[aarch64] v3: Preparatory patch to place target independent and,dependent changed code in one file

Hello Alex/Richard:

All review comments are addressed.

Common infrastructure of load store pair fusion is divided into target
independent and target dependent changed code.

Target independent code is the Generic code with pure virtual function
to interface betwwen target independent and dependent code.

Target dependent code is the implementation of pure virtual function for
aarch64 target and the call to target independent code.

Bootstrapped on aarch64-linux-gnu.

Thanks & Regards
Ajit



aarch64: Preparatory patch to place target independent and
dependent changed code in one file

Common infrastructure of load store pair fusion is divided into target
independent and target dependent changed code.

Target independent code is the Generic code with pure virtual function
to interface betwwen target independent and dependent code.

Target dependent code is the implementation of pure virtual function for
aarch64 target and the call to target independent code.

2024-05-09  Ajit Kumar Agarwal  <aagarwa1@linux.ibm.com>

gcc/ChangeLog:

	* config/aarch64/aarch64-ldp-fusion.cc: Place target
	independent and dependent changed code.
---
 gcc/config/aarch64/aarch64-ldp-fusion.cc | 542 +++++++++++++++--------
 1 file changed, 363 insertions(+), 179 deletions(-)

Hi Ajit,

Why did you send three mails for this revision of the patch?  If you're
going to send a new revision of the patch you should increment the
version number and outline the changes / reasons for the new revision.

Mostly the comments below are just style nits and things you missed from
the last review(s) (please try not to miss so many in the future).

On 09/05/2024 17:06, Ajit Agarwal wrote:
> Hello Alex/Richard:
> 
> All review comments are addressed.
> 
> Common infrastructure of load store pair fusion is divided into target
> independent and target dependent changed code.
> 
> Target independent code is the Generic code with pure virtual function
> to interface betwwen target independent and dependent code.
> 
> Target dependent code is the implementation of pure virtual function for
> aarch64 target and the call to target independent code.
> 
> Bootstrapped on aarch64-linux-gnu.
> 
> Thanks & Regards
> Ajit
> 
> 
> 
> aarch64: Preparatory patch to place target independent and
> dependent changed code in one file
> 
> Common infrastructure of load store pair fusion is divided into target
> independent and target dependent changed code.
> 
> Target independent code is the Generic code with pure virtual function
> to interface betwwen target independent and dependent code.
> 
> Target dependent code is the implementation of pure virtual function for
> aarch64 target and the call to target independent code.
> 
> 2024-05-09  Ajit Kumar Agarwal  <aagarwa1@linux.ibm.com>
> 
> gcc/ChangeLog:
> 
> 	* config/aarch64/aarch64-ldp-fusion.cc: Place target
> 	independent and dependent changed code.
> ---
>  gcc/config/aarch64/aarch64-ldp-fusion.cc | 542 +++++++++++++++--------
>  1 file changed, 363 insertions(+), 179 deletions(-)
> 
> diff --git a/gcc/config/aarch64/aarch64-ldp-fusion.cc b/gcc/config/aarch64/aarch64-ldp-fusion.cc
> index 1d9caeab05d..217790e111a 100644
> --- a/gcc/config/aarch64/aarch64-ldp-fusion.cc
> +++ b/gcc/config/aarch64/aarch64-ldp-fusion.cc
> @@ -138,6 +138,224 @@ struct alt_base
>    poly_int64 offset;
>  };
>  
> +// Virtual base class for load/store walkers used in alias analysis.
> +struct alias_walker
> +{
> +  virtual bool conflict_p (int &budget) const = 0;
> +  virtual insn_info *insn () const = 0;
> +  virtual bool valid () const = 0;
> +  virtual void advance () = 0;
> +};
> +
> +enum class writeback{

You missed a nit here.  Space before '{'.

> +  ALL,
> +  EXISTING
> +};

You also missed adding comments for the enum, please see the review for v2:
https://gcc.gnu.org/pipermail/gcc-patches/2024-May/651074.html

> +
> +struct pair_fusion {
> +  pair_fusion ()
> +  {
> +    calculate_dominance_info (CDI_DOMINATORS);
> +    df_analyze ();
> +    crtl->ssa = new rtl_ssa::function_info (cfun);
> +  };
> +
> +  // Given:
> +  // - an rtx REG_OP, the non-memory operand in a load/store insn,
> +  // - a machine_mode MEM_MODE, the mode of the MEM in that insn, and
> +  // - a boolean LOAD_P (true iff the insn is a load), then:
> +  // return true if the access should be considered an FP/SIMD access.
> +  // Such accesses are segregated from GPR accesses, since we only want
> +  // to form pairs for accesses that use the same register file.
> +  virtual bool fpsimd_op_p (rtx, machine_mode, bool)
> +  {
> +    return false;
> +  }
> +
> +  // Return true if we should consider forming ldp/stp insns from memory
> +  // accesses with operand mode MODE at this stage in compilation.
> +  virtual bool pair_operand_mode_ok_p (machine_mode mode) = 0;
> +
> +  // Return true iff REG_OP is a suitable register operand for a paired
> +  // memory access, where LOAD_P is true if we're asking about loads and
> +  // false for stores.  MEM_MODE gives the mode of the operand.
> +  virtual bool pair_reg_operand_ok_p (bool load_p, rtx reg_op,
> +				      machine_mode mode) = 0;

The comment needs updating since we changed the name of the last param,
i.e. s/MEM_MODE/MODE/.

> +
> +  // Return alias check limit.
> +  // This is needed to avoid unbounded quadratic behaviour when
> +  // performing alias analysis.
> +  virtual int pair_mem_alias_check_limit () = 0;
> +
> +  // Returns true if we should try to handle writeback opportunities
> +  // (not whether there are any).
> +  virtual bool handle_writeback_opportunities (enum writeback which) = 0 ;

Heh, the bit in parens from the v2 review probably doesn't need to go
into the comment here.

Also you should describe WHICH in the comment.

> +
> +  // Given BASE_MEM, the mem from the lower candidate access for a pair,
> +  // and LOAD_P (true if the access is a load), check if we should proceed
> +  // to form the pair given the target's code generation policy on
> +  // paired accesses.
> +  virtual bool pair_mem_ok_with_policy (rtx first_mem, bool load_p,
> +					machine_mode mode) = 0;

The name of the first param needs updating in the prototype, i.e.
s/first_mem/base_mem/.  I think you missed the bit about dropping the
mode param from the last review.

> +
> +  // Generate the pattern for a paired access. PATS gives the patterns
> +  // for the individual memory accesses (which by this point must share a
> +  // common base register).  If WRITEBACK is non-NULL, then this rtx
> +  // describes the update to the base register that should be performed by
> +  // the resulting insn.  LOAD_P is true iff the accesses are loads.
> +  virtual rtx gen_pair (rtx *pats, rtx writeback,
> +			    bool load_p) = 0;

It doesn't seem like there is a need for the line break between the params.

> +
> +  // Return true if memory writeback can be promoted, given
> +  // insn and load_p is true for load insn otherwise false.

This function isn't about writeback at all, it simply detects existing
paired accesses.  I'm also not convinced it should have a default-false
implementation.  I can see from a pragmatic point of view that it is
currently only called when trying to promote existing pairs into writeback
pairs, so it's not particularly useful for you to implement this for
rs6000 (assuming you don't want to handle writeback opportunities).

In my (lightly held) opinion it would be better to keep this as a pure
virtual function which you (later) implement for rs6000.  If you really
don't want to implement it then I suppose you could put a
gcc_unreachable (); for rs6000 with a comment explaining why it should
never be called (but that would be more brittle in the presence of
changes to the main pass, so it seems worse).

> +  virtual bool pair_mem_insn_p (rtx_insn *, bool &)
> +  {
> +     return false;
> +  }
> +
> +  // if we _should_ track loads.

Heh, the underscores were just for emphasis of the requested change, so
a comment like:

// Return true if we should track loads.

is fine.  Likewise for the store case.

> +  virtual bool track_loads_p ()
> +  {
> +    return true;
> +  }
> +
> +  // if we _should_ track stores.
> +  virtual bool track_stores_p ()
> +  {
> +    return true;
> +  }
> +
> +  // Return true if offset is in of range.
> +  virtual bool pair_mem_in_range_p (HOST_WIDE_INT off) = 0;

"in of range" doesn't make sense, drop the "of".  Also when talking
about parameter values in comments you should name the parameter in
uppercase.  s/offset/off/ for the parameter name is probably better,
too.

> +
> +  // Given a load/store pair insn in PATTERN, unpack the insn, storing
> +  // the register operands in REGS, and returning the mem.
> +  virtual rtx destructure_pair (rtx regs[2], rtx rti, bool load_p) = 0;

s/rti/pattern/ for the second parameter.  You need to describe load_p in
the comment, too.

> +
> +  // This is used when promoting existing non-writeback pairs to writeback
> +  // variants.
> +  virtual rtx gen_promote_writeback_pair (rtx wb_effect, rtx mem,
> +				  rtx regs[2], bool load_p) = 0;

You should describe the parameters in the comment here, too.  I suppose
you can just lift the comment from the implementation of
aarch64_pair_fusion::gen_promote_writeback_pair.

Also the indentation looks off here: I think the the params after each
line break should be indented to the same column as the first param.

> +
> +  virtual bool handle_out_of_range_cases (rtx base) = 0;

When I said (in the review of v2):

> Does this part really apply to rs6000?  Do you have peephole2 patterns for
> lxvp?
> If not you may want to caveat this part as being specific to aarch64.  E.g.
> "On
> aarch64, out-of-range cases ..."

I meant only for you to change the comment, not the code.  Was this an
intentional change to virtualise this bit of code, or did you just
misunderstand my review comment?

> +
> +  void ldp_fusion_bb (bb_info *bb);
> +  inline insn_info *find_trailing_add (insn_info *insns[2],
> +				       const insn_range_info &pair_range,
> +				       int initial_writeback,
> +				       rtx *writeback_effect,
> +				       def_info **add_def,
> +				       def_info *base_def,
> +				       poly_int64 initial_offset,
> +				       unsigned access_size);
> +  inline int get_viable_bases (insn_info *insns[2],
> +			       vec<base_cand> &base_cands,
> +			       rtx cand_mems[2],
> +			       unsigned access_size,
> +			       bool reversed);
> +  inline void do_alias_analysis (insn_info *alias_hazards[4],
> +				 alias_walker *walkers[4],
> +				 bool load_p);
> +  void try_promote_writeback (insn_info *insn, bool load_p);
> +  void run ();

I think these two functions should be marked inline too.

> +  ~pair_fusion()
> +  {
> +    if (crtl->ssa->perform_pending_updates ())
> +      cleanup_cfg (0);
> +
> +    free_dominance_info (CDI_DOMINATORS);
> +
> +    delete crtl->ssa;
> +    crtl->ssa = nullptr;
> +  }
> +};
> +
> +// This is the main function to start the pass.
> +void
> +pair_fusion::run ()
> +{
> +  if (!track_loads_p () && !track_stores_p ())
> +    return;
> +
> +  for (auto bb : crtl->ssa->bbs ())
> +    ldp_fusion_bb (bb);
> +}
> +
> +struct aarch64_pair_fusion : public pair_fusion
> +{
> +  // Before RA, we use the modes, noting that stores of constant zero
> +  // operands use GPRs (even in non-integer modes).  After RA, we use
> +  // the hard register numbers.
> +  bool fpsimd_op_p (rtx reg_op, machine_mode mem_mode,
> +		    bool load_p) override final
> +  {
> +    return reload_completed
> +      ? (REG_P (reg_op) && FP_REGNUM_P (REGNO (reg_op)))
> +      : (GET_MODE_CLASS (mem_mode) != MODE_INT
> +	 && (load_p || !aarch64_const_zero_rtx_p (reg_op)));
> +  }

Nit: I think it would be easier to read with a blank line between each
function body here.

> +  bool pair_mem_insn_p (rtx_insn *rti,
> +			bool &load_p) override final;

It looks like there's no need for the line break here.

> +  bool pair_mem_ok_with_policy (rtx first_mem, bool load_p,
> +				machine_mode mode)

I think this and the remaining functions in this class probably all want
to be marked override final too.

> +  {
> +    return aarch64_mem_ok_with_ldpstp_policy_model (first_mem,
> +						     load_p,
> +						     mode);
> +  }
> +  bool pair_operand_mode_ok_p (machine_mode mode);
> +  rtx gen_pair (rtx *pats, rtx writeback, bool load_p);
> +  bool pair_reg_operand_ok_p (bool load_p, rtx reg_op,
> +			      machine_mode mode)
> +  {
> +    return (load_p
> +	    ? aarch64_ldp_reg_operand (reg_op, mode)
> +	    : aarch64_stp_reg_operand (reg_op, mode));
> +  }
> +  int pair_mem_alias_check_limit ()
> +  {
> +    return aarch64_ldp_alias_check_limit;
> +  }
> +  bool handle_writeback_opportunities (enum writeback which)
> +  {
> +    if (which == writeback::ALL)
> +      return aarch64_ldp_writeback > 1;
> +    else
> +      return aarch64_ldp_writeback;
> +  }
> +  bool track_loads_p ()
> +  {
> +    return aarch64_tune_params.ldp_policy_model
> +	   != AARCH64_LDP_STP_POLICY_NEVER;
> +  }
> +  bool track_stores_p ()
> +  {
> +    return aarch64_tune_params.stp_policy_model
> +	   != AARCH64_LDP_STP_POLICY_NEVER;
> +  }
> +  bool pair_mem_in_range_p (HOST_WIDE_INT off)
> +  {
> +    return (off >= LDP_MIN_IMM && off <= LDP_MAX_IMM);
> +  }
> +  // It's better to punt when we can't be sure that the
> +  // offset is in range for paired access.  Out-of-range cases can then be
> +  // handled after RA by the out-of-range PAIR MEM  peepholes.  Eventually, it
> +  // would be nice to handle known out-of-range opportunities in the
> +  // pass itself (for stack accesses, this would be in the post-RA pass).
> +  bool handle_out_of_range_cases (rtx base)
> +  {
> +    if (!reload_completed
> +	&& (REGNO (base) == FRAME_POINTER_REGNUM
> +	   || REGNO (base) == ARG_POINTER_REGNUM))
> +      return true;
> +
> +    return false;
> +  }
> +  rtx gen_promote_writeback_pair (rtx wb_effect, rtx mem, rtx regs[2],
> +				  bool load_p);

As with the declaration in pair_fusion, the indentation looks off.

> +  rtx destructure_pair (rtx regs[2], rtx rti, bool load_p);
> +};
> +
>  // State used by the pass for a given basic block.
>  struct ldp_bb_info
>  {
> @@ -159,9 +377,10 @@ struct ldp_bb_info
>    hash_map<def_hash, alt_base> canon_base_map;
>  
>    static const size_t obstack_alignment = sizeof (void *);
> -  bb_info *m_bb;
>  
> -  ldp_bb_info (bb_info *bb) : m_bb (bb), m_emitted_tombstone (false)
> +  ldp_bb_info (bb_info *bb,
> +		      pair_fusion *d)
> +		      : m_bb (bb), m_pass (d), m_emitted_tombstone (false)

The indentation is really odd here.  I think the params want to be on
the same line and then the initializer list towards the beginning of a
new line.

>    {
>      obstack_specify_allocation (&m_obstack, OBSTACK_CHUNK_SIZE,
>  				obstack_alignment, obstack_chunk_alloc,
> @@ -181,37 +400,77 @@ struct ldp_bb_info
>    inline void track_access (insn_info *, bool load, rtx mem);
>    inline void transform ();
>    inline void cleanup_tombstones ();
> +  inline void merge_pairs (insn_list_t &, insn_list_t &,
> +		    bool load_p, unsigned access_size);
> +  inline void transform_for_base (int load_size, access_group &group);
> +
> +  inline bool try_fuse_pair (bool load_p, unsigned access_size,
> +			     insn_info *i1, insn_info *i2);
> +
> +  inline bool fuse_pair (bool load_p, unsigned access_size,
> +		  int writeback,
> +		  insn_info *i1, insn_info *i2,
> +		  base_cand &base,
> +		  const insn_range_info &move_range);
> +
> +  inline void track_tombstone (int uid);
> +
> +  inline bool track_via_mem_expr (insn_info *, rtx mem, lfs_fields lfs);

You seem to have ignored my comment about this multiple times now, why
are you changing these member functions from private to public?

>  
>  private:
>    obstack m_obstack;
> -
> +  bb_info *m_bb;
> +  pair_fusion *m_pass;
>    // State for keeping track of tombstone insns emitted for this BB.
>    bitmap_obstack m_bitmap_obstack;
>    bitmap_head m_tombstone_bitmap;
>    bool m_emitted_tombstone;
> -
> -  inline splay_tree_node<access_record *> *node_alloc (access_record *);
> -
>    template<typename Map>
> -  inline void traverse_base_map (Map &map);
> -  inline void transform_for_base (int load_size, access_group &group);
> -
> -  inline void merge_pairs (insn_list_t &, insn_list_t &,
> -			   bool load_p, unsigned access_size);
> +    void traverse_base_map (Map &map);

Why the change in indentation?  Why drop inline?

> +  inline splay_tree_node<access_record *> *node_alloc (access_record *);
> +};
>  
> -  inline bool try_fuse_pair (bool load_p, unsigned access_size,
> -			     insn_info *i1, insn_info *i2);
> +bool
> +aarch64_pair_fusion::pair_mem_insn_p (rtx_insn *rti,
> +				      bool &load_p)
> +{
> +  rtx pat = PATTERN (rti);
> +  if (GET_CODE (pat) == PARALLEL
> +      && XVECLEN (pat, 0) == 2)
> +    {
> +      const auto attr = get_attr_ldpstp (rti);
> +      if (attr == LDPSTP_NONE)
> +	return false;
>  
> -  inline bool fuse_pair (bool load_p, unsigned access_size,
> -			 int writeback,
> -			 insn_info *i1, insn_info *i2,
> -			 base_cand &base,
> -			 const insn_range_info &move_range);
> +      load_p = (attr == LDPSTP_LDP);
> +      gcc_checking_assert (load_p || attr == LDPSTP_STP);
> +      return true;
> +    }
> +  return false;
> +}
>  
> -  inline void track_tombstone (int uid);
> +rtx
> +aarch64_pair_fusion::gen_pair (rtx *pats,
> +			       rtx writeback,
> +			       bool load_p)
> +{
> +  rtx pair_pat;
>  
> -  inline bool track_via_mem_expr (insn_info *, rtx mem, lfs_fields lfs);
> -};
> +  if (writeback)
> +    {
> +      auto patvec = gen_rtvec (3, writeback, pats[0], pats[1]);
> +      return  gen_rtx_PARALLEL (VOIDmode, patvec);
> +    }
> +  else if (load_p)
> +    return aarch64_gen_load_pair (XEXP (pats[0], 0),
> +				  XEXP (pats[1], 0),
> +				  XEXP (pats[0], 1));
> +  else
> +    return aarch64_gen_store_pair (XEXP (pats[0], 0),
> +				   XEXP (pats[0], 1),
> +				   XEXP (pats[1], 1));
> +  return pair_pat;
> +}
>  
>  splay_tree_node<access_record *> *
>  ldp_bb_info::node_alloc (access_record *access)
> @@ -312,8 +571,8 @@ any_post_modify_p (rtx x)
>  
>  // Return true if we should consider forming ldp/stp insns from memory
>  // accesses with operand mode MODE at this stage in compilation.
> -static bool
> -ldp_operand_mode_ok_p (machine_mode mode)
> +bool
> +aarch64_pair_fusion::pair_operand_mode_ok_p (machine_mode mode)
>  {
>    if (!aarch64_ldpstp_operand_mode_p (mode))
>      return false;
> @@ -404,9 +663,10 @@ ldp_bb_info::track_via_mem_expr (insn_info *insn, rtx mem, lfs_fields lfs)
>    const machine_mode mem_mode = GET_MODE (mem);
>    const HOST_WIDE_INT mem_size = GET_MODE_SIZE (mem_mode).to_constant ();
>  
> -  // Punt on misaligned offsets.  LDP/STP instructions require offsets to be a
> -  // multiple of the access size, and we believe that misaligned offsets on
> -  // MEM_EXPR bases are likely to lead to misaligned offsets w.r.t. RTL bases.
> +  // Punt on misaligned offsets.  Paired memory access instructions require
> +  // offsets to be a multiple of the access size, and we believe that
> +  // misaligned offsets on MEM_EXPR bases are likely to lead to misaligned
> +  // offsets w.r.t. RTL bases.
>    if (!multiple_p (offset, mem_size))
>      return false;
>  
> @@ -430,10 +690,10 @@ ldp_bb_info::track_via_mem_expr (insn_info *insn, rtx mem, lfs_fields lfs)
>  }
>  
>  // Main function to begin pair discovery.  Given a memory access INSN,
> -// determine whether it could be a candidate for fusing into an ldp/stp,
> -// and if so, track it in the appropriate data structure for this basic
> -// block.  LOAD_P is true if the access is a load, and MEM is the mem
> -// rtx that occurs in INSN.
> +// determine whether it could be a candidate for fusing into a paired
> +// access, and if so, track it in the appropriate data structure for
> +// this basic block.  LOAD_P is true if the access is a load, and MEM
> +//  is the mem rtx that occurs in INSN.

Nit: excess space at the start of the line.

>  void
>  ldp_bb_info::track_access (insn_info *insn, bool load_p, rtx mem)
>  {
> @@ -441,35 +701,24 @@ ldp_bb_info::track_access (insn_info *insn, bool load_p, rtx mem)
>    if (MEM_VOLATILE_P (mem))
>      return;
>  
> -  // Ignore writeback accesses if the param says to do so.
> -  if (!aarch64_ldp_writeback
> +  // Ignore writeback accesses if the hook says to do so.
> +  if (!m_pass->handle_writeback_opportunities (writeback::EXISTING)
>        && GET_RTX_CLASS (GET_CODE (XEXP (mem, 0))) == RTX_AUTOINC)
>      return;
>  
>    const machine_mode mem_mode = GET_MODE (mem);
> -  if (!ldp_operand_mode_ok_p (mem_mode))
> +  if (!m_pass->pair_operand_mode_ok_p (mem_mode))
>      return;
>  
>    rtx reg_op = XEXP (PATTERN (insn->rtl ()), !load_p);
>  
> -  // Ignore the access if the register operand isn't suitable for ldp/stp.
> -  if (load_p
> -      ? !aarch64_ldp_reg_operand (reg_op, mem_mode)
> -      : !aarch64_stp_reg_operand (reg_op, mem_mode))
> +  if (!m_pass->pair_reg_operand_ok_p (load_p, reg_op, mem_mode))
>      return;
>  
>    // We want to segregate FP/SIMD accesses from GPR accesses.
> -  //
> -  // Before RA, we use the modes, noting that stores of constant zero
> -  // operands use GPRs (even in non-integer modes).  After RA, we use
> -  // the hard register numbers.
> -  const bool fpsimd_op_p
> -    = reload_completed
> -    ? (REG_P (reg_op) && FP_REGNUM_P (REGNO (reg_op)))
> -    : (GET_MODE_CLASS (mem_mode) != MODE_INT
> -       && (load_p || !aarch64_const_zero_rtx_p (reg_op)));
> +  const bool fpsimd_op_p = m_pass->fpsimd_op_p (reg_op, mem_mode, load_p);
>  
> -  // Note ldp_operand_mode_ok_p already rejected VL modes.
> +  // Note pair_operand_mode_ok_p already rejected VL modes.
>    const HOST_WIDE_INT mem_size = GET_MODE_SIZE (mem_mode).to_constant ();
>    const lfs_fields lfs = { load_p, fpsimd_op_p, mem_size };
>  
> @@ -498,8 +747,8 @@ ldp_bb_info::track_access (insn_info *insn, bool load_p, rtx mem)
>    // elimination offset pre-RA, we should postpone forming pairs on such
>    // accesses until after RA.
>    //
> -  // As it stands, addresses with offsets in range for LDR but not
> -  // in range for LDP/STP are currently reloaded inefficiently,
> +  // As it stands, addresses in range for an individual load/store but not
> +  // for a paired access are currently reloaded inefficiently,
>    // ending up with a separate base register for each pair.
>    //
>    // In theory LRA should make use of
> @@ -510,14 +759,7 @@ ldp_bb_info::track_access (insn_info *insn, bool load_p, rtx mem)
>    // constraint; this early return means we never get to the code
>    // that calls targetm.legitimize_address_displacement.
>    //
> -  // So for now, it's better to punt when we can't be sure that the
> -  // offset is in range for LDP/STP.  Out-of-range cases can then be
> -  // handled after RA by the out-of-range LDP/STP peepholes.  Eventually, it
> -  // would be nice to handle known out-of-range opportunities in the
> -  // pass itself (for stack accesses, this would be in the post-RA pass).
> -  if (!reload_completed
> -      && (REGNO (base) == FRAME_POINTER_REGNUM
> -	  || REGNO (base) == ARG_POINTER_REGNUM))
> +  if (m_pass->handle_out_of_range_cases (base))
>      return;
>  
>    // Now need to find def of base register.
> @@ -565,8 +807,8 @@ ldp_bb_info::track_access (insn_info *insn, bool load_p, rtx mem)
>  	gcc_unreachable (); // Base defs should be unique.
>      }
>  
> -  // Punt on misaligned offsets.  LDP/STP require offsets to be a multiple of
> -  // the access size.
> +  // Punt on misaligned offsets.  Paired memory accesses require offsets
> +  // to be a multiple of the access size.
>    if (!multiple_p (mem_off, mem_size))
>      return;
>  
> @@ -1199,8 +1441,8 @@ extract_writebacks (bool load_p, rtx pats[2], int changed)
>  // base register.  If there is one, we choose the first such update after
>  // PAIR_DST that is still in the same BB as our pair.  We return the new def in
>  // *ADD_DEF and the resulting writeback effect in *WRITEBACK_EFFECT.
> -static insn_info *
> -find_trailing_add (insn_info *insns[2],
> +insn_info *
> +pair_fusion::find_trailing_add (insn_info *insns[2],
>  		   const insn_range_info &pair_range,
>  		   int initial_writeback,
>  		   rtx *writeback_effect,
> @@ -1278,7 +1520,7 @@ find_trailing_add (insn_info *insns[2],
>  
>    off_hwi /= access_size;
>  
> -  if (off_hwi < LDP_MIN_IMM || off_hwi > LDP_MAX_IMM)
> +  if (!pair_mem_in_range_p (off_hwi))
>      return nullptr;
>  
>    auto dump_prefix = [&]()
> @@ -1724,8 +1966,8 @@ ldp_bb_info::fuse_pair (bool load_p,
>        rtx change_reg = XEXP (change_pat, !load_p);
>        rtx effective_base = drop_writeback (base_mem);
>        rtx adjusted_addr = plus_constant (Pmode,
> -					 XEXP (effective_base, 0),
> -					 adjust_amt);
> +					XEXP (effective_base, 0),
> +					adjust_amt);

What's this change for?

>        rtx new_mem = replace_equiv_address_nv (change_mem, adjusted_addr);
>        rtx new_set = load_p
>  	? gen_rtx_SET (change_reg, new_mem)
> @@ -1792,7 +2034,7 @@ ldp_bb_info::fuse_pair (bool load_p,
>      {
>        if (dump_file)
>  	fprintf (dump_file,
> -		 "  ldp: i%d has wb but subsequent i%d has non-wb "
> +		 "  load pair: i%d has wb but subsequent i%d has non-wb "
>  		 "update of base (r%d), dropping wb\n",
>  		 insns[0]->uid (), insns[1]->uid (), base_regno);
>        gcc_assert (writeback_effect);
> @@ -1815,7 +2057,7 @@ ldp_bb_info::fuse_pair (bool load_p,
>      }
>  
>    // If either of the original insns had writeback, but the resulting pair insn
> -  // does not (can happen e.g. in the ldp edge case above, or if the writeback
> +  // does not (can happen e.g. in the load pair edge case above, or if the writeback
>    // effects cancel out), then drop the def(s) of the base register as
>    // appropriate.
>    //
> @@ -1834,7 +2076,7 @@ ldp_bb_info::fuse_pair (bool load_p,
>    // update of the base register and try and fold it in to make this into a
>    // writeback pair.
>    insn_info *trailing_add = nullptr;
> -  if (aarch64_ldp_writeback > 1
> +  if (m_pass->handle_writeback_opportunities (writeback::ALL)
>        && !writeback_effect
>        && (!load_p || (!refers_to_regno_p (base_regno, base_regno + 1,
>  					 XEXP (pats[0], 0), nullptr)
> @@ -1842,7 +2084,7 @@ ldp_bb_info::fuse_pair (bool load_p,
>  					     XEXP (pats[1], 0), nullptr))))
>      {
>        def_info *add_def;
> -      trailing_add = find_trailing_add (insns, move_range, writeback,
> +      trailing_add = m_pass->find_trailing_add (insns, move_range, writeback,
>  					&writeback_effect,
>  					&add_def, base.def, offsets[0],
>  					access_size);
> @@ -1855,35 +2097,21 @@ ldp_bb_info::fuse_pair (bool load_p,
>      }
>  
>    // Now that we know what base mem we're going to use, check if it's OK
> -  // with the ldp/stp policy.
> +  // with the pair mem policy.
>    rtx first_mem = XEXP (pats[0], load_p);
> -  if (!aarch64_mem_ok_with_ldpstp_policy_model (first_mem,
> -						load_p,
> -						GET_MODE (first_mem)))
> +  if (!m_pass->pair_mem_ok_with_policy (first_mem,
> +			  load_p,
> +			  GET_MODE (first_mem)))
>      {
>        if (dump_file)
> -	fprintf (dump_file, "punting on pair (%d,%d), ldp/stp policy says no\n",
> +	fprintf (dump_file, "punting on pair (%d,%d), pair mem policy says no\n",
>  		 i1->uid (), i2->uid ());
>        return false;
>      }
>  
>    rtx reg_notes = combine_reg_notes (first, second, load_p);
>  
> -  rtx pair_pat;
> -  if (writeback_effect)
> -    {
> -      auto patvec = gen_rtvec (3, writeback_effect, pats[0], pats[1]);
> -      pair_pat = gen_rtx_PARALLEL (VOIDmode, patvec);
> -    }
> -  else if (load_p)
> -    pair_pat = aarch64_gen_load_pair (XEXP (pats[0], 0),
> -				      XEXP (pats[1], 0),
> -				      XEXP (pats[0], 1));
> -  else
> -    pair_pat = aarch64_gen_store_pair (XEXP (pats[0], 0),
> -				       XEXP (pats[0], 1),
> -				       XEXP (pats[1], 1));
> -
> +  rtx pair_pat = m_pass->gen_pair (pats, writeback_effect, load_p);
>    insn_change *pair_change = nullptr;
>    auto set_pair_pat = [pair_pat,reg_notes](insn_change *change) {
>      rtx_insn *rti = change->insn ()->rtl ();
> @@ -2125,15 +2353,6 @@ load_modified_by_store_p (insn_info *load,
>    return false;
>  }
>  
> -// Virtual base class for load/store walkers used in alias analysis.
> -struct alias_walker
> -{
> -  virtual bool conflict_p (int &budget) const = 0;
> -  virtual insn_info *insn () const = 0;
> -  virtual bool valid () const = 0;
> -  virtual void advance () = 0;
> -};
> -
>  // Implement some common functionality used by both store_walker
>  // and load_walker.
>  template<bool reverse>
> @@ -2251,13 +2470,13 @@ public:
>  //
>  // We try to maintain the invariant that if a walker becomes invalid, we
>  // set its pointer to null.
> -static void
> -do_alias_analysis (insn_info *alias_hazards[4],
> +void
> +pair_fusion::do_alias_analysis (insn_info *alias_hazards[4],
>  		   alias_walker *walkers[4],
>  		   bool load_p)
>  {
>    const int n_walkers = 2 + (2 * !load_p);
> -  int budget = aarch64_ldp_alias_check_limit;
> +  int budget = pair_mem_alias_check_limit ();
>  
>    auto next_walker = [walkers,n_walkers](int current) -> int {
>      for (int j = 1; j <= n_walkers; j++)
> @@ -2342,8 +2561,8 @@ do_alias_analysis (insn_info *alias_hazards[4],
>  //
>  // Returns an integer where bit (1 << i) is set if INSNS[i] uses writeback
>  // addressing.
> -static int
> -get_viable_bases (insn_info *insns[2],
> +int
> +pair_fusion::get_viable_bases (insn_info *insns[2],
>  		  vec<base_cand> &base_cands,
>  		  rtx cand_mems[2],
>  		  unsigned access_size,
> @@ -2389,7 +2608,7 @@ get_viable_bases (insn_info *insns[2],
>        if (!is_lower)
>  	base_off--;
>  
> -      if (base_off < LDP_MIN_IMM || base_off > LDP_MAX_IMM)
> +      if (!pair_mem_in_range_p (base_off))
>  	continue;
>  
>        use_info *use = find_access (insns[i]->uses (), REGNO (base));
> @@ -2446,7 +2665,7 @@ get_viable_bases (insn_info *insns[2],
>  }
>  
>  // Given two adjacent memory accesses of the same size, I1 and I2, try
> -// and see if we can merge them into a ldp or stp.
> +// and see if we can merge them into a paired access.
>  //
>  // ACCESS_SIZE gives the (common) size of a single access, LOAD_P is true
>  // if the accesses are both loads, otherwise they are both stores.
> @@ -2486,7 +2705,7 @@ ldp_bb_info::try_fuse_pair (bool load_p, unsigned access_size,
>      {
>        if (dump_file)
>  	fprintf (dump_file,
> -		 "punting on ldp due to reg conflcits (%d,%d)\n",
> +		 "punting on pair mem load  due to reg conflcits (%d,%d)\n",
>  		 insns[0]->uid (), insns[1]->uid ());
>        return false;
>      }
> @@ -2504,7 +2723,7 @@ ldp_bb_info::try_fuse_pair (bool load_p, unsigned access_size,
>  
>    auto_vec<base_cand, 2> base_cands (2);
>  
> -  int writeback = get_viable_bases (insns, base_cands, cand_mems,
> +  int writeback = m_pass->get_viable_bases (insns, base_cands, cand_mems,
>  				    access_size, reversed);
>    if (base_cands.is_empty ())
>      {
> @@ -2633,7 +2852,7 @@ ldp_bb_info::try_fuse_pair (bool load_p, unsigned access_size,
>      walkers[1] = &backward_store_walker;
>  
>    if (load_p && (mem_defs[0] || mem_defs[1]))
> -    do_alias_analysis (alias_hazards, walkers, load_p);
> +    m_pass->do_alias_analysis (alias_hazards, walkers, load_p);
>    else
>      {
>        // We want to find any loads hanging off the first store.
> @@ -2642,7 +2861,7 @@ ldp_bb_info::try_fuse_pair (bool load_p, unsigned access_size,
>        load_walker<true> backward_load_walker (mem_defs[1], insns[1], insns[0]);
>        walkers[2] = &forward_load_walker;
>        walkers[3] = &backward_load_walker;
> -      do_alias_analysis (alias_hazards, walkers, load_p);
> +      m_pass->do_alias_analysis (alias_hazards, walkers, load_p);
>        // Now consolidate hazards back down.
>        if (alias_hazards[2]
>  	  && (!alias_hazards[0] || (*alias_hazards[2] < *alias_hazards[0])))
> @@ -2956,26 +3175,6 @@ ldp_bb_info::transform ()
>    traverse_base_map (def_map);
>  }
>  
> -static void
> -ldp_fusion_init ()
> -{
> -  calculate_dominance_info (CDI_DOMINATORS);
> -  df_analyze ();
> -  crtl->ssa = new rtl_ssa::function_info (cfun);
> -}
> -
> -static void
> -ldp_fusion_destroy ()
> -{
> -  if (crtl->ssa->perform_pending_updates ())
> -    cleanup_cfg (0);
> -
> -  free_dominance_info (CDI_DOMINATORS);
> -
> -  delete crtl->ssa;
> -  crtl->ssa = nullptr;
> -}
> -
>  // Given a load pair insn in PATTERN, unpack the insn, storing
>  // the registers in REGS and returning the mem.
>  static rtx
> @@ -3015,6 +3214,15 @@ aarch64_destructure_store_pair (rtx regs[2], rtx pattern)
>    return mem;
>  }
>  
> +rtx
> +aarch64_pair_fusion::destructure_pair (rtx regs[2], rtx rti, bool load_p)
> +{
> +  if (load_p)
> +    return aarch64_destructure_load_pair (regs, rti);
> +  else
> +    return aarch64_destructure_store_pair (regs, rti);
> +}
> +
>  // Given a pair mem in PAIR_MEM, register operands in REGS, and an rtx
>  // representing the effect of writeback on the base register in WB_EFFECT,
>  // return an insn representing a writeback variant of this pair.
> @@ -3022,9 +3230,10 @@ aarch64_destructure_store_pair (rtx regs[2], rtx pattern)
>  //
>  // This is used when promoting existing non-writeback pairs to writeback
>  // variants.
> -static rtx
> -aarch64_gen_writeback_pair (rtx wb_effect, rtx pair_mem, rtx regs[2],
> -			    bool load_p)
> +rtx
> +aarch64_pair_fusion::gen_promote_writeback_pair (rtx wb_effect, rtx pair_mem,
> +						 rtx regs[2],
> +						 bool load_p)
>  {
>    auto op_mode = aarch64_operand_mode_for_pair_mode (GET_MODE (pair_mem));
>  
> @@ -3059,23 +3268,14 @@ aarch64_gen_writeback_pair (rtx wb_effect, rtx pair_mem, rtx regs[2],
>  // Given an existing pair insn INSN, look for a trailing update of
>  // the base register which we can fold in to make this pair use
>  // a writeback addressing mode.
> -static void
> -try_promote_writeback (insn_info *insn)
> +void
> +pair_fusion::try_promote_writeback (insn_info *insn, bool load_p)
>  {
> -  auto rti = insn->rtl ();
> -  const auto attr = get_attr_ldpstp (rti);
> -  if (attr == LDPSTP_NONE)
> -    return;
> -
> -  bool load_p = (attr == LDPSTP_LDP);
> -  gcc_checking_assert (load_p || attr == LDPSTP_STP);
> -
>    rtx regs[2];
>    rtx mem = NULL_RTX;
> -  if (load_p)
> -    mem = aarch64_destructure_load_pair (regs, PATTERN (rti));
> -  else
> -    mem = aarch64_destructure_store_pair (regs, PATTERN (rti));
> +
> +  mem = destructure_pair (regs, PATTERN (insn->rtl ()), load_p);
> +

Nit: no need for a blank line here?

>    gcc_checking_assert (MEM_P (mem));
>  
>    poly_int64 offset;
> @@ -3112,9 +3312,10 @@ try_promote_writeback (insn_info *insn)
>    def_info *add_def;
>    const insn_range_info pair_range (insn);
>    insn_info *insns[2] = { nullptr, insn };
> -  insn_info *trailing_add = find_trailing_add (insns, pair_range, 0, &wb_effect,
> -					       &add_def, base_def, offset,
> -					       access_size);
> +  insn_info *trailing_add
> +    = find_trailing_add (insns, pair_range, 0, &wb_effect,
> +			 &add_def, base_def, offset,
> +			 access_size);
>    if (!trailing_add)
>      return;
>  
> @@ -3124,8 +3325,10 @@ try_promote_writeback (insn_info *insn)
>    insn_change del_change (trailing_add, insn_change::DELETE);
>    insn_change *changes[] = { &pair_change, &del_change };
>  
> -  rtx pair_pat = aarch64_gen_writeback_pair (wb_effect, mem, regs, load_p);
> -  validate_unshare_change (rti, &PATTERN (rti), pair_pat, true);
> +  rtx pair_pat = gen_promote_writeback_pair (wb_effect, mem, regs,
> +					     load_p);
> +  validate_unshare_change (insn->rtl(), &PATTERN (insn->rtl()), pair_pat,
> +			   true);
>  
>    // The pair must gain the def of the base register from the add.
>    pair_change.new_defs = insert_access (attempt,
> @@ -3159,14 +3362,12 @@ try_promote_writeback (insn_info *insn)
>  // for load/store candidates.  If running after RA, also try and promote
>  // non-writeback pairs to use writeback addressing.  Then try to fuse
>  // candidates into pairs.
> -void ldp_fusion_bb (bb_info *bb)
> +void pair_fusion::ldp_fusion_bb (bb_info *bb)
>  {
> -  const bool track_loads
> -    = aarch64_tune_params.ldp_policy_model != AARCH64_LDP_STP_POLICY_NEVER;
> -  const bool track_stores
> -    = aarch64_tune_params.stp_policy_model != AARCH64_LDP_STP_POLICY_NEVER;
> +  const bool track_loads = track_loads_p ();
> +  const bool track_stores = track_stores_p ();
>  
> -  ldp_bb_info bb_state (bb);
> +  ldp_bb_info bb_state (bb, this);
>  
>    for (auto insn : bb->nondebug_insns ())
>      {
> @@ -3176,11 +3377,11 @@ void ldp_fusion_bb (bb_info *bb)
>  	continue;
>  
>        rtx pat = PATTERN (rti);
> +      bool load_p;
>        if (reload_completed
> -	  && aarch64_ldp_writeback > 1
> -	  && GET_CODE (pat) == PARALLEL
> -	  && XVECLEN (pat, 0) == 2)
> -	try_promote_writeback (insn);
> +	  && handle_writeback_opportunities (writeback::ALL)
> +	  && pair_mem_insn_p (rti, load_p))
> +	try_promote_writeback (insn, load_p);
>  
>        if (GET_CODE (pat) != SET)
>  	continue;
> @@ -3195,16 +3396,6 @@ void ldp_fusion_bb (bb_info *bb)
>    bb_state.cleanup_tombstones ();
>  }
>  
> -void ldp_fusion ()
> -{
> -  ldp_fusion_init ();
> -
> -  for (auto bb : crtl->ssa->bbs ())
> -    ldp_fusion_bb (bb);
> -
> -  ldp_fusion_destroy ();
> -}
> -
>  namespace {
>  
>  const pass_data pass_data_ldp_fusion =
> @@ -3234,14 +3425,6 @@ public:
>        if (!optimize || optimize_debug)
>  	return false;
>  
> -      // If the tuning policy says never to form ldps or stps, don't run
> -      // the pass.
> -      if ((aarch64_tune_params.ldp_policy_model
> -	   == AARCH64_LDP_STP_POLICY_NEVER)
> -	  && (aarch64_tune_params.stp_policy_model
> -	      == AARCH64_LDP_STP_POLICY_NEVER))
> -	return false;
> -
>        if (reload_completed)
>  	return flag_aarch64_late_ldp_fusion;
>        else
> @@ -3250,7 +3433,8 @@ public:
>  
>    unsigned execute (function *) final override
>      {
> -      ldp_fusion ();
> +      aarch64_pair_fusion pass;
> +      pass.run ();
>        return 0;
>      }
>  };
> -- 
> 2.39.3
> 

Thanks,
Alex

Hello Alex:

On 13/05/24 8:49 pm, Alex Coplan wrote:
> Hi Ajit,
> 
> Why did you send three mails for this revision of the patch?  If you're
> going to send a new revision of the patch you should increment the
> version number and outline the changes / reasons for the new revision.
> 

There were issues sending the patch through thunderbird, hence multople
pacthes. Sorry for inconvenience caused.

> Mostly the comments below are just style nits and things you missed from
> the last review(s) (please try not to miss so many in the future).
>

Addressed.
 
> On 09/05/2024 17:06, Ajit Agarwal wrote:
>> Hello Alex/Richard:
>>
>> All review comments are addressed.
>>
>> Common infrastructure of load store pair fusion is divided into target
>> independent and target dependent changed code.
>>
>> Target independent code is the Generic code with pure virtual function
>> to interface betwwen target independent and dependent code.
>>
>> Target dependent code is the implementation of pure virtual function for
>> aarch64 target and the call to target independent code.
>>
>> Bootstrapped on aarch64-linux-gnu.
>>
>> Thanks & Regards
>> Ajit
>>
>>
>>
>> aarch64: Preparatory patch to place target independent and
>> dependent changed code in one file
>>
>> Common infrastructure of load store pair fusion is divided into target
>> independent and target dependent changed code.
>>
>> Target independent code is the Generic code with pure virtual function
>> to interface betwwen target independent and dependent code.
>>
>> Target dependent code is the implementation of pure virtual function for
>> aarch64 target and the call to target independent code.
>>
>> 2024-05-09  Ajit Kumar Agarwal  <aagarwa1@linux.ibm.com>
>>
>> gcc/ChangeLog:
>>
>> 	* config/aarch64/aarch64-ldp-fusion.cc: Place target
>> 	independent and dependent changed code.
>> ---
>>  gcc/config/aarch64/aarch64-ldp-fusion.cc | 542 +++++++++++++++--------
>>  1 file changed, 363 insertions(+), 179 deletions(-)
>>
>> diff --git a/gcc/config/aarch64/aarch64-ldp-fusion.cc b/gcc/config/aarch64/aarch64-ldp-fusion.cc
>> index 1d9caeab05d..217790e111a 100644
>> --- a/gcc/config/aarch64/aarch64-ldp-fusion.cc
>> +++ b/gcc/config/aarch64/aarch64-ldp-fusion.cc
>> @@ -138,6 +138,224 @@ struct alt_base
>>    poly_int64 offset;
>>  };
>>  
>> +// Virtual base class for load/store walkers used in alias analysis.
>> +struct alias_walker
>> +{
>> +  virtual bool conflict_p (int &budget) const = 0;
>> +  virtual insn_info *insn () const = 0;
>> +  virtual bool valid () const = 0;
>> +  virtual void advance () = 0;
>> +};
>> +
>> +enum class writeback{
> 
> You missed a nit here.  Space before '{'.
> 

Addressed.
>> +  ALL,
>> +  EXISTING
>> +};
> 
> You also missed adding comments for the enum, please see the review for v2:
> https://gcc.gnu.org/pipermail/gcc-patches/2024-May/651074.html
> 

Addressed.
>> +
>> +struct pair_fusion {
>> +  pair_fusion ()
>> +  {
>> +    calculate_dominance_info (CDI_DOMINATORS);
>> +    df_analyze ();
>> +    crtl->ssa = new rtl_ssa::function_info (cfun);
>> +  };
>> +
>> +  // Given:
>> +  // - an rtx REG_OP, the non-memory operand in a load/store insn,
>> +  // - a machine_mode MEM_MODE, the mode of the MEM in that insn, and
>> +  // - a boolean LOAD_P (true iff the insn is a load), then:
>> +  // return true if the access should be considered an FP/SIMD access.
>> +  // Such accesses are segregated from GPR accesses, since we only want
>> +  // to form pairs for accesses that use the same register file.
>> +  virtual bool fpsimd_op_p (rtx, machine_mode, bool)
>> +  {
>> +    return false;
>> +  }
>> +
>> +  // Return true if we should consider forming ldp/stp insns from memory
>> +  // accesses with operand mode MODE at this stage in compilation.
>> +  virtual bool pair_operand_mode_ok_p (machine_mode mode) = 0;
>> +
>> +  // Return true iff REG_OP is a suitable register operand for a paired
>> +  // memory access, where LOAD_P is true if we're asking about loads and
>> +  // false for stores.  MEM_MODE gives the mode of the operand.
>> +  virtual bool pair_reg_operand_ok_p (bool load_p, rtx reg_op,
>> +				      machine_mode mode) = 0;
> 
> The comment needs updating since we changed the name of the last param,
> i.e. s/MEM_MODE/MODE/.
> 
Addressed.
>> +
>> +  // Return alias check limit.
>> +  // This is needed to avoid unbounded quadratic behaviour when
>> +  // performing alias analysis.
>> +  virtual int pair_mem_alias_check_limit () = 0;
>> +
>> +  // Returns true if we should try to handle writeback opportunities
>> +  // (not whether there are any).
>> +  virtual bool handle_writeback_opportunities (enum writeback which) = 0 ;
> 
> Heh, the bit in parens from the v2 review probably doesn't need to go
> into the comment here.
> 
> Also you should describe WHICH in the comment.
> 
>> +
>> +  // Given BASE_MEM, the mem from the lower candidate access for a pair,
>> +  // and LOAD_P (true if the access is a load), check if we should proceed
>> +  // to form the pair given the target's code generation policy on
>> +  // paired accesses.
>> +  virtual bool pair_mem_ok_with_policy (rtx first_mem, bool load_p,
>> +					machine_mode mode) = 0;
> 
> The name of the first param needs updating in the prototype, i.e.
> s/first_mem/base_mem/.  I think you missed the bit about dropping the
> mode param from the last review.
> 
>> +
>> +  // Generate the pattern for a paired access. PATS gives the patterns
>> +  // for the individual memory accesses (which by this point must share a
>> +  // common base register).  If WRITEBACK is non-NULL, then this rtx
>> +  // describes the update to the base register that should be performed by
>> +  // the resulting insn.  LOAD_P is true iff the accesses are loads.
>> +  virtual rtx gen_pair (rtx *pats, rtx writeback,
>> +			    bool load_p) = 0;
> 
> It doesn't seem like there is a need for the line break between the params.
> 

Addressed.
>> +
>> +  // Return true if memory writeback can be promoted, given
>> +  // insn and load_p is true for load insn otherwise false.
> 
> This function isn't about writeback at all, it simply detects existing
> paired accesses.  I'm also not convinced it should have a default-false
> implementation.  I can see from a pragmatic point of view that it is
> currently only called when trying to promote existing pairs into writeback
> pairs, so it's not particularly useful for you to implement this for
> rs6000 (assuming you don't want to handle writeback opportunities).
> 
> In my (lightly held) opinion it would be better to keep this as a pure
> virtual function which you (later) implement for rs6000.  If you really
> don't want to implement it then I suppose you could put a
> gcc_unreachable (); for rs6000 with a comment explaining why it should
> never be called (but that would be more brittle in the presence of
> changes to the main pass, so it seems worse).
> 
>> +  virtual bool pair_mem_insn_p (rtx_insn *, bool &)
>> +  {
>> +     return false;
>> +  }
>> +
>> +  // if we _should_ track loads.
> 

Addressed.
> Heh, the underscores were just for emphasis of the requested change, so
> a comment like:
> 
> // Return true if we should track loads.
> 
> is fine.  Likewise for the store case.
> 

Adressed,
>> +  virtual bool track_loads_p ()
>> +  {
>> +    return true;
>> +  }
>> +
>> +  // if we _should_ track stores.
>> +  virtual bool track_stores_p ()
>> +  {
>> +    return true;
>> +  }
>> +
>> +  // Return true if offset is in of range.
>> +  virtual bool pair_mem_in_range_p (HOST_WIDE_INT off) = 0;
> 
> "in of range" doesn't make sense, drop the "of".  Also when talking
> about parameter values in comments you should name the parameter in
> uppercase.  s/offset/off/ for the parameter name is probably better,
> too.
> 
>> +
>> +  // Given a load/store pair insn in PATTERN, unpack the insn, storing
>> +  // the register operands in REGS, and returning the mem.
>> +  virtual rtx destructure_pair (rtx regs[2], rtx rti, bool load_p) = 0;
> 
> s/rti/pattern/ for the second parameter.  You need to describe load_p in
> the comment, too.
> 

Addressed.
>> +
>> +  // This is used when promoting existing non-writeback pairs to writeback
>> +  // variants.
>> +  virtual rtx gen_promote_writeback_pair (rtx wb_effect, rtx mem,
>> +				  rtx regs[2], bool load_p) = 0;
> 
> You should describe the parameters in the comment here, too.  I suppose
> you can just lift the comment from the implementation of
> aarch64_pair_fusion::gen_promote_writeback_pair.
> 
> Also the indentation looks off here: I think the the params after each
> line break should be indented to the same column as the first param.
> 
>> +
>> +  virtual bool handle_out_of_range_cases (rtx base) = 0;
> 
> When I said (in the review of v2):
> 

Addressed.
>> Does this part really apply to rs6000?  Do you have peephole2 patterns for
>> lxvp?
>> If not you may want to caveat this part as being specific to aarch64.  E.g.
>> "On
>> aarch64, out-of-range cases ..."
> 
> I meant only for you to change the comment, not the code.  Was this an
> intentional change to virtualise this bit of code, or did you just
> misunderstand my review comment?
>

I have misunderstood. Addressed.
 
>> +
>> +  void ldp_fusion_bb (bb_info *bb);
>> +  inline insn_info *find_trailing_add (insn_info *insns[2],
>> +				       const insn_range_info &pair_range,
>> +				       int initial_writeback,
>> +				       rtx *writeback_effect,
>> +				       def_info **add_def,
>> +				       def_info *base_def,
>> +				       poly_int64 initial_offset,
>> +				       unsigned access_size);
>> +  inline int get_viable_bases (insn_info *insns[2],
>> +			       vec<base_cand> &base_cands,
>> +			       rtx cand_mems[2],
>> +			       unsigned access_size,
>> +			       bool reversed);
>> +  inline void do_alias_analysis (insn_info *alias_hazards[4],
>> +				 alias_walker *walkers[4],
>> +				 bool load_p);
>> +  void try_promote_writeback (insn_info *insn, bool load_p);
>> +  void run ();
> 
> I think these two functions should be marked inline too.
> 
>> +  ~pair_fusion()
>> +  {
>> +    if (crtl->ssa->perform_pending_updates ())
>> +      cleanup_cfg (0);
>> +
>> +    free_dominance_info (CDI_DOMINATORS);
>> +
>> +    delete crtl->ssa;
>> +    crtl->ssa = nullptr;
>> +  }
>> +};
>> +
>> +// This is the main function to start the pass.
>> +void
>> +pair_fusion::run ()
>> +{
>> +  if (!track_loads_p () && !track_stores_p ())
>> +    return;
>> +
>> +  for (auto bb : crtl->ssa->bbs ())
>> +    ldp_fusion_bb (bb);
>> +}
>> +
>> +struct aarch64_pair_fusion : public pair_fusion
>> +{
>> +  // Before RA, we use the modes, noting that stores of constant zero
>> +  // operands use GPRs (even in non-integer modes).  After RA, we use
>> +  // the hard register numbers.
>> +  bool fpsimd_op_p (rtx reg_op, machine_mode mem_mode,
>> +		    bool load_p) override final
>> +  {
>> +    return reload_completed
>> +      ? (REG_P (reg_op) && FP_REGNUM_P (REGNO (reg_op)))
>> +      : (GET_MODE_CLASS (mem_mode) != MODE_INT
>> +	 && (load_p || !aarch64_const_zero_rtx_p (reg_op)));
>> +  }
> 
> Nit: I think it would be easier to read with a blank line between each
> function body here.
> 

Addressed.
>> +  bool pair_mem_insn_p (rtx_insn *rti,
>> +			bool &load_p) override final;
> 
> It looks like there's no need for the line break here.
> 
>> +  bool pair_mem_ok_with_policy (rtx first_mem, bool load_p,
>> +				machine_mode mode)
> 
> I think this and the remaining functions in this class probably all want
> to be marked override final too.
> 
>> +  {
>> +    return aarch64_mem_ok_with_ldpstp_policy_model (first_mem,
>> +						     load_p,
>> +						     mode);
>> +  }
>> +  bool pair_operand_mode_ok_p (machine_mode mode);
>> +  rtx gen_pair (rtx *pats, rtx writeback, bool load_p);
>> +  bool pair_reg_operand_ok_p (bool load_p, rtx reg_op,
>> +			      machine_mode mode)
>> +  {
>> +    return (load_p
>> +	    ? aarch64_ldp_reg_operand (reg_op, mode)
>> +	    : aarch64_stp_reg_operand (reg_op, mode));
>> +  }
>> +  int pair_mem_alias_check_limit ()
>> +  {
>> +    return aarch64_ldp_alias_check_limit;
>> +  }
>> +  bool handle_writeback_opportunities (enum writeback which)
>> +  {
>> +    if (which == writeback::ALL)
>> +      return aarch64_ldp_writeback > 1;
>> +    else
>> +      return aarch64_ldp_writeback;
>> +  }
>> +  bool track_loads_p ()
>> +  {
>> +    return aarch64_tune_params.ldp_policy_model
>> +	   != AARCH64_LDP_STP_POLICY_NEVER;
>> +  }
>> +  bool track_stores_p ()
>> +  {
>> +    return aarch64_tune_params.stp_policy_model
>> +	   != AARCH64_LDP_STP_POLICY_NEVER;
>> +  }
>> +  bool pair_mem_in_range_p (HOST_WIDE_INT off)
>> +  {
>> +    return (off >= LDP_MIN_IMM && off <= LDP_MAX_IMM);
>> +  }
>> +  // It's better to punt when we can't be sure that the
>> +  // offset is in range for paired access.  Out-of-range cases can then be
>> +  // handled after RA by the out-of-range PAIR MEM  peepholes.  Eventually, it
>> +  // would be nice to handle known out-of-range opportunities in the
>> +  // pass itself (for stack accesses, this would be in the post-RA pass).
>> +  bool handle_out_of_range_cases (rtx base)
>> +  {
>> +    if (!reload_completed
>> +	&& (REGNO (base) == FRAME_POINTER_REGNUM
>> +	   || REGNO (base) == ARG_POINTER_REGNUM))
>> +      return true;
>> +
>> +    return false;
>> +  }
>> +  rtx gen_promote_writeback_pair (rtx wb_effect, rtx mem, rtx regs[2],
>> +				  bool load_p);
> 
> As with the declaration in pair_fusion, the indentation looks off.
> 

Addressed.
>> +  rtx destructure_pair (rtx regs[2], rtx rti, bool load_p);
>> +};
>> +
>>  // State used by the pass for a given basic block.
>>  struct ldp_bb_info
>>  {
>> @@ -159,9 +377,10 @@ struct ldp_bb_info
>>    hash_map<def_hash, alt_base> canon_base_map;
>>  
>>    static const size_t obstack_alignment = sizeof (void *);
>> -  bb_info *m_bb;
>>  
>> -  ldp_bb_info (bb_info *bb) : m_bb (bb), m_emitted_tombstone (false)
>> +  ldp_bb_info (bb_info *bb,
>> +		      pair_fusion *d)
>> +		      : m_bb (bb), m_pass (d), m_emitted_tombstone (false)
> 
> The indentation is really odd here.  I think the params want to be on
> the same line and then the initializer list towards the beginning of a
> new line.
> 
>>    {
>>      obstack_specify_allocation (&m_obstack, OBSTACK_CHUNK_SIZE,
>>  				obstack_alignment, obstack_chunk_alloc,
>> @@ -181,37 +400,77 @@ struct ldp_bb_info
>>    inline void track_access (insn_info *, bool load, rtx mem);
>>    inline void transform ();
>>    inline void cleanup_tombstones ();
>> +  inline void merge_pairs (insn_list_t &, insn_list_t &,
>> +		    bool load_p, unsigned access_size);
>> +  inline void transform_for_base (int load_size, access_group &group);
>> +
>> +  inline bool try_fuse_pair (bool load_p, unsigned access_size,
>> +			     insn_info *i1, insn_info *i2);
>> +
>> +  inline bool fuse_pair (bool load_p, unsigned access_size,
>> +		  int writeback,
>> +		  insn_info *i1, insn_info *i2,
>> +		  base_cand &base,
>> +		  const insn_range_info &move_range);
>> +
>> +  inline void track_tombstone (int uid);
>> +
>> +  inline bool track_via_mem_expr (insn_info *, rtx mem, lfs_fields lfs);
> 
> You seem to have ignored my comment about this multiple times now, why
> are you changing these member functions from private to public?
> 
>>  
>>  private:
>>    obstack m_obstack;
>> -
>> +  bb_info *m_bb;
>> +  pair_fusion *m_pass;
>>    // State for keeping track of tombstone insns emitted for this BB.
>>    bitmap_obstack m_bitmap_obstack;
>>    bitmap_head m_tombstone_bitmap;
>>    bool m_emitted_tombstone;
>> -
>> -  inline splay_tree_node<access_record *> *node_alloc (access_record *);
>> -
>>    template<typename Map>
>> -  inline void traverse_base_map (Map &map);
>> -  inline void transform_for_base (int load_size, access_group &group);
>> -
>> -  inline void merge_pairs (insn_list_t &, insn_list_t &,
>> -			   bool load_p, unsigned access_size);
>> +    void traverse_base_map (Map &map);
> 
> Why the change in indentation?  Why drop inline?
> 
>> +  inline splay_tree_node<access_record *> *node_alloc (access_record *);
>> +};
>>  
>> -  inline bool try_fuse_pair (bool load_p, unsigned access_size,
>> -			     insn_info *i1, insn_info *i2);
>> +bool
>> +aarch64_pair_fusion::pair_mem_insn_p (rtx_insn *rti,
>> +				      bool &load_p)
>> +{
>> +  rtx pat = PATTERN (rti);
>> +  if (GET_CODE (pat) == PARALLEL
>> +      && XVECLEN (pat, 0) == 2)
>> +    {
>> +      const auto attr = get_attr_ldpstp (rti);
>> +      if (attr == LDPSTP_NONE)
>> +	return false;
>>  
>> -  inline bool fuse_pair (bool load_p, unsigned access_size,
>> -			 int writeback,
>> -			 insn_info *i1, insn_info *i2,
>> -			 base_cand &base,
>> -			 const insn_range_info &move_range);
>> +      load_p = (attr == LDPSTP_LDP);
>> +      gcc_checking_assert (load_p || attr == LDPSTP_STP);
>> +      return true;
>> +    }
>> +  return false;
>> +}
>>  
>> -  inline void track_tombstone (int uid);
>> +rtx
>> +aarch64_pair_fusion::gen_pair (rtx *pats,
>> +			       rtx writeback,
>> +			       bool load_p)
>> +{
>> +  rtx pair_pat;
>>  
>> -  inline bool track_via_mem_expr (insn_info *, rtx mem, lfs_fields lfs);
>> -};
>> +  if (writeback)
>> +    {
>> +      auto patvec = gen_rtvec (3, writeback, pats[0], pats[1]);
>> +      return  gen_rtx_PARALLEL (VOIDmode, patvec);
>> +    }
>> +  else if (load_p)
>> +    return aarch64_gen_load_pair (XEXP (pats[0], 0),
>> +				  XEXP (pats[1], 0),
>> +				  XEXP (pats[0], 1));
>> +  else
>> +    return aarch64_gen_store_pair (XEXP (pats[0], 0),
>> +				   XEXP (pats[0], 1),
>> +				   XEXP (pats[1], 1));
>> +  return pair_pat;
>> +}
>>  
>>  splay_tree_node<access_record *> *
>>  ldp_bb_info::node_alloc (access_record *access)
>> @@ -312,8 +571,8 @@ any_post_modify_p (rtx x)
>>  
>>  // Return true if we should consider forming ldp/stp insns from memory
>>  // accesses with operand mode MODE at this stage in compilation.
>> -static bool
>> -ldp_operand_mode_ok_p (machine_mode mode)
>> +bool
>> +aarch64_pair_fusion::pair_operand_mode_ok_p (machine_mode mode)
>>  {
>>    if (!aarch64_ldpstp_operand_mode_p (mode))
>>      return false;
>> @@ -404,9 +663,10 @@ ldp_bb_info::track_via_mem_expr (insn_info *insn, rtx mem, lfs_fields lfs)
>>    const machine_mode mem_mode = GET_MODE (mem);
>>    const HOST_WIDE_INT mem_size = GET_MODE_SIZE (mem_mode).to_constant ();
>>  
>> -  // Punt on misaligned offsets.  LDP/STP instructions require offsets to be a
>> -  // multiple of the access size, and we believe that misaligned offsets on
>> -  // MEM_EXPR bases are likely to lead to misaligned offsets w.r.t. RTL bases.
>> +  // Punt on misaligned offsets.  Paired memory access instructions require
>> +  // offsets to be a multiple of the access size, and we believe that
>> +  // misaligned offsets on MEM_EXPR bases are likely to lead to misaligned
>> +  // offsets w.r.t. RTL bases.
>>    if (!multiple_p (offset, mem_size))
>>      return false;
>>  
>> @@ -430,10 +690,10 @@ ldp_bb_info::track_via_mem_expr (insn_info *insn, rtx mem, lfs_fields lfs)
>>  }
>>  
>>  // Main function to begin pair discovery.  Given a memory access INSN,
>> -// determine whether it could be a candidate for fusing into an ldp/stp,
>> -// and if so, track it in the appropriate data structure for this basic
>> -// block.  LOAD_P is true if the access is a load, and MEM is the mem
>> -// rtx that occurs in INSN.
>> +// determine whether it could be a candidate for fusing into a paired
>> +// access, and if so, track it in the appropriate data structure for
>> +// this basic block.  LOAD_P is true if the access is a load, and MEM
>> +//  is the mem rtx that occurs in INSN.
> 
> Nit: excess space at the start of the line.
> 

Addressed.
>>  void
>>  ldp_bb_info::track_access (insn_info *insn, bool load_p, rtx mem)
>>  {
>> @@ -441,35 +701,24 @@ ldp_bb_info::track_access (insn_info *insn, bool load_p, rtx mem)
>>    if (MEM_VOLATILE_P (mem))
>>      return;
>>  
>> -  // Ignore writeback accesses if the param says to do so.
>> -  if (!aarch64_ldp_writeback
>> +  // Ignore writeback accesses if the hook says to do so.
>> +  if (!m_pass->handle_writeback_opportunities (writeback::EXISTING)
>>        && GET_RTX_CLASS (GET_CODE (XEXP (mem, 0))) == RTX_AUTOINC)
>>      return;
>>  
>>    const machine_mode mem_mode = GET_MODE (mem);
>> -  if (!ldp_operand_mode_ok_p (mem_mode))
>> +  if (!m_pass->pair_operand_mode_ok_p (mem_mode))
>>      return;
>>  
>>    rtx reg_op = XEXP (PATTERN (insn->rtl ()), !load_p);
>>  
>> -  // Ignore the access if the register operand isn't suitable for ldp/stp.
>> -  if (load_p
>> -      ? !aarch64_ldp_reg_operand (reg_op, mem_mode)
>> -      : !aarch64_stp_reg_operand (reg_op, mem_mode))
>> +  if (!m_pass->pair_reg_operand_ok_p (load_p, reg_op, mem_mode))
>>      return;
>>  
>>    // We want to segregate FP/SIMD accesses from GPR accesses.
>> -  //
>> -  // Before RA, we use the modes, noting that stores of constant zero
>> -  // operands use GPRs (even in non-integer modes).  After RA, we use
>> -  // the hard register numbers.
>> -  const bool fpsimd_op_p
>> -    = reload_completed
>> -    ? (REG_P (reg_op) && FP_REGNUM_P (REGNO (reg_op)))
>> -    : (GET_MODE_CLASS (mem_mode) != MODE_INT
>> -       && (load_p || !aarch64_const_zero_rtx_p (reg_op)));
>> +  const bool fpsimd_op_p = m_pass->fpsimd_op_p (reg_op, mem_mode, load_p);
>>  
>> -  // Note ldp_operand_mode_ok_p already rejected VL modes.
>> +  // Note pair_operand_mode_ok_p already rejected VL modes.
>>    const HOST_WIDE_INT mem_size = GET_MODE_SIZE (mem_mode).to_constant ();
>>    const lfs_fields lfs = { load_p, fpsimd_op_p, mem_size };
>>  
>> @@ -498,8 +747,8 @@ ldp_bb_info::track_access (insn_info *insn, bool load_p, rtx mem)
>>    // elimination offset pre-RA, we should postpone forming pairs on such
>>    // accesses until after RA.
>>    //
>> -  // As it stands, addresses with offsets in range for LDR but not
>> -  // in range for LDP/STP are currently reloaded inefficiently,
>> +  // As it stands, addresses in range for an individual load/store but not
>> +  // for a paired access are currently reloaded inefficiently,
>>    // ending up with a separate base register for each pair.
>>    //
>>    // In theory LRA should make use of
>> @@ -510,14 +759,7 @@ ldp_bb_info::track_access (insn_info *insn, bool load_p, rtx mem)
>>    // constraint; this early return means we never get to the code
>>    // that calls targetm.legitimize_address_displacement.
>>    //
>> -  // So for now, it's better to punt when we can't be sure that the
>> -  // offset is in range for LDP/STP.  Out-of-range cases can then be
>> -  // handled after RA by the out-of-range LDP/STP peepholes.  Eventually, it
>> -  // would be nice to handle known out-of-range opportunities in the
>> -  // pass itself (for stack accesses, this would be in the post-RA pass).
>> -  if (!reload_completed
>> -      && (REGNO (base) == FRAME_POINTER_REGNUM
>> -	  || REGNO (base) == ARG_POINTER_REGNUM))
>> +  if (m_pass->handle_out_of_range_cases (base))
>>      return;
>>  
>>    // Now need to find def of base register.
>> @@ -565,8 +807,8 @@ ldp_bb_info::track_access (insn_info *insn, bool load_p, rtx mem)
>>  	gcc_unreachable (); // Base defs should be unique.
>>      }
>>  
>> -  // Punt on misaligned offsets.  LDP/STP require offsets to be a multiple of
>> -  // the access size.
>> +  // Punt on misaligned offsets.  Paired memory accesses require offsets
>> +  // to be a multiple of the access size.
>>    if (!multiple_p (mem_off, mem_size))
>>      return;
>>  
>> @@ -1199,8 +1441,8 @@ extract_writebacks (bool load_p, rtx pats[2], int changed)
>>  // base register.  If there is one, we choose the first such update after
>>  // PAIR_DST that is still in the same BB as our pair.  We return the new def in
>>  // *ADD_DEF and the resulting writeback effect in *WRITEBACK_EFFECT.
>> -static insn_info *
>> -find_trailing_add (insn_info *insns[2],
>> +insn_info *
>> +pair_fusion::find_trailing_add (insn_info *insns[2],
>>  		   const insn_range_info &pair_range,
>>  		   int initial_writeback,
>>  		   rtx *writeback_effect,
>> @@ -1278,7 +1520,7 @@ find_trailing_add (insn_info *insns[2],
>>  
>>    off_hwi /= access_size;
>>  
>> -  if (off_hwi < LDP_MIN_IMM || off_hwi > LDP_MAX_IMM)
>> +  if (!pair_mem_in_range_p (off_hwi))
>>      return nullptr;
>>  
>>    auto dump_prefix = [&]()
>> @@ -1724,8 +1966,8 @@ ldp_bb_info::fuse_pair (bool load_p,
>>        rtx change_reg = XEXP (change_pat, !load_p);
>>        rtx effective_base = drop_writeback (base_mem);
>>        rtx adjusted_addr = plus_constant (Pmode,
>> -					 XEXP (effective_base, 0),
>> -					 adjust_amt);
>> +					XEXP (effective_base, 0),
>> +					adjust_amt);
> 
> What's this change for?
> 
>>        rtx new_mem = replace_equiv_address_nv (change_mem, adjusted_addr);
>>        rtx new_set = load_p
>>  	? gen_rtx_SET (change_reg, new_mem)
>> @@ -1792,7 +2034,7 @@ ldp_bb_info::fuse_pair (bool load_p,
>>      {
>>        if (dump_file)
>>  	fprintf (dump_file,
>> -		 "  ldp: i%d has wb but subsequent i%d has non-wb "
>> +		 "  load pair: i%d has wb but subsequent i%d has non-wb "
>>  		 "update of base (r%d), dropping wb\n",
>>  		 insns[0]->uid (), insns[1]->uid (), base_regno);
>>        gcc_assert (writeback_effect);
>> @@ -1815,7 +2057,7 @@ ldp_bb_info::fuse_pair (bool load_p,
>>      }
>>  
>>    // If either of the original insns had writeback, but the resulting pair insn
>> -  // does not (can happen e.g. in the ldp edge case above, or if the writeback
>> +  // does not (can happen e.g. in the load pair edge case above, or if the writeback
>>    // effects cancel out), then drop the def(s) of the base register as
>>    // appropriate.
>>    //
>> @@ -1834,7 +2076,7 @@ ldp_bb_info::fuse_pair (bool load_p,
>>    // update of the base register and try and fold it in to make this into a
>>    // writeback pair.
>>    insn_info *trailing_add = nullptr;
>> -  if (aarch64_ldp_writeback > 1
>> +  if (m_pass->handle_writeback_opportunities (writeback::ALL)
>>        && !writeback_effect
>>        && (!load_p || (!refers_to_regno_p (base_regno, base_regno + 1,
>>  					 XEXP (pats[0], 0), nullptr)
>> @@ -1842,7 +2084,7 @@ ldp_bb_info::fuse_pair (bool load_p,
>>  					     XEXP (pats[1], 0), nullptr))))
>>      {
>>        def_info *add_def;
>> -      trailing_add = find_trailing_add (insns, move_range, writeback,
>> +      trailing_add = m_pass->find_trailing_add (insns, move_range, writeback,
>>  					&writeback_effect,
>>  					&add_def, base.def, offsets[0],
>>  					access_size);
>> @@ -1855,35 +2097,21 @@ ldp_bb_info::fuse_pair (bool load_p,
>>      }
>>  
>>    // Now that we know what base mem we're going to use, check if it's OK
>> -  // with the ldp/stp policy.
>> +  // with the pair mem policy.
>>    rtx first_mem = XEXP (pats[0], load_p);
>> -  if (!aarch64_mem_ok_with_ldpstp_policy_model (first_mem,
>> -						load_p,
>> -						GET_MODE (first_mem)))
>> +  if (!m_pass->pair_mem_ok_with_policy (first_mem,
>> +			  load_p,
>> +			  GET_MODE (first_mem)))
>>      {
>>        if (dump_file)
>> -	fprintf (dump_file, "punting on pair (%d,%d), ldp/stp policy says no\n",
>> +	fprintf (dump_file, "punting on pair (%d,%d), pair mem policy says no\n",
>>  		 i1->uid (), i2->uid ());
>>        return false;
>>      }
>>  
>>    rtx reg_notes = combine_reg_notes (first, second, load_p);
>>  
>> -  rtx pair_pat;
>> -  if (writeback_effect)
>> -    {
>> -      auto patvec = gen_rtvec (3, writeback_effect, pats[0], pats[1]);
>> -      pair_pat = gen_rtx_PARALLEL (VOIDmode, patvec);
>> -    }
>> -  else if (load_p)
>> -    pair_pat = aarch64_gen_load_pair (XEXP (pats[0], 0),
>> -				      XEXP (pats[1], 0),
>> -				      XEXP (pats[0], 1));
>> -  else
>> -    pair_pat = aarch64_gen_store_pair (XEXP (pats[0], 0),
>> -				       XEXP (pats[0], 1),
>> -				       XEXP (pats[1], 1));
>> -
>> +  rtx pair_pat = m_pass->gen_pair (pats, writeback_effect, load_p);
>>    insn_change *pair_change = nullptr;
>>    auto set_pair_pat = [pair_pat,reg_notes](insn_change *change) {
>>      rtx_insn *rti = change->insn ()->rtl ();
>> @@ -2125,15 +2353,6 @@ load_modified_by_store_p (insn_info *load,
>>    return false;
>>  }
>>  
>> -// Virtual base class for load/store walkers used in alias analysis.
>> -struct alias_walker
>> -{
>> -  virtual bool conflict_p (int &budget) const = 0;
>> -  virtual insn_info *insn () const = 0;
>> -  virtual bool valid () const = 0;
>> -  virtual void advance () = 0;
>> -};
>> -
>>  // Implement some common functionality used by both store_walker
>>  // and load_walker.
>>  template<bool reverse>
>> @@ -2251,13 +2470,13 @@ public:
>>  //
>>  // We try to maintain the invariant that if a walker becomes invalid, we
>>  // set its pointer to null.
>> -static void
>> -do_alias_analysis (insn_info *alias_hazards[4],
>> +void
>> +pair_fusion::do_alias_analysis (insn_info *alias_hazards[4],
>>  		   alias_walker *walkers[4],
>>  		   bool load_p)
>>  {
>>    const int n_walkers = 2 + (2 * !load_p);
>> -  int budget = aarch64_ldp_alias_check_limit;
>> +  int budget = pair_mem_alias_check_limit ();
>>  
>>    auto next_walker = [walkers,n_walkers](int current) -> int {
>>      for (int j = 1; j <= n_walkers; j++)
>> @@ -2342,8 +2561,8 @@ do_alias_analysis (insn_info *alias_hazards[4],
>>  //
>>  // Returns an integer where bit (1 << i) is set if INSNS[i] uses writeback
>>  // addressing.
>> -static int
>> -get_viable_bases (insn_info *insns[2],
>> +int
>> +pair_fusion::get_viable_bases (insn_info *insns[2],
>>  		  vec<base_cand> &base_cands,
>>  		  rtx cand_mems[2],
>>  		  unsigned access_size,
>> @@ -2389,7 +2608,7 @@ get_viable_bases (insn_info *insns[2],
>>        if (!is_lower)
>>  	base_off--;
>>  
>> -      if (base_off < LDP_MIN_IMM || base_off > LDP_MAX_IMM)
>> +      if (!pair_mem_in_range_p (base_off))
>>  	continue;
>>  
>>        use_info *use = find_access (insns[i]->uses (), REGNO (base));
>> @@ -2446,7 +2665,7 @@ get_viable_bases (insn_info *insns[2],
>>  }
>>  
>>  // Given two adjacent memory accesses of the same size, I1 and I2, try
>> -// and see if we can merge them into a ldp or stp.
>> +// and see if we can merge them into a paired access.
>>  //
>>  // ACCESS_SIZE gives the (common) size of a single access, LOAD_P is true
>>  // if the accesses are both loads, otherwise they are both stores.
>> @@ -2486,7 +2705,7 @@ ldp_bb_info::try_fuse_pair (bool load_p, unsigned access_size,
>>      {
>>        if (dump_file)
>>  	fprintf (dump_file,
>> -		 "punting on ldp due to reg conflcits (%d,%d)\n",
>> +		 "punting on pair mem load  due to reg conflcits (%d,%d)\n",
>>  		 insns[0]->uid (), insns[1]->uid ());
>>        return false;
>>      }
>> @@ -2504,7 +2723,7 @@ ldp_bb_info::try_fuse_pair (bool load_p, unsigned access_size,
>>  
>>    auto_vec<base_cand, 2> base_cands (2);
>>  
>> -  int writeback = get_viable_bases (insns, base_cands, cand_mems,
>> +  int writeback = m_pass->get_viable_bases (insns, base_cands, cand_mems,
>>  				    access_size, reversed);
>>    if (base_cands.is_empty ())
>>      {
>> @@ -2633,7 +2852,7 @@ ldp_bb_info::try_fuse_pair (bool load_p, unsigned access_size,
>>      walkers[1] = &backward_store_walker;
>>  
>>    if (load_p && (mem_defs[0] || mem_defs[1]))
>> -    do_alias_analysis (alias_hazards, walkers, load_p);
>> +    m_pass->do_alias_analysis (alias_hazards, walkers, load_p);
>>    else
>>      {
>>        // We want to find any loads hanging off the first store.
>> @@ -2642,7 +2861,7 @@ ldp_bb_info::try_fuse_pair (bool load_p, unsigned access_size,
>>        load_walker<true> backward_load_walker (mem_defs[1], insns[1], insns[0]);
>>        walkers[2] = &forward_load_walker;
>>        walkers[3] = &backward_load_walker;
>> -      do_alias_analysis (alias_hazards, walkers, load_p);
>> +      m_pass->do_alias_analysis (alias_hazards, walkers, load_p);
>>        // Now consolidate hazards back down.
>>        if (alias_hazards[2]
>>  	  && (!alias_hazards[0] || (*alias_hazards[2] < *alias_hazards[0])))
>> @@ -2956,26 +3175,6 @@ ldp_bb_info::transform ()
>>    traverse_base_map (def_map);
>>  }
>>  
>> -static void
>> -ldp_fusion_init ()
>> -{
>> -  calculate_dominance_info (CDI_DOMINATORS);
>> -  df_analyze ();
>> -  crtl->ssa = new rtl_ssa::function_info (cfun);
>> -}
>> -
>> -static void
>> -ldp_fusion_destroy ()
>> -{
>> -  if (crtl->ssa->perform_pending_updates ())
>> -    cleanup_cfg (0);
>> -
>> -  free_dominance_info (CDI_DOMINATORS);
>> -
>> -  delete crtl->ssa;
>> -  crtl->ssa = nullptr;
>> -}
>> -
>>  // Given a load pair insn in PATTERN, unpack the insn, storing
>>  // the registers in REGS and returning the mem.
>>  static rtx
>> @@ -3015,6 +3214,15 @@ aarch64_destructure_store_pair (rtx regs[2], rtx pattern)
>>    return mem;
>>  }
>>  
>> +rtx
>> +aarch64_pair_fusion::destructure_pair (rtx regs[2], rtx rti, bool load_p)
>> +{
>> +  if (load_p)
>> +    return aarch64_destructure_load_pair (regs, rti);
>> +  else
>> +    return aarch64_destructure_store_pair (regs, rti);
>> +}
>> +
>>  // Given a pair mem in PAIR_MEM, register operands in REGS, and an rtx
>>  // representing the effect of writeback on the base register in WB_EFFECT,
>>  // return an insn representing a writeback variant of this pair.
>> @@ -3022,9 +3230,10 @@ aarch64_destructure_store_pair (rtx regs[2], rtx pattern)
>>  //
>>  // This is used when promoting existing non-writeback pairs to writeback
>>  // variants.
>> -static rtx
>> -aarch64_gen_writeback_pair (rtx wb_effect, rtx pair_mem, rtx regs[2],
>> -			    bool load_p)
>> +rtx
>> +aarch64_pair_fusion::gen_promote_writeback_pair (rtx wb_effect, rtx pair_mem,
>> +						 rtx regs[2],
>> +						 bool load_p)
>>  {
>>    auto op_mode = aarch64_operand_mode_for_pair_mode (GET_MODE (pair_mem));
>>  
>> @@ -3059,23 +3268,14 @@ aarch64_gen_writeback_pair (rtx wb_effect, rtx pair_mem, rtx regs[2],
>>  // Given an existing pair insn INSN, look for a trailing update of
>>  // the base register which we can fold in to make this pair use
>>  // a writeback addressing mode.
>> -static void
>> -try_promote_writeback (insn_info *insn)
>> +void
>> +pair_fusion::try_promote_writeback (insn_info *insn, bool load_p)
>>  {
>> -  auto rti = insn->rtl ();
>> -  const auto attr = get_attr_ldpstp (rti);
>> -  if (attr == LDPSTP_NONE)
>> -    return;
>> -
>> -  bool load_p = (attr == LDPSTP_LDP);
>> -  gcc_checking_assert (load_p || attr == LDPSTP_STP);
>> -
>>    rtx regs[2];
>>    rtx mem = NULL_RTX;
>> -  if (load_p)
>> -    mem = aarch64_destructure_load_pair (regs, PATTERN (rti));
>> -  else
>> -    mem = aarch64_destructure_store_pair (regs, PATTERN (rti));
>> +
>> +  mem = destructure_pair (regs, PATTERN (insn->rtl ()), load_p);
>> +
>

Addressed.
 
> Nit: no need for a blank line here?
> 
>>    gcc_checking_assert (MEM_P (mem));
>>  
>>    poly_int64 offset;
>> @@ -3112,9 +3312,10 @@ try_promote_writeback (insn_info *insn)
>>    def_info *add_def;
>>    const insn_range_info pair_range (insn);
>>    insn_info *insns[2] = { nullptr, insn };
>> -  insn_info *trailing_add = find_trailing_add (insns, pair_range, 0, &wb_effect,
>> -					       &add_def, base_def, offset,
>> -					       access_size);
>> +  insn_info *trailing_add
>> +    = find_trailing_add (insns, pair_range, 0, &wb_effect,
>> +			 &add_def, base_def, offset,
>> +			 access_size);
>>    if (!trailing_add)
>>      return;
>>  
>> @@ -3124,8 +3325,10 @@ try_promote_writeback (insn_info *insn)
>>    insn_change del_change (trailing_add, insn_change::DELETE);
>>    insn_change *changes[] = { &pair_change, &del_change };
>>  
>> -  rtx pair_pat = aarch64_gen_writeback_pair (wb_effect, mem, regs, load_p);
>> -  validate_unshare_change (rti, &PATTERN (rti), pair_pat, true);
>> +  rtx pair_pat = gen_promote_writeback_pair (wb_effect, mem, regs,
>> +					     load_p);
>> +  validate_unshare_change (insn->rtl(), &PATTERN (insn->rtl()), pair_pat,
>> +			   true);
>>  
>>    // The pair must gain the def of the base register from the add.
>>    pair_change.new_defs = insert_access (attempt,
>> @@ -3159,14 +3362,12 @@ try_promote_writeback (insn_info *insn)
>>  // for load/store candidates.  If running after RA, also try and promote
>>  // non-writeback pairs to use writeback addressing.  Then try to fuse
>>  // candidates into pairs.
>> -void ldp_fusion_bb (bb_info *bb)
>> +void pair_fusion::ldp_fusion_bb (bb_info *bb)
>>  {
>> -  const bool track_loads
>> -    = aarch64_tune_params.ldp_policy_model != AARCH64_LDP_STP_POLICY_NEVER;
>> -  const bool track_stores
>> -    = aarch64_tune_params.stp_policy_model != AARCH64_LDP_STP_POLICY_NEVER;
>> +  const bool track_loads = track_loads_p ();
>> +  const bool track_stores = track_stores_p ();
>>  
>> -  ldp_bb_info bb_state (bb);
>> +  ldp_bb_info bb_state (bb, this);
>>  
>>    for (auto insn : bb->nondebug_insns ())
>>      {
>> @@ -3176,11 +3377,11 @@ void ldp_fusion_bb (bb_info *bb)
>>  	continue;
>>  
>>        rtx pat = PATTERN (rti);
>> +      bool load_p;
>>        if (reload_completed
>> -	  && aarch64_ldp_writeback > 1
>> -	  && GET_CODE (pat) == PARALLEL
>> -	  && XVECLEN (pat, 0) == 2)
>> -	try_promote_writeback (insn);
>> +	  && handle_writeback_opportunities (writeback::ALL)
>> +	  && pair_mem_insn_p (rti, load_p))
>> +	try_promote_writeback (insn, load_p);
>>  
>>        if (GET_CODE (pat) != SET)
>>  	continue;
>> @@ -3195,16 +3396,6 @@ void ldp_fusion_bb (bb_info *bb)
>>    bb_state.cleanup_tombstones ();
>>  }
>>  
>> -void ldp_fusion ()
>> -{
>> -  ldp_fusion_init ();
>> -
>> -  for (auto bb : crtl->ssa->bbs ())
>> -    ldp_fusion_bb (bb);
>> -
>> -  ldp_fusion_destroy ();
>> -}
>> -
>>  namespace {
>>  
>>  const pass_data pass_data_ldp_fusion =
>> @@ -3234,14 +3425,6 @@ public:
>>        if (!optimize || optimize_debug)
>>  	return false;
>>  
>> -      // If the tuning policy says never to form ldps or stps, don't run
>> -      // the pass.
>> -      if ((aarch64_tune_params.ldp_policy_model
>> -	   == AARCH64_LDP_STP_POLICY_NEVER)
>> -	  && (aarch64_tune_params.stp_policy_model
>> -	      == AARCH64_LDP_STP_POLICY_NEVER))
>> -	return false;
>> -
>>        if (reload_completed)
>>  	return flag_aarch64_late_ldp_fusion;
>>        else
>> @@ -3250,7 +3433,8 @@ public:
>>  
>>    unsigned execute (function *) final override
>>      {
>> -      ldp_fusion ();
>> +      aarch64_pair_fusion pass;
>> +      pass.run ();
>>        return 0;
>>      }
>>  };
>> -- 
>> 2.39.3
>>
> 

Thanks & Regards
Ajit
> Thanks,
> Alex