Bogus warning when comparing nocast short variables

Bogus warning when comparing nocast short variables

[Pavel Roskin]

Hello!

This test file causes a warning:

typedef short __attribute__((nocast)) u16;
int main(int argc, char **argv)
{
        u16 i = (u16)argc;
        u16 j = (u16)2;
        return (i == j);
}

$ sparse test1.c 
test1.c:6:17: warning: implicit cast from nocast type
test1.c:6:22: warning: implicit cast from nocast type

But this file doesn't cause any warning:

typedef short __attribute__((nocast)) u16;
int main(int argc, char **argv)
{
        u16 i = (u16)argc;
        u16 j = (u16)2;
        switch (i) {
                case j: return 1;;
                default: return 0;;
        }
}

I think the warnings are bogus.  No cast should be needed to compare
variables of the same type.

The warning was actually found in the current Linux kernel, driver
zd1121rw.  A fix was proposed, but I thing the fix belongs to the sparse
code.

-- 
Regards,
Pavel Roskin

Re: Bogus warning when comparing nocast short variables

[Chris Li]

[-- Attachment #1: Type: text/plain, Size: 682 bytes --]

On Wed, Jul 21, 2010 at 9:51 AM, Pavel Roskin <proski@gnu.org> wrote:
> Hello!
>
> This test file causes a warning:
>
> typedef short __attribute__((nocast)) u16;
> int main(int argc, char **argv)
> {
>        u16 i = (u16)argc;
>        u16 j = (u16)2;
>        return (i == j);
> }
>
> $ sparse test1.c
> test1.c:6:17: warning: implicit cast from nocast type
> test1.c:6:22: warning: implicit cast from nocast type

The warning come from the implicit cast in the compare
expression. It try to cast "i" and "j" into "int" type before the
compare.

The following patch allow the test-inspect to show the cast
expression.

No patch for the fix yet.

Chris

[-- Attachment #2: inspect-cast.patch --]
[-- Type: application/octet-stream, Size: 1480 bytes --]

diff --git a/ast-inspect.c b/ast-inspect.c
index 293334e..5363de3 100644
--- a/ast-inspect.c
+++ b/ast-inspect.c
@@ -66,6 +66,12 @@ void inspect_statement(AstNode *node)
 			ast_append_child(node, "post_statement:", stmt->iterator_post_statement,
 					 inspect_statement);
 			break;
+
+		case STMT_RETURN:
+			ast_append_child(node, "ret_value:", stmt->ret_value, inspect_expression);
+			ast_append_child(node, "ret_target:", stmt->ret_target, inspect_symbol);
+			break;
+
 		default:
 			break;
 	}
@@ -109,7 +115,7 @@ void inspect_symbol(AstNode *node)
 {
 	struct symbol *sym = node->ptr;
 	node->text = g_strdup_printf("%s %s: %s", node->text, symbol_type_name(sym->type),
-				      show_ident(sym->ident));
+				      builtin_typename(sym) ?: show_ident(sym->ident));
 	ast_append_child(node, "ctype.base_type:", sym->ctype.base_type,inspect_symbol);
 
 	switch (sym->type) {
@@ -181,6 +187,18 @@ void inspect_expression(AstNode *node)
 			ast_append_child(node, "left:", expr->left, inspect_expression);
 			ast_append_child(node, "right:", expr->right, inspect_expression);
 			break;
+
+		case EXPR_CAST:
+		case EXPR_FORCE_CAST:
+		case EXPR_IMPLIED_CAST:
+			ast_append_child(node, "cast_type:", expr->cast_type, inspect_symbol);
+			ast_append_child(node, "cast_expression:", expr->cast_expression, inspect_expression);
+			break;
+
+		case EXPR_PREOP:
+			ast_append_child(node, "unop:", expr->unop, inspect_expression);
+			break;
+		
 		default:
 			break;
 	}