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.carl...@oracle.com>
PR c++/57869
* c.opt: Add Wconditionally-supported.
/cp
2013-07-10 Paolo Carlini <paolo.carl...@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.carl...@oracle.com>
PR c++/57869
* doc/invoke.texi: Document -Wconditionally-supported.
/testsuite
2013-07-10 Paolo Carlini <paolo.carl...@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.
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 <nat...@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" }
+}
