re PR c++/60517 (warning/error for taking address of member of a temporary object)

2014-07-31  Marc Glisse  <marc.glisse@inria.fr>

	PR c++/60517
gcc/c/
	* c-typeck.c (c_finish_return): Return 0 instead of the address of
	a local variable.
gcc/cp/
	* typeck.c (maybe_warn_about_returning_address_of_local): Return
	whether it is returning the address of a local variable.
	(check_return_expr): Return 0 instead of the address of a local
	variable.
gcc/c-family/
	* c.opt (-Wreturn-local-addr): Move to common.opt.
gcc/
	* common.opt (-Wreturn-local-addr): Moved from c.opt.
	* gimple-ssa-isolate-paths.c: Include diagnostic-core.h and intl.h.
	(isolate_path): New argument to avoid inserting a trap.
	(find_implicit_erroneous_behaviour): Handle returning the address
	of a local variable.
	(find_explicit_erroneous_behaviour): Likewise.
gcc/testsuite/
	* c-c++-common/addrtmp.c: New file.
	* c-c++-common/uninit-G.c: Adapt.

From-SVN: r213323

gcc/ChangeLog

@@ -1,3 +1,13 @@
+2014-07-31  Marc Glisse  <marc.glisse@inria.fr>
+
+	PR c++/60517
+	* common.opt (-Wreturn-local-addr): Moved from c.opt.
+	* gimple-ssa-isolate-paths.c: Include diagnostic-core.h and intl.h.
+	(isolate_path): New argument to avoid inserting a trap.
+	(find_implicit_erroneous_behaviour): Handle returning the address
+	of a local variable.
+	(find_explicit_erroneous_behaviour): Likewise.
+
 2014-07-31  Bingfeng Mei <bmei@broadcom.com>
 
 	PR lto/61868

gcc/c-family/ChangeLog

@@ -1,3 +1,8 @@
+2014-07-31  Marc Glisse  <marc.glisse@inria.fr>
+
+	PR c++/60517
+	* c.opt (-Wreturn-local-addr): Move to common.opt.
+
 2014-07-30  Jason Merrill  <jason@redhat.com>
 
 	PR c++/61659

gcc/c-family/c.opt

@@ -709,10 +709,6 @@ Wreorder
 C++ ObjC++ Var(warn_reorder) Warning LangEnabledBy(C++ ObjC++,Wall)
 Warn when the compiler reorders code
 
-Wreturn-local-addr
-C ObjC C++ ObjC++ Var(warn_return_local_addr) Init(1) Warning
-Warn about returning a pointer/reference to a local or temporary variable.
-
 Wreturn-type
 C ObjC C++ ObjC++ Var(warn_return_type) Warning LangEnabledBy(C ObjC C++ ObjC++,Wall)
 Warn whenever a function's return type defaults to \"int\" (C), or about inconsistent return types (C++)

gcc/c/ChangeLog

@@ -1,3 +1,9 @@
+2014-07-31  Marc Glisse  <marc.glisse@inria.fr>
+
+	PR c++/60517
+	* c-typeck.c (c_finish_return): Return 0 instead of the address of
+	a local variable.
+
 2014-07-30  Tom Tromey  <tromey@redhat.com>
 
 	* c-typeck.c (struct constructor_stack) <designator_depth>: New

gcc/c/c-typeck.c

@@ -9350,8 +9350,12 @@ c_finish_return (location_t loc, tree retval, tree origtype)
 		    warning_at (loc, OPT_Wreturn_local_addr,
 				"function returns address of label");
 		  else
-		    warning_at (loc, OPT_Wreturn_local_addr,
-				"function returns address of local variable");
+		    {
+		      warning_at (loc, OPT_Wreturn_local_addr,
+				  "function returns address of local variable");
+		      tree zero = build_zero_cst (TREE_TYPE (res));
+		      t = build2 (COMPOUND_EXPR, TREE_TYPE (res), t, zero);
+		    }
 		}
 	      break;
 

gcc/common.opt

@@ -607,6 +607,10 @@ Wpedantic
 Common Var(pedantic) Warning
 Issue warnings needed for strict compliance to the standard
 
+Wreturn-local-addr
+Common Var(warn_return_local_addr) Init(1) Warning
+Warn about returning a pointer/reference to a local or temporary variable.
+
 Wshadow
 Common Var(warn_shadow) Warning
 Warn when one local variable shadows another

gcc/cp/ChangeLog

@@ -1,3 +1,11 @@
+2014-07-31  Marc Glisse  <marc.glisse@inria.fr>
+
+	PR c++/60517
+	* typeck.c (maybe_warn_about_returning_address_of_local): Return
+	whether it is returning the address of a local variable.
+	(check_return_expr): Return 0 instead of the address of a local
+	variable.
+
 2014-07-30  Jason Merrill  <jason@redhat.com>
 
 	PR lto/53808

gcc/cp/typeck.c

@@ -56,7 +56,7 @@ static tree pointer_diff (tree, tree, tree, tsubst_flags_t);
 static tree get_delta_difference (tree, tree, bool, bool, tsubst_flags_t);
 static void casts_away_constness_r (tree *, tree *, tsubst_flags_t);
 static bool casts_away_constness (tree, tree, tsubst_flags_t);
-static void maybe_warn_about_returning_address_of_local (tree);
+static bool maybe_warn_about_returning_address_of_local (tree);
 static tree lookup_destructor (tree, tree, tree, tsubst_flags_t);
 static void warn_args_num (location_t, tree, bool);
 static int convert_arguments (tree, vec<tree, va_gc> **, tree, int,
@@ -8296,9 +8296,9 @@ convert_for_initialization (tree exp, tree type, tree rhs, int flags,
 }
 
 /* If RETVAL is the address of, or a reference to, a local variable or
-   temporary give an appropriate warning.  */
+   temporary give an appropriate warning and return true.  */
 
-static void
+static bool
 maybe_warn_about_returning_address_of_local (tree retval)
 {
   tree valtype = TREE_TYPE (DECL_RESULT (current_function_decl));
@@ -8316,7 +8316,7 @@ maybe_warn_about_returning_address_of_local (tree retval)
     }
 
   if (TREE_CODE (whats_returned) != ADDR_EXPR)
-    return;
+    return false;
   whats_returned = TREE_OPERAND (whats_returned, 0);
 
   while (TREE_CODE (whats_returned) == COMPONENT_REF
@@ -8329,14 +8329,14 @@ maybe_warn_about_returning_address_of_local (tree retval)
 	  || TREE_CODE (whats_returned) == TARGET_EXPR)
 	{
 	  warning (OPT_Wreturn_local_addr, "returning reference to temporary");
-	  return;
+	  return true;
 	}
       if (VAR_P (whats_returned)
 	  && DECL_NAME (whats_returned)
 	  && TEMP_NAME_P (DECL_NAME (whats_returned)))
 	{
 	  warning (OPT_Wreturn_local_addr, "reference to non-lvalue returned");
-	  return;
+	  return true;
 	}
     }
 
@@ -8356,8 +8356,10 @@ maybe_warn_about_returning_address_of_local (tree retval)
       else
 	warning (OPT_Wreturn_local_addr, "address of local variable %q+D "
 		 "returned", whats_returned);
-      return;
+      return true;
     }
+
+  return false;
 }
 
 /* Check that returning RETVAL from the current function is valid.
@@ -8650,8 +8652,9 @@ check_return_expr (tree retval, bool *no_warning)
 	       && TREE_CODE (TREE_OPERAND (retval, 1)) == AGGR_INIT_EXPR)
 	retval = build2 (COMPOUND_EXPR, TREE_TYPE (retval), retval,
 			 TREE_OPERAND (retval, 0));
-      else
-	maybe_warn_about_returning_address_of_local (retval);
+      else if (maybe_warn_about_returning_address_of_local (retval))
+	retval = build2 (COMPOUND_EXPR, TREE_TYPE (retval), retval,
+			 build_zero_cst (TREE_TYPE (retval)));
     }
 
   /* Actually copy the value returned into the appropriate location.  */

gcc/gimple-ssa-isolate-paths.c

@@ -42,6 +42,8 @@ along with GCC; see the file COPYING3.  If not see
 #include "cfgloop.h"
 #include "tree-pass.h"
 #include "tree-cfg.h"
+#include "diagnostic-core.h"
+#include "intl.h"
 
 
 static bool cfg_altered;
@@ -132,13 +134,15 @@ insert_trap_and_remove_trailing_statements (gimple_stmt_iterator *si_p, tree op)
    Optimization is simple as well.  Replace STMT in BB' with an
    unconditional trap and remove all outgoing edges from BB'.
 
+   If RET_ZERO, do not trap, only return NULL.
+
    DUPLICATE is a pre-existing duplicate, use it as BB' if it exists.
 
    Return BB'.  */
 
 basic_block
 isolate_path (basic_block bb, basic_block duplicate,
-	      edge e, gimple stmt, tree op)
+	      edge e, gimple stmt, tree op, bool ret_zero)
 {
   gimple_stmt_iterator si, si2;
   edge_iterator ei;
@@ -151,8 +155,9 @@ isolate_path (basic_block bb, basic_block duplicate,
   if (!duplicate)
     {
       duplicate = duplicate_block (bb, NULL, NULL);
-      for (ei = ei_start (duplicate->succs); (e2 = ei_safe_edge (ei)); )
-	remove_edge (e2);
+      if (!ret_zero)
+	for (ei = ei_start (duplicate->succs); (e2 = ei_safe_edge (ei)); )
+	  remove_edge (e2);
     }
 
   /* Complete the isolation step by redirecting E to reach DUPLICATE.  */
@@ -197,7 +202,17 @@ isolate_path (basic_block bb, basic_block duplicate,
      SI2 points to the duplicate of STMT in DUPLICATE.  Insert a trap
      before SI2 and remove SI2 and all trailing statements.  */
   if (!gsi_end_p (si2))
-    insert_trap_and_remove_trailing_statements (&si2, op);
+    {
+      if (ret_zero)
+	{
+	  gimple ret = gsi_stmt (si2);
+	  tree zero = build_zero_cst (TREE_TYPE (gimple_return_retval (ret)));
+	  gimple_return_set_retval (ret, zero);
+	  update_stmt (ret);
+	}
+      else
+	insert_trap_and_remove_trailing_statements (&si2, op);
+    }
 
   return duplicate;
 }
@@ -255,16 +270,49 @@ find_implicit_erroneous_behaviour (void)
 	       i = next_i)
 	    {
 	      tree op = gimple_phi_arg_def (phi, i);
-
-	      next_i = i + 1;
-
-	      if (!integer_zerop (op))
-		continue;
-
 	      edge e = gimple_phi_arg_edge (phi, i);
 	      imm_use_iterator iter;
 	      gimple use_stmt;
 
+	      next_i = i + 1;
+
+	      if (TREE_CODE (op) == ADDR_EXPR)
+		{
+		  tree valbase = get_base_address (TREE_OPERAND (op, 0));
+		  if ((TREE_CODE (valbase) == VAR_DECL
+		       && !is_global_var (valbase))
+		      || TREE_CODE (valbase) == PARM_DECL)
+		    {
+		      FOR_EACH_IMM_USE_STMT (use_stmt, iter, lhs)
+			{
+			  if (gimple_code (use_stmt) != GIMPLE_RETURN
+			      || gimple_return_retval (use_stmt) != lhs)
+			    continue;
+
+			  if (warning_at (gimple_location (use_stmt),
+					  OPT_Wreturn_local_addr,
+					  "function may return address "
+					  "of local variable"))
+			    inform (DECL_SOURCE_LOCATION(valbase),
+				    "declared here");
+
+			  if (gimple_bb (use_stmt) == bb)
+			    {
+			      duplicate = isolate_path (bb, duplicate, e,
+							use_stmt, lhs, true);
+
+			      /* When we remove an incoming edge, we need to
+				 reprocess the Ith element.  */
+			      next_i = i;
+			      cfg_altered = true;
+			    }
+			}
+		    }
+		}
+
+	      if (!integer_zerop (op))
+		continue;
+
 	      /* We've got a NULL PHI argument.  Now see if the
  	         PHI's result is dereferenced within BB.  */
 	      FOR_EACH_IMM_USE_STMT (use_stmt, iter, lhs)
@@ -280,8 +328,8 @@ find_implicit_erroneous_behaviour (void)
 					   flag_isolate_erroneous_paths_attribute))
 
 		    {
-		      duplicate = isolate_path (bb, duplicate,
-						e, use_stmt, lhs);
+		      duplicate = isolate_path (bb, duplicate, e,
+						use_stmt, lhs, false);
 
 		      /* When we remove an incoming edge, we need to
 			 reprocess the Ith element.  */
@@ -347,9 +395,45 @@ find_explicit_erroneous_behaviour (void)
 	      cfg_altered = true;
 	      break;
 	    }
+
+	  /* Detect returning the address of a local variable.  This only
+	     becomes undefined behavior if the result is used, so we do not
+	     insert a trap and only return NULL instead.  */
+	  if (gimple_code (stmt) == GIMPLE_RETURN)
+	    {
+	      tree val = gimple_return_retval (stmt);
+	      if (val && TREE_CODE (val) == ADDR_EXPR)
+		{
+		  tree valbase = get_base_address (TREE_OPERAND (val, 0));
+		  if ((TREE_CODE (valbase) == VAR_DECL
+		       && !is_global_var (valbase))
+		      || TREE_CODE (valbase) == PARM_DECL)
+		    {
+		      /* We only need it for this particular case.  */
+		      calculate_dominance_info (CDI_POST_DOMINATORS);
+		      const char* msg;
+		      bool always_executed = dominated_by_p
+			(CDI_POST_DOMINATORS,
+			 single_succ (ENTRY_BLOCK_PTR_FOR_FN (cfun)), bb);
+		      if (always_executed)
+			msg = N_("function returns address of local variable");
+		      else
+			msg = N_("function may return address of "
+				 "local variable");
+
+		      if (warning_at (gimple_location (stmt),
+				      OPT_Wreturn_local_addr, msg))
+			inform (DECL_SOURCE_LOCATION(valbase), "declared here");
+		      tree zero = build_zero_cst (TREE_TYPE (val));
+		      gimple_return_set_retval (stmt, zero);
+		      update_stmt (stmt);
+		    }
+		}
+	    }
 	}
     }
 }
+
 /* Search the function for statements which, if executed, would cause
    the program to fault such as a dereference of a NULL pointer.
 

gcc/testsuite/ChangeLog

@@ -1,3 +1,9 @@
+2014-07-31  Marc Glisse  <marc.glisse@inria.fr>
+
+	PR c++/60517
+	* c-c++-common/addrtmp.c: New file.
+	* c-c++-common/uninit-G.c: Adapt.
+
 2014-07-31  Bingfeng Mei  <bmei@broadcom.com>
 
 	PR lto/61868

gcc/testsuite/c-c++-common/addrtmp.c

@@ -0,0 +1,29 @@
+/* { dg-do compile } */
+/* { dg-options "-O2" } */
+
+typedef struct A { int a,b; } A;
+int*g(int*x){return x;}
+int*f1(){
+  A x[2]={{1,2},{3,4}};
+  return g(&x[1].a); // { dg-warning "returns address of local variable" }
+}
+int*f2(int n){
+  A x[2]={{1,2},{3,4}};
+  return n?0:g(&x[1].a); // { dg-warning "may return address of local variable" }
+}
+A y[2]={{1,2},{3,4}};
+int*h(){
+  return g(&y[1].a);
+}
+int*j(int n){
+  A x[2]={{1,2},{3,4}};
+  int*p=g(&y[1].a);
+  if(n==1)p=g(&x[1].a);
+  if(n==2)p=g(&x[0].b);
+  return p; // { dg-warning "may return address of local variable" }
+}
+int*s()
+{
+  static int i;
+  return &i;
+}

gcc/testsuite/c-c++-common/uninit-G.c

@@ -2,8 +2,9 @@
 /* { dg-do compile } */
 /* { dg-options "-O -Wuninitialized" } */
 
-void *f()
+void g(void*);
+void f()
 {
   void *i = &i;
-  return i;
+  g(i);
 }