re PR c++/62153 (warn for bool expression compared with integer different from 0/1)

	PR c++/62153
	* doc/invoke.texi: Document -Wbool-compare.
c-family/
	* c-common.c (maybe_warn_bool_compare): New function.
	* c-common.h (maybe_warn_bool_compare): Declare.
	* c.opt (Wbool-compare): New option.
c/
	* c-typeck.c (build_binary_op): If either operand of a comparison
	is a boolean expression, call maybe_warn_bool_compare.
cp/
	* call.c (build_new_op_1): Remember the type of arguments for
	a comparison.  If either operand of a comparison is a boolean
	expression, call maybe_warn_bool_compare.
testsuite/
	* c-c++-common/Wbool-compare-1.c: New test.

From-SVN: r214183

4 files changed, 45 insertions, 0 deletions

diff --git a/gcc/c-family/ChangeLog b/gcc/c-family/ChangeLog
index e25f1d8..e458f5e 100644
--- a/gcc/c-family/ChangeLog
+++ b/gcc/c-family/ChangeLog
@@ -1,5 +1,12 @@
 2014-08-19  Marek Polacek  <polacek@redhat.com>
 
+	PR c++/62153
+	* c-common.c (maybe_warn_bool_compare): New function.
+	* c-common.h (maybe_warn_bool_compare): Declare.
+	* c.opt (Wbool-compare): New option.
+
+2014-08-19  Marek Polacek  <polacek@redhat.com>
+
 	* c.opt (Wc99-c11-compat): New option.
 
 2014-08-19  Marek Polacek  <polacek@redhat.com>
diff --git a/gcc/c-family/c-common.c b/gcc/c-family/c-common.c
index acc9a20..901a5ed 100644
--- a/gcc/c-family/c-common.c
+++ b/gcc/c-family/c-common.c
@@ -11612,6 +11612,39 @@ maybe_warn_unused_local_typedefs (void)
   vec_free (l->local_typedefs);
 }
 
+/* Warn about boolean expression compared with an integer value different
+   from true/false.  Warns also e.g. about "(i1 == i2) == 2".
+   LOC is the location of the comparison, CODE is its code, OP0 and OP1
+   are the operands of the comparison.  The caller must ensure that
+   either operand is a boolean expression.  */
+
+void
+maybe_warn_bool_compare (location_t loc, enum tree_code code, tree op0,
+			 tree op1)
+{
+  if (TREE_CODE_CLASS (code) != tcc_comparison)
+    return;
+
+  tree cst = (TREE_CODE (op0) == INTEGER_CST)
+	     ? op0 : (TREE_CODE (op1) == INTEGER_CST) ? op1 : NULL_TREE;
+  if (!cst)
+    return;
+
+  if (!integer_zerop (cst) && !integer_onep (cst))
+    {
+      int sign = (TREE_CODE (op0) == INTEGER_CST)
+		 ? tree_int_cst_sgn (cst) : -tree_int_cst_sgn (cst);
+      if (code == EQ_EXPR
+	  || ((code == GT_EXPR || code == GE_EXPR) && sign < 0)
+	  || ((code == LT_EXPR || code == LE_EXPR) && sign > 0))
+	warning_at (loc, OPT_Wbool_compare, "comparison of constant %qE "
+		    "with boolean expression is always false", cst);
+      else
+	warning_at (loc, OPT_Wbool_compare, "comparison of constant %qE "
+		    "with boolean expression is always true", cst);
+    }
+}
+
 /* The C and C++ parsers both use vectors to hold function arguments.
    For efficiency, we keep a cache of unused vectors.  This is the
    cache.  */
diff --git a/gcc/c-family/c-common.h b/gcc/c-family/c-common.h
index 26aaee2..995bc8c 100644
--- a/gcc/c-family/c-common.h
+++ b/gcc/c-family/c-common.h
@@ -1015,6 +1015,7 @@ extern void record_types_used_by_current_var_decl (tree);
 extern void record_locally_defined_typedef (tree);
 extern void maybe_record_typedef_use (tree);
 extern void maybe_warn_unused_local_typedefs (void);
+extern void maybe_warn_bool_compare (location_t, enum tree_code, tree, tree);
 extern vec<tree, va_gc> *make_tree_vector (void);
 extern void release_tree_vector (vec<tree, va_gc> *);
 extern vec<tree, va_gc> *make_tree_vector_single (tree);
diff --git a/gcc/c-family/c.opt b/gcc/c-family/c.opt
index 4848399..f97a11a 100644
--- a/gcc/c-family/c.opt
+++ b/gcc/c-family/c.opt
@@ -287,6 +287,10 @@ Wbad-function-cast
 C ObjC Var(warn_bad_function_cast) Warning
 Warn about casting functions to incompatible types
 
+Wbool-compare
+C ObjC C++ ObjC++ Var(warn_bool_compare) Warning LangEnabledBy(C ObjC C++ ObjC++,Wall)
+Warn about boolean expression compared with an integer value different from true/false
+
 Wbuiltin-macro-redefined
 C ObjC C++ ObjC++ Warning
 Warn when a built-in preprocessor macro is undefined or redefined