gcc/gimple-range-phi.cc

/* Gimple range phi analysis.
   Copyright (C) 2023-2024 Free Software Foundation, Inc.
   Contributed by Andrew MacLeod <amacleod@redhat.com>.

This file is part of GCC.

GCC is free software; you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
the Free Software Foundation; either version 3, or (at your option)
any later version.

GCC is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
GNU General Public License for more details.

You should have received a copy of the GNU General Public License
along with GCC; see the file COPYING3.  If not see
<http://www.gnu.org/licenses/>.  */

#include "config.h"
#include "system.h"
#include "coretypes.h"
#include "backend.h"
#include "insn-codes.h"
#include "tree.h"
#include "gimple.h"
#include "ssa.h"
#include "gimple-pretty-print.h"
#include "gimple-range.h"
#include "gimple-range-cache.h"
#include "value-range-storage.h"
#include "tree-cfg.h"
#include "target.h"
#include "attribs.h"
#include "gimple-iterator.h"
#include "gimple-walk.h"
#include "cfganal.h"

// There can be only one running at a time.
static phi_analyzer *phi_analysis_object = NULL;

// Initialize a PHI analyzer with range query Q.

void
phi_analysis_initialize (range_query &q)
{
  gcc_checking_assert (!phi_analysis_object);
  phi_analysis_object = new phi_analyzer (q);
}

// Terminate the current PHI analyzer.  if F is non-null, dump the tables

void
phi_analysis_finalize ()
{
  gcc_checking_assert (phi_analysis_object);
  delete phi_analysis_object;
  phi_analysis_object = NULL;
}

// Return TRUE is there is a PHI analyzer operating.
bool
phi_analysis_available_p ()
{
  return phi_analysis_object != NULL;
}

// Return the phi analyzer object.

phi_analyzer &phi_analysis ()
{
  gcc_checking_assert (phi_analysis_object);
  return *phi_analysis_object;
}

// Initialize a phi_group from another group G.

phi_group::phi_group (const phi_group &g)
{
  m_group = g.m_group;
  m_modifier = g.m_modifier;
  m_modifier_op = g.m_modifier_op;
  m_vr = g.m_vr;
}

// Create a new phi_group with members BM, initial range INIT_RANGE, modifier
// statement MOD on edge MOD_EDGE, and resolve values using query Q.  Calculate
// the range for the group if possible, otherwise set it to VARYING.

phi_group::phi_group (bitmap bm, irange &init_range, gimple *mod,
		      range_query *q)
{
  // we dont expect a modifer and no inital value, so trap to have a look.
  // perhaps they are dead cycles and we can just used UNDEFINED.
  gcc_checking_assert (!init_range.undefined_p ());
  gcc_checking_assert (!init_range.varying_p ());

  m_modifier_op = is_modifier_p (mod, bm);
  m_group = bm;
  m_vr = init_range;
  m_modifier = mod;
  // No modifier means the initial range is the full range.
  // Otherwise try to calculate a range.
  if (!m_modifier_op || calculate_using_modifier (q))
    return;
  // Couldn't calculate a range, set to varying.
  m_vr.set_varying (init_range.type ());
}

// Return 0 if S is not a modifier statment for group members BM.
// If it could be a modifier, return which operand position (1 or 2)
// the phi member occurs in.
unsigned
phi_group::is_modifier_p (gimple *s, const bitmap bm)
{
  if (!s)
    return 0;
  gimple_range_op_handler handler (s);
  if (handler)
    {
      tree op1 = gimple_range_ssa_p (handler.operand1 ());
      tree op2 = gimple_range_ssa_p (handler.operand2 ());
      // Also disallow modifiers that have 2 ssa-names.
      if (op1 && !op2 && bitmap_bit_p (bm, SSA_NAME_VERSION (op1)))
	return 1;
      else if (op2 && !op1 && bitmap_bit_p (bm, SSA_NAME_VERSION (op2)))
	return 2;
    }
  return 0;
}

// Calulcate the range of the phi group using range_query Q.

bool
phi_group::calculate_using_modifier (range_query *q)
{
  // Look at the modifier for any relation
  relation_trio trio = fold_relations (m_modifier, q);
  relation_kind k = VREL_VARYING;
  if (m_modifier_op == 1)
    k = trio.lhs_op1 ();
  else if (m_modifier_op == 2)
    k = trio.lhs_op2 ();
  else
    return false;

  // Examine modifier and run 10 iterations to see if it convergences.
  // The constructor initilaized m_vr to the initial value already.
  const unsigned num_iter = 10;
  int_range_max nv;
  int_range_max iter_value = m_vr;
  for (unsigned x = 0; x < num_iter; x++)
    {
      if (!fold_range (nv, m_modifier, iter_value, q))
	break;
      // If union does nothing, then we have convergence.
      if (!iter_value.union_ (nv))
	{
	  if (iter_value.varying_p ())
	    break;
	  m_vr = iter_value;
	  return true;
	}
    }

  // If we can resolve the range using relations, use that range.
  if (refine_using_relation (k))
    return true;

  // Never converged, so bail for now. we could examine the pattern
  // from m_initial to m_vr as an extension  Especially if we had a way
  // to project the actual number of iterations (SCEV?)
  //
  //  We can also try to identify "parallel" phis to get loop counts and
  //  determine the number of iterations of these parallel PHIs.
  //
  return false;
}


// IF the modifier statement has a relation K between the modifier and the
// PHI member in it, we can project a range based on that.
// ie,  a_2 = PHI <0, a_3>   and a_3 = a_2 + 1
// if the relation a_3 > a_2 is present, the know the range is [0, +INF]
// m_vr contains the initial value for the PHI range.

bool
phi_group::refine_using_relation (relation_kind k)
{
  if (k == VREL_VARYING)
    return false;
  tree type = m_vr.type ();
  // If the type wraps, then relations dont tell us much.
  if (TYPE_OVERFLOW_WRAPS (type))
    return false;

  int_range<2> type_range;
  type_range.set_varying (type);
  switch (k)
    {
    case VREL_LT:
    case VREL_LE:
      {
	// Value always decreases.
	m_vr.set (type, type_range.lower_bound (), m_vr.upper_bound ());
	return true;
      }

    case VREL_GT:
    case VREL_GE:
      {
	// Value always increases.
	m_vr.set (type, m_vr.lower_bound (), type_range.upper_bound ());
	return true;
      }

      // If its always equal, then its simply the initial value.
      // which is what m_vr has already been set to.
    case VREL_EQ:
      return true;

    default:
      break;
    }

  return false;
}

// Dump the information for a phi group to file F.

void
phi_group::dump (FILE *f)
{
  unsigned i;
  bitmap_iterator bi;
  fprintf (f, "PHI GROUP < ");

  EXECUTE_IF_SET_IN_BITMAP (m_group, 0, i, bi)
    {
      print_generic_expr (f, ssa_name (i), TDF_SLIM);
      fputc (' ',f);
    }
  fprintf (f, "> : range : ");
  m_vr.dump (f);
  fprintf (f, "\n  Modifier : ");
  if (m_modifier)
    print_gimple_stmt (f, m_modifier, 0, TDF_SLIM);
  else
    fprintf (f, "NONE\n");
}

// -------------------------------------------------------------------------

// Construct a phi analyzer which uses range_query G to pick up values.

phi_analyzer::phi_analyzer (range_query &g) : m_global (g), m_phi_groups (vNULL)
{
  m_work.create (0);
  m_work.safe_grow (20);

  m_tab.create (0);
//   m_tab.safe_grow_cleared (num_ssa_names + 100);
  bitmap_obstack_initialize (&m_bitmaps);
  m_simple = BITMAP_ALLOC (&m_bitmaps);
  m_current = BITMAP_ALLOC (&m_bitmaps);
}

// Destruct a PHI analyzer.

phi_analyzer::~phi_analyzer ()
{
  bitmap_obstack_release (&m_bitmaps);
  m_tab.release ();
  m_work.release ();
  for (auto grp : m_phi_groups)
    delete grp;
  m_phi_groups.release ();
}

//  Return the group, if any, that NAME is part of.  Do no analysis.

phi_group *
phi_analyzer::group (tree name) const
{
  gcc_checking_assert (TREE_CODE (name) == SSA_NAME);
  if (!is_a<gphi *> (SSA_NAME_DEF_STMT (name)))
    return NULL;
  unsigned v = SSA_NAME_VERSION (name);
  if (v >= m_tab.length ())
    return NULL;
  return m_tab[v];
}

// Return the group NAME is associated with, if any.  If name has not been
// procvessed yet, do the analysis to determine if it is part of a group
// and return that.

phi_group *
phi_analyzer::operator[] (tree name)
{
  gcc_checking_assert (TREE_CODE (name) == SSA_NAME);

  //  Initial support for irange only.
  if (!irange::supports_p (TREE_TYPE (name)))
    return NULL;
  if (!is_a<gphi *> (SSA_NAME_DEF_STMT (name)))
    return NULL;

  unsigned v = SSA_NAME_VERSION (name);
  // Already been processed and not part of a group.
  if (bitmap_bit_p (m_simple, v))
    return NULL;

  if (v >= m_tab.length () || !m_tab[v])
    {
      process_phi (as_a<gphi *> (SSA_NAME_DEF_STMT (name)));
      if (bitmap_bit_p (m_simple, v))
	return  NULL;
     // If m_simple bit isn't set, and process_phi didn't allocated the table
     // no group was created, so return NULL.
     if (v >= m_tab.length ())
      return NULL;
    }
  return m_tab[v];
}

// Process phi node PHI to see if it is part of a group.

void
phi_analyzer::process_phi (gphi *phi)
{
  gcc_checking_assert (!group (gimple_phi_result (phi)));
  bool cycle_p = true;

  // Start with the LHS of the PHI in the worklist.
  unsigned x;
  m_work.truncate (0);
  m_work.safe_push (gimple_phi_result (phi));
  unsigned phi_count = 1;
  bitmap_clear (m_current);

  // We can only have 2 externals: an initial value and a modifier.
  // Any more than that and this fails to be a group.
  unsigned m_num_extern = 0;
  tree m_external[2];
  edge m_ext_edge[2];
  int_range_max init_range;
  init_range.set_undefined ();

  while (m_work.length () > 0)
    {
      tree phi_def = m_work.pop ();
      gphi *phi_stmt = as_a<gphi *> (SSA_NAME_DEF_STMT (phi_def));
      // if the phi is already in a different cycle, we don't try to merge.
      if (group (phi_def))
	{
	  cycle_p = false;
	  break;
	}
      bitmap_set_bit (m_current, SSA_NAME_VERSION (phi_def));
      // Process the args.
      for (x = 0; x < gimple_phi_num_args (phi_stmt); x++)
	{
	  tree arg = gimple_phi_arg_def (phi_stmt, x);
	  if (arg == phi_def)
	    continue;
	  enum tree_code code = TREE_CODE (arg);
	  if (code == SSA_NAME)
	    {
	      unsigned v = SSA_NAME_VERSION (arg);
	      // Already a member of this potential group.
	      if (bitmap_bit_p (m_current, v))
		continue;
	      // Part of a different group ends cycle possibility.
	      if (group (arg) || bitmap_bit_p (m_simple, v))
		{
		  cycle_p = false;
		  break;
		}
	      // Check if its a PHI to examine.
	      gimple *arg_stmt = SSA_NAME_DEF_STMT (arg);
	      if (arg_stmt && is_a<gphi *> (arg_stmt))
		{
		  phi_count++;
		  m_work.safe_push (arg);
		  continue;
		}
	      // More than 2 outside names is too complicated.
	      if (m_num_extern >= 2)
		{
		  cycle_p = false;
		  break;
		}
	      m_external[m_num_extern] = arg;
	      m_ext_edge[m_num_extern++] = gimple_phi_arg_edge (phi_stmt, x);
	    }
	  else if (code == INTEGER_CST)
	    {
	      // Constants are just added to the initialization value.
	      int_range<1> val (TREE_TYPE (arg), wi::to_wide (arg),
				wi::to_wide (arg));
	      init_range.union_ (val);
	    }
	  else
	    {
	      // Everything else terminates the cycle.
	      cycle_p = false;
	      break;
	    }
	}
    }

  // If there are less than 2 names, just return.  This PHI may be included
  // by another PHI, making it simple or a group of one will prevent a larger
  // group from being formed.
  if (phi_count < 2)
    return;
  gcc_checking_assert (!bitmap_empty_p (m_current));

  phi_group *g = NULL;
  if (cycle_p)
    {
      bool valid = true;
      gimple *mod = NULL;
      signed init_idx = -1;
      // At this point all the PHIs have been added to the bitmap.
      // the external list needs to be checked for initial values and modifiers.
      for (x = 0; x < m_num_extern; x++)
	{
	  tree name = m_external[x];
	  if (TREE_CODE (name) == SSA_NAME
	      && phi_group::is_modifier_p (SSA_NAME_DEF_STMT (name), m_current))
	    {
	      // Can't have multiple modifiers.
	      if (mod)
		valid = false;
	      mod = SSA_NAME_DEF_STMT (name);
	      continue;
	    }
	  // Can't have 2 initializers either.
	  if (init_idx != -1)
	    valid = false;
	  init_idx = x;
	}
      int_range_max init_sym;
      // If there is an symbolic initializer as well, include it here.
      if (valid && init_idx != -1)
	{
	  if (m_global.range_on_edge (init_sym, m_ext_edge[init_idx],
				      m_external[init_idx]))
	    init_range.union_ (init_sym);
	  else
	    valid = false;
	}
      if (valid && !init_range.varying_p () && !init_range.undefined_p ())
	{
	  // Try to create a group based on m_current. If a result comes back
	  // with a range that isn't varying, create the group.
	  phi_group cyc (m_current, init_range, mod, &m_global);
	  if (!cyc.range ().varying_p ())
	    {
	      g = new phi_group (cyc);
	      m_phi_groups.safe_push (g);
	      if (dump_file && (dump_flags & TDF_DETAILS))
		{
		  fprintf (dump_file, "PHI ANALYZER : New ");
		  g->dump (dump_file);
		  fprintf (dump_file,"  Initial range was ");
		  init_range.dump (dump_file);
		  if (init_idx != -1)
		    {
		      fprintf (dump_file, " including symbolic ");
		      print_generic_expr (dump_file, m_external[init_idx],
					  TDF_SLIM);
		      fprintf (dump_file, " on edge %d->%d with range ",
			       m_ext_edge[init_idx]->src->index,
			       m_ext_edge[init_idx]->dest->index);
		      init_sym.dump (dump_file);
		    }
		  fputc ('\n',dump_file);
		}
	    }
	}
    }
  // If this dpoesn;t form a group, all members are instead simple phis.
  if (!g)
    {
      bitmap_ior_into (m_simple, m_current);
      return;
    }

  if (num_ssa_names >= m_tab.length ())
    m_tab.safe_grow_cleared (num_ssa_names + 100);

  // Now set all entries in the group to this record.
  unsigned i;
  bitmap_iterator bi;
  EXECUTE_IF_SET_IN_BITMAP (m_current, 0, i, bi)
    {
      // Can't be in more than one group.
      gcc_checking_assert (m_tab[i] == NULL);
      m_tab[i] = g;
    }
  // Allocate a new bitmap for the next time as the original one is now part
  // of the new phi group.
  m_current = BITMAP_ALLOC (&m_bitmaps);
}

void
phi_analyzer::dump (FILE *f)
{
  bool header = false;
  bitmap_clear (m_current);
  for (unsigned x = 0; x < m_tab.length (); x++)
    {
      if (bitmap_bit_p (m_simple, x))
	continue;
      if (bitmap_bit_p (m_current, x))
	continue;
      if (m_tab[x] == NULL)
	continue;
      phi_group *g = m_tab[x];
      bitmap_ior_into (m_current, g->group ());
      if (!header)
	{
	  header = true;
	  fprintf (f, "\nPHI GROUPS:\n");
	}
      g->dump (f);
    }
}