analyzer: reimplement -Wanalyzer-use-of-uninitialized-value [PR95006 et al]

The initial gcc 10 era commit of the analyzer (in
757bf1dff5e8cee34c0a75d06140ca972bfecfa7) had an implementation of
-Wanalyzer-use-of-uninitialized-value, but was sufficiently buggy
that I removed it in 78b9783774bfd3540f38f5b1e3c7fc9f719653d7 before
the release of gcc 10.1

This patch reintroduces the warning, heavily rewritten, with (I hope)
a less buggy implementation this time, for GCC 12.

gcc/analyzer/ChangeLog:
	PR analyzer/95006
	PR analyzer/94713
	PR analyzer/94714
	* analyzer.cc (maybe_reconstruct_from_def_stmt): Split out
	GIMPLE_ASSIGN case into...
	(get_diagnostic_tree_for_gassign_1): New.
	(get_diagnostic_tree_for_gassign): New.
	* analyzer.h (get_diagnostic_tree_for_gassign): New decl.
	* analyzer.opt (Wanalyzer-write-to-string-literal): New.
	* constraint-manager.cc (class svalue_purger): New.
	(constraint_manager::purge_state_involving): New.
	* constraint-manager.h
	(constraint_manager::purge_state_involving): New.
	* diagnostic-manager.cc (saved_diagnostic::supercedes_p): New.
	(dedupe_winners::handle_interactions): New.
	(diagnostic_manager::emit_saved_diagnostics): Call it.
	* diagnostic-manager.h (saved_diagnostic::supercedes_p): New decl.
	* engine.cc (impl_region_model_context::warn): Convert return type
	to bool.  Return false if the diagnostic isn't saved.
	(impl_region_model_context::purge_state_involving): New.
	(impl_sm_context::get_state): Use NULL ctxt when querying old
	rvalue.
	(impl_sm_context::set_next_state): Use new sval when querying old
	state.
	(class dump_path_diagnostic): Move to region-model.cc
	(exploded_node::on_stmt): Move to on_stmt_pre and on_stmt_post.
	Remove call to purge_state_involving.
	(exploded_node::on_stmt_pre): New, based on the above.  Move most
	of it to region_model::on_stmt_pre.
	(exploded_node::on_stmt_post): Likewise, moving to
	region_model::on_stmt_post.
	(class stale_jmp_buf): Fix parent class to use curiously recurring
	template pattern.
	(feasibility_state::maybe_update_for_edge): Call on_call_pre and
	on_call_post on gcalls.
	* exploded-graph.h (impl_region_model_context::warn): Return bool.
	(impl_region_model_context::purge_state_involving): New decl.
	(exploded_node::on_stmt_pre): New decl.
	(exploded_node::on_stmt_post): New decl.
	* pending-diagnostic.h (pending_diagnostic::use_of_uninit_p): New.
	(pending_diagnostic::supercedes_p): New.
	* program-state.cc (sm_state_map::get_state): Inherit state for
	conjured_svalue as well as initial_svalue.
	(sm_state_map::purge_state_involving): Also support SK_CONJURED.
	* region-model-impl-calls.cc (call_details::get_uncertainty):
	Handle m_ctxt being NULL.
	(call_details::get_or_create_conjured_svalue): New.
	(region_model::impl_call_fgets): New.
	(region_model::impl_call_fread): New.
	* region-model-manager.cc
	(region_model_manager::get_or_create_initial_value): Return an
	uninitialized poisoned value for regions that can't have initial
	values.
	* region-model-reachability.cc
	(reachable_regions::mark_escaped_clusters): Handle ctxt being
	NULL.
	* region-model.cc (region_to_value_map::purge_state_involving): New.
	(poisoned_value_diagnostic::use_of_uninit_p): New.
	(poisoned_value_diagnostic::emit): Handle POISON_KIND_UNINIT.
	(poisoned_value_diagnostic::describe_final_event): Likewise.
	(region_model::check_for_poison): New.
	(region_model::on_assignment): Call it.
	(class dump_path_diagnostic): Move here from engine.cc.
	(region_model::on_stmt_pre): New, based on exploded_node::on_stmt.
	(region_model::on_call_pre): Move the setting of the LHS to a
	conjured svalue to before the checks for specific functions.
	Handle "fgets", "fgets_unlocked", and "fread".
	(region_model::purge_state_involving): New.
	(region_model::handle_unrecognized_call): Handle ctxt being NULL.
	(region_model::get_rvalue): Call check_for_poison.
	(selftest::test_stack_frames): Use NULL for context when getting
	uninitialized rvalue.
	(selftest::test_alloca): Likewise.
	* region-model.h (region_to_value_map::purge_state_involving): New
	decl.
	(call_details::get_or_create_conjured_svalue): New decl.
	(region_model::on_stmt_pre): New decl.
	(region_model::purge_state_involving): New decl.
	(region_model::impl_call_fgets): New decl.
	(region_model::impl_call_fread): New decl.
	(region_model::check_for_poison): New decl.
	(region_model_context::warn): Return bool.
	(region_model_context::purge_state_involving): New.
	(noop_region_model_context::warn): Return bool.
	(noop_region_model_context::purge_state_involving): New.
	(test_region_model_context:: warn): Return bool.
	* region.cc (region::get_memory_space): New.
	(region::can_have_initial_svalue_p): New.
	(region::involves_p): New.
	* region.h (enum memory_space): New.
	(region::get_memory_space): New decl.
	(region::can_have_initial_svalue_p): New decl.
	(region::involves_p): New decl.
	* sm-malloc.cc (use_after_free::supercedes_p): New.
	* store.cc (binding_cluster::purge_state_involving): New.
	(store::purge_state_involving): New.
	* store.h (class symbolic_binding): New forward decl.
	(binding_key::dyn_cast_symbolic_binding): New.
	(symbolic_binding::dyn_cast_symbolic_binding): New.
	(binding_cluster::purge_state_involving): New.
	(store::purge_state_involving): New.
	* svalue.cc (svalue::can_merge_p): Reject attempts to merge
	poisoned svalues with other svalues, so that we identify
	paths in which a variable is conditionally uninitialized.
	(involvement_visitor::visit_conjured_svalue): New.
	(svalue::involves_p): Also handle SK_CONJURED.
	(poison_kind_to_str): Handle POISON_KIND_UNINIT.
	(poisoned_svalue::maybe_fold_bits_within): New.
	* svalue.h (enum poison_kind): Add POISON_KIND_UNINIT.
	(poisoned_svalue::maybe_fold_bits_within): New decl.

gcc/ChangeLog:
	PR analyzer/95006
	PR analyzer/94713
	PR analyzer/94714
	* doc/invoke.texi: Add -Wanalyzer-use-of-uninitialized-value.

gcc/testsuite/ChangeLog:
	PR analyzer/95006
	PR analyzer/94713
	PR analyzer/94714
	* g++.dg/analyzer/pr93212.C: Update location of warning.
	* g++.dg/analyzer/pr94011.C: Add
	-Wno-analyzer-use-of-uninitialized-value.
	* g++.dg/analyzer/pr94503.C: Likewise.
	* gcc.dg/analyzer/clobbers-1.c: Convert "f" from a local to a
	param to avoid uninitialized warning.
	* gcc.dg/analyzer/data-model-1.c (test_12): Add test for
	uninitialized value on result of alloca.
	(test_12a): Add expected warning.
	(test_12c): Likewise.
	(test_19): Likewise.
	(test_29b): Likewise.
	(test_29c): Likewise.
	(test_37): Remove xfail.
	(test_37a): Likewise.
	* gcc.dg/analyzer/data-model-20.c: Add warning about leak.
	* gcc.dg/analyzer/explode-2.c: Remove params; add
	-Wno-analyzer-too-complex, -Wno-analyzer-malloc-leak, and xfails.
	Initialize the locals.
	* gcc.dg/analyzer/explode-2a.c: Initialize the locals.  Add
	expected leak.
	* gcc.dg/analyzer/fgets-1.c: New test.
	* gcc.dg/analyzer/fread-1.c: New test.
	* gcc.dg/analyzer/malloc-1.c (test_16): Add expected warning.
	(test_40): Likewise.
	* gcc.dg/analyzer/memset-CVE-2017-18549-1.c: Check for
	uninitialized padding.
	* gcc.dg/analyzer/pr93355-localealias-feasibility.c (fread): New
	decl.
	(read_alias_file): Call it.
	* gcc.dg/analyzer/pr94047.c: Add expected warnings.
	* gcc.dg/analyzer/pr94851-2.c: Likewise.
	* gcc.dg/analyzer/pr96841.c: Convert local to a param.
	* gcc.dg/analyzer/pr98628.c: Likewise.
	* gcc.dg/analyzer/pr99042.c: Updated expected location of leak
	diagnostics.
	* gcc.dg/analyzer/symbolic-1.c: Add expected warnings.
	* gcc.dg/analyzer/symbolic-7.c: Likewise.
	* gcc.dg/analyzer/torture/pr93649.c: Add expected warning.  Skip
	with -fno-fat-lto-objects.
	* gcc.dg/analyzer/uninit-1.c: New test.
	* gcc.dg/analyzer/uninit-2.c: New test.
	* gcc.dg/analyzer/uninit-3.c: New test.
	* gcc.dg/analyzer/uninit-4.c: New test.
	* gcc.dg/analyzer/uninit-pr94713.c: New test.
	* gcc.dg/analyzer/uninit-pr94714.c: New test.
	* gcc.dg/analyzer/use-after-free-2.c: New test.
	* gcc.dg/analyzer/use-after-free-3.c: New test.
	* gcc.dg/analyzer/zlib-3.c: Add expected warning.
	* gcc.dg/analyzer/zlib-6.c: Convert locals to params to avoid
	uninitialized warnings.  Remove xfail.
	* gcc.dg/analyzer/zlib-6a.c: New test, based on the old version
	of the above.
	* gfortran.dg/analyzer/pr97668.f: Add
	-Wno-analyzer-use-of-uninitialized-value and
	-Wno-analyzer-too-complex.

Signed-off-by: David Malcolm <dmalcolm@redhat.com>

23 files changed, 880 insertions, 233 deletions

diff --git a/gcc/analyzer/analyzer.cc b/gcc/analyzer/analyzer.cc
index a8ee1a1..ddace9a 100644
--- a/gcc/analyzer/analyzer.cc
+++ b/gcc/analyzer/analyzer.cc
@@ -63,6 +63,51 @@ get_stmt_location (const gimple *stmt, function *fun)
 static tree
 fixup_tree_for_diagnostic_1 (tree expr, hash_set<tree> *visited);
 
+/* Attemp to generate a tree for the LHS of ASSIGN_STMT.
+   VISITED must be non-NULL; it is used to ensure termination.  */
+
+static tree
+get_diagnostic_tree_for_gassign_1 (const gassign *assign_stmt,
+				   hash_set<tree> *visited)
+{
+  enum tree_code code = gimple_assign_rhs_code (assign_stmt);
+
+  /* Reverse the effect of extract_ops_from_tree during
+     gimplification.  */
+  switch (get_gimple_rhs_class (code))
+    {
+    default:
+    case GIMPLE_INVALID_RHS:
+      gcc_unreachable ();
+    case GIMPLE_TERNARY_RHS:
+    case GIMPLE_BINARY_RHS:
+    case GIMPLE_UNARY_RHS:
+      {
+	tree t = make_node (code);
+	TREE_TYPE (t) = TREE_TYPE (gimple_assign_lhs (assign_stmt));
+	unsigned num_rhs_args = gimple_num_ops (assign_stmt) - 1;
+	for (unsigned i = 0; i < num_rhs_args; i++)
+	  {
+	    tree op = gimple_op (assign_stmt, i + 1);
+	    if (op)
+	      {
+		op = fixup_tree_for_diagnostic_1 (op, visited);
+		if (op == NULL_TREE)
+		  return NULL_TREE;
+	      }
+	    TREE_OPERAND (t, i) = op;
+	  }
+	return t;
+      }
+    case GIMPLE_SINGLE_RHS:
+      {
+	tree op = gimple_op (assign_stmt, 1);
+	op = fixup_tree_for_diagnostic_1 (op, visited);
+	return op;
+      }
+    }
+}
+
 /*  Subroutine of fixup_tree_for_diagnostic_1, called on SSA names.
     Attempt to reconstruct a a tree expression for SSA_NAME
     based on its def-stmt.
@@ -91,45 +136,8 @@ maybe_reconstruct_from_def_stmt (tree ssa_name,
       /* Can't handle these.  */
       return NULL_TREE;
     case GIMPLE_ASSIGN:
-      {
-	enum tree_code code = gimple_assign_rhs_code (def_stmt);
-
-	/* Reverse the effect of extract_ops_from_tree during
-	   gimplification.  */
-	switch (get_gimple_rhs_class (code))
-	  {
-	  default:
-	  case GIMPLE_INVALID_RHS:
-	    gcc_unreachable ();
-	  case GIMPLE_TERNARY_RHS:
-	  case GIMPLE_BINARY_RHS:
-	  case GIMPLE_UNARY_RHS:
-	    {
-	      tree t = make_node (code);
-	      TREE_TYPE (t) = TREE_TYPE (ssa_name);
-	      unsigned num_rhs_args = gimple_num_ops (def_stmt) - 1;
-	      for (unsigned i = 0; i < num_rhs_args; i++)
-		{
-		  tree op = gimple_op (def_stmt, i + 1);
-		  if (op)
-		    {
-		      op = fixup_tree_for_diagnostic_1 (op, visited);
-		      if (op == NULL_TREE)
-			return NULL_TREE;
-		    }
-		  TREE_OPERAND (t, i) = op;
-		}
-	      return t;
-	    }
-	  case GIMPLE_SINGLE_RHS:
-	    {
-	      tree op = gimple_op (def_stmt, 1);
-	      op = fixup_tree_for_diagnostic_1 (op, visited);
-	      return op;
-	    }
-	  }
-      }
-      break;
+      return get_diagnostic_tree_for_gassign_1
+	(as_a <const gassign *> (def_stmt), visited);
     case GIMPLE_CALL:
       {
 	gcall *call_stmt = as_a <gcall *> (def_stmt);
@@ -193,6 +201,15 @@ fixup_tree_for_diagnostic (tree expr)
   return fixup_tree_for_diagnostic_1 (expr, &visited);
 }
 
+/* Attempt to generate a tree for the LHS of ASSIGN_STMT.  */
+
+tree
+get_diagnostic_tree_for_gassign (const gassign *assign_stmt)
+{
+  hash_set<tree> visited;
+  return get_diagnostic_tree_for_gassign_1 (assign_stmt, &visited);
+}
+
 } // namespace ana
 
 /* Helper function for checkers.  Is the CALL to the given function name,
diff --git a/gcc/analyzer/analyzer.h b/gcc/analyzer/analyzer.h
index 02830e4..d42bee7 100644
--- a/gcc/analyzer/analyzer.h
+++ b/gcc/analyzer/analyzer.h
@@ -112,6 +112,7 @@ extern void print_quoted_type (pretty_printer *pp, tree t);
 extern int readability_comparator (const void *p1, const void *p2);
 extern int tree_cmp (const void *p1, const void *p2);
 extern tree fixup_tree_for_diagnostic (tree);
+extern tree get_diagnostic_tree_for_gassign (const gassign *);
 
 /* A tree, extended with stack frame information for locals, so that
    we can distinguish between different values of locals within a potentially
diff --git a/gcc/analyzer/analyzer.opt b/gcc/analyzer/analyzer.opt
index 7b77ae8..6ddb6e3 100644
--- a/gcc/analyzer/analyzer.opt
+++ b/gcc/analyzer/analyzer.opt
@@ -134,6 +134,10 @@ Wanalyzer-write-to-string-literal
 Common Var(warn_analyzer_write_to_string_literal) Init(1) Warning
 Warn about code paths which attempt to write to a string literal.
 
+Wanalyzer-use-of-uninitialized-value
+Common Var(warn_analyzer_use_of_uninitialized_value) Init(1) Warning
+Warn about code paths in which an uninitialized value is used.
+
 Wanalyzer-too-complex
 Common Var(warn_analyzer_too_complex) Init(0) Warning
 Warn if the code is too complicated for the analyzer to fully explore.
diff --git a/gcc/analyzer/constraint-manager.cc b/gcc/analyzer/constraint-manager.cc
index 51cf522..5b5a9de 100644
--- a/gcc/analyzer/constraint-manager.cc
+++ b/gcc/analyzer/constraint-manager.cc
@@ -1653,6 +1653,29 @@ on_liveness_change (const svalue_set &live_svalues,
   purge (p, NULL);
 }
 
+class svalue_purger
+{
+public:
+  svalue_purger (const svalue *sval) : m_sval (sval) {}
+
+  bool should_purge_p (const svalue *sval) const
+  {
+    return sval->involves_p (m_sval);
+  }
+
+private:
+  const svalue *m_sval;
+};
+
+/* Purge any state involving SVAL.  */
+
+void
+constraint_manager::purge_state_involving (const svalue *sval)
+{
+  svalue_purger p (sval);
+  purge (p, NULL);
+}
+
 /* Comparator for use by constraint_manager::canonicalize.
    Sort a pair of equiv_class instances, using the representative
    svalue as a sort key.  */
diff --git a/gcc/analyzer/constraint-manager.h b/gcc/analyzer/constraint-manager.h
index 3173610..2bb3215 100644
--- a/gcc/analyzer/constraint-manager.h
+++ b/gcc/analyzer/constraint-manager.h
@@ -269,6 +269,7 @@ public:
 
   void on_liveness_change (const svalue_set &live_svalues,
 			   const region_model *model);
+  void purge_state_involving (const svalue *sval);
 
   void canonicalize ();
 
diff --git a/gcc/analyzer/diagnostic-manager.cc b/gcc/analyzer/diagnostic-manager.cc
index d005fac..631fef6 100644
--- a/gcc/analyzer/diagnostic-manager.cc
+++ b/gcc/analyzer/diagnostic-manager.cc
@@ -722,6 +722,18 @@ saved_diagnostic::add_duplicate (saved_diagnostic *other)
   m_duplicates.safe_push (other);
 }
 
+/* Return true if this diagnostic supercedes OTHER, and that OTHER should
+   therefore not be emitted.  */
+
+bool
+saved_diagnostic::supercedes_p (const saved_diagnostic &other) const
+{
+  /* They should be at the same stmt.  */
+  if (m_stmt != other.m_stmt)
+    return false;
+  return m_d->supercedes_p (*other.m_d);
+}
+
 /* State for building a checker_path from a particular exploded_path.
    In particular, this precomputes reachability information: the set of
    source enodes for which a path be found to the diagnostic enode.  */
@@ -1021,6 +1033,38 @@ public:
       }
   }
 
+  /* Handle interactions between the dedupe winners, so that some
+     diagnostics can supercede others (of different kinds).
+
+     We want use-after-free to supercede use-of-unitialized-value,
+     so that if we have these at the same stmt, we don't emit
+     a use-of-uninitialized, just the use-after-free.  */
+
+  void handle_interactions (diagnostic_manager *dm)
+  {
+    LOG_SCOPE (dm->get_logger ());
+    auto_vec<const dedupe_key *> superceded;
+    for (auto outer : m_map)
+      {
+	const saved_diagnostic *outer_sd = outer.second;
+	for (auto inner : m_map)
+	  {
+	    const saved_diagnostic *inner_sd = inner.second;
+	    if (inner_sd->supercedes_p (*outer_sd))
+	      {
+		superceded.safe_push (outer.first);
+		if (dm->get_logger ())
+		  dm->log ("sd[%i] \"%s\" superceded by sd[%i] \"%s\"",
+			   outer_sd->get_index (), outer_sd->m_d->get_kind (),
+			   inner_sd->get_index (), inner_sd->m_d->get_kind ());
+		break;
+	      }
+	  }
+      }
+    for (auto iter : superceded)
+      m_map.remove (iter);
+  }
+
  /* Emit the simplest diagnostic within each set.  */
 
   void emit_best (diagnostic_manager *dm,
@@ -1095,6 +1139,8 @@ diagnostic_manager::emit_saved_diagnostics (const exploded_graph &eg)
   FOR_EACH_VEC_ELT (m_saved_diagnostics, i, sd)
     best_candidates.add (get_logger (), &pf, sd);
 
+  best_candidates.handle_interactions (this);
+
   /* For each dedupe-key, call emit_saved_diagnostic on the "best"
      saved_diagnostic.  */
   best_candidates.emit_best (this, eg);
diff --git a/gcc/analyzer/diagnostic-manager.h b/gcc/analyzer/diagnostic-manager.h
index fc8ac26..ad2eb4d 100644
--- a/gcc/analyzer/diagnostic-manager.h
+++ b/gcc/analyzer/diagnostic-manager.h
@@ -58,6 +58,8 @@ public:
 
   unsigned get_index () const { return m_idx; }
 
+  bool supercedes_p (const saved_diagnostic &other) const;
+
   //private:
   const state_machine *m_sm;
   const exploded_node *m_enode;
diff --git a/gcc/analyzer/engine.cc b/gcc/analyzer/engine.cc
index dc07a79..7662a7f 100644
--- a/gcc/analyzer/engine.cc
+++ b/gcc/analyzer/engine.cc
@@ -108,14 +108,29 @@ impl_region_model_context (program_state *state,
 {
 }
 
-void
+bool
 impl_region_model_context::warn (pending_diagnostic *d)
 {
   LOG_FUNC (get_logger ());
+  if (m_stmt == NULL && m_stmt_finder == NULL)
+    {
+      if (get_logger ())
+	get_logger ()->log ("rejecting diagnostic: no stmt");
+      delete d;
+      return false;
+    }
   if (m_eg)
-    m_eg->get_diagnostic_manager ().add_diagnostic
-      (m_enode_for_diag, m_enode_for_diag->get_supernode (),
-       m_stmt, m_stmt_finder, d);
+    {
+      m_eg->get_diagnostic_manager ().add_diagnostic
+	(m_enode_for_diag, m_enode_for_diag->get_supernode (),
+	 m_stmt, m_stmt_finder, d);
+      return true;
+    }
+  else
+    {
+      delete d;
+      return false;
+    }
 }
 
 void
@@ -155,6 +170,19 @@ impl_region_model_context::get_uncertainty ()
   return m_uncertainty;
 }
 
+/* Purge state involving SVAL.  The region_model has already been purged,
+   so we only need to purge other state in the program_state:
+   the sm-state.  */
+
+void
+impl_region_model_context::purge_state_involving (const svalue *sval)
+{
+  int i;
+  sm_state_map *smap;
+  FOR_EACH_VEC_ELT (m_new_state->m_checker_states, i, smap)
+    smap->purge_state_involving (sval, m_ext_state);
+}
+
 /* struct setjmp_record.  */
 
 int
@@ -230,16 +258,15 @@ public:
     return model->get_fndecl_for_call (call, &old_ctxt);
   }
 
-  state_machine::state_t get_state (const gimple *stmt,
+  state_machine::state_t get_state (const gimple *stmt ATTRIBUTE_UNUSED,
 				    tree var)
   {
     logger * const logger = get_logger ();
     LOG_FUNC (logger);
-    impl_region_model_context old_ctxt
-      (m_eg, m_enode_for_diag, NULL, NULL/*m_enode->get_state ()*/,
-       NULL, stmt);
+    /* Use NULL ctxt on this get_rvalue call to avoid triggering
+       uninitialized value warnings.  */
     const svalue *var_old_sval
-      = m_old_state->m_region_model->get_rvalue (var, &old_ctxt);
+      = m_old_state->m_region_model->get_rvalue (var, NULL);
 
     state_machine::state_t current
       = m_old_smap->get_state (var_old_sval, m_eg.get_ext_state ());
@@ -263,12 +290,6 @@ public:
   {
     logger * const logger = get_logger ();
     LOG_FUNC (logger);
-    impl_region_model_context old_ctxt
-      (m_eg, m_enode_for_diag, NULL, NULL/*m_enode->get_state ()*/,
-       NULL, stmt);
-    const svalue *var_old_sval
-      = m_old_state->m_region_model->get_rvalue (var, &old_ctxt);
-
     impl_region_model_context new_ctxt (m_eg, m_enode_for_diag,
 					m_old_state, m_new_state,
 					NULL,
@@ -278,8 +299,9 @@ public:
     const svalue *origin_new_sval
       = m_new_state->m_region_model->get_rvalue (origin, &new_ctxt);
 
+    /* We use the new sval here to avoid issues with uninitialized values.  */
     state_machine::state_t current
-      = m_old_smap->get_state (var_old_sval, m_eg.get_ext_state ());
+      = m_old_smap->get_state (var_new_sval, m_eg.get_ext_state ());
     if (logger)
       logger->log ("%s: state transition of %qE: %s -> %s",
 		   m_sm.get_name (),
@@ -1160,26 +1182,6 @@ fndecl_has_gimple_body_p (tree fndecl)
 
 namespace ana {
 
-/* A pending_diagnostic subclass for implementing "__analyzer_dump_path".  */
-
-class dump_path_diagnostic
-  : public pending_diagnostic_subclass<dump_path_diagnostic>
-{
-public:
-  bool emit (rich_location *richloc) FINAL OVERRIDE
-  {
-    inform (richloc, "path");
-    return true;
-  }
-
-  const char *get_kind () const FINAL OVERRIDE { return "dump_path_diagnostic"; }
-
-  bool operator== (const dump_path_diagnostic &) const
-  {
-    return true;
-  }
-};
-
 /* Modify STATE in place, applying the effects of the stmt at this node's
    point.  */
 
@@ -1218,89 +1220,8 @@ exploded_node::on_stmt (exploded_graph &eg,
   bool unknown_side_effects = false;
   bool terminate_path = false;
 
-  switch (gimple_code (stmt))
-    {
-    default:
-      /* No-op for now.  */
-      break;
-
-    case GIMPLE_ASSIGN:
-      {
-	const gassign *assign = as_a <const gassign *> (stmt);
-	state->m_region_model->on_assignment (assign, &ctxt);
-      }
-      break;
-
-    case GIMPLE_ASM:
-      /* No-op for now.  */
-      break;
-
-    case GIMPLE_CALL:
-      {
-	/* Track whether we have a gcall to a function that's not recognized by
-	   anything, for which we don't have a function body, or for which we
-	   don't know the fndecl.  */
-	const gcall *call = as_a <const gcall *> (stmt);
-
-	/* Debugging/test support.  */
-	if (is_special_named_call_p (call, "__analyzer_describe", 2))
-	  state->m_region_model->impl_call_analyzer_describe (call, &ctxt);
-	else if (is_special_named_call_p (call, "__analyzer_dump", 0))
-	  {
-	    /* Handle the builtin "__analyzer_dump" by dumping state
-	       to stderr.  */
-	    state->dump (eg.get_ext_state (), true);
-	  }
-	else if (is_special_named_call_p (call, "__analyzer_dump_capacity", 1))
-	  state->m_region_model->impl_call_analyzer_dump_capacity (call, &ctxt);
-	else if (is_special_named_call_p (call, "__analyzer_dump_path", 0))
-	  {
-	    /* Handle the builtin "__analyzer_dump_path" by queuing a
-	       diagnostic at this exploded_node.  */
-	    ctxt.warn (new dump_path_diagnostic ());
-	  }
-	else if (is_special_named_call_p (call, "__analyzer_dump_region_model",
-					  0))
-	  {
-	    /* Handle the builtin "__analyzer_dump_region_model" by dumping
-	       the region model's state to stderr.  */
-	    state->m_region_model->dump (false);
-	  }
-	else if (is_special_named_call_p (call, "__analyzer_eval", 1))
-	  state->m_region_model->impl_call_analyzer_eval (call, &ctxt);
-	else if (is_special_named_call_p (call, "__analyzer_break", 0))
-	  {
-	    /* Handle the builtin "__analyzer_break" by triggering a
-	       breakpoint.  */
-	    /* TODO: is there a good cross-platform way to do this?  */
-	    raise (SIGINT);
-	  }
-	else if (is_special_named_call_p (call,
-					  "__analyzer_dump_exploded_nodes",
-					  1))
-	  {
-	    /* This is handled elsewhere.  */
-	  }
-	else if (is_setjmp_call_p (call))
-	  state->m_region_model->on_setjmp (call, this, &ctxt);
-	else if (is_longjmp_call_p (call))
-	  {
-	    on_longjmp (eg, call, state, &ctxt);
-	    return on_stmt_flags::terminate_path ();
-	  }
-	else
-	  unknown_side_effects
-	    = state->m_region_model->on_call_pre (call, &ctxt, &terminate_path);
-      }
-      break;
-
-    case GIMPLE_RETURN:
-      {
-	const greturn *return_ = as_a <const greturn *> (stmt);
-	state->m_region_model->on_return (return_, &ctxt);
-      }
-      break;
-    }
+  on_stmt_pre (eg, stmt, state, &terminate_path,
+	       &unknown_side_effects, &ctxt);
 
   if (terminate_path)
     return on_stmt_flags::terminate_path ();
@@ -1316,41 +1237,71 @@ exploded_node::on_stmt (exploded_graph &eg,
       impl_sm_context sm_ctxt (eg, sm_idx, sm, this, &old_state, state,
 			       old_smap, new_smap);
 
-      /* If we're at the def-stmt of an SSA name, then potentially purge
-	 any sm-state for svalues that involve that SSA name.  This avoids
-	 false positives in loops, since a symbolic value referring to the
-	 SSA name will be referring to the previous value of that SSA name.
-	 For example, in:
-	   while ((e = hashmap_iter_next(&iter))) {
-	     struct oid2strbuf *e_strbuf = (struct oid2strbuf *)e;
-	     free (e_strbuf->value);
-	   }
-	 at the def-stmt of e_8:
-	   e_8 = hashmap_iter_next (&iter);
-	 we should purge the "freed" state of:
-	   INIT_VAL(CAST_REG(‘struct oid2strbuf’, (*INIT_VAL(e_8))).value)
-	 which is the "e_strbuf->value" value from the previous iteration,
-	 or we will erroneously report a double-free - the "e_8" within it
-	 refers to the previous value.  */
-      if (tree lhs = gimple_get_lhs (stmt))
-	if (TREE_CODE (lhs) == SSA_NAME)
-	  {
-	    const svalue *sval
-	      = old_state.m_region_model->get_rvalue (lhs, &ctxt);
-	    new_smap->purge_state_involving (sval, eg.get_ext_state ());
-	  }
-
       /* Allow the state_machine to handle the stmt.  */
       if (sm.on_stmt (&sm_ctxt, snode, stmt))
 	unknown_side_effects = false;
     }
 
-  if (const gcall *call = dyn_cast <const gcall *> (stmt))
-    state->m_region_model->on_call_post (call, unknown_side_effects, &ctxt);
+  on_stmt_post (stmt, state, unknown_side_effects, &ctxt);
 
   return on_stmt_flags ();
 }
 
+/* Handle the pre-sm-state part of STMT, modifying STATE in-place.
+   Write true to *OUT_TERMINATE_PATH if the path should be terminated.
+   Write true to *OUT_UNKNOWN_SIDE_EFFECTS if the stmt has unknown
+   side effects.  */
+
+void
+exploded_node::on_stmt_pre (exploded_graph &eg,
+			    const gimple *stmt,
+			    program_state *state,
+			    bool *out_terminate_path,
+			    bool *out_unknown_side_effects,
+			    region_model_context *ctxt)
+{
+  /* Handle special-case calls that require the full program_state.  */
+  if (const gcall *call = dyn_cast <const gcall *> (stmt))
+    {
+      if (is_special_named_call_p (call, "__analyzer_dump", 0))
+	{
+	  /* Handle the builtin "__analyzer_dump" by dumping state
+	     to stderr.  */
+	  state->dump (eg.get_ext_state (), true);
+	  return;
+	}
+      else if (is_setjmp_call_p (call))
+	{
+	  state->m_region_model->on_setjmp (call, this, ctxt);
+	  return;
+	}
+      else if (is_longjmp_call_p (call))
+	{
+	  on_longjmp (eg, call, state, ctxt);
+	  *out_terminate_path = true;
+	  return;
+	}
+    }
+
+  /* Otherwise, defer to m_region_model.  */
+  state->m_region_model->on_stmt_pre (stmt,
+				      out_terminate_path,
+				      out_unknown_side_effects,
+				      ctxt);
+}
+
+/* Handle the post-sm-state part of STMT, modifying STATE in-place.  */
+
+void
+exploded_node::on_stmt_post (const gimple *stmt,
+			     program_state *state,
+			     bool unknown_side_effects,
+			     region_model_context *ctxt)
+{
+  if (const gcall *call = dyn_cast <const gcall *> (stmt))
+    state->m_region_model->on_call_post (call, unknown_side_effects, ctxt);
+}
+
 /* Consider the effect of following superedge SUCC from this node.
 
    Return true if it's feasible to follow the edge, or false
@@ -1415,7 +1366,7 @@ valid_longjmp_stack_p (const program_point &longjmp_point,
    where the enclosing function of the "setjmp" has returned (and thus
    the stack frame no longer exists).  */
 
-class stale_jmp_buf : public pending_diagnostic_subclass<dump_path_diagnostic>
+class stale_jmp_buf : public pending_diagnostic_subclass<stale_jmp_buf>
 {
 public:
   stale_jmp_buf (const gcall *setjmp_call, const gcall *longjmp_call,
@@ -3763,6 +3714,13 @@ feasibility_state::maybe_update_for_edge (logger *logger,
 
       if (const gassign *assign = dyn_cast <const gassign *> (stmt))
 	m_model.on_assignment (assign, NULL);
+      else if (const gcall *call = dyn_cast <const gcall *> (stmt))
+	{
+	  bool terminate_path;
+	  bool unknown_side_effects
+	    = m_model.on_call_pre (call, NULL, &terminate_path);
+	  m_model.on_call_post (call, unknown_side_effects, NULL);
+	}
       else if (const greturn *return_ = dyn_cast <const greturn *> (stmt))
 	m_model.on_return (return_, NULL);
     }
diff --git a/gcc/analyzer/exploded-graph.h b/gcc/analyzer/exploded-graph.h
index 1d8b73d..8f48d8a 100644
--- a/gcc/analyzer/exploded-graph.h
+++ b/gcc/analyzer/exploded-graph.h
@@ -46,7 +46,7 @@ class impl_region_model_context : public region_model_context
 			     uncertainty_t *uncertainty,
 			     logger *logger = NULL);
 
-  void warn (pending_diagnostic *d) FINAL OVERRIDE;
+  bool warn (pending_diagnostic *d) FINAL OVERRIDE;
   void on_svalue_leak (const svalue *) OVERRIDE;
   void on_liveness_change (const svalue_set &live_svalues,
 			   const region_model *model) FINAL OVERRIDE;
@@ -74,6 +74,8 @@ class impl_region_model_context : public region_model_context
 
   uncertainty_t *get_uncertainty () FINAL OVERRIDE;
 
+  void purge_state_involving (const svalue *sval) FINAL OVERRIDE;
+
   exploded_graph *m_eg;
   log_user m_logger;
   exploded_node *m_enode_for_diag;
@@ -223,6 +225,17 @@ class exploded_node : public dnode<eg_traits>
 			 const gimple *stmt,
 			 program_state *state,
 			 uncertainty_t *uncertainty);
+  void on_stmt_pre (exploded_graph &eg,
+		    const gimple *stmt,
+		    program_state *state,
+		    bool *out_terminate_path,
+		    bool *out_unknown_side_effects,
+		    region_model_context *ctxt);
+  void on_stmt_post (const gimple *stmt,
+		     program_state *state,
+		     bool unknown_side_effects,
+		     region_model_context *ctxt);
+
   bool on_edge (exploded_graph &eg,
 		const superedge *succ,
 		program_point *next_point,
diff --git a/gcc/analyzer/pending-diagnostic.h b/gcc/analyzer/pending-diagnostic.h
index 571fc1b..48e2b3e 100644
--- a/gcc/analyzer/pending-diagnostic.h
+++ b/gcc/analyzer/pending-diagnostic.h
@@ -154,6 +154,9 @@ class pending_diagnostic
   /* Hand-coded RTTI: get an ID for the subclass.  */
   virtual const char *get_kind () const = 0;
 
+  /* A vfunc for identifying "use of uninitialized value".  */
+  virtual bool use_of_uninit_p () const { return false; }
+
   /* Compare for equality with OTHER, which might be of a different
      subclass.  */
 
@@ -269,6 +272,16 @@ class pending_diagnostic
   {
     return false;
   }
+
+  /* Vfunc for determining that this pending_diagnostic supercedes OTHER,
+     and that OTHER should therefore not be emitted.
+     They have already been tested for being at the same stmt.  */
+
+  virtual bool
+  supercedes_p (const pending_diagnostic &other ATTRIBUTE_UNUSED) const
+  {
+    return false;
+  }
 };
 
 /* A template to make it easier to make subclasses of pending_diagnostic.
diff --git a/gcc/analyzer/program-state.cc b/gcc/analyzer/program-state.cc
index 6d60c04..23cfcb0 100644
--- a/gcc/analyzer/program-state.cc
+++ b/gcc/analyzer/program-state.cc
@@ -372,21 +372,31 @@ sm_state_map::get_state (const svalue *sval,
      INIT_VAL(foo).  */
   if (m_sm.inherited_state_p ())
     if (region_model_manager *mgr = ext_state.get_model_manager ())
-      if (const initial_svalue *init_sval = sval->dyn_cast_initial_svalue ())
-	{
-	  const region *reg = init_sval->get_region ();
-	  /* Try recursing upwards (up to the base region for the cluster).  */
-	  if (!reg->base_region_p ())
-	    if (const region *parent_reg = reg->get_parent_region ())
-	      {
-		const svalue *parent_init_sval
-		  = mgr->get_or_create_initial_value (parent_reg);
-		state_machine::state_t parent_state
-		  = get_state (parent_init_sval, ext_state);
-		if (parent_state)
-		  return parent_state;
-	      }
-	}
+      {
+	if (const initial_svalue *init_sval = sval->dyn_cast_initial_svalue ())
+	  {
+	    const region *reg = init_sval->get_region ();
+	    /* Try recursing upwards (up to the base region for the
+	       cluster).  */
+	    if (!reg->base_region_p ())
+	      if (const region *parent_reg = reg->get_parent_region ())
+		{
+		  const svalue *parent_init_sval
+		    = mgr->get_or_create_initial_value (parent_reg);
+		  state_machine::state_t parent_state
+		    = get_state (parent_init_sval, ext_state);
+		  if (parent_state)
+		    return parent_state;
+		}
+	  }
+	else if (const sub_svalue *sub_sval = sval->dyn_cast_sub_svalue ())
+	  {
+	    const svalue *parent_sval = sub_sval->get_parent ();
+	    if (state_machine::state_t parent_state
+		  = get_state (parent_sval, ext_state))
+	      return parent_state;
+	  }
+      }
 
   return m_sm.get_default_state (sval);
 }
@@ -596,7 +606,8 @@ sm_state_map::purge_state_involving (const svalue *sval,
 				     const extrinsic_state &ext_state)
 {
   /* Currently svalue::involves_p requires this.  */
-  if (sval->get_kind () != SK_INITIAL)
+  if (!(sval->get_kind () == SK_INITIAL
+	|| sval->get_kind () == SK_CONJURED))
     return;
 
   svalue_set svals_to_unset;
diff --git a/gcc/analyzer/region-model-impl-calls.cc b/gcc/analyzer/region-model-impl-calls.cc
index 466d397..4be6550 100644
--- a/gcc/analyzer/region-model-impl-calls.cc
+++ b/gcc/analyzer/region-model-impl-calls.cc
@@ -84,7 +84,10 @@ call_details::call_details (const gcall *call, region_model *model,
 uncertainty_t *
 call_details::get_uncertainty () const
 {
-  return m_ctxt->get_uncertainty ();
+  if (m_ctxt)
+    return m_ctxt->get_uncertainty ();
+  else
+    return NULL;
 }
 
 /* If the callsite has a left-hand-side region, set it to RESULT
@@ -173,6 +176,15 @@ call_details::dump (bool simple) const
   pp_flush (&pp);
 }
 
+/* Get a conjured_svalue for this call for REG.  */
+
+const svalue *
+call_details::get_or_create_conjured_svalue (const region *reg) const
+{
+  region_model_manager *mgr = m_model->get_manager ();
+  return mgr->get_or_create_conjured_svalue (reg->get_type (), m_call, reg);
+}
+
 /* Implementations of specific functions.  */
 
 /* Handle the on_call_pre part of "alloca".  */
@@ -305,6 +317,42 @@ region_model::impl_call_error (const call_details &cd, unsigned min_args,
   return true;
 }
 
+/* Handle the on_call_pre part of "fgets" and "fgets_unlocked".  */
+
+void
+region_model::impl_call_fgets (const call_details &cd)
+{
+  /* Ideally we would bifurcate state here between the
+     error vs no error cases.  */
+  const svalue *ptr_sval = cd.get_arg_svalue (0);
+  if (const region_svalue *ptr_to_region_sval
+      = ptr_sval->dyn_cast_region_svalue ())
+    {
+      const region *reg = ptr_to_region_sval->get_pointee ();
+      const region *base_reg = reg->get_base_region ();
+      const svalue *new_sval = cd.get_or_create_conjured_svalue (base_reg);
+      purge_state_involving (new_sval, cd.get_ctxt ());
+      set_value (base_reg, new_sval, cd.get_ctxt ());
+    }
+}
+
+/* Handle the on_call_pre part of "fread".  */
+
+void
+region_model::impl_call_fread (const call_details &cd)
+{
+  const svalue *ptr_sval = cd.get_arg_svalue (0);
+  if (const region_svalue *ptr_to_region_sval
+      = ptr_sval->dyn_cast_region_svalue ())
+    {
+      const region *reg = ptr_to_region_sval->get_pointee ();
+      const region *base_reg = reg->get_base_region ();
+      const svalue *new_sval = cd.get_or_create_conjured_svalue (base_reg);
+      purge_state_involving (new_sval, cd.get_ctxt ());
+      set_value (base_reg, new_sval, cd.get_ctxt ());
+    }
+}
+
 /* Handle the on_call_post part of "free", after sm-handling.
 
    If the ptr points to an underlying heap region, delete the region,
diff --git a/gcc/analyzer/region-model-manager.cc b/gcc/analyzer/region-model-manager.cc
index 55acb90..7a52a64 100644
--- a/gcc/analyzer/region-model-manager.cc
+++ b/gcc/analyzer/region-model-manager.cc
@@ -252,6 +252,10 @@ region_model_manager::get_or_create_unknown_svalue (tree type)
 const svalue *
 region_model_manager::get_or_create_initial_value (const region *reg)
 {
+  if (!reg->can_have_initial_svalue_p ())
+    return get_or_create_poisoned_svalue (POISON_KIND_UNINIT,
+					  reg->get_type ());
+
   /* The initial value of a cast is a cast of the initial value.  */
   if (const cast_region *cast_reg = reg->dyn_cast_cast_region ())
     {
diff --git a/gcc/analyzer/region-model-reachability.cc b/gcc/analyzer/region-model-reachability.cc
index e165cda..1f65307 100644
--- a/gcc/analyzer/region-model-reachability.cc
+++ b/gcc/analyzer/region-model-reachability.cc
@@ -267,7 +267,6 @@ reachable_regions::handle_parm (const svalue *sval, tree param_type)
 void
 reachable_regions::mark_escaped_clusters (region_model_context *ctxt)
 {
-  gcc_assert (ctxt);
   auto_vec<const function_region *> escaped_fn_regs
     (m_mutable_base_regs.elements ());
   for (hash_set<const region *>::iterator iter = m_mutable_base_regs.begin ();
@@ -281,12 +280,15 @@ reachable_regions::mark_escaped_clusters (region_model_context *ctxt)
       if (const function_region *fn_reg = base_reg->dyn_cast_function_region ())
 	escaped_fn_regs.quick_push (fn_reg);
     }
-  /* Sort to ensure deterministic results.  */
-  escaped_fn_regs.qsort (region::cmp_ptr_ptr);
-  unsigned i;
-  const function_region *fn_reg;
-  FOR_EACH_VEC_ELT (escaped_fn_regs, i, fn_reg)
-    ctxt->on_escaped_function (fn_reg->get_fndecl ());
+  if (ctxt)
+    {
+      /* Sort to ensure deterministic results.  */
+      escaped_fn_regs.qsort (region::cmp_ptr_ptr);
+      unsigned i;
+      const function_region *fn_reg;
+      FOR_EACH_VEC_ELT (escaped_fn_regs, i, fn_reg)
+	ctxt->on_escaped_function (fn_reg->get_fndecl ());
+    }
 }
 
 /* Dump SET to PP, sorting it to avoid churn when comparing dumps.  */
diff --git a/gcc/analyzer/region-model.cc b/gcc/analyzer/region-model.cc
index acbbd11..3fe2cce 100644
--- a/gcc/analyzer/region-model.cc
+++ b/gcc/analyzer/region-model.cc
@@ -221,6 +221,23 @@ region_to_value_map::can_merge_with_p (const region_to_value_map &other,
   return true;
 }
 
+/* Purge any state involving SVAL.  */
+
+void
+region_to_value_map::purge_state_involving (const svalue *sval)
+{
+  auto_vec<const region *> to_purge;
+  for (auto iter : *this)
+    {
+      const region *iter_reg = iter.first;
+      const svalue *iter_sval = iter.second;
+      if (iter_reg->involves_p (sval) || iter_sval->involves_p (sval))
+	to_purge.safe_push (iter_reg);
+    }
+  for (auto iter : to_purge)
+    m_hash_map.remove (iter);
+}
+
 /* class region_model.  */
 
 /* Ctor for region_model: construct an "empty" model.  */
@@ -442,6 +459,11 @@ public:
 
   const char *get_kind () const FINAL OVERRIDE { return "poisoned_value_diagnostic"; }
 
+  bool use_of_uninit_p () const FINAL OVERRIDE
+  {
+    return m_pkind == POISON_KIND_UNINIT;
+  }
+
   bool operator== (const poisoned_value_diagnostic &other) const
   {
     return m_expr == other.m_expr;
@@ -453,6 +475,16 @@ public:
       {
       default:
 	gcc_unreachable ();
+      case POISON_KIND_UNINIT:
+	{
+	  diagnostic_metadata m;
+	  m.add_cwe (457); /* "CWE-457: Use of Uninitialized Variable".  */
+	  return warning_meta (rich_loc, m,
+			       OPT_Wanalyzer_use_of_uninitialized_value,
+			       "use of uninitialized value %qE",
+			       m_expr);
+	}
+	break;
       case POISON_KIND_FREED:
 	{
 	  diagnostic_metadata m;
@@ -482,6 +514,9 @@ public:
       {
       default:
 	gcc_unreachable ();
+      case POISON_KIND_UNINIT:
+	return ev.formatted_print ("use of uninitialized value %qE here",
+				   m_expr);
       case POISON_KIND_FREED:
 	return ev.formatted_print ("use after %<free%> of %qE here",
 				   m_expr);
@@ -782,6 +817,41 @@ region_model::get_gassign_result (const gassign *assign,
     }
 }
 
+/* Check for SVAL being poisoned, adding a warning to CTXT.
+   Return SVAL, or, if a warning is added, another value, to avoid
+   repeatedly complaining about the same poisoned value in followup code.  */
+
+const svalue *
+region_model::check_for_poison (const svalue *sval,
+				tree expr,
+				region_model_context *ctxt) const
+{
+  if (!ctxt)
+    return sval;
+
+  if (const poisoned_svalue *poisoned_sval = sval->dyn_cast_poisoned_svalue ())
+    {
+      /* If we have an SSA name for a temporary, we don't want to print
+	 '<unknown>'.
+	 Poisoned values are shared by type, and so we can't reconstruct
+	 the tree other than via the def stmts, using
+	 fixup_tree_for_diagnostic.  */
+      tree diag_arg = fixup_tree_for_diagnostic (expr);
+      enum poison_kind pkind = poisoned_sval->get_poison_kind ();
+      if (ctxt->warn (new poisoned_value_diagnostic (diag_arg, pkind)))
+	{
+	  /* We only want to report use of a poisoned value at the first
+	     place it gets used; return an unknown value to avoid generating
+	     a chain of followup warnings.  */
+	  sval = m_mgr->get_or_create_unknown_svalue (sval->get_type ());
+	}
+
+      return sval;
+    }
+
+  return sval;
+}
+
 /* Update this model for the ASSIGN stmt, using CTXT to report any
    diagnostics.  */
 
@@ -798,6 +868,8 @@ region_model::on_assignment (const gassign *assign, region_model_context *ctxt)
      for some SVALUE.  */
   if (const svalue *sval = get_gassign_result (assign, ctxt))
     {
+      tree expr = get_diagnostic_tree_for_gassign (assign);
+      check_for_poison (sval, expr, ctxt);
       set_value (lhs_reg, sval, ctxt);
       return;
     }
@@ -863,6 +935,109 @@ region_model::on_assignment (const gassign *assign, region_model_context *ctxt)
     }
 }
 
+/* A pending_diagnostic subclass for implementing "__analyzer_dump_path".  */
+
+class dump_path_diagnostic
+  : public pending_diagnostic_subclass<dump_path_diagnostic>
+{
+public:
+  bool emit (rich_location *richloc) FINAL OVERRIDE
+  {
+    inform (richloc, "path");
+    return true;
+  }
+
+  const char *get_kind () const FINAL OVERRIDE { return "dump_path_diagnostic"; }
+
+  bool operator== (const dump_path_diagnostic &) const
+  {
+    return true;
+  }
+};
+
+/* Handle the pre-sm-state part of STMT, modifying this object in-place.
+   Write true to *OUT_TERMINATE_PATH if the path should be terminated.
+   Write true to *OUT_UNKNOWN_SIDE_EFFECTS if the stmt has unknown
+   side effects.  */
+
+void
+region_model::on_stmt_pre (const gimple *stmt,
+			   bool *out_terminate_path,
+			   bool *out_unknown_side_effects,
+			   region_model_context *ctxt)
+{
+  switch (gimple_code (stmt))
+    {
+    default:
+      /* No-op for now.  */
+      break;
+
+    case GIMPLE_ASSIGN:
+      {
+	const gassign *assign = as_a <const gassign *> (stmt);
+	on_assignment (assign, ctxt);
+      }
+      break;
+
+    case GIMPLE_ASM:
+      /* No-op for now.  */
+      break;
+
+    case GIMPLE_CALL:
+      {
+	/* Track whether we have a gcall to a function that's not recognized by
+	   anything, for which we don't have a function body, or for which we
+	   don't know the fndecl.  */
+	const gcall *call = as_a <const gcall *> (stmt);
+
+	/* Debugging/test support.  */
+	if (is_special_named_call_p (call, "__analyzer_describe", 2))
+	  impl_call_analyzer_describe (call, ctxt);
+	else if (is_special_named_call_p (call, "__analyzer_dump_capacity", 1))
+	  impl_call_analyzer_dump_capacity (call, ctxt);
+	else if (is_special_named_call_p (call, "__analyzer_dump_path", 0))
+	  {
+	    /* Handle the builtin "__analyzer_dump_path" by queuing a
+	       diagnostic at this exploded_node.  */
+	    ctxt->warn (new dump_path_diagnostic ());
+	  }
+	else if (is_special_named_call_p (call, "__analyzer_dump_region_model",
+					  0))
+	  {
+	    /* Handle the builtin "__analyzer_dump_region_model" by dumping
+	       the region model's state to stderr.  */
+	    dump (false);
+	  }
+	else if (is_special_named_call_p (call, "__analyzer_eval", 1))
+	  impl_call_analyzer_eval (call, ctxt);
+	else if (is_special_named_call_p (call, "__analyzer_break", 0))
+	  {
+	    /* Handle the builtin "__analyzer_break" by triggering a
+	       breakpoint.  */
+	    /* TODO: is there a good cross-platform way to do this?  */
+	    raise (SIGINT);
+	  }
+	else if (is_special_named_call_p (call,
+					  "__analyzer_dump_exploded_nodes",
+					  1))
+	  {
+	    /* This is handled elsewhere.  */
+	  }
+	else
+	  *out_unknown_side_effects = on_call_pre (call, ctxt,
+						   out_terminate_path);
+      }
+      break;
+
+    case GIMPLE_RETURN:
+      {
+	const greturn *return_ = as_a <const greturn *> (stmt);
+	on_return (return_, ctxt);
+      }
+      break;
+    }
+}
+
 /* Update this model for the CALL stmt, using CTXT to report any
    diagnostics - the first half.
 
@@ -885,6 +1060,22 @@ region_model::on_call_pre (const gcall *call, region_model_context *ctxt,
 
   bool unknown_side_effects = false;
 
+  /* Some of the cases below update the lhs of the call based on the
+     return value, but not all.  Provide a default value, which may
+     get overwritten below.  */
+  if (tree lhs = gimple_call_lhs (call))
+    {
+      const region *lhs_region = get_lvalue (lhs, ctxt);
+      if (TREE_CODE (lhs) == SSA_NAME)
+	{
+	  const svalue *sval
+	    = m_mgr->get_or_create_conjured_svalue (TREE_TYPE (lhs), call,
+						    lhs_region);
+	  purge_state_involving (sval, ctxt);
+	  set_value (lhs_region, sval, ctxt);
+	}
+    }
+
   if (gimple_call_internal_p (call))
     {
       switch (gimple_call_internal_fn (call))
@@ -994,6 +1185,17 @@ region_model::on_call_pre (const gcall *call, region_model_context *ctxt,
 	  else
 	    unknown_side_effects = true;
 	}
+      else if (is_named_call_p (callee_fndecl, "fgets", call, 3)
+	       || is_named_call_p (callee_fndecl, "fgets_unlocked", call, 3))
+	{
+	  impl_call_fgets (cd);
+	  return false;
+	}
+      else if (is_named_call_p (callee_fndecl, "fread", call, 4))
+	{
+	  impl_call_fread (cd);
+	  return false;
+	}
       else if (is_named_call_p (callee_fndecl, "getchar", call, 0))
 	{
 	  /* No side-effects (tracking stream state is out-of-scope
@@ -1029,19 +1231,6 @@ region_model::on_call_pre (const gcall *call, region_model_context *ctxt,
   else
     unknown_side_effects = true;
 
-  /* Some of the above cases update the lhs of the call based on the
-     return value.  If we get here, it hasn't been done yet, so do that
-     now.  */
-  if (tree lhs = gimple_call_lhs (call))
-    {
-      const region *lhs_region = get_lvalue (lhs, ctxt);
-      if (TREE_CODE (lhs) == SSA_NAME)
-	{
-	  const svalue *sval = m_mgr->get_or_create_initial_value (lhs_region);
-	  set_value (lhs_region, sval, ctxt);
-	}
-    }
-
   return unknown_side_effects;
 }
 
@@ -1090,6 +1279,38 @@ region_model::on_call_post (const gcall *call,
     handle_unrecognized_call (call, ctxt);
 }
 
+/* Purge state involving SVAL from this region_model, using CTXT
+   (if non-NULL) to purge other state in a program_state.
+
+   For example, if we're at the def-stmt of an SSA name, then we need to
+   purge any state for svalues that involve that SSA name.  This avoids
+   false positives in loops, since a symbolic value referring to the
+   SSA name will be referring to the previous value of that SSA name.
+
+   For example, in:
+     while ((e = hashmap_iter_next(&iter))) {
+       struct oid2strbuf *e_strbuf = (struct oid2strbuf *)e;
+       free (e_strbuf->value);
+     }
+   at the def-stmt of e_8:
+     e_8 = hashmap_iter_next (&iter);
+   we should purge the "freed" state of:
+     INIT_VAL(CAST_REG(‘struct oid2strbuf’, (*INIT_VAL(e_8))).value)
+   which is the "e_strbuf->value" value from the previous iteration,
+   or we will erroneously report a double-free - the "e_8" within it
+   refers to the previous value.  */
+
+void
+region_model::purge_state_involving (const svalue *sval,
+				     region_model_context *ctxt)
+{
+  m_store.purge_state_involving (sval, m_mgr);
+  m_constraints->purge_state_involving (sval);
+  m_dynamic_extents.purge_state_involving (sval);
+  if (ctxt)
+    ctxt->purge_state_involving (sval);
+}
+
 /* Handle a call CALL to a function with unknown behavior.
 
    Traverse the regions in this model, determining what regions are
@@ -1135,7 +1356,7 @@ region_model::handle_unrecognized_call (const gcall *call,
       }
   }
 
-  uncertainty_t *uncertainty = ctxt->get_uncertainty ();
+  uncertainty_t *uncertainty = ctxt ? ctxt->get_uncertainty () : NULL;
 
   /* Purge sm-state for the svalues that were reachable,
      both in non-mutable and mutable form.  */
@@ -1144,14 +1365,16 @@ region_model::handle_unrecognized_call (const gcall *call,
        iter != reachable_regs.end_reachable_svals (); ++iter)
     {
       const svalue *sval = (*iter);
-      ctxt->on_unknown_change (sval, false);
+      if (ctxt)
+	ctxt->on_unknown_change (sval, false);
     }
   for (svalue_set::iterator iter
 	 = reachable_regs.begin_mutable_svals ();
        iter != reachable_regs.end_mutable_svals (); ++iter)
     {
       const svalue *sval = (*iter);
-      ctxt->on_unknown_change (sval, true);
+      if (ctxt)
+	ctxt->on_unknown_change (sval, true);
       if (uncertainty)
 	uncertainty->on_mutable_sval_at_unknown_call (sval);
     }
@@ -1603,6 +1826,8 @@ region_model::get_rvalue (path_var pv, region_model_context *ctxt) const
 
   assert_compat_types (result_sval->get_type (), TREE_TYPE (pv.m_tree));
 
+  result_sval = check_for_poison (result_sval, pv.m_tree, ctxt);
+
   return result_sval;
 }
 
@@ -4307,7 +4532,7 @@ test_stack_frames ()
 
   /* Verify that p (which was pointing at the local "x" in the popped
      frame) has been poisoned.  */
-  const svalue *new_p_sval = model.get_rvalue (p, &ctxt);
+  const svalue *new_p_sval = model.get_rvalue (p, NULL);
   ASSERT_EQ (new_p_sval->get_kind (), SK_POISONED);
   ASSERT_EQ (new_p_sval->dyn_cast_poisoned_svalue ()->get_poison_kind (),
 	     POISON_KIND_POPPED_STACK);
@@ -5397,7 +5622,7 @@ test_alloca ()
   /* Verify that the pointers to the alloca region are replaced by
      poisoned values when the frame is popped.  */
   model.pop_frame (NULL, NULL, &ctxt);
-  ASSERT_EQ (model.get_rvalue (p, &ctxt)->get_kind (), SK_POISONED);
+  ASSERT_EQ (model.get_rvalue (p, NULL)->get_kind (), SK_POISONED);
 }
 
 /* Verify that svalue::involves_p works.  */
diff --git a/gcc/analyzer/region-model.h b/gcc/analyzer/region-model.h
index cf5232d..71f6b3e 100644
--- a/gcc/analyzer/region-model.h
+++ b/gcc/analyzer/region-model.h
@@ -171,6 +171,8 @@ public:
   bool can_merge_with_p (const region_to_value_map &other,
 			 region_to_value_map *out) const;
 
+  void purge_state_involving (const svalue *sval);
+
 private:
   hash_map_t m_hash_map;
 };
@@ -470,6 +472,8 @@ public:
   void dump_to_pp (pretty_printer *pp, bool simple) const;
   void dump (bool simple) const;
 
+  const svalue *get_or_create_conjured_svalue (const region *) const;
+
 private:
   const gcall *m_call;
   region_model *m_model;
@@ -518,6 +522,12 @@ class region_model
   void canonicalize ();
   bool canonicalized_p () const;
 
+  void
+  on_stmt_pre (const gimple *stmt,
+	       bool *out_terminate_path,
+	       bool *out_unknown_side_effects,
+	       region_model_context *ctxt);
+
   void on_assignment (const gassign *stmt, region_model_context *ctxt);
   const svalue *get_gassign_result (const gassign *assign,
 				    region_model_context *ctxt);
@@ -527,6 +537,8 @@ class region_model
 		     bool unknown_side_effects,
 		     region_model_context *ctxt);
 
+  void purge_state_involving (const svalue *sval, region_model_context *ctxt);
+
   /* Specific handling for on_call_pre.  */
   bool impl_call_alloca (const call_details &cd);
   void impl_call_analyzer_describe (const gcall *call,
@@ -539,6 +551,8 @@ class region_model
   bool impl_call_calloc (const call_details &cd);
   bool impl_call_error (const call_details &cd, unsigned min_args,
 			bool *out_terminate_path);
+  void impl_call_fgets (const call_details &cd);
+  void impl_call_fread (const call_details &cd);
   void impl_call_free (const call_details &cd);
   bool impl_call_malloc (const call_details &cd);
   void impl_call_memcpy (const call_details &cd);
@@ -727,6 +741,10 @@ class region_model
   bool called_from_main_p () const;
   const svalue *get_initial_value_for_global (const region *reg) const;
 
+  const svalue *check_for_poison (const svalue *sval,
+				  tree expr,
+				  region_model_context *ctxt) const;
+
   void check_for_writable_region (const region* dest_reg,
 				  region_model_context *ctxt) const;
 
@@ -757,7 +775,9 @@ class region_model
 class region_model_context
 {
  public:
-  virtual void warn (pending_diagnostic *d) = 0;
+  /* Hook for clients to store pending diagnostics.
+     Return true if the diagnostic was stored, or false if it was deleted.  */
+  virtual bool warn (pending_diagnostic *d) = 0;
 
   /* Hook for clients to be notified when an SVAL that was reachable
      in a previous state is no longer live, so that clients can emit warnings
@@ -799,6 +819,9 @@ class region_model_context
   virtual void on_escaped_function (tree fndecl) = 0;
 
   virtual uncertainty_t *get_uncertainty () = 0;
+
+  /* Hook for clients to purge state involving SVAL.  */
+  virtual void purge_state_involving (const svalue *sval) = 0;
 };
 
 /* A "do nothing" subclass of region_model_context.  */
@@ -806,7 +829,7 @@ class region_model_context
 class noop_region_model_context : public region_model_context
 {
 public:
-  void warn (pending_diagnostic *) OVERRIDE {}
+  bool warn (pending_diagnostic *) OVERRIDE { return false; }
   void on_svalue_leak (const svalue *) OVERRIDE {}
   void on_liveness_change (const svalue_set &,
 			   const region_model *) OVERRIDE {}
@@ -829,6 +852,8 @@ public:
   void on_escaped_function (tree) OVERRIDE {}
 
   uncertainty_t *get_uncertainty () OVERRIDE { return NULL; }
+
+  void purge_state_involving (const svalue *sval ATTRIBUTE_UNUSED) OVERRIDE {}
 };
 
 /* A subclass of region_model_context for determining if operations fail
@@ -931,9 +956,10 @@ using namespace ::selftest;
 class test_region_model_context : public noop_region_model_context
 {
 public:
-  void warn (pending_diagnostic *d) FINAL OVERRIDE
+  bool warn (pending_diagnostic *d) FINAL OVERRIDE
   {
     m_diagnostics.safe_push (d);
+    return true;
   }
 
   unsigned get_num_diagnostics () const { return m_diagnostics.length (); }
diff --git a/gcc/analyzer/region.cc b/gcc/analyzer/region.cc
index 4633717..6cccb0f 100644
--- a/gcc/analyzer/region.cc
+++ b/gcc/analyzer/region.cc
@@ -168,6 +168,109 @@ region::maybe_get_frame_region () const
   return NULL;
 }
 
+/* Get the memory space of this region.  */
+
+enum memory_space
+region::get_memory_space () const
+{
+  const region *iter = this;
+  while (iter)
+    {
+      switch (iter->get_kind ())
+	{
+	default:
+	  break;
+	case RK_GLOBALS:
+	  return MEMSPACE_GLOBALS;
+	case RK_CODE:
+	case RK_FUNCTION:
+	case RK_LABEL:
+	  return MEMSPACE_CODE;
+	case RK_FRAME:
+	case RK_STACK:
+	case RK_ALLOCA:
+	  return MEMSPACE_STACK;
+	case RK_HEAP:
+	case RK_HEAP_ALLOCATED:
+	  return MEMSPACE_HEAP;
+	case RK_STRING:
+	  return MEMSPACE_READONLY_DATA;
+	}
+      if (iter->get_kind () == RK_CAST)
+	iter = iter->dyn_cast_cast_region ()->get_original_region ();
+      else
+	iter = iter->get_parent_region ();
+    }
+  return MEMSPACE_UNKNOWN;
+}
+
+/* Subroutine for use by region_model_manager::get_or_create_initial_value.
+   Return true if this region has an initial_svalue.
+   Return false if attempting to use INIT_VAL(this_region) should give
+   the "UNINITIALIZED" poison value.  */
+
+bool
+region::can_have_initial_svalue_p () const
+{
+  const region *base_reg = get_base_region ();
+
+  /* Check for memory spaces that are uninitialized by default.  */
+  enum memory_space mem_space = base_reg->get_memory_space ();
+  switch (mem_space)
+    {
+    default:
+      gcc_unreachable ();
+    case MEMSPACE_UNKNOWN:
+    case MEMSPACE_CODE:
+    case MEMSPACE_GLOBALS:
+    case MEMSPACE_READONLY_DATA:
+      /* Such regions have initial_svalues.  */
+      return true;
+
+    case MEMSPACE_HEAP:
+      /* Heap allocations are uninitialized by default.  */
+      return false;
+
+    case MEMSPACE_STACK:
+      if (tree decl = base_reg->maybe_get_decl ())
+	{
+	  /* See the assertion in frame_region::get_region_for_local for the
+	     tree codes we need to handle here.  */
+	  switch (TREE_CODE (decl))
+	    {
+	    default:
+	      gcc_unreachable ();
+
+	    case PARM_DECL:
+	      /* Parameters have initial values.  */
+	      return true;
+
+	    case VAR_DECL:
+	    case RESULT_DECL:
+	      /* Function locals don't have initial values.  */
+	      return false;
+
+	    case SSA_NAME:
+	      {
+		tree ssa_name = decl;
+		/* SSA names that are the default defn of a PARM_DECL
+		   have initial_svalues; other SSA names don't.  */
+		if (SSA_NAME_IS_DEFAULT_DEF (ssa_name)
+		    && SSA_NAME_VAR (ssa_name)
+		    && TREE_CODE (SSA_NAME_VAR (ssa_name)) == PARM_DECL)
+		  return true;
+		else
+		  return false;
+	      }
+	    }
+	}
+
+      /* If we have an on-stack region that isn't associated with a decl
+	 or SSA name, then we have VLA/alloca, which is uninitialized.  */
+      return false;
+    }
+}
+
 /* If this region is a decl_region, return the decl.
    Otherwise return NULL.  */
 
@@ -584,6 +687,20 @@ region::non_null_p () const
     }
 }
 
+/* Return true iff this region is defined in terms of SVAL.  */
+
+bool
+region::involves_p (const svalue *sval) const
+{
+  if (const symbolic_region *symbolic_reg = dyn_cast_symbolic_region ())
+    {
+      if (symbolic_reg->get_pointer ()->involves_p (sval))
+	return true;
+    }
+
+  return false;
+}
+
 /* Comparator for trees to impose a deterministic ordering on
    T1 and T2.  */
 
diff --git a/gcc/analyzer/region.h b/gcc/analyzer/region.h
index 353d5c4..a17e73c 100644
--- a/gcc/analyzer/region.h
+++ b/gcc/analyzer/region.h
@@ -25,6 +25,18 @@ along with GCC; see the file COPYING3.  If not see
 
 namespace ana {
 
+/* An enum for identifying different spaces within memory.  */
+
+enum memory_space
+{
+  MEMSPACE_UNKNOWN,
+  MEMSPACE_CODE,
+  MEMSPACE_GLOBALS,
+  MEMSPACE_STACK,
+  MEMSPACE_HEAP,
+  MEMSPACE_READONLY_DATA
+};
+
 /* An enum for discriminating between the different concrete subclasses
    of region.  */
 
@@ -123,6 +135,8 @@ public:
   bool base_region_p () const;
   bool descendent_of_p (const region *elder) const;
   const frame_region *maybe_get_frame_region () const;
+  enum memory_space get_memory_space () const;
+  bool can_have_initial_svalue_p () const;
 
   tree maybe_get_decl () const;
 
@@ -141,6 +155,8 @@ public:
 
   static int cmp_ptr_ptr (const void *, const void *);
 
+  bool involves_p (const svalue *sval) const;
+
   region_offset get_offset () const;
 
   /* Attempt to get the size of this region as a concrete number of bytes.
diff --git a/gcc/analyzer/sm-malloc.cc b/gcc/analyzer/sm-malloc.cc
index 40e64b3..9707a68 100644
--- a/gcc/analyzer/sm-malloc.cc
+++ b/gcc/analyzer/sm-malloc.cc
@@ -1198,6 +1198,25 @@ public:
 				 funcname, ev.m_expr);
   }
 
+  /* Implementation of pending_diagnostic::supercedes_p for
+     use_after_free.
+
+     We want use-after-free to supercede use-of-unitialized-value,
+     so that if we have these at the same stmt, we don't emit
+     a use-of-uninitialized, just the use-after-free.
+     (this is because we fully purge information about freed
+     buffers when we free them to avoid state explosions, so
+     that if they are accessed after the free, it looks like
+     they are uninitialized).  */
+
+  bool supercedes_p (const pending_diagnostic &other) const FINAL OVERRIDE
+  {
+    if (other.use_of_uninit_p ())
+      return true;
+
+    return false;
+  }
+
 private:
   diagnostic_event_id_t m_free_event;
   const deallocator *m_deallocator;
diff --git a/gcc/analyzer/store.cc b/gcc/analyzer/store.cc
index a65c741..0042a20 100644
--- a/gcc/analyzer/store.cc
+++ b/gcc/analyzer/store.cc
@@ -1316,6 +1316,38 @@ binding_cluster::mark_region_as_unknown (store_manager *mgr,
   bind (mgr, reg, sval);
 }
 
+/* Purge state involving SVAL.  */
+
+void
+binding_cluster::purge_state_involving (const svalue *sval,
+					region_model_manager *sval_mgr)
+{
+  auto_vec<const binding_key *> to_remove;
+  for (auto iter : m_map)
+    {
+      const binding_key *iter_key = iter.first;
+      if (const symbolic_binding *symbolic_key
+	    = iter_key->dyn_cast_symbolic_binding ())
+	{
+	  const region *reg = symbolic_key->get_region ();
+	  if (reg->involves_p (sval))
+	    to_remove.safe_push (iter_key);
+	}
+      const svalue *iter_sval = iter.second;
+      if (iter_sval->involves_p (sval))
+	{
+	  const svalue *new_sval
+	    = sval_mgr->get_or_create_unknown_svalue (iter_sval->get_type ());
+	  m_map.put (iter_key, new_sval);
+	}
+    }
+  for (auto iter : to_remove)
+    {
+      m_map.remove (iter);
+      m_touched = true;
+    }
+}
+
 /* Get any SVAL bound to REG within this cluster via kind KIND,
    without checking parent regions of REG.  */
 
@@ -2447,6 +2479,29 @@ store::mark_region_as_unknown (store_manager *mgr, const region *reg,
   cluster->mark_region_as_unknown (mgr, reg, uncertainty);
 }
 
+/* Purge state involving SVAL.  */
+
+void
+store::purge_state_involving (const svalue *sval,
+			      region_model_manager *sval_mgr)
+{
+  auto_vec <const region *> base_regs_to_purge;
+  for (auto iter : m_cluster_map)
+    {
+      const region *base_reg = iter.first;
+      if (base_reg->involves_p (sval))
+	base_regs_to_purge.safe_push (base_reg);
+      else
+	{
+	  binding_cluster *cluster = iter.second;
+	  cluster->purge_state_involving (sval, sval_mgr);
+	}
+    }
+
+  for (auto iter : base_regs_to_purge)
+    purge_cluster (iter);
+}
+
 /* Get the cluster for BASE_REG, or NULL (const version).  */
 
 const binding_cluster *
diff --git a/gcc/analyzer/store.h b/gcc/analyzer/store.h
index 2ac2923..bc58694 100644
--- a/gcc/analyzer/store.h
+++ b/gcc/analyzer/store.h
@@ -198,6 +198,7 @@ private:
 
 class byte_range;
 class concrete_binding;
+class symbolic_binding;
 
 /* Abstract base class for describing ranges of bits within a binding_map
    that can have svalues bound to them.  */
@@ -220,6 +221,8 @@ public:
 
   virtual const concrete_binding *dyn_cast_concrete_binding () const
   { return NULL; }
+  virtual const symbolic_binding *dyn_cast_symbolic_binding () const
+  { return NULL; }
 };
 
 /* A concrete range of bits.  */
@@ -420,6 +423,9 @@ public:
 
   void dump_to_pp (pretty_printer *pp, bool simple) const FINAL OVERRIDE;
 
+  const symbolic_binding *dyn_cast_symbolic_binding () const FINAL OVERRIDE
+  { return this; }
+
   const region *get_region () const { return m_region; }
 
   static int cmp_ptr_ptr (const void *, const void *);
@@ -563,6 +569,8 @@ public:
   void zero_fill_region (store_manager *mgr, const region *reg);
   void mark_region_as_unknown (store_manager *mgr, const region *reg,
 			       uncertainty_t *uncertainty);
+  void purge_state_involving (const svalue *sval,
+			      region_model_manager *sval_mgr);
 
   const svalue *get_binding (store_manager *mgr, const region *reg) const;
   const svalue *get_binding_recursive (store_manager *mgr,
@@ -697,6 +705,8 @@ public:
   void zero_fill_region (store_manager *mgr, const region *reg);
   void mark_region_as_unknown (store_manager *mgr, const region *reg,
 			       uncertainty_t *uncertainty);
+  void purge_state_involving (const svalue *sval,
+			      region_model_manager *sval_mgr);
 
   const binding_cluster *get_cluster (const region *base_reg) const;
   binding_cluster *get_cluster (const region *base_reg);
diff --git a/gcc/analyzer/svalue.cc b/gcc/analyzer/svalue.cc
index 70c23f0..22da769 100644
--- a/gcc/analyzer/svalue.cc
+++ b/gcc/analyzer/svalue.cc
@@ -158,6 +158,13 @@ svalue::can_merge_p (const svalue *other,
       || (other->get_kind () == SK_UNMERGEABLE))
     return NULL;
 
+  /* Reject attempts to merge poisoned svalues with other svalues
+     (either non-poisoned, or other kinds of poison), so that e.g.
+     we identify paths in which a variable is conditionally uninitialized.  */
+  if (get_kind () == SK_POISONED
+      || other->get_kind () == SK_POISONED)
+    return NULL;
+
   /* Reject attempts to merge NULL pointers with not-NULL-pointers.  */
   if (POINTER_TYPE_P (get_type ()))
     {
@@ -516,6 +523,12 @@ public:
       m_found = true;
   }
 
+  void visit_conjured_svalue (const conjured_svalue *candidate)
+  {
+    if (candidate == m_needle)
+      m_found = true;
+  }
+
   bool found_p () const { return m_found; }
 
 private:
@@ -528,8 +541,9 @@ private:
 bool
 svalue::involves_p (const svalue *other) const
 {
-  /* Currently only implemented for initial_svalue.  */
-  gcc_assert (other->get_kind () == SK_INITIAL);
+  /* Currently only implemented for these kinds.  */
+  gcc_assert (other->get_kind () == SK_INITIAL
+	      || other->get_kind () == SK_CONJURED);
 
   involvement_visitor v (other);
   accept (&v);
@@ -811,6 +825,8 @@ poison_kind_to_str (enum poison_kind kind)
     {
     default:
       gcc_unreachable ();
+    case POISON_KIND_UNINIT:
+      return "uninit";
     case POISON_KIND_FREED:
       return "freed";
     case POISON_KIND_POPPED_STACK:
@@ -847,6 +863,18 @@ poisoned_svalue::accept (visitor *v) const
   v->visit_poisoned_svalue (this);
 }
 
+/* Implementation of svalue::maybe_fold_bits_within vfunc
+   for poisoned_svalue.  */
+
+const svalue *
+poisoned_svalue::maybe_fold_bits_within (tree type,
+					 const bit_range &,
+					 region_model_manager *mgr) const
+{
+  /* Bits within a poisoned value are also poisoned.  */
+  return mgr->get_or_create_poisoned_svalue (m_kind, type);
+}
+
 /* class setjmp_svalue's implementation is in engine.cc, so that it can use
    the declaration of exploded_node.  */
 
diff --git a/gcc/analyzer/svalue.h b/gcc/analyzer/svalue.h
index 5552fcf..54b97f8 100644
--- a/gcc/analyzer/svalue.h
+++ b/gcc/analyzer/svalue.h
@@ -324,6 +324,9 @@ public:
 
 enum poison_kind
 {
+  /* For use to describe uninitialized memory.  */
+  POISON_KIND_UNINIT,
+
   /* For use to describe freed memory.  */
   POISON_KIND_FREED,
 
@@ -378,6 +381,11 @@ public:
   void dump_to_pp (pretty_printer *pp, bool simple) const FINAL OVERRIDE;
   void accept (visitor *v) const FINAL OVERRIDE;
 
+  const svalue *
+  maybe_fold_bits_within (tree type,
+			  const bit_range &subrange,
+			  region_model_manager *mgr) const FINAL OVERRIDE;
+
   enum poison_kind get_poison_kind () const { return m_kind; }
 
  private: