* [C++ PATCH] Allow some function pointer conversions
@ 2004-10-20 14:34 Nathan Sidwell
2004-10-20 17:22 ` Mark Mitchell
0 siblings, 1 reply; 6+ messages in thread
From: Nathan Sidwell @ 2004-10-20 14:34 UTC (permalink / raw)
To: GCC Patches; +Cc: Mark Mitchell, Andreas Schwab, Jason Merrill
[-- Attachment #1: Type: text/plain, Size: 1582 bytes --]
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
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[-- Type: text/plain, Size: 5960 bytes --]
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();
}
^ permalink raw reply [flat|nested] 6+ messages in thread
* Re: [C++ PATCH] Allow some function pointer conversions
2004-10-20 14:34 [C++ PATCH] Allow some function pointer conversions Nathan Sidwell
@ 2004-10-20 17:22 ` Mark Mitchell
2004-10-20 17:26 ` Gabriel Dos Reis
0 siblings, 1 reply; 6+ messages in thread
From: Mark Mitchell @ 2004-10-20 17:22 UTC (permalink / raw)
To: Nathan Sidwell; +Cc: GCC Patches, Andreas Schwab, Jason Merrill
Nathan Sidwell wrote:
> 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.
I think that if we want to implement DR195, I'd be happiest if we just
removed the diagnostic. (Before my patch, things were inconsistent; we
issued a pedwarn for reinterpret_cast, but not for a C-style cast. I
made the two match up.)
I think that we could just remove the diangostic altogether to implement
DR195.
We could also turn it into a warning, which might be the most
conservative choice; we would still conform to TC1, but also implement
DR195.
--
Mark Mitchell
CodeSourcery, LLC
(916) 791-8304
mark@codesourcery.com
^ permalink raw reply [flat|nested] 6+ messages in thread
* Re: [C++ PATCH] Allow some function pointer conversions
2004-10-20 17:22 ` Mark Mitchell
@ 2004-10-20 17:26 ` Gabriel Dos Reis
2004-10-20 20:03 ` Jason Merrill
0 siblings, 1 reply; 6+ messages in thread
From: Gabriel Dos Reis @ 2004-10-20 17:26 UTC (permalink / raw)
To: Mark Mitchell; +Cc: Nathan Sidwell, GCC Patches, Andreas Schwab, Jason Merrill
Mark Mitchell <mark@codesourcery.com> writes:
| Nathan Sidwell wrote:
|
| > 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.
|
| I think that if we want to implement DR195, I'd be happiest if we just
| removed the diagnostic. (Before my patch, things were inconsistent;
| we issued a pedwarn for reinterpret_cast, but not for a C-style cast.
| I made the two match up.) I think that we could just remove the
| diangostic altogether to implement DR195.
|
| We could also turn it into a warning, which might be the most
| conservative choice; we would still conform to TC1, but also implement
| DR195.
If we believe we really want to implement DR195, then I would
recommend we do not remove the diagnostic, but make it a warning.
Jason?
-- Gaby
^ permalink raw reply [flat|nested] 6+ messages in thread
* Re: [C++ PATCH] Allow some function pointer conversions
2004-10-20 17:26 ` Gabriel Dos Reis
@ 2004-10-20 20:03 ` Jason Merrill
2004-10-20 20:38 ` Gabriel Dos Reis
2004-10-21 0:09 ` Mark Mitchell
0 siblings, 2 replies; 6+ messages in thread
From: Jason Merrill @ 2004-10-20 20:03 UTC (permalink / raw)
To: Gabriel Dos Reis
Cc: Mark Mitchell, Nathan Sidwell, GCC Patches, Andreas Schwab
On 20 Oct 2004 12:25:12 -0500, Gabriel Dos Reis <gdr@cs.tamu.edu> wrote:
> Mark Mitchell <mark@codesourcery.com> writes:
>
> | Nathan Sidwell wrote:
> |
> | I think that if we want to implement DR195, I'd be happiest if we just
> | removed the diagnostic. (Before my patch, things were inconsistent;
> | we issued a pedwarn for reinterpret_cast, but not for a C-style cast.
> | I made the two match up.) I think that we could just remove the
> | diangostic altogether to implement DR195.
> |
> | We could also turn it into a warning, which might be the most
> | conservative choice; we would still conform to TC1, but also implement
> | DR195.
>
> If we believe we really want to implement DR195, then I would
> recommend we do not remove the diagnostic, but make it a warning.
My preference would be for a warning only under -pedantic. This pattern is
supported on all of our platforms, and is in wide use. Warning about it
would just be useless noise unless people are specifically interested in
extreme portability. A hard error is unacceptable.
Jason
^ permalink raw reply [flat|nested] 6+ messages in thread
* Re: [C++ PATCH] Allow some function pointer conversions
2004-10-20 20:03 ` Jason Merrill
@ 2004-10-20 20:38 ` Gabriel Dos Reis
2004-10-21 0:09 ` Mark Mitchell
1 sibling, 0 replies; 6+ messages in thread
From: Gabriel Dos Reis @ 2004-10-20 20:38 UTC (permalink / raw)
To: Jason Merrill; +Cc: Mark Mitchell, Nathan Sidwell, GCC Patches, Andreas Schwab
Jason Merrill <jason@redhat.com> writes:
| On 20 Oct 2004 12:25:12 -0500, Gabriel Dos Reis <gdr@cs.tamu.edu> wrote:
|
| > Mark Mitchell <mark@codesourcery.com> writes:
| >
| > | Nathan Sidwell wrote:
| > |
| > | I think that if we want to implement DR195, I'd be happiest if we just
| > | removed the diagnostic. (Before my patch, things were inconsistent;
| > | we issued a pedwarn for reinterpret_cast, but not for a C-style cast.
| > | I made the two match up.) I think that we could just remove the
| > | diangostic altogether to implement DR195.
| > |
| > | We could also turn it into a warning, which might be the most
| > | conservative choice; we would still conform to TC1, but also implement
| > | DR195.
| >
| > If we believe we really want to implement DR195, then I would
| > recommend we do not remove the diagnostic, but make it a warning.
|
| My preference would be for a warning only under -pedantic. This pattern is
| supported on all of our platforms, and is in wide use. Warning about it
| would just be useless noise unless people are specifically interested in
| extreme portability. A hard error is unacceptable.
noted.
-- Gaby
^ permalink raw reply [flat|nested] 6+ messages in thread
* Re: [C++ PATCH] Allow some function pointer conversions
2004-10-20 20:03 ` Jason Merrill
2004-10-20 20:38 ` Gabriel Dos Reis
@ 2004-10-21 0:09 ` Mark Mitchell
1 sibling, 0 replies; 6+ messages in thread
From: Mark Mitchell @ 2004-10-21 0:09 UTC (permalink / raw)
To: Jason Merrill
Cc: Gabriel Dos Reis, Nathan Sidwell, GCC Patches, Andreas Schwab
Jason Merrill wrote:
>On 20 Oct 2004 12:25:12 -0500, Gabriel Dos Reis <gdr@cs.tamu.edu> wrote:
>
>
>
>>Mark Mitchell <mark@codesourcery.com> writes:
>>
>>| Nathan Sidwell wrote:
>>|
>>| I think that if we want to implement DR195, I'd be happiest if we just
>>| removed the diagnostic. (Before my patch, things were inconsistent;
>>| we issued a pedwarn for reinterpret_cast, but not for a C-style cast.
>>| I made the two match up.) I think that we could just remove the
>>| diangostic altogether to implement DR195.
>>|
>>| We could also turn it into a warning, which might be the most
>>| conservative choice; we would still conform to TC1, but also implement
>>| DR195.
>>
>>If we believe we really want to implement DR195, then I would
>>recommend we do not remove the diagnostic, but make it a warning.
>>
>>
>
>My preference would be for a warning only under -pedantic. This pattern is
>supported on all of our platforms, and is in wide use. Warning about it
>would just be useless noise unless people are specifically interested in
>extreme portability. A hard error is unacceptable.
>
Good; I think we're in agreement.
Nathan, I see that your patch for DR195 has gone in. Shall I revert
that and replace the current pedwarn with a warning, thereby
implementing the above solution? Or, do you want to do that? Or, do
you not like this plan at all?
Thanks,
--
Mark Mitchell
CodeSourcery, LLC
(916) 791-8304
mark@codesourcery.com
^ permalink raw reply [flat|nested] 6+ messages in thread
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2004-10-20 14:34 [C++ PATCH] Allow some function pointer conversions Nathan Sidwell
2004-10-20 17:22 ` Mark Mitchell
2004-10-20 17:26 ` Gabriel Dos Reis
2004-10-20 20:03 ` Jason Merrill
2004-10-20 20:38 ` Gabriel Dos Reis
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