Re: [RFC PATCH] ipa-guarded-deref: Add new pass to dereference function pointers

[Richard Biener <richard.guenther@gmail.com>]

On Sun, Nov 13, 2022 at 4:09 PM Christoph Muellner
<christoph.muellner@vrull.eu> wrote:
>
> From: Christoph Müllner <christoph.muellner@vrull.eu>
>
> This patch adds a new pass that looks up function pointer assignments,
> and adds guarded direct calls to the call sites of the function
> pointers.
>
> E.g.: Lets assume an assignment to a function pointer as follows:
>         b->cb = &myfun;
>       Other part of the program can use the function pointer as follows:
>         b->cb ();
>       With this pass the invocation will be transformed to:
>         if (b->cb == myfun)
>           myfun();
>         else
>            b->cb ()
>
> The impact of the dynamic guard is expected to be less than the speedup
> gained by enabled optimizations (e.g. inlining or constant propagation).

We have speculative devirtualization doing this very transform, shouldn't you
instead improve that instead of inventing another specialized pass?

Thanks,
Richard.

> PR ipa/107666
> gcc/ChangeLog:
>
>         * Makefile.in: Add new pass.
>         * common.opt: Add flag -fipa-guarded-deref.
>         * lto-section-in.cc: Add new section "ipa_guarded_deref".
>         * lto-streamer.h (enum lto_section_type): Add new section.
>         * passes.def: Add new pass.
>         * timevar.def (TV_IPA_GUARDED_DEREF): Add time var.
>         * tree-pass.h (make_pass_ipa_guarded_deref): New prototype.
>         * ipa-guarded-deref.cc: New file.
>
> Signed-off-by: Christoph Müllner <christoph.muellner@vrull.eu>
> ---
>  gcc/Makefile.in          |    1 +
>  gcc/common.opt           |    4 +
>  gcc/ipa-guarded-deref.cc | 1115 ++++++++++++++++++++++++++++++++++++++
>  gcc/lto-section-in.cc    |    1 +
>  gcc/lto-streamer.h       |    1 +
>  gcc/passes.def           |    1 +
>  gcc/timevar.def          |    1 +
>  gcc/tree-pass.h          |    1 +
>  8 files changed, 1125 insertions(+)
>  create mode 100644 gcc/ipa-guarded-deref.cc
>
> diff --git a/gcc/Makefile.in b/gcc/Makefile.in
> index f672e6ea549..402c4a6ea3f 100644
> --- a/gcc/Makefile.in
> +++ b/gcc/Makefile.in
> @@ -1462,6 +1462,7 @@ OBJS = \
>         ipa-sra.o \
>         ipa-devirt.o \
>         ipa-fnsummary.o \
> +       ipa-guarded-deref.o \
>         ipa-polymorphic-call.o \
>         ipa-split.o \
>         ipa-inline.o \
> diff --git a/gcc/common.opt b/gcc/common.opt
> index bce3e514f65..8344940ae5b 100644
> --- a/gcc/common.opt
> +++ b/gcc/common.opt
> @@ -1933,6 +1933,10 @@ fipa-bit-cp
>  Common Var(flag_ipa_bit_cp) Optimization
>  Perform interprocedural bitwise constant propagation.
>
> +fipa-guarded-deref
> +Common Var(flag_ipa_guarded_deref) Optimization
> +Perform guarded function pointer derferencing.
> +
>  fipa-modref
>  Common Var(flag_ipa_modref) Optimization
>  Perform interprocedural modref analysis.
> diff --git a/gcc/ipa-guarded-deref.cc b/gcc/ipa-guarded-deref.cc
> new file mode 100644
> index 00000000000..198fb9b33ad
> --- /dev/null
> +++ b/gcc/ipa-guarded-deref.cc
> @@ -0,0 +1,1115 @@
> +/* IPA pass to transform indirect calls to guarded direct calls.
> +   Copyright (C) 2022 Free Software Foundation, Inc.
> +   Contributed by Christoph Muellner (Vrull GmbH)
> +   Based on work by Erick Ochoa (Vrull GmbH)
> +
> +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/>.  */
> +
> +/* Indirect calls are used to separate callees from their call sites.
> +   This helps to implement proper abstraction layers, but prevents
> +   optimizations like constant-propagation or function specialization.
> +
> +   Assuming that we identify a function pointer that gets assigned
> +   only a small amount of times, we can convert the indirect calls
> +   to the target function into guarded direct calls and let later
> +   passes apply additional optimizations.
> +
> +   This pass does this by:
> +   * Identifying function pointers that are assigned up to N=1 times
> +     to struct fields.
> +   * Convert the indirect calls into a test for the call target
> +     and a direct call
> +   * If the test fails, then the indirect call will be executed.
> +
> +   E.g.:
> +   - function foo's address is taken and stored in a field of struct
> +       o->func = foo;
> +   - the program writes into this struct field only once
> +   - it is possible, that we miss a store (we would need strong guarantees)
> +     therefore, we do the following conversion:
> +       o->func ()
> +     <-->
> +       if (o->func == foo)
> +        foo ()
> +       else
> +        o->func ()
> +
> +   This pass is implemented as a full IPA pass that uses the LTO section
> +   "ipa_guarded_deref".  */
> +
> +#include "config.h"
> +#include "system.h"
> +#include "coretypes.h"
> +#include "backend.h"
> +#include "tree.h"
> +#include "gimple.h"
> +#include "alloc-pool.h"
> +#include "tree-pass.h"
> +#include "tree-cfg.h"
> +#include "ssa.h"
> +#include "cgraph.h"
> +#include "gimple-pretty-print.h"
> +#include "gimple-iterator.h"
> +#include "symbol-summary.h"
> +#include "ipa-utils.h"
> +
> +#include "attr-fnspec.h"
> +#include "gimple-ssa.h"
> +#include "data-streamer.h"
> +#include "lto-streamer.h"
> +#include "print-tree.h"
> +#include "calls.h"
> +#include "gimple-fold.h"
> +#include "tree-vrp.h"
> +#include "ipa-prop.h"
> +#include "ipa-fnsummary.h"
> +#include "demangle.h"
> +#include "dbgcnt.h"
> +#include "intl.h"
> +#include "stringpool.h"
> +#include "attribs.h"
> +#include "streamer-hooks.h"
> +
> +#include "alloc-pool.h"
> +#include "tree-pass.h"
> +#include "gimple-iterator.h"
> +#include "tree-dfa.h"
> +#include "cgraph.h"
> +#include "ipa-utils.h"
> +#include "symbol-summary.h"
> +#include "gimple-pretty-print.h"
> +#include "gimple-walk.h"
> +#include "print-tree.h"
> +#include "tree-streamer.h"
> +#include "alias.h"
> +#include "calls.h"
> +#include "ipa-modref-tree.h"
> +#include "ipa-modref.h"
> +#include "value-range.h"
> +#include "ipa-prop.h"
> +#include "ipa-fnsummary.h"
> +#include "attr-fnspec.h"
> +#include "symtab-clones.h"
> +#include "gimple-ssa.h"
> +#include "tree-phinodes.h"
> +#include "tree-ssa-operands.h"
> +#include "ssa-iterators.h"
> +#include "stringpool.h"
> +#include "tree-ssanames.h"
> +#include "attribs.h"
> +#include "tree-cfg.h"
> +#include "tree-eh.h"
> +#include "hash-traits.h"
> +
> +/* Struct that holds a function pointer type.
> +   In our context a function pointer type is a record-field pair,
> +   with the field being of a function pointer type.  */
> +
> +struct function_pointer_type
> +{
> +  /* Record type hosting the function pointer.  */
> +  tree record;
> +  /* field_decl of the function pointer.  */
> +  tree field;
> +};
> +
> +/* Add a default hash trait for the type function_pointer_type, so it can be used
> +   as key in hash collections (hash_map, hash_set, etc.).  */
> +
> +template <>
> +struct default_hash_traits <function_pointer_type>
> +  : typed_noop_remove <function_pointer_type>
> +{
> +  GTY((skip)) typedef function_pointer_type value_type;
> +  GTY((skip)) typedef function_pointer_type compare_type;
> +  static hashval_t
> +  hash (function_pointer_type p)
> +    {
> +      return TYPE_UID (p.record) ^ DECL_UID (p.field);
> +    }
> +  static const bool empty_zero_p = true;
> +  static bool
> +  is_empty (function_pointer_type p)
> +    {
> +      return p.record == NULL_TREE;
> +    }
> +  static bool
> +  is_deleted (function_pointer_type p ATTRIBUTE_UNUSED)
> +    {
> +      return false;
> +    }
> +  static bool
> +  equal (const function_pointer_type &l,
> +        const function_pointer_type &r)
> +    {
> +      return (l.record == r.record) && (l.field == r.field);
> +    }
> +  static void
> +  mark_empty (function_pointer_type &p)
> +    {
> +      p.record = NULL_TREE;
> +      p.field = NULL_TREE;
> +    }
> +  static void
> +  mark_deleted (function_pointer_type &p)
> +    {
> +      p.record = NULL_TREE;
> +      p.field = NULL_TREE;
> +    }
> +};
> +
> +/* Store a call target to a function-pointer-type.
> +   With this class we can correlate a field-record-pair
> +   with a function pointer field with a call target.
> +
> +   We maintain a 1:N mapping here, i.e. a fpt can have exactly 1 call target,
> +   but a call target can be referenced by multiple fpts.
> +
> +   Note, that the information needs to be extracted with
> +   the function pointer type as key and the call target as value.
> +   However, on call graph modification events, we need a reverse
> +   lookup (currenlty we don't optimize this code path).  */
> +
> +class function_pointer_type_assignments
> +{
> +private:
> +  /* Track function-pointer-types and their assigned call targets.  */
> +  hash_map <function_pointer_type, cgraph_node *> m_assignments;
> +
> +public:
> +  function_pointer_type_assignments () {}
> +
> +  /* Get the call target for a function pointer type (if any).  */
> +  cgraph_node *get_target (const function_pointer_type &v)
> +    {
> +      cgraph_node **pnode = m_assignments.get (v);
> +      return pnode ? *pnode : NULL;
> +    }
> +
> +  /* Add a new assignment for a function pointer type.  */
> +
> +  void
> +  add_assignment (function_pointer_type fpt, cgraph_node *target)
> +    {
> +      bool existed_p;
> +      cgraph_node *&node = m_assignments.get_or_insert (fpt, &existed_p);
> +      if (existed_p)
> +         /* More, than one target -> set call target to NULL (unknown).  */
> +         node = NULL;
> +      else
> +         node = target;
> +    }
> +
> +  /* Print all stored information.  */
> +
> +  void
> +  print (void)
> +    {
> +      if (!dump_file)
> +       return;
> +
> +      fprintf (dump_file,
> +              "Collected the following function pointer assignments:\n");
> +
> +      hash_map<function_pointer_type, cgraph_node*>::iterator iter
> +              = m_assignments.begin ();
> +      for (; iter != m_assignments.end (); ++iter)
> +       {
> +         function_pointer_type fpt = (*iter).first;
> +         cgraph_node* callee = (*iter).second;
> +
> +         if (fpt.record == NULL_TREE
> +             || fpt.field == NULL_TREE
> +             || callee == NULL)
> +           continue;
> +
> +         fprintf (dump_file, "  ");
> +         print_generic_expr (dump_file, fpt.record, TDF_NONE);
> +         fprintf (dump_file, "::");
> +         print_generic_expr (dump_file, fpt.field, TDF_NONE);
> +         fprintf (dump_file, " := %s\n", callee ? callee->name () : "<unknown>");
> +       }
> +    }
> +
> +  /* Callback for node removal.  */
> +
> +  void
> +  remove (cgraph_node *node)
> +    {
> +      /* Iterators are not removal-safe.
> +        Therefore we need to advance the iterator before
> +        we delete the element pointed to by the iterator.
> +        To do so, we use a helper pointer.  */
> +      function_pointer_type to_delete;
> +      bool delete_fpt = false;
> +
> +      /* We iterate over all entries, which is not optimal.
> +        To improve this, we need a way for a reverse-lookup.  */
> +      hash_map<function_pointer_type, cgraph_node*>::iterator iter
> +              = m_assignments.begin ();
> +      for (; iter != m_assignments.end (); ++iter)
> +       {
> +         /* Deletion comes *after* iterator advancement.  */
> +         if (delete_fpt)
> +           {
> +             m_assignments.remove (to_delete);
> +             delete_fpt = false;
> +           }
> +
> +         /* Get the cgraph node and check if it matches.  */
> +         cgraph_node* n = (*iter).second;
> +         if (n == node)
> +           {
> +             /* Mark for removal (see above).  */
> +             to_delete = (*iter).first;
> +             delete_fpt = true;
> +           }
> +       }
> +
> +      /* Deletion comes *after* iterator advancement.  */
> +      if (delete_fpt)
> +       {
> +         m_assignments.remove (to_delete);
> +         delete_fpt = false;
> +       }
> +    }
> +
> +  void
> +  serialize (struct output_block *ob, lto_symtab_encoder_t &encoder)
> +    {
> +      unsigned HOST_WIDE_INT elements = m_assignments.elements ();
> +
> +      /* Write the number of elements.  */
> +      streamer_write_uhwi (ob, elements);
> +
> +      hash_map<function_pointer_type, cgraph_node*>::iterator iter
> +              = m_assignments.begin ();
> +      for (; iter != m_assignments.end (); ++iter)
> +       {
> +         /* Write the function pointer type.  */
> +         function_pointer_type fpt = (*iter).first;
> +         stream_write_tree_ref (ob, fpt.record);
> +         stream_write_tree_ref (ob, fpt.field);
> +
> +         /* Write the callee.  */
> +         unsigned HOST_WIDE_INT symid;
> +         cgraph_node* callee = (*iter).second;
> +         if (callee)
> +           symid = lto_symtab_encoder_encode (encoder, callee);
> +         else
> +           symid = 0;
> +
> +         streamer_write_uhwi (ob, symid);
> +       }
> +    }
> +
> +  void
> +  deserialize (lto_input_block &ib, class data_in *data_in,
> +              lto_symtab_encoder_t &encoder)
> +    {
> +      size_t elements = streamer_read_uhwi (&ib);
> +      for (size_t i = 0; i < elements; i++)
> +       {
> +         /* Read the function pointer type.  */
> +         function_pointer_type fpt;
> +         fpt.record = stream_read_tree_ref (&ib, data_in);
> +         fpt.field = stream_read_tree_ref (&ib, data_in);
> +
> +         /* Read the callee.  */
> +         cgraph_node *callee = NULL;
> +         unsigned HOST_WIDE_INT symid = streamer_read_uhwi (&ib);
> +         if (symid)
> +           {
> +             symtab_node *scallee = lto_symtab_encoder_deref (encoder, symid);
> +             callee = dyn_cast <cgraph_node *> (scallee);
> +           }
> +
> +         /* Add the function pointer type assignment.  */
> +         add_assignment (fpt, callee);
> +       }
> +    }
> +
> +  ~function_pointer_type_assignments () {}
> +};
> +
> +/* Store a record-field-pair to a call graph edge.
> +   With this class we can correlate an indirect call with
> +   the field-record-pair of its call site.
> +
> +   Note, that the information needs to be extracted with
> +   the edge as key and the function pointer type as value.  */
> +
> +class indirect_call_summary
> +  :  public call_summary<function_pointer_type *>
> +{
> +public:
> +  indirect_call_summary (symbol_table *table)
> +    : call_summary <function_pointer_type *> (table)
> +  { }
> +
> +  /* Hook that is called by summary when an edge is duplicated.  */
> +  virtual void duplicate (cgraph_edge *src ATTRIBUTE_UNUSED,
> +                         cgraph_edge *dst ATTRIBUTE_UNUSED,
> +                         function_pointer_type *old_fpt,
> +                         function_pointer_type *new_fpt)
> +    {
> +      /* We may not have record-field-pair, because not every edge
> +        is an indirect call.  */
> +      if (!old_fpt)
> +       return;
> +
> +      new_fpt->record = old_fpt->record;
> +      new_fpt->field = old_fpt->field;
> +    }
> +
> +  /* Print all stored information.  */
> +
> +  void
> +  print (void)
> +    {
> +      if (!dump_file)
> +       return;
> +
> +      fprintf (dump_file,
> +              "Collected the following indirect calls:\n");
> +
> +      cgraph_node *caller = NULL;
> +      FOR_EACH_FUNCTION_WITH_GIMPLE_BODY (caller)
> +       {
> +         for (cgraph_edge *e = caller->indirect_calls; e; e = e->next_callee)
> +           {
> +             function_pointer_type *fpt = get (e);
> +             if (fpt && fpt->record && fpt->field)
> +               {
> +                 fprintf (dump_file, "  ");
> +                 fprintf (dump_file, "%s -> ", caller->name ());
> +                 print_generic_expr (dump_file, fpt->record, TDF_NONE);
> +                 fprintf (dump_file, "::");
> +                 print_generic_expr (dump_file, fpt->field, TDF_NONE);
> +                 fprintf (dump_file, "\n");
> +               }
> +           }
> +       }
> +     }
> +
> +  void
> +  serialize (struct output_block *ob, lto_symtab_encoder_t encoder)
> +    {
> +      unsigned HOST_WIDE_INT elements = 0;
> +
> +      /* We iterate over all (cnodes x edges) and store all that have
> +        additional information stored.  */
> +
> +      lto_symtab_encoder_iterator it;
> +      for (it = lsei_start_function_in_partition (encoder); !lsei_end_p (it);
> +          lsei_next_function_in_partition (&it))
> +       {
> +         cgraph_node *node = lsei_cgraph_node (it);
> +         if (node->has_gimple_body_p ())
> +           elements++;
> +       }
> +
> +      /* Write the number of elements.  */
> +      streamer_write_uhwi (ob, elements);
> +
> +      for (it = lsei_start_function_in_partition (encoder); !lsei_end_p (it);
> +          lsei_next_function_in_partition (&it))
> +       {
> +         cgraph_node *caller = lsei_cgraph_node (it);
> +         if (!caller->has_gimple_body_p ())
> +           continue;
> +
> +         /* Write caller.  */
> +         unsigned HOST_WIDE_INT symid = lto_symtab_encoder_encode (encoder,
> +                                                                   caller);
> +         streamer_write_uhwi (ob, symid);
> +
> +         for (cgraph_edge *e = caller->indirect_calls; e; e = e->next_callee)
> +           {
> +             function_pointer_type *fpt = get (e);
> +             if (fpt && fpt->record && fpt->field)
> +               {
> +                 /* Write the function pointer type.  */
> +                 stream_write_tree_ref (ob, fpt->record);
> +                 stream_write_tree_ref (ob, fpt->field);
> +               }
> +             else
> +               {
> +                 stream_write_tree_ref (ob, NULL_TREE);
> +                 stream_write_tree_ref (ob, NULL_TREE);
> +               }
> +           }
> +       }
> +    }
> +
> +  void
> +  deserialize (lto_input_block &ib, class data_in *data_in,
> +              lto_symtab_encoder_t &encoder)
> +    {
> +      /* Read the number of elements.  */
> +      size_t elements = streamer_read_uhwi (&ib);
> +
> +      for (size_t i = 0; i < elements; i++)
> +       {
> +         /* Read caller.  */
> +         unsigned HOST_WIDE_INT symid = streamer_read_uhwi (&ib);
> +         symtab_node *scaller = lto_symtab_encoder_deref (encoder, symid);
> +         cgraph_node *caller = dyn_cast <cgraph_node *> (scaller);
> +
> +         for (cgraph_edge *e = caller->indirect_calls; e; e = e->next_callee)
> +           {
> +             tree record = stream_read_tree_ref (&ib, data_in);
> +             tree field = stream_read_tree_ref (&ib, data_in);
> +             if (record == NULL_TREE && field == NULL_TREE)
> +               continue;
> +
> +             function_pointer_type *fpt = get_create (e);
> +             fpt->record = record;
> +             fpt->field = field;
> +           }
> +       }
> +    }
> +};
> +
> +class gimple_walker
> +{
> +public:
> +  gimple_walker () {}
> +
> +  void walk (void* data);
> +
> +protected:
> +  /* Overload these callbacks.  */
> +  virtual void walk_gassign (__attribute__ ((unused)) cgraph_node*,
> +                            __attribute__ ((unused)) gassign*,
> +                            __attribute__ ((unused)) void*) {}
> +  virtual void walk_gcall (__attribute__ ((unused)) cgraph_node*,
> +                          __attribute__ ((unused)) gcall*,
> +                          __attribute__ ((unused)) void*) {}
> +
> +private:
> +  /* Will walk declarations, locals, ssa names, and basic blocks.  */
> +  void _walk_cnode (cgraph_node *cnode, void *data);
> +
> +  /* Iterate over all basic blocks in CNODE.  */
> +  void _walk_bb (cgraph_node *cnode, basic_block bb, void *data);
> +
> +  /* Iterate over all gimple_stmt in BB.  */
> +  void _walk_gimple (cgraph_node *cnode, gimple *stmt, void *data);
> +};
> +
> +void
> +gimple_walker::walk (void *data)
> +{
> +  hash_set<tree> fndecls2;
> +  cgraph_node *node = NULL;
> +
> +  FOR_EACH_FUNCTION_WITH_GIMPLE_BODY (node)
> +    {
> +      node->get_body ();
> +      tree decl = node->decl;
> +      gcc_assert (decl);
> +      const bool already_in_set = fndecls2.contains (decl);
> +
> +      /* I think it is possible for different nodes to point to the same
> +        declaration.  */
> +      if (already_in_set)
> +       continue;
> +
> +      if (dump_file)
> +       dump_function_to_file (node->decl, dump_file, TDF_NONE);
> +
> +      _walk_cnode (node, data);
> +
> +      /* Add to set of known declarations.  */
> +      fndecls2.add (decl);
> +    }
> +}
> +
> +/* Walk over all basic blocks in CNODE.  */
> +
> +void
> +gimple_walker::_walk_cnode (cgraph_node *cnode, void *data)
> +{
> +  cnode->get_body ();
> +  tree decl = cnode->decl;
> +  gcc_assert (decl);
> +
> +  function *func = DECL_STRUCT_FUNCTION (decl);
> +  gcc_assert (func);
> +
> +  basic_block bb = NULL;
> +
> +  push_cfun (func);
> +  FOR_EACH_BB_FN (bb, func)
> +    {
> +      _walk_bb (cnode, bb, data);
> +    }
> +  pop_cfun ();
> +}
> +
> +/* Walk over each gimple statement in BB.  */
> +
> +void
> +gimple_walker::_walk_bb (cgraph_node *cnode, basic_block bb, void *data)
> +{
> +  gimple_stmt_iterator gsi;
> +  for (gsi = gsi_start_bb (bb); !gsi_end_p (gsi); gsi_next (&gsi))
> +    {
> +      gimple *stmt = gsi_stmt (gsi);
> +      _walk_gimple (cnode, stmt, data);
> +    }
> +}
> +
> +/* Switch for different gimple instruction types.  */
> +
> +void
> +gimple_walker::_walk_gimple (cgraph_node *cnode, gimple *stmt, void *data)
> +{
> +  const enum gimple_code code = gimple_code (stmt);
> +  switch (code)
> +    {
> +      case GIMPLE_ASSIGN:
> +       {
> +         gassign *assign = dyn_cast<gassign *> (stmt);
> +         walk_gassign (cnode, assign, data);
> +         break;
> +       }
> +      case GIMPLE_CALL:
> +       {
> +         gcall *call = dyn_cast<gcall *> (stmt);
> +         walk_gcall (cnode, call, data);
> +         break;
> +       }
> +      default:
> +       break;
> +    }
> +}
> +
> +class gimple_assignment_collector : public gimple_walker
> +{
> +protected:
> +  virtual void walk_gassign (cgraph_node *cnode, gassign *stmt, void *data)
> +    {
> +      if (dump_file)
> +       fprintf (dump_file, "%s: Entering.\n", __func__);
> +
> +      function_pointer_type_assignments *fpas
> +       = (function_pointer_type_assignments*) data;
> +
> +      tree lhs = gimple_assign_lhs (stmt);
> +      gcc_assert (lhs);
> +
> +      /* We only care about a rhs which is a variable or a constant.
> +        Therefore, we only need to look at unary or single rhs.  */
> +      const enum gimple_rhs_class gclass = gimple_assign_rhs_class (stmt);
> +      if (gclass != GIMPLE_UNARY_RHS
> +         && gclass != GIMPLE_SINGLE_RHS)
> +       {
> +         if (dump_file)
> +           fprintf (dump_file, "%s: RHS class not matching.\n", __func__);
> +         return;
> +       }
> +
> +      tree rhs = gimple_assign_rhs1 (stmt);
> +
> +      if (dump_file)
> +       {
> +         fprintf (dump_file, "%s: Analysing assignment:\n", __func__);
> +         fprintf (dump_file, " Function: %s\n", cnode->name ());
> +         fprintf (dump_file, " LHS: ");
> +         print_generic_expr (dump_file, lhs, TDF_NONE);
> +         fprintf (dump_file, "\n RHS: ");
> +         print_generic_expr (dump_file, rhs, TDF_NONE);
> +         fprintf (dump_file, "\n");
> +       }
> +
> +      /* We are only interested in function pointers.  */
> +      tree rhs_t = TREE_TYPE (rhs);
> +      tree lhs_t = TREE_TYPE (lhs);
> +      if (TREE_CODE (rhs_t) != POINTER_TYPE
> +         || TREE_CODE (lhs_t) != POINTER_TYPE)
> +       {
> +         if (dump_file)
> +           fprintf (dump_file, "%s: LHS not pointer type.\n", __func__);
> +         return;
> +       }
> +      if (TREE_CODE (TREE_TYPE (rhs_t)) != FUNCTION_TYPE
> +         || TREE_CODE (TREE_TYPE (lhs_t)) != FUNCTION_TYPE)
> +       {
> +         if (dump_file)
> +           fprintf (dump_file, "%s: RHS not function type.\n", __func__);
> +         return;
> +       }
> +
> +      /* We only care about function pointers assigned to fields.
> +        So we look for COMPONENT_REF.  */
> +      const enum tree_code code = TREE_CODE (lhs);
> +      if (code != COMPONENT_REF)
> +       {
> +         if (dump_file)
> +           fprintf (dump_file, "%s: LHS not component ref.\n", __func__);
> +         return;
> +       }
> +
> +      tree base = TREE_OPERAND (lhs, 0);
> +      tree base_t = TREE_TYPE (base);
> +
> +      /* We either have a record or a pointer to a record.  */
> +      if (TREE_CODE (base_t) == POINTER_TYPE)
> +       base_t = TREE_TYPE (base_t);
> +
> +      if (TREE_CODE (base_t) != RECORD_TYPE)
> +       {
> +         if (dump_file)
> +           {
> +             fprintf (dump_file, "%s: Base type not record type.\n", __func__);
> +             fprintf (dump_file, "%s: base: ", __func__);
> +             print_generic_expr (dump_file, base, TDF_DETAILS);
> +             fprintf (dump_file, "%s: base_t: ", __func__);
> +             print_generic_expr (dump_file, base_t, TDF_DETAILS);
> +           }
> +         return;
> +       }
> +
> +      /* We only care about addr expressions.  */
> +      if (TREE_CODE (rhs) != ADDR_EXPR)
> +       {
> +         if (dump_file)
> +           fprintf (dump_file, "%s: RHS is not addr expr.\n", __func__);
> +         return;
> +       }
> +
> +      tree possible_decl = TREE_OPERAND (rhs, 0);
> +      if (TREE_CODE (possible_decl) != FUNCTION_DECL)
> +       {
> +         if (dump_file)
> +           fprintf (dump_file, "%s: RHS addr expr is not a function decl.\n",
> +                    __func__);
> +         return;
> +       }
> +
> +      tree field = TREE_OPERAND (lhs, 1);
> +
> +      /* Add record type and field decl to global summary.  */
> +      function_pointer_type pair;
> +      pair.record = base_t;
> +      pair.field = field;
> +      cgraph_node *node = cgraph_node::get (possible_decl);
> +
> +      /* This is a candidate for optimization.  */
> +      if (dump_file)
> +       {
> +         cgraph_node *orig = cgraph_node::get (cfun->decl);
> +         fprintf (dump_file, "Candidate found in %s:\n", orig->name ());
> +         print_gimple_stmt (dump_file, stmt, dump_flags);
> +       }
> +
> +      fpas->add_assignment (pair, node);
> +    }
> +
> +  virtual void walk_gcall (cgraph_node *cnode, gcall *stmt, void *data)
> +    {
> +      (void)cnode;
> +
> +      if (dump_file)
> +       fprintf (dump_file, "%s: Entering.\n", __func__);
> +
> +      function_pointer_type_assignments *fpas
> +       = (function_pointer_type_assignments*) data;
> +
> +      gcc_assert (stmt);
> +      tree lhs = gimple_call_lhs (stmt);
> +      if (!lhs)
> +       return;
> +
> +      tree lhs_t = TREE_TYPE (lhs);
> +      /* We are only interested in function pointers.  */
> +      if (TREE_CODE (lhs_t) != POINTER_TYPE)
> +       return;
> +      if (TREE_CODE (TREE_TYPE (lhs_t)) != FUNCTION_TYPE)
> +       return;
> +
> +      /* We only care about function pointers assigned to fields.
> +        So we look for COMPONENT_REF.  */
> +      const enum tree_code code = TREE_CODE (lhs);
> +      if (code != COMPONENT_REF)
> +       return;
> +
> +      /* We either have a record or a pointer to a record.  */
> +      tree base = TREE_OPERAND (lhs, 0);
> +      tree base_t = TREE_TYPE (base);
> +      if (TREE_CODE (base_t) != POINTER_TYPE)
> +       return;
> +      base_t = TREE_TYPE (base_t);
> +      if (TREE_CODE (base_t) != RECORD_TYPE)
> +       return;
> +      if (!TYPE_P (base_t))
> +       return;
> +
> +      tree field = TREE_OPERAND (lhs, 1);
> +
> +      /* Add record type and field decl to global summary.  */
> +      function_pointer_type pair;
> +      pair.record = base_t;
> +      pair.field = field;
> +
> +      /* This is a reason to not optimize this pointer.  */
> +      if (dump_file)
> +       {
> +         cgraph_node *orig = cgraph_node::get (cfun->decl);
> +         fprintf (dump_file, "Counter-candidate found in %s:\n", orig->name ());
> +         print_gimple_stmt (dump_file, stmt, dump_flags);
> +       }
> +
> +      fpas->add_assignment (pair, NULL);
> +    }
> +};
> +
> +/* Globals (prefixed by '_').  */
> +static function_pointer_type_assignments *_function_pointer_type_assignments;
> +static indirect_call_summary *_indirect_call_summaries;
> +static struct cgraph_node_hook_list *_cgraph_removal_hook_holder;
> +
> +/* Function updates our global summary.  */
> +
> +static void
> +remove_cgraph_callback (cgraph_node *node, void *data ATTRIBUTE_UNUSED)
> +{
> +  if (dump_file)
> +    fprintf (dump_file, "%s: node removal: %s\n", __func__, node->name ());
> +  _function_pointer_type_assignments->remove (node);
> +}
> +
> +/* Register notification callbacks.  */
> +
> +static void
> +guarded_deref_register_cgraph_hooks (void)
> +{
> +  _cgraph_removal_hook_holder
> +    = symtab->add_cgraph_removal_hook (&remove_cgraph_callback, NULL);
> +}
> +
> +/* Unregister notification callbacks.  */
> +
> +static void
> +guarded_deref_unregister_cgraph_hooks (void)
> +{
> +  if (_cgraph_removal_hook_holder)
> +    symtab->remove_cgraph_removal_hook (_cgraph_removal_hook_holder);
> +  _cgraph_removal_hook_holder = NULL;
> +}
> +
> +static void
> +guarded_deref_find_indirect (struct cgraph_node *node,
> +                            indirect_call_summary *ics)
> +{
> +  if (!node || node->inlined_to || !node->has_gimple_body_p ())
> +    return;
> +
> +  for (cgraph_edge *e = node->indirect_calls; e; e = e->next_callee)
> +    {
> +      gimple *stmt = e->call_stmt;
> +      if (gimple_code (stmt) != GIMPLE_CALL)
> +       continue;
> +
> +      gcall *call_stmt = dyn_cast<gcall *> (stmt);
> +      tree target = gimple_call_fn (call_stmt);
> +      if (!target)
> +       continue;
> +
> +      if (TREE_CODE (target) != SSA_NAME)
> +       continue;
> +
> +      gimple *def = SSA_NAME_DEF_STMT (target);
> +
> +      if (!gimple_assign_load_p (def))
> +       continue;
> +
> +      const enum gimple_rhs_class gclass = gimple_assign_rhs_class (def);
> +      const bool valid = gclass == GIMPLE_UNARY_RHS || gclass == GIMPLE_SINGLE_RHS;
> +      if (!valid)
> +       continue;
> +
> +      tree rhs = gimple_assign_rhs1 (def);
> +      const enum tree_code code = TREE_CODE (rhs);
> +      bool is_load = COMPONENT_REF == code;
> +      if (!is_load)
> +       continue;
> +
> +      tree base = TREE_OPERAND (rhs, 0);
> +      tree field = TREE_OPERAND (rhs, 1);
> +      if (RECORD_TYPE != TREE_CODE (TREE_TYPE (base)))
> +       continue;
> +
> +      function_pointer_type *fpt = ics->get_create (e);
> +      fpt->record = TREE_TYPE (base);
> +      fpt->field = field;
> +    }
> +}
> +
> +static void
> +guarded_deref_generate_summary (void)
> +{
> +  if (dump_file)
> +    fprintf (dump_file, "%s: Entering.\n", __func__);
> +
> +  /* Allocate globals.  */
> +  _function_pointer_type_assignments = new function_pointer_type_assignments;
> +  _indirect_call_summaries = new indirect_call_summary (symtab);
> +
> +  /* First collect all function pointer assignments.  */
> +  gimple_assignment_collector collector;
> +  collector.walk (_function_pointer_type_assignments);
> +
> +  /* Now collect all indirect calls.  */
> +  cgraph_node *cnode = NULL;
> +  FOR_EACH_FUNCTION_WITH_GIMPLE_BODY (cnode)
> +    {
> +      guarded_deref_find_indirect (cnode, _indirect_call_summaries);
> +    }
> +
> +  /* Print collected information.  */
> +  _function_pointer_type_assignments->print ();
> +  _indirect_call_summaries-> print ();
> +
> +  /* Register hooks for cgraph changes in other passes.  */
> +  guarded_deref_register_cgraph_hooks ();
> +}
> +
> +static void
> +guarded_deref_write_summary (void)
> +{
> +  if (dump_file)
> +    fprintf (dump_file, "%s: Entering.\n", __func__);
> +
> +  /* Only run if we are in a sane state.  */
> +  if (!_function_pointer_type_assignments || !_indirect_call_summaries)
> +    return;
> +
> +  /* Print collected information.  */
> +  _function_pointer_type_assignments->print ();
> +  _indirect_call_summaries-> print ();
> +
> +  /* Unregister cgraph change hooks.  */
> +  guarded_deref_unregister_cgraph_hooks ();
> +
> +  /* Create an output block to write out information into.  */
> +  struct output_block *ob = create_output_block (LTO_section_ipa_guarded_deref);
> +
> +  /* Get the cgraph_node encoder.  */
> +  lto_symtab_encoder_t encoder = ob->decl_state->symtab_node_encoder;
> +
> +  /* Write collected function pointer assignments to the OB.  */
> +  _function_pointer_type_assignments->serialize (ob, encoder);
> +
> +  /* Write edge summaries.  */
> +  _indirect_call_summaries->serialize (ob, encoder);
> +
> +  /* Delete the information in memory.  */
> +  delete _function_pointer_type_assignments;
> +  _function_pointer_type_assignments = NULL;
> +  delete _indirect_call_summaries;
> +  _indirect_call_summaries = NULL;
> +
> +  /* Write the contents of the output block into the instruction stream.  */
> +  produce_asm (ob, NULL);
> +
> +  /* Now destroy the output block.  */
> +  destroy_output_block (ob);
> +}
> +
> +static void
> +guarded_deref_read_summary (void)
> +{
> +  if (dump_file)
> +    fprintf (dump_file, "%s: Entering.\n", __func__);
> +
> +  if (_indirect_call_summaries || _function_pointer_type_assignments)
> +    return;
> +
> +  /* Allocate globals.  */
> +  _indirect_call_summaries = new indirect_call_summary (symtab);
> +  _function_pointer_type_assignments = new function_pointer_type_assignments;
> +
> +  struct lto_file_decl_data **file_data_vec = lto_get_file_decl_data ();
> +  struct lto_file_decl_data *file_data;
> +  unsigned int j = 0;
> +  while ((file_data = file_data_vec[j++]))
> +    {
> +      size_t len;
> +      const char *data = lto_get_summary_section_data (file_data,
> +                                                      LTO_section_ipa_guarded_deref,
> +                                                      &len);
> +      if (!data)
> +       continue;
> +
> +      const struct lto_function_header *header
> +       = (const struct lto_function_header*) data;
> +
> +      const int cfg_offset = sizeof (*header);
> +      const int main_offset = cfg_offset + header->cfg_size;
> +      const int string_offset = main_offset + header->main_size;
> +      class data_in *data_in;
> +
> +      lto_input_block ib ((const char *) data + main_offset,
> +                         header->main_size, file_data->mode_table);
> +      data_in = lto_data_in_create (file_data,
> +                                   (const char *) data + string_offset,
> +                                   header->string_size, vNULL);
> +
> +      lto_symtab_encoder_t encoder = file_data->symtab_node_encoder;
> +
> +      /* Read collected function pointer assignments from LTO stream.  */
> +      _function_pointer_type_assignments->deserialize (ib, data_in, encoder);
> +
> +       /* Read collected indirect call summary from LTO stream.  */
> +      _indirect_call_summaries->deserialize (ib, data_in, encoder);
> +
> +      lto_free_section_data (file_data, LTO_section_ipa_guarded_deref, NULL,
> +                            data, len);
> +      lto_data_in_delete (data_in);
> +    }
> +
> +  /* Print collected information.  */
> +  _function_pointer_type_assignments->print ();
> +  _indirect_call_summaries-> print ();
> +
> +  /* Register hooks for cgraph changes in other passes.  */
> +  guarded_deref_register_cgraph_hooks ();
> +}
> +
> +static unsigned int
> +guarded_deref_execute (void)
> +{
> +  if (dump_file)
> +    fprintf (dump_file, "%s: Entering.\n", __func__);
> +
> +  if (!_function_pointer_type_assignments
> +      || !_indirect_call_summaries)
> +    return 0;
> +
> +  /* Unregister cgraph change hooks.  */
> +  guarded_deref_unregister_cgraph_hooks ();
> +
> +  /* Print collected information.  */
> +  _function_pointer_type_assignments->print ();
> +  _indirect_call_summaries-> print ();
> +
> +  if (dump_file)
> +    fprintf (dump_file, "%s: Starting propagation.\n", __func__);
> +
> +  cgraph_node *cnode = NULL;
> +  FOR_EACH_FUNCTION_WITH_GIMPLE_BODY (cnode)
> +    {
> +      if (cnode->inlined_to)
> +       continue;
> +
> +      for (cgraph_edge *e = cnode->indirect_calls; e; e = e->next_callee)
> +       {
> +         /* Get the function pointer type for the edge (if any).  */
> +         function_pointer_type *fpt = _indirect_call_summaries->get (e);
> +         if (!fpt || !fpt->record || !fpt->field)
> +           continue;
> +
> +         if (dump_file)
> +           {
> +             fprintf (dump_file, "looking for...:");
> +             print_generic_expr (dump_file, fpt->record, TDF_NONE);
> +             fprintf (dump_file, " ");
> +             print_generic_expr (dump_file, fpt->field, TDF_NONE);
> +             fprintf (dump_file, "\n");
> +           }
> +
> +         /* Now get the call target (if any).  */
> +         cgraph_node *target = _function_pointer_type_assignments->get_target (*fpt);
> +         if (!target || !target->decl)
> +           continue;
> +
> +         if (dump_file)
> +           {
> +             fprintf (dump_file,
> +                      "Replacing indirect call in %s by "
> +                      "speculative direct call to %s\n",
> +                      e->caller->name (), target->name ());
> +           }
> +
> +         /* Convert the indirect call to a direct (speculative) call.  */
> +         ipa_make_edge_direct_to_target (e, target->decl, true);
> +
> +         /* Update the function summaries.  */
> +         ipa_update_overall_fn_summary (cnode);
> +       }
> +    }
> +
> +  if (dump_file)
> +    fprintf (dump_file, "%s: Finished propagation.\n", __func__);
> +
> +  return 0;
> +}
> +
> +namespace {
> +
> +const pass_data pass_data_ipa_guarded_deref =
> +{
> +  IPA_PASS, /* type */
> +  "guarded-deref", /* name */
> +  OPTGROUP_NONE, /* optinfo_flags */
> +  TV_IPA_GUARDED_DEREF, /* tv_id */
> +  0, /* properties_required */
> +  0, /* properties_provided */
> +  0, /* properties_destroyed */
> +  0, /* todo_flags_start */
> +  0, /* todo_flags_finish */
> +};
> +
> +class pass_ipa_guarded_deref : public ipa_opt_pass_d
> +{
> +public:
> +  pass_ipa_guarded_deref (gcc::context *ctxt)
> +    : ipa_opt_pass_d (pass_data_ipa_guarded_deref, ctxt,
> +                     guarded_deref_generate_summary, /* generate_summary */
> +                     guarded_deref_write_summary, /* write_summary */
> +                     guarded_deref_read_summary, /* read_summary */
> +                     NULL, /* write_optimization_summary */
> +                     NULL, /* read_optimization_summary */
> +                     NULL, /* stmt_fixup */
> +                     0, /* function_transform_todo_flags_start */
> +                     NULL, /* function_transform */
> +                     NULL) /* variable_transform */
> +  {}
> +
> +  /* opt_pass methods: */
> +  bool gate (function *) final override
> +    {
> +      return ((in_lto_p || flag_lto) && flag_ipa_guarded_deref);
> +    }
> +
> +  unsigned int execute (function *) final override
> +    {
> +      return guarded_deref_execute ();
> +    }
> +
> +}; // class pass_ipa_guarded_deref
> +
> +} // anon namespace
> +
> +ipa_opt_pass_d *
> +make_pass_ipa_guarded_deref (gcc::context *ctxt)
> +{
> +  return new pass_ipa_guarded_deref (ctxt);
> +}
> diff --git a/gcc/lto-section-in.cc b/gcc/lto-section-in.cc
> index ba87c727670..22f6b66a291 100644
> --- a/gcc/lto-section-in.cc
> +++ b/gcc/lto-section-in.cc
> @@ -57,6 +57,7 @@ const char *lto_section_name[LTO_N_SECTION_TYPES] =
>    "ipa_sra",
>    "odr_types",
>    "ipa_modref",
> +  "ipa_guarded_deref",
>  };
>
>  /* Hooks so that the ipa passes can call into the lto front end to get
> diff --git a/gcc/lto-streamer.h b/gcc/lto-streamer.h
> index 2e3abd97959..744e8738376 100644
> --- a/gcc/lto-streamer.h
> +++ b/gcc/lto-streamer.h
> @@ -229,6 +229,7 @@ enum lto_section_type
>    LTO_section_ipa_sra,
>    LTO_section_odr_types,
>    LTO_section_ipa_modref,
> +  LTO_section_ipa_guarded_deref,
>    LTO_N_SECTION_TYPES          /* Must be last.  */
>  };
>
> diff --git a/gcc/passes.def b/gcc/passes.def
> index 193b5794749..60c029e0515 100644
> --- a/gcc/passes.def
> +++ b/gcc/passes.def
> @@ -154,6 +154,7 @@ along with GCC; see the file COPYING3.  If not see
>    NEXT_PASS (pass_ipa_whole_program_visibility);
>    NEXT_PASS (pass_ipa_profile);
>    NEXT_PASS (pass_ipa_icf);
> +  NEXT_PASS (pass_ipa_guarded_deref);
>    NEXT_PASS (pass_ipa_devirt);
>    NEXT_PASS (pass_ipa_cp);
>    NEXT_PASS (pass_ipa_sra);
> diff --git a/gcc/timevar.def b/gcc/timevar.def
> index 63d9b005180..38fd7798768 100644
> --- a/gcc/timevar.def
> +++ b/gcc/timevar.def
> @@ -72,6 +72,7 @@ DEFTIMEVAR (TV_CGRAPH_FUNC_EXPANSION , "callgraph functions expansion")
>  DEFTIMEVAR (TV_CGRAPH_IPA_PASSES     , "callgraph ipa passes")
>  DEFTIMEVAR (TV_IPA_ODR              , "ipa ODR types")
>  DEFTIMEVAR (TV_IPA_FNSUMMARY         , "ipa function summary")
> +DEFTIMEVAR (TV_IPA_GUARDED_DEREF     , "ipa guarded deref")
>  DEFTIMEVAR (TV_IPA_UNREACHABLE       , "ipa dead code removal")
>  DEFTIMEVAR (TV_IPA_INHERITANCE       , "ipa inheritance graph")
>  DEFTIMEVAR (TV_IPA_VIRTUAL_CALL      , "ipa virtual call target")
> diff --git a/gcc/tree-pass.h b/gcc/tree-pass.h
> index 8480d41384b..6cc200bd83e 100644
> --- a/gcc/tree-pass.h
> +++ b/gcc/tree-pass.h
> @@ -525,6 +525,7 @@ extern ipa_opt_pass_d *make_pass_ipa_inline (gcc::context *ctxt);
>  extern simple_ipa_opt_pass *make_pass_ipa_free_lang_data (gcc::context *ctxt);
>  extern simple_ipa_opt_pass *make_pass_ipa_free_fn_summary (gcc::context *ctxt);
>  extern ipa_opt_pass_d *make_pass_ipa_cp (gcc::context *ctxt);
> +extern ipa_opt_pass_d *make_pass_ipa_guarded_deref (gcc::context *ctxt);
>  extern ipa_opt_pass_d *make_pass_ipa_sra (gcc::context *ctxt);
>  extern ipa_opt_pass_d *make_pass_ipa_icf (gcc::context *ctxt);
>  extern ipa_opt_pass_d *make_pass_ipa_devirt (gcc::context *ctxt);
> --
> 2.38.1
>