c: Support for -Wuseless-cast [PR84510]

Add support for Wuseless-cast C (and ObjC).

	PR c/84510

gcc/c/:
	* c-typeck.cc (build_c_cast): Add warning.

gcc/c-family/:
	* c.opt: Enable warning for C and ObjC.

gcc/:
	* doc/invoke.texi: Update.

gcc/testsuite/:
	* gcc.dg/Wuseless-cast.c: New test.

diff --git a/gcc/c-family/c.opt b/gcc/c-family/c.opt
index 0ed87fcc7be974a424a880d4d9a1f2b38bf78653..c7b567ba7abd12be6e7887b5ea44c0501c312413 100644 (file)
--- a/gcc/c-family/c.opt
+++ b/gcc/c-family/c.opt
@@ -1490,7 +1490,7 @@ C++ ObjC++ Var(warn_zero_as_null_pointer_constant) Warning
 Warn when a literal '0' is used as null pointer.
 
 Wuseless-cast
-C++ ObjC++ Var(warn_useless_cast) Warning
+C ObjC C++ ObjC++ Var(warn_useless_cast) Warning
 Warn about useless casts.
 
 Wsubobject-linkage

diff --git a/gcc/c/c-typeck.cc b/gcc/c/c-typeck.cc
index 7cf411155c60d45bf7d17238055625bfe8b7a039..6f2fff51683a449d528ee18421897b5c343f52d2 100644 (file)
--- a/gcc/c/c-typeck.cc
+++ b/gcc/c/c-typeck.cc
@@ -6062,9 +6062,13 @@ build_c_cast (location_t loc, tree type, tree expr)
 
   if (type == TYPE_MAIN_VARIANT (TREE_TYPE (value)))
     {
-      if (RECORD_OR_UNION_TYPE_P (type))
-       pedwarn (loc, OPT_Wpedantic,
-                "ISO C forbids casting nonscalar to the same type");
+      if (RECORD_OR_UNION_TYPE_P (type)
+         && pedwarn (loc, OPT_Wpedantic,
+                     "ISO C forbids casting nonscalar to the same type"))
+             ;
+      else if (warn_useless_cast)
+       warning_at (loc, OPT_Wuseless_cast,
+                   "useless cast to type %qT", type);
 
       /* Convert to remove any qualifiers from VALUE's type.  */
       value = convert (type, value);

diff --git a/gcc/doc/invoke.texi b/gcc/doc/invoke.texi
index ef5162d23fda9cf86b8fa4e52595937f812c1c5b..5bfdd6e945d87206808c46967730aa2d61e04a28 100644 (file)
--- a/gcc/doc/invoke.texi
+++ b/gcc/doc/invoke.texi
@@ -4773,7 +4773,7 @@ pointers after reallocation.
 
 @opindex Wuseless-cast
 @opindex Wno-useless-cast
-@item -Wuseless-cast @r{(C++ and Objective-C++ only)}
+@item -Wuseless-cast @r{(C, Objective-C, C++ and Objective-C++ only)}
 Warn when an expression is cast to its own type.  This warning does not
 occur when a class object is converted to a non-reference type as that
 is a way to create a temporary:

diff --git a/gcc/testsuite/gcc.dg/Wuseless-cast.c b/gcc/testsuite/gcc.dg/Wuseless-cast.c
new file mode 100644 (file)
index 0000000..86e8758
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/Wuseless-cast.c
@@ -0,0 +1,26 @@
+/* { dg-do compile } */
+/* { dg-options "-Wuseless-cast" } */
+
+void foo(void)
+{      
+       // casts to the same type
+       int i = 0;
+       const int ic = 0;
+       struct foo { int x; } x = { 0 };
+       int q[3];
+       (int)ic;                /* { dg-warning "useless cast" } */
+       (int)i;                 /* { dg-warning "useless cast" } */
+       (const int)ic;          /* { dg-warning "useless cast" } */
+       (const int)i;           /* { dg-warning "useless cast" } */
+       (struct foo)x;          /* { dg-warning "useless cast" } */
+       (int(*)[3])&q;          /* { dg-warning "useless cast" } */
+       (_Atomic(int))i;        /* { dg-warning "useless cast" } */
+
+       // not the same
+       int n = 3;
+       (int(*)[n])&q;          // no warning
+       int j = (int)0UL;
+       enum X { A = 1 } xx = { A };
+       enum Y { B = 1 } yy = (enum Y)xx;
+}
+