On Tue, 25 Jul 2023, Richard Biener wrote:

> The following removes the code checking whether a noop copy
> is between something involved in the return sequence composed
> of a SET and USE.  Instead of checking for this special-case
> the following makes us only ever remove noop copies between
> pseudos - which is the case that is necessary for IRA/LRA
> interfacing to function according to the comment.  That makes
> looking for the return reg special case unnecessary, reducing
> the compile-time in LRA non-specific to zero for the testcase.
> 
> Bootstrapped and tested on x86_64-unknown-linux-gnu with
> all languages and {,-m32}.
> 
> OK?

Ping.

> Thanks,
> Richard.
> 
>       PR rtl-optimization/110587
>       * lra-spills.cc (return_regno_p): Remove.
>       (regno_in_use_p): Likewise.
>       (lra_final_code_change): Do not remove noop moves
>       between hard registers.
> ---
>  gcc/lra-spills.cc | 69 +----------------------------------------------
>  1 file changed, 1 insertion(+), 68 deletions(-)
> 
> diff --git a/gcc/lra-spills.cc b/gcc/lra-spills.cc
> index 3a7bb7e8cd9..fe58f162d05 100644
> --- a/gcc/lra-spills.cc
> +++ b/gcc/lra-spills.cc
> @@ -705,72 +705,6 @@ alter_subregs (rtx *loc, bool final_p)
>    return res;
>  }
>  
> -/* Return true if REGNO is used for return in the current
> -   function.  */
> -static bool
> -return_regno_p (unsigned int regno)
> -{
> -  rtx outgoing = crtl->return_rtx;
> -
> -  if (! outgoing)
> -    return false;
> -
> -  if (REG_P (outgoing))
> -    return REGNO (outgoing) == regno;
> -  else if (GET_CODE (outgoing) == PARALLEL)
> -    {
> -      int i;
> -
> -      for (i = 0; i < XVECLEN (outgoing, 0); i++)
> -     {
> -       rtx x = XEXP (XVECEXP (outgoing, 0, i), 0);
> -
> -       if (REG_P (x) && REGNO (x) == regno)
> -         return true;
> -     }
> -    }
> -  return false;
> -}
> -
> -/* Return true if REGNO is in one of subsequent USE after INSN in the
> -   same BB.  */
> -static bool
> -regno_in_use_p (rtx_insn *insn, unsigned int regno)
> -{
> -  static lra_insn_recog_data_t id;
> -  static struct lra_static_insn_data *static_id;
> -  struct lra_insn_reg *reg;
> -  int i, arg_regno;
> -  basic_block bb = BLOCK_FOR_INSN (insn);
> -
> -  while ((insn = next_nondebug_insn (insn)) != NULL_RTX)
> -    {
> -      if (BARRIER_P (insn) || bb != BLOCK_FOR_INSN (insn))
> -     return false;
> -      if (! INSN_P (insn))
> -     continue;
> -      if (GET_CODE (PATTERN (insn)) == USE
> -       && REG_P (XEXP (PATTERN (insn), 0))
> -       && regno == REGNO (XEXP (PATTERN (insn), 0)))
> -     return true;
> -      /* Check that the regno is not modified.  */
> -      id = lra_get_insn_recog_data (insn);
> -      for (reg = id->regs; reg != NULL; reg = reg->next)
> -     if (reg->type != OP_IN && reg->regno == (int) regno)
> -       return false;
> -      static_id = id->insn_static_data;
> -      for (reg = static_id->hard_regs; reg != NULL; reg = reg->next)
> -     if (reg->type != OP_IN && reg->regno == (int) regno)
> -       return false;
> -      if (id->arg_hard_regs != NULL)
> -     for (i = 0; (arg_regno = id->arg_hard_regs[i]) >= 0; i++)
> -       if ((int) regno == (arg_regno >= FIRST_PSEUDO_REGISTER
> -                           ? arg_regno : arg_regno - FIRST_PSEUDO_REGISTER))
> -         return false;
> -    }
> -  return false;
> -}
> -
>  /* Final change of pseudos got hard registers into the corresponding
>     hard registers and removing temporary clobbers.  */
>  void
> @@ -821,8 +755,7 @@ lra_final_code_change (void)
>         if (NONJUMP_INSN_P (insn) && GET_CODE (pat) == SET
>             && REG_P (SET_SRC (pat)) && REG_P (SET_DEST (pat))
>             && REGNO (SET_SRC (pat)) == REGNO (SET_DEST (pat))
> -           && (! return_regno_p (REGNO (SET_SRC (pat)))
> -               || ! regno_in_use_p (insn, REGNO (SET_SRC (pat)))))
> +           && REGNO (SET_SRC (pat)) >= FIRST_PSEUDO_REGISTER)
>           {
>             lra_invalidate_insn_data (insn);
>             delete_insn (insn);
> 

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