: ---

gcc version 8.0.1 20180207 (experimental) [trunk revision 257435] (Debian
8-20180207-2):

Test case:

void test(void (*fn)(void), unsigned long i)
{ 
        while (i--)
                fn();
}

Generates code:

  2c:   18 00 41 f8     std     r2,24(r1)
  30:   00 00 00 60     nop
  34:   00 00 00 60     nop
  38:   00 00 00 60     nop
  3c:   00 00 42 60     ori     r2,r2,0
  40:   78 f3 cc 7f     mr      r12,r30
  44:   a6 03 c9 7f     mtctr   r30
  48:   ff ff ff 3b     addi    r31,r31,-1
  4c:   21 04 80 4e     bctrl
  50:   18 00 41 e8     ld      r2,24(r1)
  54:   ff ff bf 2f     cmpdi   cr7,r31,-1
  58:   e8 ff 9e 40     bne     cr7,40 <test+0x40>

The r2 load could be moved out of the loop.