RE: [PATCH] Machine_Mode: Extend machine_mode from 8 to 16 bits

["Li, Pan2" <pan2.li@intel.com>]

Thanks Richard for comments. In previous, I am not sure it is reasonable to let everywhere consume the same macro in rtl.h (As the includes you mentioned). Thus, make a conservative change in PATCH v1.

I will address the comments and try to align the bit size to the one and the only one macro soon.

Pan


-----Original Message-----
From: Richard Sandiford <richard.sandiford@arm.com> 
Sent: Friday, May 12, 2023 4:24 PM
To: Li, Pan2 <pan2.li@intel.com>
Cc: gcc-patches@gcc.gnu.org; juzhe.zhong@rivai.ai; kito.cheng@sifive.com; Wang, Yanzhang <yanzhang.wang@intel.com>; jeffreyalaw@gmail.com; rguenther@suse.de
Subject: Re: [PATCH] Machine_Mode: Extend machine_mode from 8 to 16 bits

pan2.li@intel.com writes:
> From: Pan Li <pan2.li@intel.com>
>
> We are running out of the machine_mode(8 bits) in RISC-V backend. Thus 
> we would like to extend the machine mode bit size from 8 to 16 bits.
> However, it is sensitive to extend the memory size in common structure 
> like tree or rtx. This patch would like to extend the machine mode 
> bits to 16 bits by shrinking, like:
>
> * Swap the bit size of code and machine code in rtx_def.
> * Reconcile the machine_mode location and spare in tree.
>
> The memory impact of this patch for correlated structure looks like below:
>
> +-------------------+----------+---------+------+
> | struct/bytes      | upstream | patched | diff |
> +-------------------+----------+---------+------+
> | rtx_obj_reference |        8 |      12 |   +4 |
> | ext_modified      |        2 |       3 |   +1 |
> | ira_allocno       |      192 |     200 |   +8 |
> | qty_table_elem    |       40 |      40 |    0 |
> | reg_stat_type     |       64 |      64 |    0 |
> | rtx_def           |       40 |      40 |    0 |
> | table_elt         |       80 |      80 |    0 |
> | tree_decl_common  |      112 |     112 |    0 |
> | tree_type_common  |      128 |     128 |    0 |
> +-------------------+----------+---------+------+
>
> The tree and rtx related struct has no memory changes after this 
> patch, and the machine_mode changes to 16 bits already.
>
> Signed-off-by: Pan Li <pan2.li@intel.com>
> Co-authored-by: Ju-Zhe Zhong <juzhe.zhong@rivai.ai>
> Co-authored-by: Kito Cheng <kito.cheng@sifive.com>
>
> gcc/ChangeLog:
>
> 	* combine.cc (struct reg_stat_type): Extended machine mode to 16 bits.
> 	* cse.cc (struct qty_table_elem): Ditto.
> 	(struct table_elt): Ditto.
> 	(struct set): Ditto.
> 	* genopinit.cc (main): Reconciled the machine mode limit.
> 	* ira-int.h (struct ira_allocno): Extended machine mode to 16 bits.
> 	* ree.cc (struct ATTRIBUTE_PACKED): Ditto.
> 	* rtl-ssa/accesses.h: Ditto.
> 	* rtl.h (RTX_CODE_BITSIZE): New macro.
> 	(RTX_MACHINE_MODE_BITSIZE): Ditto.
> 	(struct GTY): Swap bit size between code and machine mode.
> 	(subreg_shape::unique_id): Reconciled the machine mode limit.
> 	* rtlanal.h: Extended machine mode to 16 bits.
> 	* tree-core.h (struct tree_type_common): Ditto.
> 	(struct tree_decl_common): Reconciled the locate and extended
> 	bit size of machine mode.
> ---
>  gcc/combine.cc         |  4 ++--
>  gcc/cse.cc             |  8 ++++----
>  gcc/genopinit.cc       |  3 ++-
>  gcc/ira-int.h          | 12 ++++++++----
>  gcc/ree.cc             |  2 +-
>  gcc/rtl-ssa/accesses.h |  6 ++++--
>  gcc/rtl.h              |  9 ++++++---
>  gcc/rtlanal.h          |  5 +++--
>  gcc/tree-core.h        | 11 ++++++++---
>  9 files changed, 38 insertions(+), 22 deletions(-)
>
> diff --git a/gcc/combine.cc b/gcc/combine.cc index 
> 5aa0ec5c45a..bdf6f635c80 100644
> --- a/gcc/combine.cc
> +++ b/gcc/combine.cc
> @@ -200,7 +200,7 @@ struct reg_stat_type {
>  
>    unsigned HOST_WIDE_INT	last_set_nonzero_bits;
>    char				last_set_sign_bit_copies;
> -  ENUM_BITFIELD(machine_mode)	last_set_mode : 8;
> +  ENUM_BITFIELD(machine_mode)	last_set_mode : RTX_MACHINE_MODE_BITSIZE;
>  
>    /* Set nonzero if references to register n in expressions should not be
>       used.  last_set_invalid is set nonzero when this register is 
> being @@ -235,7 +235,7 @@ struct reg_stat_type {
>       truncation if we know that value already contains a truncated
>       value.  */
>  
> -  ENUM_BITFIELD(machine_mode)	truncated_to_mode : 8;
> +  ENUM_BITFIELD(machine_mode)	truncated_to_mode : RTX_MACHINE_MODE_BITSIZE;
>  };
>  
>  
> diff --git a/gcc/cse.cc b/gcc/cse.cc
> index b10c9b0c94d..fe594c1bc3d 100644
> --- a/gcc/cse.cc
> +++ b/gcc/cse.cc
> @@ -250,8 +250,8 @@ struct qty_table_elem
>    unsigned int first_reg, last_reg;
>    /* The sizes of these fields should match the sizes of the
>       code and mode fields of struct rtx_def (see rtl.h).  */

The comment can be removed, since you're now adding macros to ensure this (thanks).  Same for other instances of the comment.

> -  ENUM_BITFIELD(rtx_code) comparison_code : 16;
> -  ENUM_BITFIELD(machine_mode) mode : 8;
> +  ENUM_BITFIELD(rtx_code) comparison_code : RTX_CODE_BITSIZE;
> +  ENUM_BITFIELD(machine_mode) mode : RTX_MACHINE_MODE_BITSIZE;

Please put the mode first, so that the 16-bit value is aligned to 16 bits.

>  };
>  
>  /* The table of all qtys, indexed by qty number.  */ @@ -406,7 +406,7 
> @@ struct table_elt
>    int regcost;
>    /* The size of this field should match the size
>       of the mode field of struct rtx_def (see rtl.h).  */
> -  ENUM_BITFIELD(machine_mode) mode : 8;
> +  ENUM_BITFIELD(machine_mode) mode : RTX_MACHINE_MODE_BITSIZE;
>    char in_memory;
>    char is_const;
>    char flag;
> @@ -4155,7 +4155,7 @@ struct set
>    /* Original machine mode, in case it becomes a CONST_INT.
>       The size of this field should match the size of the mode
>       field of struct rtx_def (see rtl.h).  */
> -  ENUM_BITFIELD(machine_mode) mode : 8;
> +  ENUM_BITFIELD(machine_mode) mode : RTX_MACHINE_MODE_BITSIZE;
>    /* Hash value of constant equivalent for SET_SRC.  */
>    unsigned src_const_hash;
>    /* A constant equivalent for SET_SRC, if any.  */ diff --git 
> a/gcc/genopinit.cc b/gcc/genopinit.cc index 83cb7504fa1..2add8b925da 
> 100644
> --- a/gcc/genopinit.cc
> +++ b/gcc/genopinit.cc
> @@ -182,7 +182,8 @@ main (int argc, const char **argv)
>  
>    progname = "genopinit";
>  
> -  if (NUM_OPTABS > 0xffff || MAX_MACHINE_MODE >= 0xff)
> +  if (NUM_OPTABS > 0xffff
> +    || MAX_MACHINE_MODE >= ((1 << RTX_MACHINE_MODE_BITSIZE) - 1))
>      fatal ("genopinit range assumptions invalid");
>  
>    if (!init_rtx_reader_args_cb (argc, argv, handle_arg)) diff --git 
> a/gcc/ira-int.h b/gcc/ira-int.h index e2de47213b4..124e14200b1 100644
> --- a/gcc/ira-int.h
> +++ b/gcc/ira-int.h
> @@ -280,11 +280,15 @@ struct ira_allocno
>    /* Regno for allocno or cap.  */
>    int regno;
>    /* Mode of the allocno which is the mode of the corresponding
> -     pseudo-register.  */
> -  ENUM_BITFIELD (machine_mode) mode : 8;
> +     pseudo-register.  Note the bitsize of mode should be exactly
> +     the same as the definition of rtx_def, aka RTX_MACHINE_MODE_BITSIZE
> +     in rtl.h.  */
> +  ENUM_BITFIELD (machine_mode) mode : 16;
>    /* Widest mode of the allocno which in at least one case could be
> -     for paradoxical subregs where wmode > mode.  */
> -  ENUM_BITFIELD (machine_mode) wmode : 8;
> +     for paradoxical subregs where wmode > mode.  Note the bitsize of
> +     wmode should be exactly the same as the definition of rtx_def,
> +     aka RTX_MACHINE_MODE_BITSIZE in rtl.h.  */  ENUM_BITFIELD 
> + (machine_mode) wmode : 16;
>    /* Register class which should be used for allocation for given
>       allocno.  NO_REGS means that we should use memory.  */
>    ENUM_BITFIELD (reg_class) aclass : 16;

Why not use the BITSIZE macros directly?  Any reasonable use of ira-int.h will also need rtl.h.  If something includes ira-int.h before rtl.h then we should change that.

To avoid growing this structure, please move something into one of the holes later in the structure.  E.g. hard_regno could go before num_objects.

> diff --git a/gcc/ree.cc b/gcc/ree.cc
> index 413aec7c8eb..fb011bc907c 100644
> --- a/gcc/ree.cc
> +++ b/gcc/ree.cc
> @@ -567,7 +567,7 @@ enum ext_modified_kind  struct ATTRIBUTE_PACKED 
> ext_modified  {
>    /* Mode from which ree has zero or sign extended the destination.  
> */
> -  ENUM_BITFIELD(machine_mode) mode : 8;
> +  ENUM_BITFIELD(machine_mode) mode : RTX_MACHINE_MODE_BITSIZE;
>  
>    /* Kind of modification of the insn.  */
>    ENUM_BITFIELD(ext_modified_kind) kind : 2; diff --git 
> a/gcc/rtl-ssa/accesses.h b/gcc/rtl-ssa/accesses.h index 
> c5180b9308a..2e73004cafa 100644
> --- a/gcc/rtl-ssa/accesses.h
> +++ b/gcc/rtl-ssa/accesses.h
> @@ -253,8 +253,10 @@ private:
>    // Bits for future expansion.
>    unsigned int m_spare : 2;
>  
> -  // The value returned by the accessor above.
> -  machine_mode m_mode : 8;
> +  // The value returned by the accessor above.  Note the bitsize of  
> + // m_mode should be exactly the same as the definition of rtx_def,  
> + // aka RTX_MACHINE_MODE_BITSIZE in rtl.h.
> +  machine_mode m_mode : 16;
>  };
>  
>  // A contiguous array of access_info pointers.  Used to represent a 
> diff --git a/gcc/rtl.h b/gcc/rtl.h index f634cab730b..a18ecf7632f 
> 100644
> --- a/gcc/rtl.h
> +++ b/gcc/rtl.h
> @@ -63,6 +63,9 @@ enum rtx_code  {
>  # define NON_GENERATOR_NUM_RTX_CODE ((int) MATCH_OPERAND)  #endif
>  
> +#define RTX_CODE_BITSIZE 8
> +#define RTX_MACHINE_MODE_BITSIZE 16
> +
>  /* Register Transfer Language EXPRESSIONS CODE CLASSES */
>  
>  enum rtx_class  {
> @@ -310,10 +313,10 @@ struct GTY((desc("0"), tag("0"),
>  	    chain_next ("RTX_NEXT (&%h)"),
>  	    chain_prev ("RTX_PREV (&%h)"))) rtx_def {
>    /* The kind of expression this is.  */
> -  ENUM_BITFIELD(rtx_code) code: 16;
> +  ENUM_BITFIELD(rtx_code) code: RTX_CODE_BITSIZE;
>  
>    /* The kind of value the expression has.  */
> -  ENUM_BITFIELD(machine_mode) mode : 8;
> +  ENUM_BITFIELD(machine_mode) mode : RTX_MACHINE_MODE_BITSIZE;

Please swap the fields around, as discussed previously.

>  
>    /* 1 in a MEM if we should keep the alias set for this mem unchanged
>       when we access a component.
> @@ -2164,7 +2167,7 @@ subreg_shape::operator != (const subreg_shape 
> &other) const  inline unsigned HOST_WIDE_INT  subreg_shape::unique_id 
> () const  {
> -  { STATIC_ASSERT (MAX_MACHINE_MODE <= 256); }
> +  { STATIC_ASSERT (MAX_MACHINE_MODE <= (1 << 
> + RTX_MACHINE_MODE_BITSIZE)); }
>    { STATIC_ASSERT (NUM_POLY_INT_COEFFS <= 3); }
>    { STATIC_ASSERT (sizeof (offset.coeffs[0]) <= 2); }
>    int res = (int) inner_mode + ((int) outer_mode << 8); diff --git 
> a/gcc/rtlanal.h b/gcc/rtlanal.h index 5fbed816e20..15aba0dec7a 100644
> --- a/gcc/rtlanal.h
> +++ b/gcc/rtlanal.h
> @@ -99,8 +99,9 @@ public:
>    unsigned int flags : 16;
>  
>    /* The mode of the reference.  If IS_MULTIREG, this is the mode of
> -     REGNO - MULTIREG_OFFSET.  */
> -  machine_mode mode : 8;
> +     REGNO - MULTIREG_OFFSET.  Note the bitsize of mode should be exactly
> +     the same as the definition of rtx_def,  */  machine_mode mode : 
> + 16;
>  
>    /* If IS_MULTIREG, the offset of REGNO from the start of the register.  */
>    unsigned int multireg_offset : 8;

Like with ira-int.h, any reasonable use of rtlanal.h will also need rtl.h, so we should be able to use the BITSIZE macro directly.  Please swap #includes around if necessary.

> diff --git a/gcc/tree-core.h b/gcc/tree-core.h index 
> a1aea136e75..001d232f433 100644
> --- a/gcc/tree-core.h
> +++ b/gcc/tree-core.h
> @@ -1680,8 +1680,11 @@ struct GTY(()) tree_type_common {
>    tree attributes;
>    unsigned int uid;
>  
> +  /* Note the bitsize of wmode should be exactly the same as the
> +     definition of rtx_def,  aka RTX_MACHINE_MODE_BITSIZE in rtl.h.  
> + */
> +  ENUM_BITFIELD(machine_mode) mode : 16;
> +
>    unsigned int precision : 16;
> -  ENUM_BITFIELD(machine_mode) mode : 8;
>    unsigned lang_flag_0 : 1;
>    unsigned lang_flag_1 : 1;
>    unsigned lang_flag_2 : 1;
> @@ -1712,7 +1715,7 @@ struct GTY(()) tree_type_common {
>    unsigned empty_flag : 1;
>    unsigned indivisible_p : 1;
>    unsigned no_named_args_stdarg_p : 1;
> -  unsigned spare : 9;
> +  unsigned spare : 1;
>  
>    alias_set_type alias_set;
>    tree pointer_to;
> @@ -1770,7 +1773,9 @@ struct GTY(()) tree_decl_common {
>    struct tree_decl_minimal common;
>    tree size;
>  
> -  ENUM_BITFIELD(machine_mode) mode : 8;
> +  /* Note the bitsize of wmode should be exactly the same as the
> +     definition of rtx_def,  aka RTX_MACHINE_MODE_BITSIZE in rtl.h.  
> + */
> +  ENUM_BITFIELD(machine_mode) mode : 16;
>  
>    unsigned nonlocal_flag : 1;
>    unsigned virtual_flag : 1;

Please also update:

  /* 13 bits unused.  */

to account for the difference.

Thanks,
Richard