Patchwork [C++] PR 57869

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Submitter Paolo Carlini
Date July 10, 2013, 10:51 a.m.
Message ID <51DD3CC2.8000407@oracle.com>
Download mbox | patch
Permalink /patch/258010/
State New
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Comments

Paolo Carlini - July 10, 2013, 10:51 a.m.
Hi,

On 07/10/2013 02:40 AM, Jason Merrill wrote:
> On 07/09/2013 07:46 PM, Paolo Carlini wrote:
>> Daniel noticed that, per to the resolution of DR195, we shouldn't warn
>> in c++11 mode, not even with -pedantic, for this kind of
>> reinterpret_cast (*). Straightforward change tested x86_64-linux, not
>> sure if we want to do something slightly different for C++98, or
>> something more.
>
> I think we should apply DR195 to C++98, too.  We might add the warning 
> to a new -Wconditionally-supported flag that could later warn about 
> other conditionally-supported constructs as well.
Ok. I prepared the below, tested x86_64-linux, the wording is quite terse.

Thanks,
Paolo.

////////////////
/c-family
2013-07-10  Paolo Carlini  <paolo.carlini@oracle.com>

	PR c++/57869
	* c.opt: Add Wconditionally-supported.

/cp
2013-07-10  Paolo Carlini  <paolo.carlini@oracle.com>

	PR c++/57869
	* typeck.c (build_reinterpret_cast_1): With -Wconditionally-supported
	warn about casting between pointer-to-function and pointer-to-object.

/gcc
2013-07-10  Paolo Carlini  <paolo.carlini@oracle.com>

	PR c++/57869
	* doc/invoke.texi: Document -Wconditionally-supported.

/testsuite
2013-07-10  Paolo Carlini  <paolo.carlini@oracle.com>

	PR c++/57869
	* g++.dg/cpp0x/reinterpret_cast1.C: New.
	* g++.dg/warn/Wconditionally-supported-1.C: Likewise.
	* g++.dg/conversion/dr195.C: Update.
	* g++.dg/expr/cast2.C: Likewise.
Jason Merrill - July 10, 2013, 3:59 p.m.
OK, thanks.

Jason

Patch

Index: c-family/c.opt
===================================================================
--- c-family/c.opt	(revision 200867)
+++ c-family/c.opt	(working copy)
@@ -319,6 +319,10 @@  Wcomments
 C ObjC C++ ObjC++ Warning Alias(Wcomment)
 Synonym for -Wcomment
 
+Wconditionally-supported
+C++ ObjC++ Var(warn_conditionally_supported) Warning
+Warn for conditionally-supported constructs
+
 Wconversion
 C ObjC C++ ObjC++ Var(warn_conversion) Warning
 Warn for implicit type conversions that may change a value
Index: cp/typeck.c
===================================================================
--- cp/typeck.c	(revision 200867)
+++ cp/typeck.c	(working copy)
@@ -6722,12 +6722,12 @@  build_reinterpret_cast_1 (tree type, tree expr, bo
   else if ((TYPE_PTRFN_P (type) && TYPE_PTROBV_P (intype))
 	   || (TYPE_PTRFN_P (intype) && TYPE_PTROBV_P (type)))
     {
-      if (pedantic && (complain & tf_warning))
-	/* Only issue a warning, as we have always supported this
-	   where possible, and it is necessary in some cases.  DR 195
-	   addresses this issue, but as of 2004/10/26 is still in
-	   drafting.  */
-	warning (0, "ISO C++ forbids casting between pointer-to-function and pointer-to-object");
+      if (complain & tf_warning)
+	/* C++11 5.2.10 p8 says that "Converting a function pointer to an "
+	   object pointer type or vice versa is conditionally-supported."  */
+	warning (OPT_Wconditionally_supported,
+		 "casting between pointer-to-function and pointer-to-object "
+		 "is conditionally-supported");
       return fold_if_not_in_template (build_nop (type, expr));
     }
   else if (TREE_CODE (type) == VECTOR_TYPE)
Index: doc/invoke.texi
===================================================================
--- doc/invoke.texi	(revision 200867)
+++ doc/invoke.texi	(working copy)
@@ -237,7 +237,7 @@  Objective-C and Objective-C++ Dialects}.
 -Waggressive-loop-optimizations -Warray-bounds @gol
 -Wno-attributes -Wno-builtin-macro-redefined @gol
 -Wc++-compat -Wc++11-compat -Wcast-align  -Wcast-qual  @gol
--Wchar-subscripts -Wclobbered  -Wcomment @gol
+-Wchar-subscripts -Wclobbered  -Wcomment -Wconditionally-supported  @gol
 -Wconversion  -Wcoverage-mismatch  -Wno-cpp  -Wno-deprecated  @gol
 -Wno-deprecated-declarations -Wdisabled-optimization  @gol
 -Wno-div-by-zero -Wdouble-promotion -Wempty-body  -Wenum-compare @gol
@@ -4393,6 +4393,11 @@  programs.
 Warn for variables that might be changed by @samp{longjmp} or
 @samp{vfork}.  This warning is also enabled by @option{-Wextra}.
 
+@item -Wconditionally-supported @r{(C++ and Objective-C++ only)}
+@opindex Wconditionally-supported
+@opindex Wno-conditionally-supported
+Warn for conditionally-supported (C++11 [intro.defs]) constructs.
+
 @item -Wconversion
 @opindex Wconversion
 @opindex Wno-conversion
Index: testsuite/g++.dg/conversion/dr195.C
===================================================================
--- testsuite/g++.dg/conversion/dr195.C	(revision 200867)
+++ testsuite/g++.dg/conversion/dr195.C	(working copy)
@@ -1,11 +1,12 @@ 
 // Copyright (C) 2004 Free Software Foundation, Inc.
 // Contributed by Nathan Sidwell 20 Oct 2004 <nathan@codesourcery.com>
 
-// DR 195 will allow conversions between function and object pointers
-// under some circumstances. It is in drafting, so we don't implement
-// it (yet).
+// DR 195 was about allowing conversions between function and object
+// pointers under some circumstances.  The issue got resolved for C++11,
+// which, in 5.2.10 p8 says that: "Converting a function pointer to an
+// object pointer type or vice versa is conditionally-supported."  */
 
-// This checks we warn when being pedantic.
+// This checks we don't warn anymore with -pedantic.
 
 typedef void (*PF)(void);
 typedef void *PV;
@@ -18,12 +19,12 @@  void foo ()
   PO po;
 
   /* the following two will almost definitly be ok with 195.  */
-  pf = reinterpret_cast <PF>(pv); // { dg-warning "casting between" "" }
-  pv = reinterpret_cast <PV>(pf); // { dg-warning "casting between" "" }
+  pf = reinterpret_cast <PF>(pv);
+  pv = reinterpret_cast <PV>(pf);
 
   /* the following two might or might not be ok with 195.  */
-  pf = reinterpret_cast <PF>(po); // { dg-warning "casting between" "" }
-  po = reinterpret_cast <PO>(pf); // { dg-warning "casting between" "" }
+  pf = reinterpret_cast <PF>(po);
+  po = reinterpret_cast <PO>(pf);
 
   /* These will never be ok, as they are implicit.  */
   pv = pf; // { dg-error "invalid conversion" "" }
Index: testsuite/g++.dg/cpp0x/reinterpret_cast1.C
===================================================================
--- testsuite/g++.dg/cpp0x/reinterpret_cast1.C	(revision 0)
+++ testsuite/g++.dg/cpp0x/reinterpret_cast1.C	(working copy)
@@ -0,0 +1,6 @@ 
+// PR c++/57869
+// { dg-do compile { target c++11 } }
+
+void* po = 0;
+void (*pf)() = reinterpret_cast<decltype(pf)>(po);
+static_assert(sizeof(po) >= sizeof(pf), "Conversion not supported");
Index: testsuite/g++.dg/expr/cast2.C
===================================================================
--- testsuite/g++.dg/expr/cast2.C	(revision 200867)
+++ testsuite/g++.dg/expr/cast2.C	(working copy)
@@ -1,5 +1,5 @@ 
 void (*p)();
 
 void f() {
-  (void *)p; // { dg-warning "forbids cast" }
+  (void *)p;
 }
Index: testsuite/g++.dg/warn/Wconditionally-supported-1.C
===================================================================
--- testsuite/g++.dg/warn/Wconditionally-supported-1.C	(revision 0)
+++ testsuite/g++.dg/warn/Wconditionally-supported-1.C	(working copy)
@@ -0,0 +1,25 @@ 
+// { dg-options "-Wconditionally-supported" }
+
+// DR 195 was about allowing conversions between function and object
+// pointers under some circumstances.  The issue got resolved for C++11,
+// which, in 5.2.10 p8 says that: "Converting a function pointer to an 
+// object pointer type or vice versa is conditionally-supported."  */
+
+// This checks we warn with -Wconditionally-supported.
+
+typedef void (*PF)(void);
+typedef void *PV;
+typedef int *PO;
+
+void foo ()
+{
+  PF pf;
+  PV pv;
+  PO po;
+
+  pf = reinterpret_cast <PF>(pv); // { dg-warning "conditionally-supported" }
+  pv = reinterpret_cast <PV>(pf); // { dg-warning "conditionally-supported" }
+
+  pf = reinterpret_cast <PF>(po); // { dg-warning "conditionally-supported" }
+  po = reinterpret_cast <PO>(pf); // { dg-warning "conditionally-supported" }
+}