Re: [RFC PATCH] -Wmemset-transposed-args (PR middle-end/61294)

[Jakub Jelinek <jakub at redhat dot com>]

On Wed, Jul 09, 2014 at 12:26:09PM +0200, Richard Biener wrote:
> > I suppose we could use an INTEGER_CST distinct from the one in
> > TYPE_CACHED_VALUES for raw 0, with a TREE_LANG_FLAG set.
> 
> Ick.  (please no - at least make sure it doesn't survive anywhere to the
> middle-end, like fold or gimple).

Why?  I don't think the middle-end ever compares INTEGER_CSTs for equality.

Here is my WIP on Jason's suggestion (untested of course other than the
testcase), the C++ FE is changed to do that, the C FE is not.

Sure, I could add another bool argument to
cp_parser_parenthesized_expression_list whether the caller expects to see
the literal zeros, and replace them with normal INTEGER_CSTs after the test.

--- gcc/c/c-typeck.c.jj	2014-07-08 17:38:09.612266656 +0200
+++ gcc/c/c-typeck.c	2014-07-09 10:41:38.931018088 +0200
@@ -2987,6 +2987,16 @@ c_build_function_call_vec (location_t lo
   /* Convert anything with function type to a pointer-to-function.  */
   if (TREE_CODE (function) == FUNCTION_DECL)
     {
+      if (warn_memset_transposed_args
+	  && DECL_BUILT_IN_CLASS (function) == BUILT_IN_NORMAL
+	  && DECL_FUNCTION_CODE (function) == BUILT_IN_MEMSET
+	  && vec_safe_length (params) == 3
+	  && integer_zerop ((*params)[2])
+	  && !integer_zerop ((*params)[1]))
+	warning_at (loc, OPT_Wmemset_transposed_args,
+		    "%<memset%> used with constant zero length parameter; "
+		    "this could be due to transposed parameters");
+
       /* Implement type-directed function overloading for builtins.
 	 resolve_overloaded_builtin and targetm.resolve_overloaded_builtin
 	 handle all the type checking.  The result is a complete expression
--- gcc/cp/cp-tree.h.jj	2014-07-07 10:39:44.000000000 +0200
+++ gcc/cp/cp-tree.h	2014-07-09 11:48:12.534274257 +0200
@@ -4187,6 +4187,10 @@ more_aggr_init_expr_args_p (const aggr_i
 #define SIZEOF_EXPR_TYPE_P(NODE) \
   TREE_LANG_FLAG_0 (SIZEOF_EXPR_CHECK (NODE))
 
+/* True if INTEGER_CST is a zero literal seen in function argument list.  */
+#define LITERAL_ZERO_P(NODE) \
+  (INTEGER_CST_CHECK (NODE)->base.nothrow_flag)
+
 /* An enumeration of the kind of tags that C++ accepts.  */
 enum tag_types {
   none_type = 0, /* Not a tag type.  */
--- gcc/cp/parser.c.jj	2014-07-09 10:41:12.000000000 +0200
+++ gcc/cp/parser.c	2014-07-09 11:36:40.195693369 +0200
@@ -6142,6 +6142,19 @@ cp_parser_postfix_expression (cp_parser
 		  }
 	      }
 
+	  if (warn_memset_transposed_args
+	      && TREE_CODE (postfix_expression) == FUNCTION_DECL
+	      && DECL_BUILT_IN_CLASS (postfix_expression) == BUILT_IN_NORMAL
+	      && DECL_FUNCTION_CODE (postfix_expression) == BUILT_IN_MEMSET
+	      && vec_safe_length (args) == 3
+	      && integer_zerop ((*args)[2])
+	      && LITERAL_ZERO_P ((*args)[2])
+	      && !(integer_zerop ((*args)[1])
+		   && LITERAL_ZERO_P ((*args)[1])))
+	    warning (OPT_Wmemset_transposed_args,
+		     "%<memset%> used with constant zero length parameter; "
+		     "this could be due to transposed parameters");
+
 	    if (TREE_CODE (postfix_expression) == COMPONENT_REF)
 	      {
 		tree instance = TREE_OPERAND (postfix_expression, 0);
@@ -6630,6 +6643,10 @@ cp_parser_postfix_dot_deref_expression (
   return postfix_expression;
 }
 
+/* Cache of LITERAL_ZERO_P constants.  */
+
+static GTY(()) tree literal_zeros[itk_none];
+
 /* Parse a parenthesized expression-list.
 
    expression-list:
@@ -6724,7 +6741,50 @@ cp_parser_parenthesized_expression_list
 		  *non_constant_p = true;
 	      }
 	    else
-	      expr = cp_parser_assignment_expression (parser, cast_p, NULL);
+	      {
+		expr = NULL_TREE;
+		cp_token *tok = cp_lexer_peek_token (parser->lexer);
+		switch (tok->type)
+		  {
+		  case CPP_NUMBER:
+		  case CPP_CHAR:
+		  case CPP_WCHAR:
+		  case CPP_CHAR16:
+		  case CPP_CHAR32:
+		    /* If a parameter is literal zero alone, remember it
+		       for -Wmemset-transposed-args warning.  */
+		    if (integer_zerop (tok->u.value)
+			&& !TREE_OVERFLOW (tok->u.value)
+			&& is_attribute_list == non_attr
+			&& (cp_lexer_peek_nth_token (parser->lexer, 2)->type
+			    == CPP_COMMA
+			    || cp_lexer_peek_nth_token (parser->lexer, 2)->type
+			       == CPP_CLOSE_PAREN))
+		      {
+			unsigned int i;
+			for (i = 0; i < itk_none; ++i)
+			  if (TREE_TYPE (tok->u.value) == integer_types[i])
+			    break;
+			if (i < itk_none && literal_zeros[i])
+			  expr = literal_zeros[i];
+			else
+			  {
+			    expr = copy_node (tok->u.value);
+			    LITERAL_ZERO_P (expr) = 1;
+			    if (i < itk_none)
+			      literal_zeros[i] = expr;
+			  }
+			/* Consume the 0 token (or '\0', 0LL etc.).  */
+			cp_lexer_consume_token (parser->lexer);
+		      }
+		    break;
+		  default:
+		    break;
+		  }
+		if (expr == NULL_TREE)
+		  expr = cp_parser_assignment_expression (parser, cast_p,
+							  NULL);
+	      }
 
 	    if (fold_expr_p)
 	      expr = fold_non_dependent_expr (expr);
--- gcc/doc/invoke.texi.jj	2014-07-08 17:38:09.301268037 +0200
+++ gcc/doc/invoke.texi	2014-07-09 10:41:38.950017994 +0200
@@ -257,8 +257,8 @@ Objective-C and Objective-C++ Dialects}.
 -Wno-int-to-pointer-cast -Wno-invalid-offsetof @gol
 -Winvalid-pch -Wlarger-than=@var{len}  -Wunsafe-loop-optimizations @gol
 -Wlogical-op -Wlogical-not-parentheses -Wlong-long @gol
--Wmain -Wmaybe-uninitialized -Wmissing-braces  -Wmissing-field-initializers @gol
--Wmissing-include-dirs @gol
+-Wmain -Wmaybe-uninitialized -Wmemset-transposed-args  -Wmissing-braces @gol
+-Wmissing-field-initializers -Wmissing-include-dirs @gol
 -Wno-multichar  -Wnonnull  -Wno-overflow -Wopenmp-simd @gol
 -Woverlength-strings  -Wpacked  -Wpacked-bitfield-compat  -Wpadded @gol
 -Wparentheses  -Wpedantic-ms-format -Wno-pedantic-ms-format @gol
@@ -4683,6 +4683,15 @@ Warn when the @code{sizeof} operator is
 declared as an array in a function definition.  This warning is enabled by
 default for C and C++ programs.
 
+@item -Wmemset-transposed-args
+@opindex Wmemset-transposed-args
+@opindex Wno-memset-transposed-args
+Warn for suspicious calls to the memset built-in function, if the
+second argument is not zero and third argument is zero.  This warns e.g.@
+about @code{memset (buf, sizeof buf, 0);} where most probably
+@code{memset (buf, 0, sizeof buf);} was meant instead.  This warning is
+enabled by @option{-Wall}.
+
 @item -Waddress
 @opindex Waddress
 @opindex Wno-address
--- gcc/testsuite/g++.dg/warn/Wmemset-transposed-args-1.C.jj	2014-07-09 10:41:38.969017900 +0200
+++ gcc/testsuite/g++.dg/warn/Wmemset-transposed-args-1.C	2014-07-09 12:12:40.850993778 +0200
@@ -0,0 +1,74 @@
+// { dg-do compile }
+// { dg-options "-Wall" }
+
+typedef __SIZE_TYPE__ size_t;
+extern "C" void *memset (void *, int, size_t);
+char buf[1024];
+namespace std
+{
+  extern "C" void *memset (void *, int, size_t);
+}
+
+template <int N>
+void
+foo ()
+{
+  memset (buf, sizeof buf, 0);	/* { dg-warning ".memset. used with constant zero length parameter; this could be due to transposed parameters" } */
+  memset (buf, sizeof buf, '\0'); /* { dg-warning ".memset. used with constant zero length parameter; this could be due to transposed parameters" } */
+  memset (buf, sizeof buf, L'\0'); /* { dg-warning ".memset. used with constant zero length parameter; this could be due to transposed parameters" } */
+  memset (buf, sizeof buf, N);
+  memset (buf, 1, 1 - 1);
+  memset (buf, 1, 0 - 0);
+  memset (buf, 1, N - N);
+  memset (buf, 0, 0);
+  memset (buf, 1 - 1, 0); /* { dg-warning ".memset. used with constant zero length parameter; this could be due to transposed parameters" } */
+  memset (buf, 0 - 0, 0); /* { dg-warning ".memset. used with constant zero length parameter; this could be due to transposed parameters" } */
+  memset (buf, sizeof buf, 0L);	/* { dg-warning ".memset. used with constant zero length parameter; this could be due to transposed parameters" } */
+  memset (buf, sizeof buf, 0UL); /* { dg-warning ".memset. used with constant zero length parameter; this could be due to transposed parameters" } */
+  memset (buf, sizeof buf, 0LL); /* { dg-warning ".memset. used with constant zero length parameter; this could be due to transposed parameters" } */
+  memset (buf, sizeof buf, 0ULL); /* { dg-warning ".memset. used with constant zero length parameter; this could be due to transposed parameters" } */
+  memset (buf, sizeof buf, (int) 0);
+  memset (buf, sizeof buf, -0);
+}
+
+template <int N>
+void
+baz ()
+{
+  std::memset (buf, sizeof buf, 0);	/* { dg-warning ".memset. used with constant zero length parameter; this could be due to transposed parameters" } */
+  std::memset (buf, sizeof buf, '\0'); /* { dg-warning ".memset. used with constant zero length parameter; this could be due to transposed parameters" } */
+  std::memset (buf, sizeof buf, L'\0'); /* { dg-warning ".memset. used with constant zero length parameter; this could be due to transposed parameters" } */
+  std::memset (buf, sizeof buf, N);
+  std::memset (buf, 1, 1 - 1);
+  std::memset (buf, 1, 0 - 0);
+  std::memset (buf, 1, N - N);
+  std::memset (buf, 0, 0);
+  std::memset (buf, 1 - 1, 0); /* { dg-warning ".memset. used with constant zero length parameter; this could be due to transposed parameters" } */
+  std::memset (buf, 0 - 0, 0); /* { dg-warning ".memset. used with constant zero length parameter; this could be due to transposed parameters" } */
+  std::memset (buf, sizeof buf, 0L);	/* { dg-warning ".memset. used with constant zero length parameter; this could be due to transposed parameters" } */
+  std::memset (buf, sizeof buf, 0UL); /* { dg-warning ".memset. used with constant zero length parameter; this could be due to transposed parameters" } */
+  std::memset (buf, sizeof buf, 0LL); /* { dg-warning ".memset. used with constant zero length parameter; this could be due to transposed parameters" } */
+  std::memset (buf, sizeof buf, 0ULL); /* { dg-warning ".memset. used with constant zero length parameter; this could be due to transposed parameters" } */
+  std::memset (buf, sizeof buf, (int) 0);
+  std::memset (buf, sizeof buf, -0);
+}
+
+void
+bar ()
+{
+  foo<0> ();
+  std::memset (buf, sizeof buf, 0);	/* { dg-warning ".memset. used with constant zero length parameter; this could be due to transposed parameters" } */
+  std::memset (buf, sizeof buf, '\0'); /* { dg-warning ".memset. used with constant zero length parameter; this could be due to transposed parameters" } */
+  std::memset (buf, sizeof buf, L'\0'); /* { dg-warning ".memset. used with constant zero length parameter; this could be due to transposed parameters" } */
+  std::memset (buf, 1, 1 - 1);
+  std::memset (buf, 1, 0 - 0);
+  std::memset (buf, 0, 0);
+  std::memset (buf, 1 - 1, 0); /* { dg-warning ".memset. used with constant zero length parameter; this could be due to transposed parameters" } */
+  std::memset (buf, 0 - 0, 0); /* { dg-warning ".memset. used with constant zero length parameter; this could be due to transposed parameters" } */
+  std::memset (buf, sizeof buf, 0L);	/* { dg-warning ".memset. used with constant zero length parameter; this could be due to transposed parameters" } */
+  std::memset (buf, sizeof buf, 0UL); /* { dg-warning ".memset. used with constant zero length parameter; this could be due to transposed parameters" } */
+  std::memset (buf, sizeof buf, 0LL); /* { dg-warning ".memset. used with constant zero length parameter; this could be due to transposed parameters" } */
+  std::memset (buf, sizeof buf, 0ULL); /* { dg-warning ".memset. used with constant zero length parameter; this could be due to transposed parameters" } */
+  std::memset (buf, sizeof buf, (int) 0);
+  std::memset (buf, sizeof buf, -0);
+}
--- gcc/testsuite/c-c++-common/Wmemset-transposed-args1.c.jj	2014-07-09 10:41:38.969017900 +0200
+++ gcc/testsuite/c-c++-common/Wmemset-transposed-args1.c	2014-07-09 11:51:12.000000000 +0200
@@ -0,0 +1,29 @@
+/* { dg-do compile } */
+/* { dg-options "-Wall" } */
+
+typedef __SIZE_TYPE__ size_t;
+extern
+#ifdef __cplusplus
+"C"
+#endif
+void *memset (void *, int, size_t);
+char buf[1024];
+
+void
+foo ()
+{
+  memset (buf, sizeof buf, 0);	/* { dg-warning ".memset. used with constant zero length parameter; this could be due to transposed parameters" } */
+  memset (buf, sizeof buf, '\0'); /* { dg-warning ".memset. used with constant zero length parameter; this could be due to transposed parameters" } */
+  memset (buf, sizeof buf, L'\0'); /* { dg-warning ".memset. used with constant zero length parameter; this could be due to transposed parameters" } */
+  memset (buf, 1, 1 - 1);
+  memset (buf, 1, 0 - 0);
+  memset (buf, 0, 0);
+  memset (buf, 1 - 1, 0); /* { dg-warning ".memset. used with constant zero length parameter; this could be due to transposed parameters" } */
+  memset (buf, 0 - 0, 0); /* { dg-warning ".memset. used with constant zero length parameter; this could be due to transposed parameters" } */
+  memset (buf, sizeof buf, 0L);	/* { dg-warning ".memset. used with constant zero length parameter; this could be due to transposed parameters" } */
+  memset (buf, sizeof buf, 0UL); /* { dg-warning ".memset. used with constant zero length parameter; this could be due to transposed parameters" } */
+  memset (buf, sizeof buf, 0LL); /* { dg-warning ".memset. used with constant zero length parameter; this could be due to transposed parameters" } */
+  memset (buf, sizeof buf, 0ULL); /* { dg-warning ".memset. used with constant zero length parameter; this could be due to transposed parameters" } */
+  memset (buf, sizeof buf, (int) 0);
+  memset (buf, sizeof buf, -0);
+}
--- gcc/c-family/c.opt.jj	2014-07-08 17:38:09.249268240 +0200
+++ gcc/c-family/c.opt	2014-07-09 10:41:38.909018201 +0200
@@ -518,6 +518,10 @@ Wmain
 LangEnabledBy(C ObjC C++ ObjC++,Wpedantic, 2, 0)
 ;
 
+Wmemset-transposed-args
+C ObjC C++ ObjC++ Var(warn_memset_transposed_args) Warning LangEnabledBy(C ObjC C++ ObjC++,Wall)
+Warn about suspicious call to memset where the third argument is constant zero and second is not zero
+
 Wmissing-braces
 C ObjC C++ ObjC++ Var(warn_missing_braces) Warning LangEnabledBy(C ObjC,Wall)
 Warn about possibly missing braces around initializers


	Jakub