[PATCH, GCC, stage1] Fallback to copy-prop if constant-prop not possible

[Steven Bosscher]

On Mon, Feb 16, 2015 at 11:26 AM, Thomas Preud'homme wrote:

>  /* Subroutine of cprop_insn that tries to propagate constants into
> @@ -1044,40 +1042,41 @@ cprop_insn (rtx_insn *insn)

> -      /* Constant propagation.  */
> -      if (cprop_constant_p (src))
> -       {
> -          if (constprop_register (reg_used, src, insn))
> +         /* Constant propagation.  */
> +         if (src_cst && cprop_constant_p (src_cst)
> +             && constprop_register (reg_used, src_cst, insn))
>             {
>               changed_this_round = changed = 1;
>               global_const_prop_count++;

The cprop_constant_p test is redundant, you only have non-NULL src_cst
if it is a cprop_constant_p (as you test for it in find_avail_set()).


> @@ -1087,18 +1086,16 @@ retry:
>                            "GLOBAL CONST-PROP: Replacing reg %d in ", regno);
>                   fprintf (dump_file, "insn %d with constant ",
>                            INSN_UID (insn));
> -                 print_rtl (dump_file, src);
> +                 print_rtl (dump_file, src_cst);
>                   fprintf (dump_file, "\n");
>                 }
>               if (insn->deleted ())
>                 return 1;
>             }
> -       }
> -      else if (REG_P (src)
> -              && REGNO (src) >= FIRST_PSEUDO_REGISTER
> -              && REGNO (src) != regno)
> -       {
> -         if (try_replace_reg (reg_used, src, insn))
> +         else if (src_reg && REG_P (src_reg)
> +                  && REGNO (src_reg) >= FIRST_PSEUDO_REGISTER
> +                  && REGNO (src_reg) != regno
> +                  && try_replace_reg (reg_used, src_reg, insn))

Likewise for the REG_P and ">= FIRST_PSEUDO_REGISTER" tests here (with
the equivalent and IMHO preferable HARD_REGISTER_P test in
find_avail_set()).


Looks good to me otherwise.

Ciao!
Steven