gimplify.c

/* Tree lowering pass.  This pass converts the GENERIC functions-as-trees
   tree representation into the GIMPLE form.
   Copyright (C) 2002-2015 Free Software Foundation, Inc.
   Major work done by Sebastian Pop <s.pop@laposte.net>,
   Diego Novillo <dnovillo@redhat.com> and Jason Merrill <jason@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 "target.h"
#include "rtl.h"
#include "tree.h"
#include "gimple.h"
#include "gimple-predict.h"
#include "tree-pass.h"		/* FIXME: only for PROP_gimple_any */
#include "ssa.h"
#include "cgraph.h"
#include "tree-pretty-print.h"
#include "diagnostic-core.h"
#include "alias.h"
#include "fold-const.h"
#include "calls.h"
#include "varasm.h"
#include "stmt.h"
#include "expr.h"
#include "gimple-fold.h"
#include "tree-eh.h"
#include "gimplify.h"
#include "gimple-iterator.h"
#include "stor-layout.h"
#include "print-tree.h"
#include "tree-iterator.h"
#include "tree-inline.h"
#include "langhooks.h"
#include "tree-cfg.h"
#include "tree-ssa.h"
#include "omp-low.h"
#include "gimple-low.h"
#include "cilk.h"
#include "gomp-constants.h"
#include "tree-dump.h"

#include "langhooks-def.h"	/* FIXME: for lhd_set_decl_assembler_name */
#include "builtins.h"

enum gimplify_omp_var_data
{
  GOVD_SEEN = 1,
  GOVD_EXPLICIT = 2,
  GOVD_SHARED = 4,
  GOVD_PRIVATE = 8,
  GOVD_FIRSTPRIVATE = 16,
  GOVD_LASTPRIVATE = 32,
  GOVD_REDUCTION = 64,
  GOVD_LOCAL = 128,
  GOVD_MAP = 256,
  GOVD_DEBUG_PRIVATE = 512,
  GOVD_PRIVATE_OUTER_REF = 1024,
  GOVD_LINEAR = 2048,
  GOVD_ALIGNED = 4096,

  /* Flag for GOVD_MAP: don't copy back.  */
  GOVD_MAP_TO_ONLY = 8192,

  /* Flag for GOVD_LINEAR or GOVD_LASTPRIVATE: no outer reference.  */
  GOVD_LINEAR_LASTPRIVATE_NO_OUTER = 16384,

  GOVD_MAP_0LEN_ARRAY = 32768,

  /* Flag for GOVD_MAP, if it is always, to or always, tofrom mapping.  */
  GOVD_MAP_ALWAYS_TO = 65536,

  GOVD_DATA_SHARE_CLASS = (GOVD_SHARED | GOVD_PRIVATE | GOVD_FIRSTPRIVATE
			   | GOVD_LASTPRIVATE | GOVD_REDUCTION | GOVD_LINEAR
			   | GOVD_LOCAL)
};


enum omp_region_type
{
  ORT_WORKSHARE = 0,
  ORT_SIMD = 1,
  ORT_PARALLEL = 2,
  ORT_COMBINED_PARALLEL = 3,
  ORT_TASK = 4,
  ORT_UNTIED_TASK = 5,
  ORT_TEAMS = 8,
  ORT_COMBINED_TEAMS = 9,
  /* Data region.  */
  ORT_TARGET_DATA = 16,
  /* Data region with offloading.  */
  ORT_TARGET = 32,
  ORT_COMBINED_TARGET = 33,
  /* Dummy OpenMP region, used to disable expansion of
     DECL_VALUE_EXPRs in taskloop pre body.  */
  ORT_NONE = 64
};

/* Gimplify hashtable helper.  */

struct gimplify_hasher : free_ptr_hash <elt_t>
{
  static inline hashval_t hash (const elt_t *);
  static inline bool equal (const elt_t *, const elt_t *);
};

struct gimplify_ctx
{
  struct gimplify_ctx *prev_context;

  vec<gbind *> bind_expr_stack;
  tree temps;
  gimple_seq conditional_cleanups;
  tree exit_label;
  tree return_temp;

  vec<tree> case_labels;
  /* The formal temporary table.  Should this be persistent?  */
  hash_table<gimplify_hasher> *temp_htab;

  int conditions;
  bool save_stack;
  bool into_ssa;
  bool allow_rhs_cond_expr;
  bool in_cleanup_point_expr;
};

struct gimplify_omp_ctx
{
  struct gimplify_omp_ctx *outer_context;
  splay_tree variables;
  hash_set<tree> *privatized_types;
  /* Iteration variables in an OMP_FOR.  */
  vec<tree> loop_iter_var;
  location_t location;
  enum omp_clause_default_kind default_kind;
  enum omp_region_type region_type;
  bool combined_loop;
  bool distribute;
  bool target_map_scalars_firstprivate;
  bool target_map_pointers_as_0len_arrays;
  bool target_firstprivatize_array_bases;
};

static struct gimplify_ctx *gimplify_ctxp;
static struct gimplify_omp_ctx *gimplify_omp_ctxp;

/* Forward declaration.  */
static enum gimplify_status gimplify_compound_expr (tree *, gimple_seq *, bool);

/* Shorter alias name for the above function for use in gimplify.c
   only.  */

static inline void
gimplify_seq_add_stmt (gimple_seq *seq_p, gimple *gs)
{
  gimple_seq_add_stmt_without_update (seq_p, gs);
}

/* Append sequence SRC to the end of sequence *DST_P.  If *DST_P is
   NULL, a new sequence is allocated.   This function is
   similar to gimple_seq_add_seq, but does not scan the operands.
   During gimplification, we need to manipulate statement sequences
   before the def/use vectors have been constructed.  */

static void
gimplify_seq_add_seq (gimple_seq *dst_p, gimple_seq src)
{
  gimple_stmt_iterator si;

  if (src == NULL)
    return;

  si = gsi_last (*dst_p);
  gsi_insert_seq_after_without_update (&si, src, GSI_NEW_STMT);
}


/* Pointer to a list of allocated gimplify_ctx structs to be used for pushing
   and popping gimplify contexts.  */

static struct gimplify_ctx *ctx_pool = NULL;

/* Return a gimplify context struct from the pool.  */

static inline struct gimplify_ctx *
ctx_alloc (void)
{
  struct gimplify_ctx * c = ctx_pool;

  if (c)
    ctx_pool = c->prev_context;
  else
    c = XNEW (struct gimplify_ctx);

  memset (c, '\0', sizeof (*c));
  return c;
}

/* Put gimplify context C back into the pool.  */

static inline void
ctx_free (struct gimplify_ctx *c)
{
  c->prev_context = ctx_pool;
  ctx_pool = c;
}

/* Free allocated ctx stack memory.  */

void
free_gimplify_stack (void)
{
  struct gimplify_ctx *c;

  while ((c = ctx_pool))
    {
      ctx_pool = c->prev_context;
      free (c);
    }
}


/* Set up a context for the gimplifier.  */

void
push_gimplify_context (bool in_ssa, bool rhs_cond_ok)
{
  struct gimplify_ctx *c = ctx_alloc ();

  c->prev_context = gimplify_ctxp;
  gimplify_ctxp = c;
  gimplify_ctxp->into_ssa = in_ssa;
  gimplify_ctxp->allow_rhs_cond_expr = rhs_cond_ok;
}

/* Tear down a context for the gimplifier.  If BODY is non-null, then
   put the temporaries into the outer BIND_EXPR.  Otherwise, put them
   in the local_decls.

   BODY is not a sequence, but the first tuple in a sequence.  */

void
pop_gimplify_context (gimple *body)
{
  struct gimplify_ctx *c = gimplify_ctxp;

  gcc_assert (c
              && (!c->bind_expr_stack.exists ()
		  || c->bind_expr_stack.is_empty ()));
  c->bind_expr_stack.release ();
  gimplify_ctxp = c->prev_context;

  if (body)
    declare_vars (c->temps, body, false);
  else
    record_vars (c->temps);

  delete c->temp_htab;
  c->temp_htab = NULL;
  ctx_free (c);
}

/* Push a GIMPLE_BIND tuple onto the stack of bindings.  */

static void
gimple_push_bind_expr (gbind *bind_stmt)
{
  gimplify_ctxp->bind_expr_stack.reserve (8);
  gimplify_ctxp->bind_expr_stack.safe_push (bind_stmt);
}

/* Pop the first element off the stack of bindings.  */

static void
gimple_pop_bind_expr (void)
{
  gimplify_ctxp->bind_expr_stack.pop ();
}

/* Return the first element of the stack of bindings.  */

gbind *
gimple_current_bind_expr (void)
{
  return gimplify_ctxp->bind_expr_stack.last ();
}

/* Return the stack of bindings created during gimplification.  */

vec<gbind *>
gimple_bind_expr_stack (void)
{
  return gimplify_ctxp->bind_expr_stack;
}

/* Return true iff there is a COND_EXPR between us and the innermost
   CLEANUP_POINT_EXPR.  This info is used by gimple_push_cleanup.  */

static bool
gimple_conditional_context (void)
{
  return gimplify_ctxp->conditions > 0;
}

/* Note that we've entered a COND_EXPR.  */

static void
gimple_push_condition (void)
{
#ifdef ENABLE_GIMPLE_CHECKING
  if (gimplify_ctxp->conditions == 0)
    gcc_assert (gimple_seq_empty_p (gimplify_ctxp->conditional_cleanups));
#endif
  ++(gimplify_ctxp->conditions);
}

/* Note that we've left a COND_EXPR.  If we're back at unconditional scope
   now, add any conditional cleanups we've seen to the prequeue.  */

static void
gimple_pop_condition (gimple_seq *pre_p)
{
  int conds = --(gimplify_ctxp->conditions);

  gcc_assert (conds >= 0);
  if (conds == 0)
    {
      gimplify_seq_add_seq (pre_p, gimplify_ctxp->conditional_cleanups);
      gimplify_ctxp->conditional_cleanups = NULL;
    }
}

/* A stable comparison routine for use with splay trees and DECLs.  */

static int
splay_tree_compare_decl_uid (splay_tree_key xa, splay_tree_key xb)
{
  tree a = (tree) xa;
  tree b = (tree) xb;

  return DECL_UID (a) - DECL_UID (b);
}

/* Create a new omp construct that deals with variable remapping.  */

static struct gimplify_omp_ctx *
new_omp_context (enum omp_region_type region_type)
{
  struct gimplify_omp_ctx *c;

  c = XCNEW (struct gimplify_omp_ctx);
  c->outer_context = gimplify_omp_ctxp;
  c->variables = splay_tree_new (splay_tree_compare_decl_uid, 0, 0);
  c->privatized_types = new hash_set<tree>;
  c->location = input_location;
  c->region_type = region_type;
  if ((region_type & ORT_TASK) == 0)
    c->default_kind = OMP_CLAUSE_DEFAULT_SHARED;
  else
    c->default_kind = OMP_CLAUSE_DEFAULT_UNSPECIFIED;

  return c;
}

/* Destroy an omp construct that deals with variable remapping.  */

static void
delete_omp_context (struct gimplify_omp_ctx *c)
{
  splay_tree_delete (c->variables);
  delete c->privatized_types;
  c->loop_iter_var.release ();
  XDELETE (c);
}

static void omp_add_variable (struct gimplify_omp_ctx *, tree, unsigned int);
static bool omp_notice_variable (struct gimplify_omp_ctx *, tree, bool);

/* Both gimplify the statement T and append it to *SEQ_P.  This function
   behaves exactly as gimplify_stmt, but you don't have to pass T as a
   reference.  */

void
gimplify_and_add (tree t, gimple_seq *seq_p)
{
  gimplify_stmt (&t, seq_p);
}

/* Gimplify statement T into sequence *SEQ_P, and return the first
   tuple in the sequence of generated tuples for this statement.
   Return NULL if gimplifying T produced no tuples.  */

static gimple *
gimplify_and_return_first (tree t, gimple_seq *seq_p)
{
  gimple_stmt_iterator last = gsi_last (*seq_p);

  gimplify_and_add (t, seq_p);

  if (!gsi_end_p (last))
    {
      gsi_next (&last);
      return gsi_stmt (last);
    }
  else
    return gimple_seq_first_stmt (*seq_p);
}

/* Returns true iff T is a valid RHS for an assignment to an un-renamed
   LHS, or for a call argument.  */

static bool
is_gimple_mem_rhs (tree t)
{
  /* If we're dealing with a renamable type, either source or dest must be
     a renamed variable.  */
  if (is_gimple_reg_type (TREE_TYPE (t)))
    return is_gimple_val (t);
  else
    return is_gimple_val (t) || is_gimple_lvalue (t);
}

/* Return true if T is a CALL_EXPR or an expression that can be
   assigned to a temporary.  Note that this predicate should only be
   used during gimplification.  See the rationale for this in
   gimplify_modify_expr.  */

static bool
is_gimple_reg_rhs_or_call (tree t)
{
  return (get_gimple_rhs_class (TREE_CODE (t)) != GIMPLE_INVALID_RHS
	  || TREE_CODE (t) == CALL_EXPR);
}

/* Return true if T is a valid memory RHS or a CALL_EXPR.  Note that
   this predicate should only be used during gimplification.  See the
   rationale for this in gimplify_modify_expr.  */

static bool
is_gimple_mem_rhs_or_call (tree t)
{
  /* If we're dealing with a renamable type, either source or dest must be
     a renamed variable.  */
  if (is_gimple_reg_type (TREE_TYPE (t)))
    return is_gimple_val (t);
  else
    return (is_gimple_val (t) || is_gimple_lvalue (t)
	    || TREE_CODE (t) == CALL_EXPR);
}

/* Create a temporary with a name derived from VAL.  Subroutine of
   lookup_tmp_var; nobody else should call this function.  */

static inline tree
create_tmp_from_val (tree val)
{
  /* Drop all qualifiers and address-space information from the value type.  */
  tree type = TYPE_MAIN_VARIANT (TREE_TYPE (val));
  tree var = create_tmp_var (type, get_name (val));
  if (TREE_CODE (TREE_TYPE (var)) == COMPLEX_TYPE
      || TREE_CODE (TREE_TYPE (var)) == VECTOR_TYPE)
    DECL_GIMPLE_REG_P (var) = 1;
  return var;
}

/* Create a temporary to hold the value of VAL.  If IS_FORMAL, try to reuse
   an existing expression temporary.  */

static tree
lookup_tmp_var (tree val, bool is_formal)
{
  tree ret;

  /* If not optimizing, never really reuse a temporary.  local-alloc
     won't allocate any variable that is used in more than one basic
     block, which means it will go into memory, causing much extra
     work in reload and final and poorer code generation, outweighing
     the extra memory allocation here.  */
  if (!optimize || !is_formal || TREE_SIDE_EFFECTS (val))
    ret = create_tmp_from_val (val);
  else
    {
      elt_t elt, *elt_p;
      elt_t **slot;

      elt.val = val;
      if (!gimplify_ctxp->temp_htab)
        gimplify_ctxp->temp_htab = new hash_table<gimplify_hasher> (1000);
      slot = gimplify_ctxp->temp_htab->find_slot (&elt, INSERT);
      if (*slot == NULL)
	{
	  elt_p = XNEW (elt_t);
	  elt_p->val = val;
	  elt_p->temp = ret = create_tmp_from_val (val);
	  *slot = elt_p;
	}
      else
	{
	  elt_p = *slot;
          ret = elt_p->temp;
	}
    }

  return ret;
}

/* Helper for get_formal_tmp_var and get_initialized_tmp_var.  */

static tree
internal_get_tmp_var (tree val, gimple_seq *pre_p, gimple_seq *post_p,
                      bool is_formal)
{
  tree t, mod;

  /* Notice that we explicitly allow VAL to be a CALL_EXPR so that we
     can create an INIT_EXPR and convert it into a GIMPLE_CALL below.  */
  gimplify_expr (&val, pre_p, post_p, is_gimple_reg_rhs_or_call,
		 fb_rvalue);

  if (gimplify_ctxp->into_ssa
      && is_gimple_reg_type (TREE_TYPE (val)))
    t = make_ssa_name (TYPE_MAIN_VARIANT (TREE_TYPE (val)));
  else
    t = lookup_tmp_var (val, is_formal);

  mod = build2 (INIT_EXPR, TREE_TYPE (t), t, unshare_expr (val));

  SET_EXPR_LOCATION (mod, EXPR_LOC_OR_LOC (val, input_location));

  /* gimplify_modify_expr might want to reduce this further.  */
  gimplify_and_add (mod, pre_p);
  ggc_free (mod);

  return t;
}

/* Return a formal temporary variable initialized with VAL.  PRE_P is as
   in gimplify_expr.  Only use this function if:

   1) The value of the unfactored expression represented by VAL will not
      change between the initialization and use of the temporary, and
   2) The temporary will not be otherwise modified.

   For instance, #1 means that this is inappropriate for SAVE_EXPR temps,
   and #2 means it is inappropriate for && temps.

   For other cases, use get_initialized_tmp_var instead.  */

tree
get_formal_tmp_var (tree val, gimple_seq *pre_p)
{
  return internal_get_tmp_var (val, pre_p, NULL, true);
}

/* Return a temporary variable initialized with VAL.  PRE_P and POST_P
   are as in gimplify_expr.  */

tree
get_initialized_tmp_var (tree val, gimple_seq *pre_p, gimple_seq *post_p)
{
  return internal_get_tmp_var (val, pre_p, post_p, false);
}

/* Declare all the variables in VARS in SCOPE.  If DEBUG_INFO is true,
   generate debug info for them; otherwise don't.  */

void
declare_vars (tree vars, gimple *gs, bool debug_info)
{
  tree last = vars;
  if (last)
    {
      tree temps, block;

      gbind *scope = as_a <gbind *> (gs);

      temps = nreverse (last);

      block = gimple_bind_block (scope);
      gcc_assert (!block || TREE_CODE (block) == BLOCK);
      if (!block || !debug_info)
	{
	  DECL_CHAIN (last) = gimple_bind_vars (scope);
	  gimple_bind_set_vars (scope, temps);
	}
      else
	{
	  /* We need to attach the nodes both to the BIND_EXPR and to its
	     associated BLOCK for debugging purposes.  The key point here
	     is that the BLOCK_VARS of the BIND_EXPR_BLOCK of a BIND_EXPR
	     is a subchain of the BIND_EXPR_VARS of the BIND_EXPR.  */
	  if (BLOCK_VARS (block))
	    BLOCK_VARS (block) = chainon (BLOCK_VARS (block), temps);
	  else
	    {
	      gimple_bind_set_vars (scope,
	      			    chainon (gimple_bind_vars (scope), temps));
	      BLOCK_VARS (block) = temps;
	    }
	}
    }
}

/* For VAR a VAR_DECL of variable size, try to find a constant upper bound
   for the size and adjust DECL_SIZE/DECL_SIZE_UNIT accordingly.  Abort if
   no such upper bound can be obtained.  */

static void
force_constant_size (tree var)
{
  /* The only attempt we make is by querying the maximum size of objects
     of the variable's type.  */

  HOST_WIDE_INT max_size;

  gcc_assert (TREE_CODE (var) == VAR_DECL);

  max_size = max_int_size_in_bytes (TREE_TYPE (var));

  gcc_assert (max_size >= 0);

  DECL_SIZE_UNIT (var)
    = build_int_cst (TREE_TYPE (DECL_SIZE_UNIT (var)), max_size);
  DECL_SIZE (var)
    = build_int_cst (TREE_TYPE (DECL_SIZE (var)), max_size * BITS_PER_UNIT);
}

/* Push the temporary variable TMP into the current binding.  */

void
gimple_add_tmp_var_fn (struct function *fn, tree tmp)
{
  gcc_assert (!DECL_CHAIN (tmp) && !DECL_SEEN_IN_BIND_EXPR_P (tmp));

  /* Later processing assumes that the object size is constant, which might
     not be true at this point.  Force the use of a constant upper bound in
     this case.  */
  if (!tree_fits_uhwi_p (DECL_SIZE_UNIT (tmp)))
    force_constant_size (tmp);

  DECL_CONTEXT (tmp) = fn->decl;
  DECL_SEEN_IN_BIND_EXPR_P (tmp) = 1;

  record_vars_into (tmp, fn->decl);
}

/* Push the temporary variable TMP into the current binding.  */

void
gimple_add_tmp_var (tree tmp)
{
  gcc_assert (!DECL_CHAIN (tmp) && !DECL_SEEN_IN_BIND_EXPR_P (tmp));

  /* Later processing assumes that the object size is constant, which might
     not be true at this point.  Force the use of a constant upper bound in
     this case.  */
  if (!tree_fits_uhwi_p (DECL_SIZE_UNIT (tmp)))
    force_constant_size (tmp);

  DECL_CONTEXT (tmp) = current_function_decl;
  DECL_SEEN_IN_BIND_EXPR_P (tmp) = 1;

  if (gimplify_ctxp)
    {
      DECL_CHAIN (tmp) = gimplify_ctxp->temps;
      gimplify_ctxp->temps = tmp;

      /* Mark temporaries local within the nearest enclosing parallel.  */
      if (gimplify_omp_ctxp)
	{
	  struct gimplify_omp_ctx *ctx = gimplify_omp_ctxp;
	  while (ctx
		 && (ctx->region_type == ORT_WORKSHARE
		     || ctx->region_type == ORT_SIMD))
	    ctx = ctx->outer_context;
	  if (ctx)
	    omp_add_variable (ctx, tmp, GOVD_LOCAL | GOVD_SEEN);
	}
    }
  else if (cfun)
    record_vars (tmp);
  else
    {
      gimple_seq body_seq;

      /* This case is for nested functions.  We need to expose the locals
	 they create.  */
      body_seq = gimple_body (current_function_decl);
      declare_vars (tmp, gimple_seq_first_stmt (body_seq), false);
    }
}



/* This page contains routines to unshare tree nodes, i.e. to duplicate tree
   nodes that are referenced more than once in GENERIC functions.  This is
   necessary because gimplification (translation into GIMPLE) is performed
   by modifying tree nodes in-place, so gimplication of a shared node in a
   first context could generate an invalid GIMPLE form in a second context.

   This is achieved with a simple mark/copy/unmark algorithm that walks the
   GENERIC representation top-down, marks nodes with TREE_VISITED the first
   time it encounters them, duplicates them if they already have TREE_VISITED
   set, and finally removes the TREE_VISITED marks it has set.

   The algorithm works only at the function level, i.e. it generates a GENERIC
   representation of a function with no nodes shared within the function when
   passed a GENERIC function (except for nodes that are allowed to be shared).

   At the global level, it is also necessary to unshare tree nodes that are
   referenced in more than one function, for the same aforementioned reason.
   This requires some cooperation from the front-end.  There are 2 strategies:

     1. Manual unsharing.  The front-end needs to call unshare_expr on every
        expression that might end up being shared across functions.

     2. Deep unsharing.  This is an extension of regular unsharing.  Instead
        of calling unshare_expr on expressions that might be shared across
        functions, the front-end pre-marks them with TREE_VISITED.  This will
        ensure that they are unshared on the first reference within functions
        when the regular unsharing algorithm runs.  The counterpart is that
        this algorithm must look deeper than for manual unsharing, which is
        specified by LANG_HOOKS_DEEP_UNSHARING.

  If there are only few specific cases of node sharing across functions, it is
  probably easier for a front-end to unshare the expressions manually.  On the
  contrary, if the expressions generated at the global level are as widespread
  as expressions generated within functions, deep unsharing is very likely the
  way to go.  */

/* Similar to copy_tree_r but do not copy SAVE_EXPR or TARGET_EXPR nodes.
   These nodes model computations that must be done once.  If we were to
   unshare something like SAVE_EXPR(i++), the gimplification process would
   create wrong code.  However, if DATA is non-null, it must hold a pointer
   set that is used to unshare the subtrees of these nodes.  */

static tree
mostly_copy_tree_r (tree *tp, int *walk_subtrees, void *data)
{
  tree t = *tp;
  enum tree_code code = TREE_CODE (t);

  /* Do not copy SAVE_EXPR, TARGET_EXPR or BIND_EXPR nodes themselves, but
     copy their subtrees if we can make sure to do it only once.  */
  if (code == SAVE_EXPR || code == TARGET_EXPR || code == BIND_EXPR)
    {
      if (data && !((hash_set<tree> *)data)->add (t))
	;
      else
	*walk_subtrees = 0;
    }

  /* Stop at types, decls, constants like copy_tree_r.  */
  else if (TREE_CODE_CLASS (code) == tcc_type
	   || TREE_CODE_CLASS (code) == tcc_declaration
	   || TREE_CODE_CLASS (code) == tcc_constant
	   /* We can't do anything sensible with a BLOCK used as an
	      expression, but we also can't just die when we see it
	      because of non-expression uses.  So we avert our eyes
	      and cross our fingers.  Silly Java.  */
	   || code == BLOCK)
    *walk_subtrees = 0;

  /* Cope with the statement expression extension.  */
  else if (code == STATEMENT_LIST)
    ;

  /* Leave the bulk of the work to copy_tree_r itself.  */
  else
    copy_tree_r (tp, walk_subtrees, NULL);

  return NULL_TREE;
}

/* Callback for walk_tree to unshare most of the shared trees rooted at *TP.
   If *TP has been visited already, then *TP is deeply copied by calling
   mostly_copy_tree_r.  DATA is passed to mostly_copy_tree_r unmodified.  */

static tree
copy_if_shared_r (tree *tp, int *walk_subtrees, void *data)
{
  tree t = *tp;
  enum tree_code code = TREE_CODE (t);

  /* Skip types, decls, and constants.  But we do want to look at their
     types and the bounds of types.  Mark them as visited so we properly
     unmark their subtrees on the unmark pass.  If we've already seen them,
     don't look down further.  */
  if (TREE_CODE_CLASS (code) == tcc_type
      || TREE_CODE_CLASS (code) == tcc_declaration
      || TREE_CODE_CLASS (code) == tcc_constant)
    {
      if (TREE_VISITED (t))
	*walk_subtrees = 0;
      else
	TREE_VISITED (t) = 1;
    }

  /* If this node has been visited already, unshare it and don't look
     any deeper.  */
  else if (TREE_VISITED (t))
    {
      walk_tree (tp, mostly_copy_tree_r, data, NULL);
      *walk_subtrees = 0;
    }

  /* Otherwise, mark the node as visited and keep looking.  */
  else
    TREE_VISITED (t) = 1;

  return NULL_TREE;
}

/* Unshare most of the shared trees rooted at *TP.  DATA is passed to the
   copy_if_shared_r callback unmodified.  */

static inline void
copy_if_shared (tree *tp, void *data)
{
  walk_tree (tp, copy_if_shared_r, data, NULL);
}

/* Unshare all the trees in the body of FNDECL, as well as in the bodies of
   any nested functions.  */

static void
unshare_body (tree fndecl)
{
  struct cgraph_node *cgn = cgraph_node::get (fndecl);
  /* If the language requires deep unsharing, we need a pointer set to make
     sure we don't repeatedly unshare subtrees of unshareable nodes.  */
  hash_set<tree> *visited
    = lang_hooks.deep_unsharing ? new hash_set<tree> : NULL;

  copy_if_shared (&DECL_SAVED_TREE (fndecl), visited);
  copy_if_shared (&DECL_SIZE (DECL_RESULT (fndecl)), visited);
  copy_if_shared (&DECL_SIZE_UNIT (DECL_RESULT (fndecl)), visited);

  delete visited;

  if (cgn)
    for (cgn = cgn->nested; cgn; cgn = cgn->next_nested)
      unshare_body (cgn->decl);
}

/* Callback for walk_tree to unmark the visited trees rooted at *TP.
   Subtrees are walked until the first unvisited node is encountered.  */

static tree
unmark_visited_r (tree *tp, int *walk_subtrees, void *data ATTRIBUTE_UNUSED)
{
  tree t = *tp;

  /* If this node has been visited, unmark it and keep looking.  */
  if (TREE_VISITED (t))
    TREE_VISITED (t) = 0;

  /* Otherwise, don't look any deeper.  */
  else
    *walk_subtrees = 0;

  return NULL_TREE;
}

/* Unmark the visited trees rooted at *TP.  */

static inline void
unmark_visited (tree *tp)
{
  walk_tree (tp, unmark_visited_r, NULL, NULL);
}

/* Likewise, but mark all trees as not visited.  */

static void
unvisit_body (tree fndecl)
{
  struct cgraph_node *cgn = cgraph_node::get (fndecl);

  unmark_visited (&DECL_SAVED_TREE (fndecl));
  unmark_visited (&DECL_SIZE (DECL_RESULT (fndecl)));
  unmark_visited (&DECL_SIZE_UNIT (DECL_RESULT (fndecl)));

  if (cgn)
    for (cgn = cgn->nested; cgn; cgn = cgn->next_nested)
      unvisit_body (cgn->decl);
}

/* Unconditionally make an unshared copy of EXPR.  This is used when using
   stored expressions which span multiple functions, such as BINFO_VTABLE,
   as the normal unsharing process can't tell that they're shared.  */

tree
unshare_expr (tree expr)
{
  walk_tree (&expr, mostly_copy_tree_r, NULL, NULL);
  return expr;
}

/* Worker for unshare_expr_without_location.  */

static tree
prune_expr_location (tree *tp, int *walk_subtrees, void *)
{
  if (EXPR_P (*tp))
    SET_EXPR_LOCATION (*tp, UNKNOWN_LOCATION);
  else
    *walk_subtrees = 0;
  return NULL_TREE;
}

/* Similar to unshare_expr but also prune all expression locations
   from EXPR.  */

tree
unshare_expr_without_location (tree expr)
{
  walk_tree (&expr, mostly_copy_tree_r, NULL, NULL);
  if (EXPR_P (expr))
    walk_tree (&expr, prune_expr_location, NULL, NULL);
  return expr;
}

/* WRAPPER is a code such as BIND_EXPR or CLEANUP_POINT_EXPR which can both
   contain statements and have a value.  Assign its value to a temporary
   and give it void_type_node.  Return the temporary, or NULL_TREE if
   WRAPPER was already void.  */

tree
voidify_wrapper_expr (tree wrapper, tree temp)
{
  tree type = TREE_TYPE (wrapper);
  if (type && !VOID_TYPE_P (type))
    {
      tree *p;

      /* Set p to point to the body of the wrapper.  Loop until we find
	 something that isn't a wrapper.  */
      for (p = &wrapper; p && *p; )
	{
	  switch (TREE_CODE (*p))
	    {
	    case BIND_EXPR:
	      TREE_SIDE_EFFECTS (*p) = 1;
	      TREE_TYPE (*p) = void_type_node;
	      /* For a BIND_EXPR, the body is operand 1.  */
	      p = &BIND_EXPR_BODY (*p);
	      break;

	    case CLEANUP_POINT_EXPR:
	    case TRY_FINALLY_EXPR:
	    case TRY_CATCH_EXPR:
	      TREE_SIDE_EFFECTS (*p) = 1;
	      TREE_TYPE (*p) = void_type_node;
	      p = &TREE_OPERAND (*p, 0);
	      break;

	    case STATEMENT_LIST:
	      {
		tree_stmt_iterator i = tsi_last (*p);
		TREE_SIDE_EFFECTS (*p) = 1;
		TREE_TYPE (*p) = void_type_node;
		p = tsi_end_p (i) ? NULL : tsi_stmt_ptr (i);
	      }
	      break;

	    case COMPOUND_EXPR:
	      /* Advance to the last statement.  Set all container types to
		 void.  */
	      for (; TREE_CODE (*p) == COMPOUND_EXPR; p = &TREE_OPERAND (*p, 1))
		{
		  TREE_SIDE_EFFECTS (*p) = 1;
		  TREE_TYPE (*p) = void_type_node;
		}
	      break;

	    case TRANSACTION_EXPR:
	      TREE_SIDE_EFFECTS (*p) = 1;
	      TREE_TYPE (*p) = void_type_node;
	      p = &TRANSACTION_EXPR_BODY (*p);
	      break;