Emit -Waddress warnings for comparing address of reference against NULL

gcc/c-family/ChangeLog:

	PR c++/65168
	* c-common.c (c_common_truthvalue_conversion): Warn when
	converting an address of a reference to a truth value.

gcc/cp/ChangeLog:

	PR c++/65168
	* typeck.c (cp_build_binary_op): Warn when comparing an address
	of a reference against NULL.

gcc/testsuite/ChangeLog:

	PR c++/65168
	g++.dg/warn/Walways-true-3.C: New test.

From-SVN: r224455

6 files changed, 111 insertions, 0 deletions

diff --git a/gcc/c-family/ChangeLog b/gcc/c-family/ChangeLog
index a2324a4..80c3e48 100644
--- a/gcc/c-family/ChangeLog
+++ b/gcc/c-family/ChangeLog
@@ -1,3 +1,9 @@
+2015-06-13  Patrick Palka  <ppalka@gcc.gnu.org>
+
+	PR c++/65168
+	* c-common.c (c_common_truthvalue_conversion): Warn when
+	converting an address of a reference to a truth value.
+
 2015-06-08  Andrew MacLeod  <amacleod@redhat.com>
 
 	* array-notation-common.c : Adjust include files.
diff --git a/gcc/c-family/c-common.c b/gcc/c-family/c-common.c
index 5b76567..b1af682 100644
--- a/gcc/c-family/c-common.c
+++ b/gcc/c-family/c-common.c
@@ -4973,6 +4973,20 @@ c_common_truthvalue_conversion (location_t location, tree expr)
 	tree totype = TREE_TYPE (expr);
 	tree fromtype = TREE_TYPE (TREE_OPERAND (expr, 0));
 
+	if (POINTER_TYPE_P (totype)
+	    && TREE_CODE (fromtype) == REFERENCE_TYPE)
+	  {
+	    tree inner = expr;
+	    STRIP_NOPS (inner);
+
+	    if (DECL_P (inner))
+	      warning_at (location,
+			  OPT_Waddress,
+			  "the compiler can assume that the address of "
+			  "%qD will always evaluate to %<true%>",
+			  inner);
+	  }
+
 	/* Don't cancel the effect of a CONVERT_EXPR from a REFERENCE_TYPE,
 	   since that affects how `default_conversion' will behave.  */
 	if (TREE_CODE (totype) == REFERENCE_TYPE
diff --git a/gcc/cp/ChangeLog b/gcc/cp/ChangeLog
index b18a893..c091617 100644
--- a/gcc/cp/ChangeLog
+++ b/gcc/cp/ChangeLog
@@ -1,3 +1,9 @@
+2015-06-13  Patrick Palka  <ppalka@gcc.gnu.org>
+
+	PR c++/65168
+	* typeck.c (cp_build_binary_op): Warn when comparing an address
+	of a reference against NULL.
+
 2015-06-12  Jason Merrill  <jason@redhat.com>
 
 	PR c++/65719
diff --git a/gcc/cp/typeck.c b/gcc/cp/typeck.c
index 5b09b73..7716c21 100644
--- a/gcc/cp/typeck.c
+++ b/gcc/cp/typeck.c
@@ -4430,6 +4430,23 @@ cp_build_binary_op (location_t location,
 		warning (OPT_Waddress, "the address of %qD will never be NULL",
 			 TREE_OPERAND (op0, 0));
 	    }
+
+	  if (CONVERT_EXPR_P (op0)
+	      && TREE_CODE (TREE_TYPE (TREE_OPERAND (op0, 0)))
+		 == REFERENCE_TYPE)
+	    {
+	      tree inner_op0 = op0;
+	      STRIP_NOPS (inner_op0);
+
+	      if ((complain & tf_warning)
+		  && c_inhibit_evaluation_warnings == 0
+		  && !TREE_NO_WARNING (op0)
+		  && DECL_P (inner_op0))
+		warning_at (location, OPT_Waddress,
+			    "the compiler can assume that the address of "
+			    "%qD will never be NULL",
+			    inner_op0);
+	    }
 	}
       else if (((code1 == POINTER_TYPE || TYPE_PTRDATAMEM_P (type1))
 		&& null_ptr_cst_p (op0))
@@ -4452,6 +4469,23 @@ cp_build_binary_op (location_t location,
 		warning (OPT_Waddress, "the address of %qD will never be NULL",
 			 TREE_OPERAND (op1, 0));
 	    }
+
+	  if (CONVERT_EXPR_P (op1)
+	      && TREE_CODE (TREE_TYPE (TREE_OPERAND (op1, 0)))
+		 == REFERENCE_TYPE)
+	    {
+	      tree inner_op1 = op1;
+	      STRIP_NOPS (inner_op1);
+
+	      if ((complain & tf_warning)
+		  && c_inhibit_evaluation_warnings == 0
+		  && !TREE_NO_WARNING (op1)
+		  && DECL_P (inner_op1))
+		warning_at (location, OPT_Waddress,
+			    "the compiler can assume that the address of "
+			    "%qD will never be NULL",
+			    inner_op1);
+	    }
 	}
       else if ((code0 == POINTER_TYPE && code1 == POINTER_TYPE)
 	       || (TYPE_PTRDATAMEM_P (type0) && TYPE_PTRDATAMEM_P (type1)))
diff --git a/gcc/testsuite/ChangeLog b/gcc/testsuite/ChangeLog
index 35822f3..b9b96e7 100644
--- a/gcc/testsuite/ChangeLog
+++ b/gcc/testsuite/ChangeLog
@@ -1,3 +1,8 @@
+2015-06-13  Patrick Palka  <ppalka@gcc.gnu.org>
+
+	PR c++/65168
+	g++.dg/warn/Walways-true-3.C: New test.
+
 2015-06-13  Tom de Vries  <tom@codesourcery.com>
 
 	* gcc.dg/parloops-exit-first-loop-alt-4.c: New test.
diff --git a/gcc/testsuite/g++.dg/warn/Walways-true-3.C b/gcc/testsuite/g++.dg/warn/Walways-true-3.C
new file mode 100644
index 0000000..d6e9df4
--- /dev/null
+++ b/gcc/testsuite/g++.dg/warn/Walways-true-3.C
@@ -0,0 +1,46 @@
+// PR c++/65168
+// { dg-options "-Waddress" }
+
+void foo (void);
+
+int d;
+int &c = d;
+
+void
+bar (int &a)
+{
+  int &b = a;
+
+  if ((int *)&a) // { dg-warning "address of" }
+    foo ();
+
+  if (&b) // { dg-warning "address of" }
+    foo ();
+
+  if (!&c) // { dg-warning "address of" }
+    foo ();
+
+  if (!&(int &)(int &)a) // { dg-warning "address of" }
+    foo ();
+
+  if (&a == 0) // { dg-warning "never be NULL" }
+    foo ();
+
+  if (&b != 0) // { dg-warning "never be NULL" }
+    foo ();
+
+  if (0 == &(int &)(int &)c) // { dg-warning "never be NULL" }
+    foo ();
+
+  if (&a != (int *)0) // { dg-warning "never be NULL" }
+    foo ();
+}
+
+bool
+bar_1 (int &a)
+{
+  if (d == 5)
+    return &a; // { dg-warning "address of" }
+  else
+    return !&(int &)(int &)a; // { dg-warning "address of" }
+}