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

[Christoph Muellner <christoph.muellner@vrull.eu>]

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).

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