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[C++ PATCH] Allow some function pointer conversions
- From: Nathan Sidwell <nathan at codesourcery dot com>
- To: GCC Patches <gcc-patches at gcc dot gnu dot org>
- Cc: Mark Mitchell <mark at codesourcery dot com>, Andreas Schwab <schwab at suse dot de>,Jason Merrill <jason at redhat dot com>
- Date: Wed, 20 Oct 2004 15:29:35 +0100
- Subject: [C++ PATCH] Allow some function pointer conversions
- Organization: Codesourcery LLC
This patch implements the smallest parts of DR195 that I think are
appropriate right now. DR195 is in drafting, but has been kicking around
for several years. The patch fixes the regressions caused by Mark's patch
for 14035 in the C++ testsuite.
The new testcase g++.dg/expr/cast2.C, still fails. It think it
should probably be removed as the testcase with this patch is doing
more complete checking. Also I changed g++.old-deja/g++.mike/p10148.C.
I couldn't really see the point of the c-cast there -- it was converting
the function pointer to a base (of the current class) pointer. I suspect
some parens might have been missed.
I've not documented the casts this patch permits, but will do so once
we've agreed on the desired semantics. Specifically, this patch permits
*) pointer-to-function to be explicitly converted to pointer-to-void,
provided there is no loss of precision.
*) pointer-to-void can be explicitly converted to pointer-to-function,
regardless of precision loss. The reason for a lack of precision check
here, is so one can convert a function-pointer to a void-pointer and back
again, so long as the void-pointer has at least as many bits.
DR195 does not single out pointer-to-void, but I consider void pointers
to be a reasonable restriction right now. We can always relax it later.
Let me know if you don't think this is the correct approach.
booted & tested on i686-pc-linux-gnu.
nathan
--
Nathan Sidwell :: http://www.codesourcery.com :: CodeSourcery LLC
nathan@codesourcery.com :: http://www.planetfall.pwp.blueyonder.co.uk
2004-10-20 Nathan Sidwell <nathan@codesourcery.com>
* typeck.c (composite_pointer_type): Add comment about DR 195
(build_reinterpret_cast_1): Add for_reinterpret_cast_p parameter.
Allow function pointer conversions that DR195 suggests.
(build_reinterpret_cast, build_c_cast): Update
build_reinterpret_cast_1 calls.
2004-10-20 Nathan Sidwell <nathan@codesourcery.com>
* g++.dg/conversion/dr195.C: New.
* g++.old-deja/g++.mike/p10148.C: Remove ill-formed cast.
Index: cp/typeck.c
===================================================================
RCS file: /cvs/gcc/gcc/gcc/cp/typeck.c,v
retrieving revision 1.584
diff -c -3 -p -r1.584 typeck.c
*** cp/typeck.c 19 Oct 2004 23:24:18 -0000 1.584
--- cp/typeck.c 20 Oct 2004 12:04:41 -0000
*************** composite_pointer_type (tree t1, tree t2
*** 507,512 ****
--- 507,514 ----
tree result_type;
if (pedantic && TYPE_PTRFN_P (t2))
+ /* Although DR195 suggests allowing this when no precision is
+ lost, that is only allowed in a reinterpret_cast. */
pedwarn ("ISO C++ forbids %s between pointer of type %<void *%> "
"and pointer-to-function", location);
result_type
*************** convert_member_func_to_ptr (tree type, t
*** 4803,4809 ****
static tree
build_reinterpret_cast_1 (tree type, tree expr, bool c_cast_p,
! bool *valid_p)
{
tree intype;
--- 4805,4811 ----
static tree
build_reinterpret_cast_1 (tree type, tree expr, bool c_cast_p,
! bool for_reinterpret_ref_p, bool *valid_p)
{
tree intype;
*************** build_reinterpret_cast_1 (tree type, tre
*** 4843,4849 ****
expr = build_unary_op (ADDR_EXPR, expr, 0);
if (expr != error_mark_node)
expr = build_reinterpret_cast_1
! (build_pointer_type (TREE_TYPE (type)), expr, c_cast_p,
valid_p);
if (expr != error_mark_node)
expr = build_indirect_ref (expr, 0);
--- 4845,4851 ----
expr = build_unary_op (ADDR_EXPR, expr, 0);
if (expr != error_mark_node)
expr = build_reinterpret_cast_1
! (build_pointer_type (TREE_TYPE (type)), expr, c_cast_p, true,
valid_p);
if (expr != error_mark_node)
expr = build_indirect_ref (expr, 0);
*************** build_reinterpret_cast_1 (tree type, tre
*** 4922,4928 ****
|| (TYPE_PTRFN_P (intype) && TYPE_PTROBV_P (type)))
{
if (pedantic || !c_cast_p)
! pedwarn ("ISO C++ forbids casting between pointer-to-function and pointer-to-object");
expr = decl_constant_value (expr);
return fold_if_not_in_template (build_nop (type, expr));
}
--- 4924,4947 ----
|| (TYPE_PTRFN_P (intype) && TYPE_PTROBV_P (type)))
{
if (pedantic || !c_cast_p)
! {
! /* DR 195 suggests allowing such casts if they do not lose
! precision. We allow conversion to pointer-to-void, if it
! does not lose precision, and we allow conversion from
! pointer-to-void regardless, so that one may convert
! back again without warning. Such conversions are not
! permitted when we are recursively called to deal with
! reinterpretting reference casts. */
! if (!for_reinterpret_ref_p && VOID_TYPE_P (TREE_TYPE (type)))
! {
! if (TYPE_PRECISION (type) < TYPE_PRECISION (intype))
! warning ("conversion from %qT to %qT loses precision",
! intype, type);
! }
! else if (for_reinterpret_ref_p || !VOID_TYPE_P (TREE_TYPE (intype)))
! pedwarn ("ISO C++ forbids casting between pointer-to-function and pointer-to-object");
! }
!
expr = decl_constant_value (expr);
return fold_if_not_in_template (build_nop (type, expr));
}
*************** build_reinterpret_cast (tree type, tree
*** 4955,4960 ****
--- 4974,4980 ----
}
return build_reinterpret_cast_1 (type, expr, /*c_cast_p=*/false,
+ /*for_reinterpret_ref=*/false,
/*valid_p=*/NULL);
}
*************** build_c_cast (tree type, tree expr)
*** 5157,5162 ****
--- 5177,5183 ----
/* Or a reinterpret_cast. */
if (!valid_p)
result = build_reinterpret_cast_1 (type, value, /*c_cast_p=*/true,
+ /*for_reinterpret_ref_p=*/false,
&valid_p);
/* The static_cast or reinterpret_cast may be followed by a
const_cast. */
Index: testsuite/g++.dg/conversion/dr195.C
===================================================================
RCS file: testsuite/g++.dg/conversion/dr195.C
diff -N testsuite/g++.dg/conversion/dr195.C
*** /dev/null 1 Jan 1970 00:00:00 -0000
--- testsuite/g++.dg/conversion/dr195.C 20 Oct 2004 13:29:45 -0000
***************
*** 0 ****
--- 1,25 ----
+ // Copyright (C) 2004 Free Software Foundation, Inc.
+ // Contributed by Nathan Sidwell 20 Oct 2004 <nathan@codesourcery.com>
+
+ // DR 195 allows conversions between function and object pointers
+ // under some circumstances.
+
+ typedef void (*PF)(void);
+ typedef void *PV;
+ typedef int *PO;
+
+
+ void foo ()
+ {
+ PF pf;
+ PV pv;
+ PO po;
+
+ pf = reinterpret_cast <PF>(pv);
+ pv = reinterpret_cast <PV>(pf);
+ pf = reinterpret_cast <PF>(po); // { dg-error "casting between" "" }
+ po = reinterpret_cast <PO>(pf); // { dg-error "casting between" "" }
+
+ pv = pf; // { dg-error "invalid conversion" "" }
+ pf = pv; // { dg-error "invalid conversion" "" }
+ }
Index: testsuite/g++.old-deja/g++.mike/p10148.C
===================================================================
RCS file: /cvs/gcc/gcc/gcc/testsuite/g++.old-deja/g++.mike/p10148.C,v
retrieving revision 1.4
diff -c -3 -p -r1.4 p10148.C
*** testsuite/g++.old-deja/g++.mike/p10148.C 1 May 2003 02:02:45 -0000 1.4
--- testsuite/g++.old-deja/g++.mike/p10148.C 20 Oct 2004 13:29:54 -0000
*************** public:
*** 23,29 ****
};
void TCRCB::eat () {
! void *vp = (TIRD*)this->itc;
this->itc();
}
--- 23,29 ----
};
void TCRCB::eat () {
! void *vp = (void *)((TIRD*)this)->itc;
this->itc();
}