🚀 go-pugleaf

Dear GCC,

Can you explain the following comment in combine.c :

   On machines where SMALL_REGISTER_CLASSES is defined, we don't combine
   if the destination of a SET is a hard register.

This makes all call_value insns very inefficient,  because 

C program :
main()
{
  foo();
}

.combine:
(insn 8 7 9 (set (reg:QI 13)
       (symbol_ref:QI ("foo"))) -1 (nil)
   (expr_list:REG_EQUAL (symbol_ref:QI ("foo"))
       (nil)))

(call_insn 9 8 0 (set (reg:QI 2)
       (call (mem:QI (reg:QI 13))
           (const_int 0))) -1 (insn_list 8 (nil))
   (expr_list:REG_DEAD (reg:QI 13)
       (expr_list:REG_UNUSED (reg:QI 2)
           (nil))))


should have been combined to :
(call_insn 9 8 0 (set (reg:QI 2)
       (call (mem:QI (symbol_ref:QI ("foo")))
           (const_int 0))) 25 {call_value} (nil)
   (expr_list:REG_UNUSED (reg:QI 2)
       (nil)))

Thanks for your help

Dong