Re: [PATCH 02/12] Allow generating pseudo register with specific alignment

[Richard Sandiford <richard.sandiford@arm.com>]

"H.J. Lu via Gcc-patches" <gcc-patches@gcc.gnu.org> writes:
> gen_reg_rtx tracks stack alignment needed for pseudo registers so that
> associated hard registers can be properly spilled onto stack.  But there
> are cases where associated hard registers will never be spilled onto
> stack.  gen_reg_rtx is changed to take an argument for register alignment
> so that stack realignment can be avoided when not needed.

How is it guaranteed that they will never be spilled though?
I don't think that that guarantee exists for any kind of pseudo,
except perhaps for the temporary pseudos that the RA creates to
replace (match_scratch …)es.

Thanks,
Richard

> 	* emit-rtl.c (gen_reg_rtx): Add an argument for register
> 	alignment and use it if it isn't zero.
> 	* explow.c (force_reg): Add an argument for register alignment
> 	and pass it to gen_reg_rtx.
> 	* explow.h (force_reg): Add an argument for register alignment
> 	and default it to 0.
> 	* expr.h (convert_to_mode): Likewise.
> 	(convert_modes): Likewise.
> 	* expr.c (convert_to_mode): Add an argument for register
> 	alignment and pass it to convert_modes.
> 	(convert_modes): Add an argument for register alignment and
> 	pass it to gen_reg_rtx.
> ---
>  gcc/emit-rtl.c |  5 +++--
>  gcc/explow.c   |  6 +++---
>  gcc/explow.h   |  2 +-
>  gcc/expr.c     | 10 ++++++----
>  gcc/expr.h     |  6 ++++--
>  gcc/rtl.h      |  2 +-
>  6 files changed, 18 insertions(+), 13 deletions(-)
>
> diff --git a/gcc/emit-rtl.c b/gcc/emit-rtl.c
> index 07e908624a0..4accf851d23 100644
> --- a/gcc/emit-rtl.c
> +++ b/gcc/emit-rtl.c
> @@ -1160,10 +1160,11 @@ subreg_memory_offset (const_rtx x)
>     This pseudo is assigned the next sequential register number.  */
>  
>  rtx
> -gen_reg_rtx (machine_mode mode)
> +gen_reg_rtx (machine_mode mode, unsigned int align)
>  {
>    rtx val;
> -  unsigned int align = GET_MODE_ALIGNMENT (mode);
> +  if (align == 0)
> +    align = GET_MODE_ALIGNMENT (mode);
>  
>    gcc_assert (can_create_pseudo_p ());
>  
> diff --git a/gcc/explow.c b/gcc/explow.c
> index b6da277f689..c8673ce512d 100644
> --- a/gcc/explow.c
> +++ b/gcc/explow.c
> @@ -663,7 +663,7 @@ copy_to_mode_reg (machine_mode mode, rtx x)
>     since we mark it as a "constant" register.  */
>  
>  rtx
> -force_reg (machine_mode mode, rtx x)
> +force_reg (machine_mode mode, rtx x, unsigned int reg_align)
>  {
>    rtx temp, set;
>    rtx_insn *insn;
> @@ -673,7 +673,7 @@ force_reg (machine_mode mode, rtx x)
>  
>    if (general_operand (x, mode))
>      {
> -      temp = gen_reg_rtx (mode);
> +      temp = gen_reg_rtx (mode, reg_align);
>        insn = emit_move_insn (temp, x);
>      }
>    else
> @@ -683,7 +683,7 @@ force_reg (machine_mode mode, rtx x)
>  	insn = get_last_insn ();
>        else
>  	{
> -	  rtx temp2 = gen_reg_rtx (mode);
> +	  rtx temp2 = gen_reg_rtx (mode, reg_align);
>  	  insn = emit_move_insn (temp2, temp);
>  	  temp = temp2;
>  	}
> diff --git a/gcc/explow.h b/gcc/explow.h
> index 698f2a2a21c..621cdd7d356 100644
> --- a/gcc/explow.h
> +++ b/gcc/explow.h
> @@ -40,7 +40,7 @@ extern rtx copy_to_suggested_reg (rtx, rtx, machine_mode);
>  
>  /* Copy a value to a register if it isn't already a register.
>     Args are mode (in case value is a constant) and the value.  */
> -extern rtx force_reg (machine_mode, rtx);
> +extern rtx force_reg (machine_mode, rtx, unsigned int reg_align = 0);
>  
>  /* Return given rtx, copied into a new temp reg if it was in memory.  */
>  extern rtx force_not_mem (rtx);
> diff --git a/gcc/expr.c b/gcc/expr.c
> index b4c110f8c17..42db4ddbe0a 100644
> --- a/gcc/expr.c
> +++ b/gcc/expr.c
> @@ -658,9 +658,10 @@ convert_mode_scalar (rtx to, rtx from, int unsignedp)
>     or by copying to a new temporary with conversion.  */
>  
>  rtx
> -convert_to_mode (machine_mode mode, rtx x, int unsignedp)
> +convert_to_mode (machine_mode mode, rtx x, int unsignedp,
> +		 unsigned int reg_align)
>  {
> -  return convert_modes (mode, VOIDmode, x, unsignedp);
> +  return convert_modes (mode, VOIDmode, x, unsignedp, reg_align);
>  }
>  
>  /* Return an rtx for a value that would result
> @@ -674,7 +675,8 @@ convert_to_mode (machine_mode mode, rtx x, int unsignedp)
>     You can give VOIDmode for OLDMODE, if you are sure X has a nonvoid mode.  */
>  
>  rtx
> -convert_modes (machine_mode mode, machine_mode oldmode, rtx x, int unsignedp)
> +convert_modes (machine_mode mode, machine_mode oldmode, rtx x,
> +	       int unsignedp, unsigned int reg_align)
>  {
>    rtx temp;
>    scalar_int_mode int_mode;
> @@ -734,7 +736,7 @@ convert_modes (machine_mode mode, machine_mode oldmode, rtx x, int unsignedp)
>        return simplify_gen_subreg (mode, x, oldmode, 0);
>      }
>  
> -  temp = gen_reg_rtx (mode);
> +  temp = gen_reg_rtx (mode, reg_align);
>    convert_move (temp, x, unsignedp);
>    return temp;
>  }
> diff --git a/gcc/expr.h b/gcc/expr.h
> index 9a2736f69fa..2b06da1a889 100644
> --- a/gcc/expr.h
> +++ b/gcc/expr.h
> @@ -66,10 +66,12 @@ extern void init_expr (void);
>  extern void convert_move (rtx, rtx, int);
>  
>  /* Convert an rtx to specified machine mode and return the result.  */
> -extern rtx convert_to_mode (machine_mode, rtx, int);
> +extern rtx convert_to_mode (machine_mode, rtx, int,
> +			    unsigned int reg_align = 0);
>  
>  /* Convert an rtx to MODE from OLDMODE and return the result.  */
> -extern rtx convert_modes (machine_mode, machine_mode, rtx, int);
> +extern rtx convert_modes (machine_mode, machine_mode, rtx, int,
> +			  unsigned int reg_align = 0);
>  
>  /* Expand a call to memcpy or memmove or memcmp, and return the result.  */
>  extern rtx emit_block_op_via_libcall (enum built_in_function, rtx, rtx, rtx,
> diff --git a/gcc/rtl.h b/gcc/rtl.h
> index 398d745aff5..c72f7fd59b9 100644
> --- a/gcc/rtl.h
> +++ b/gcc/rtl.h
> @@ -3125,7 +3125,7 @@ subreg_promoted_mode (rtx x)
>  /* In emit-rtl.c */
>  extern rtvec gen_rtvec_v (int, rtx *);
>  extern rtvec gen_rtvec_v (int, rtx_insn **);
> -extern rtx gen_reg_rtx (machine_mode);
> +extern rtx gen_reg_rtx (machine_mode, unsigned int align = 0);
>  extern rtx gen_rtx_REG_offset (rtx, machine_mode, unsigned int, poly_int64);
>  extern rtx gen_reg_rtx_offset (rtx, machine_mode, int);
>  extern rtx gen_reg_rtx_and_attrs (rtx);