This patch adds the missing support for -Wuseless-cast
to the C FE as requested by some users. It found about
50 useless casts in one of my projects without false
positives.
(I also implemented a detection for various
unneeded pointer casts in convert_for_assignment
such as unneeded casts from / to void or casts
followed by an implicit conversion to the original
type, but I did not figure out how to reliably
identify casts there... But this would be a potential
future enhancement.)
Regression tested on bootstrapped on x86_64-pc-linux-gnu.
c: Support for -Wuseless-cast [RR84510]
Add support for Wuseless-cast C (and ObjC).
PR c/84510
gcc/c/:
* c-typeck.cc (build_c_cast): Add warning.
gcc/doc/:
* invoke.texi: Update.
gcc/testsuite/:
* Wuseless-cast.c: New test.
diff --git a/gcc/c-family/c.opt b/gcc/c-family/c.opt
index 0ed87fcc7be..c7b567ba7ab 100644
--- 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 7cf411155c6..6f2fff51683 100644
--- 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 674f956f4b8..75ca72f3190 100644
--- a/gcc/doc/invoke.texi
+++ b/gcc/doc/invoke.texi
@@ -4772,7 +4772,7 @@ 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
index 000..86e87584b87
--- /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]) /* { dg-warning "useless cast" } */
+ (_Atomic(int))i;/* { dg-warning "useless cast" } */
+
+ // not the same
+ int n = 3;
+ (int(*)[n]) // no warning
+ int j = (int)0UL;
+ enum X { A = 1 } xx = { A };
+ enum Y { B = 1 } yy = (enum Y)xx;
+}
+
