From 68783211f660a501dee203aec11dae99bf9808ba Mon Sep 17 00:00:00 2001
From: Martin Uecker <uecker@tugraz.at>
Date: Thu, 10 Aug 2023 10:39:41 +0200
Subject: [PATCH] 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.
---
gcc/c-family/c.opt | 2 +-
gcc/c/c-typeck.cc | 10 +++++++---
gcc/doc/invoke.texi | 2 +-
gcc/testsuite/gcc.dg/Wuseless-cast.c | 26 ++++++++++++++++++++++++++
4 files changed, 35 insertions(+), 5 deletions(-)
create mode 100644 gcc/testsuite/gcc.dg/Wuseless-cast.c
diff --git a/gcc/c-family/c.opt b/gcc/c-family/c.opt
index 0ed87fcc7be9..c7b567ba7abd 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 7cf411155c60..6f2fff51683a 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 ef5162d23fda..5bfdd6e945d8 100644
--- 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
index 000000000000..86e87584b87d
--- /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;
+}
+
--
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