Patchwork [C] Fix up diagnostics (PR c/25801)

login
register
mail settings
Submitter Marek Polacek
Date April 18, 2014, 8:25 p.m.
Message ID <20140418202533.GN20332@redhat.com>
Download mbox | patch
Permalink /patch/340422/
State New
Headers show

Comments

Marek Polacek - April 18, 2014, 8:25 p.m.
Here's a patch that tidies up diagnostics given when there's
an arithmetic on pointer to an incomplete type.  Firstly, we ought not
to say "unknown structure" when the type is not a structure; secondly,
we shouldn't report identical error twice.
(It might make sense to instead "increment/decrement of" just say
"arithmetic on", but I'm not changing that now.)

Regtested on x86_64-unknown-linux-gnu, bootstrapped on
powerpc64-unknown-linux-gnu, ok for trunk?

2014-04-18  Marek Polacek  <polacek@redhat.com>

	PR c/25801
	* c-typeck.c (c_size_in_bytes): Don't call error.
	(pointer_diff): Remove comment.
	(build_unary_op): Improve error messages.

	* gcc.dg/pr25801.c: New test.


	Marek
Joseph S. Myers - May 1, 2014, 10:54 p.m.
On Fri, 18 Apr 2014, Marek Polacek wrote:

> @@ -1760,15 +1760,10 @@ c_size_in_bytes (const_tree type)

I think the comment on this function should be updated to explain the 
interface contract when an incomplete (or function) type is passed (i.e. 
return size_one_node, caller is responsible for any diagnostics).

> diff --git gcc/testsuite/gcc.dg/pr25801.c gcc/testsuite/gcc.dg/pr25801.c
> index e69de29..70b4ef8 100644
> --- gcc/testsuite/gcc.dg/pr25801.c
> +++ gcc/testsuite/gcc.dg/pr25801.c
> @@ -0,0 +1,19 @@
> +/* PR c/25801 */
> +/* { dg-do compile } */
> +
> +int (*a)[];
> +struct S *s;
> +
> +void
> +f (void)
> +{
> +  a++; /* { dg-error "increment of pointer to an incomplete type" } */
> +  ++a; /* { dg-error "increment of pointer to an incomplete type" } */
> +  a--; /* { dg-error "decrement of pointer to an incomplete type" } */
> +  --a; /* { dg-error "decrement of pointer to an incomplete type" } */
> +
> +  s++; /* { dg-error "increment of pointer to an incomplete type" } */
> +  ++s; /* { dg-error "increment of pointer to an incomplete type" } */
> +  s--; /* { dg-error "decrement of pointer to an incomplete type" } */
> +  --s; /* { dg-error "decrement of pointer to an incomplete type" } */
> +}

The test should I think also cover incomplete union types, and pointer 
subtraction for all the different cases of incomplete types, and the += 
and -= operators (i.e. cover invalid arithmetic on pointers to incomplete 
types more thoroughly, even if not actually affected by this patch).

Patch

diff --git gcc/c/c-typeck.c gcc/c/c-typeck.c
index 65aad45..bc977a7 100644
--- gcc/c/c-typeck.c
+++ gcc/c/c-typeck.c
@@ -1760,15 +1760,10 @@  c_size_in_bytes (const_tree type)
 {
   enum tree_code code = TREE_CODE (type);
 
-  if (code == FUNCTION_TYPE || code == VOID_TYPE || code == ERROR_MARK)
+  if (code == FUNCTION_TYPE || code == VOID_TYPE || code == ERROR_MARK
+      || !COMPLETE_OR_VOID_TYPE_P (type))
     return size_one_node;
 
-  if (!COMPLETE_OR_VOID_TYPE_P (type))
-    {
-      error ("arithmetic on pointer to an incomplete type");
-      return size_one_node;
-    }
-
   /* Convert in case a char is more than one unit.  */
   return size_binop_loc (input_location, CEIL_DIV_EXPR, TYPE_SIZE_UNIT (type),
 			 size_int (TYPE_PRECISION (char_type_node)
@@ -3528,7 +3523,6 @@  pointer_diff (location_t loc, tree op0, tree op1)
   if (!COMPLETE_OR_VOID_TYPE_P (TREE_TYPE (TREE_TYPE (orig_op1))))
     error_at (loc, "arithmetic on pointer to an incomplete type");
 
-  /* This generates an error if op0 is pointer to incomplete type.  */
   op1 = c_size_in_bytes (target_type);
 
   if (pointer_to_zero_sized_aggr_p (TREE_TYPE (orig_op1)))
@@ -4002,16 +3996,18 @@  build_unary_op (location_t location,
 
 	if (typecode == POINTER_TYPE)
 	  {
-	    /* If pointer target is an undefined struct,
+	    /* If pointer target is an incomplete type,
 	       we just cannot know how to do the arithmetic.  */
 	    if (!COMPLETE_OR_VOID_TYPE_P (TREE_TYPE (argtype)))
 	      {
 		if (code == PREINCREMENT_EXPR || code == POSTINCREMENT_EXPR)
 		  error_at (location,
-			    "increment of pointer to unknown structure");
+			    "increment of pointer to an incomplete type %qT",
+			    TREE_TYPE (argtype));
 		else
 		  error_at (location,
-			    "decrement of pointer to unknown structure");
+			    "decrement of pointer to an incomplete type %qT",
+			    TREE_TYPE (argtype));
 	      }
 	    else if (TREE_CODE (TREE_TYPE (argtype)) == FUNCTION_TYPE
 		     || TREE_CODE (TREE_TYPE (argtype)) == VOID_TYPE)
diff --git gcc/testsuite/gcc.dg/pr25801.c gcc/testsuite/gcc.dg/pr25801.c
index e69de29..70b4ef8 100644
--- gcc/testsuite/gcc.dg/pr25801.c
+++ gcc/testsuite/gcc.dg/pr25801.c
@@ -0,0 +1,19 @@ 
+/* PR c/25801 */
+/* { dg-do compile } */
+
+int (*a)[];
+struct S *s;
+
+void
+f (void)
+{
+  a++; /* { dg-error "increment of pointer to an incomplete type" } */
+  ++a; /* { dg-error "increment of pointer to an incomplete type" } */
+  a--; /* { dg-error "decrement of pointer to an incomplete type" } */
+  --a; /* { dg-error "decrement of pointer to an incomplete type" } */
+
+  s++; /* { dg-error "increment of pointer to an incomplete type" } */
+  ++s; /* { dg-error "increment of pointer to an incomplete type" } */
+  s--; /* { dg-error "decrement of pointer to an incomplete type" } */
+  --s; /* { dg-error "decrement of pointer to an incomplete type" } */
+}