re PR c/7776 (const char* p = "foo"; if (p == "foo") ... is compiled without warning!)

	PR c/7776
	* common.opt (Wstring-literal-comparison): New command line option.
	* c-opts.c (c_common_handle_option): Set it with -Wall.
	* c-typeck.c (parser_build_binary_op): Issue warning if either
	operand of a comparison operator is a string literal, except for
	testing equality or inequality against NULL.

	* doc/invoke.texi: Document new -Wstring-literal-comparison option.

	* gcc.dg/Wstring-literal-comparison-1.c: New test case.
	* gcc.dg/Wstring-literal-comparison-2.c: Likewise.
	* gcc.dg/Wstring-literal-comparison-3.c: Likewise.
	* gcc.dg/Wstring-literal-comparison-4.c: Likewise.

From-SVN: r108018

9 files changed, 154 insertions, 0 deletions

diff --git a/gcc/ChangeLog b/gcc/ChangeLog
index afe22a0..d8fc531 100644
--- a/gcc/ChangeLog
+++ b/gcc/ChangeLog
@@ -1,3 +1,14 @@
+2005-12-04  Roger Sayle  <roger@eyesopen.com>
+
+	PR c/7776
+	* common.opt (Wstring-literal-comparison): New command line option.
+	* c-opts.c (c_common_handle_option): Set it with -Wall.
+	* c-typeck.c (parser_build_binary_op): Issue warning if either
+	operand of a comparison operator is a string literal, except for
+	testing equality or inequality against NULL.
+
+	* doc/invoke.texi: Document new -Wstring-literal-comparison option.
+
 2005-12-03  Joseph S. Myers  <joseph@codesourcery.com>
 
 	* c-common.c (c_sizeof_or_alignof_type): Use fold_convert instead
diff --git a/gcc/c-opts.c b/gcc/c-opts.c
index 62db668..86f2244 100644
--- a/gcc/c-opts.c
+++ b/gcc/c-opts.c
@@ -386,6 +386,7 @@ c_common_handle_option (size_t scode, const char *arg, int value)
 	warn_sign_compare = value;
       warn_switch = value;
       warn_strict_aliasing = value;
+      warn_string_literal_comparison = value;
 
       /* Only warn about unknown pragmas that are not in system
 	 headers.  */
diff --git a/gcc/c-typeck.c b/gcc/c-typeck.c
index 8b8eb56..062de7c 100644
--- a/gcc/c-typeck.c
+++ b/gcc/c-typeck.c
@@ -2552,6 +2552,20 @@ parser_build_binary_op (enum tree_code code, struct c_expr arg1,
 
     }
 
+  /* Warn about comparisons against string literals, with the exception
+     of testing for equality or inequality of a string literal with NULL.  */
+  if (code == EQ_EXPR || code == NE_EXPR)
+    {
+      if ((code1 == STRING_CST && !integer_zerop (arg2.value))
+	  || (code2 == STRING_CST && !integer_zerop (arg1.value)))
+	warning (OPT_Wstring_literal_comparison,
+		 "comparison with string literal");
+    }
+  else if (TREE_CODE_CLASS (code) == tcc_comparison
+	   && (code1 == STRING_CST || code2 == STRING_CST))
+    warning (OPT_Wstring_literal_comparison,
+	     "comparison with string literal");
+
   unsigned_conversion_warning (result.value, arg1.value);
   unsigned_conversion_warning (result.value, arg2.value);
   overflow_warning (result.value);
diff --git a/gcc/common.opt b/gcc/common.opt
index 6ac77fd..e49838a 100644
--- a/gcc/common.opt
+++ b/gcc/common.opt
@@ -125,6 +125,10 @@ Wstrict-aliasing=
 Common Joined UInteger
 Warn about code which might break strict aliasing rules
 
+Wstring-literal-comparison
+Common Var(warn_string_literal_comparison)
+Warn about comparisons to constant string literals
+
 Wswitch
 Common Var(warn_switch)
 Warn about enumerated switches, with no default, missing a case
diff --git a/gcc/testsuite/ChangeLog b/gcc/testsuite/ChangeLog
index 257c74a..f08c252 100644
--- a/gcc/testsuite/ChangeLog
+++ b/gcc/testsuite/ChangeLog
@@ -1,3 +1,11 @@
+2005-12-04  Roger Sayle  <roger@eyesopen.com>
+
+	PR c/7776
+	* gcc.dg/Wstring-literal-comparison-1.c: New test case.
+	* gcc.dg/Wstring-literal-comparison-2.c: Likewise.
+	* gcc.dg/Wstring-literal-comparison-3.c: Likewise.
+	* gcc.dg/Wstring-literal-comparison-4.c: Likewise.
+
 2005-12-03  Joseph S. Myers  <joseph@codesourcery.com>
 
 	* gcc.dg/cast-pretty-print-1.c: New test.
diff --git a/gcc/testsuite/gcc.dg/Wstring-literal-comparison-1.c b/gcc/testsuite/gcc.dg/Wstring-literal-comparison-1.c
new file mode 100644
index 0000000..c5dea46
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/Wstring-literal-comparison-1.c
@@ -0,0 +1,29 @@
+/* PR c/7776 */
+/* { dg-do compile } */
+/* { dg-options "-Wstring-literal-comparison" } */
+
+int test1(char *ptr)
+{
+  return ptr == "foo";  /* { dg-warning "comparison with string" } */
+}
+
+int test2()
+{
+  return "foo" != (const char*)0;
+}
+
+int test3()
+{
+  return "foo" == (const char*)0;
+}
+
+int test4()
+{
+  return (const char*)0 != "foo";
+}
+
+int test5()
+{
+  return (const char*)0 == "foo";
+}
+
diff --git a/gcc/testsuite/gcc.dg/Wstring-literal-comparison-2.c b/gcc/testsuite/gcc.dg/Wstring-literal-comparison-2.c
new file mode 100644
index 0000000..3eb91ee
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/Wstring-literal-comparison-2.c
@@ -0,0 +1,29 @@
+/* PR c/7776 */
+/* { dg-do compile } */
+/* { dg-options "-Wall" } */
+
+int test1(char *ptr)
+{
+  return ptr == "foo";  /* { dg-warning "comparison with string" } */
+}
+
+int test2()
+{
+  return "foo" != (const char*)0;
+}
+
+int test3()
+{
+  return "foo" == (const char*)0;
+}
+
+int test4()
+{
+  return (const char*)0 != "foo";
+}
+
+int test5()
+{
+  return (const char*)0 == "foo";
+}
+
diff --git a/gcc/testsuite/gcc.dg/Wstring-literal-comparison-3.c b/gcc/testsuite/gcc.dg/Wstring-literal-comparison-3.c
new file mode 100644
index 0000000..f700a51
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/Wstring-literal-comparison-3.c
@@ -0,0 +1,29 @@
+/* PR c/7776 */
+/* { dg-do compile } */
+/* { dg-options "" } */
+
+int test1(char *ptr)
+{
+  return ptr == "foo";
+}
+
+int test2()
+{
+  return "foo" != (const char*)0;
+}
+
+int test3()
+{
+  return "foo" == (const char*)0;
+}
+
+int test4()
+{
+  return (const char*)0 != "foo";
+}
+
+int test5()
+{
+  return (const char*)0 == "foo";
+}
+
diff --git a/gcc/testsuite/gcc.dg/Wstring-literal-comparison-4.c b/gcc/testsuite/gcc.dg/Wstring-literal-comparison-4.c
new file mode 100644
index 0000000..27f25f3
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/Wstring-literal-comparison-4.c
@@ -0,0 +1,29 @@
+/* PR c/7776 */
+/* { dg-do compile } */
+/* { dg-options "-Wall -Wno-string-literal-comparison" } */
+
+int test1(char *ptr)
+{
+  return ptr == "foo";
+}
+
+int test2()
+{
+  return "foo" != (const char*)0;
+}
+
+int test3()
+{
+  return "foo" == (const char*)0;
+}
+
+int test4()
+{
+  return (const char*)0 != "foo";
+}
+
+int test5()
+{
+  return (const char*)0 == "foo";
+}
+