[Bug c++/60755] New: lambda capturing `this` doesn't honor the const qualifier of the enclosing member function

[Bug c++/60755] New: lambda capturing `this` doesn't honor the const qualifier of the enclosing member function

[filip.roseen at gmail dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=60755

            Bug ID: 60755
           Summary: lambda capturing `this` doesn't honor the const
                    qualifier of the enclosing member function
           Product: gcc
           Version: 4.9.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: filip.roseen at gmail dot com

Created attachment 32539
  --> http://gcc.gnu.org/bugzilla/attachment.cgi?id=32539&action=edit
testcase.cpp

#include <iostream>

struct A {
  void f () const { std::cerr << "const "; }
  void f ()       { std::cerr << "non-const "; }

  void g () const {
    [this] { f (); this->f (); } ();
  }
};

int main () {
  A {}.g ();
}


-----------------------------------------------------------------

The above prints "non-const const", even though the type of `this`
should be `A const *` in both `f()` and `this->f()` inside the
anonymous lambda.

[ Note: `clang` will generate a binary which correctly outputs "const const" ]

-----------------------------------------------------------------

[expr.prim.lambda]p18 states:

  > If `this` is captured, each odr-use of `this` is transformed into an
  > access to the corresponding unnamed data member of the closure type,
  > cast (5.4) to the type of `this`.

[Bug c++/60755] lambda capturing `this` doesn't honor the const qualifier of the enclosing member function

[filip.roseen at gmail dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=60755

--- Comment #1 from Filip Roséen <filip.roseen at gmail dot com> ---
Reduced testcase:

-----------------------------------------------------------------

struct A {
  void f () { }

  void g () const {
    [this] { f (); } ();
  }
};

int main () {
  A {}.g ();
}

-----------------------------------------------------------------

`gcc` compiles this with no diagnostics, `clang` correctly issues:


  testcase.cpp:5:14: error: member function 'f' not viable: 'this'
                            argument has type 'const A', but function
                            is not marked const
      [this] { f (); } ();
             ^
  testcase.cpp:2:8: note: 'f' declared here
    void f () { }
>From gcc-bugs-return-448247-listarch-gcc-bugs=gcc.gnu.org@gcc.gnu.org Fri Apr 04 00:49:23 2014
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From: "rth at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug debug/60756] New: var-tracking selects wrong registers
Date: Fri, 04 Apr 2014 00:49:00 -0000
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http://gcc.gnu.org/bugzilla/show_bug.cgi?id`756

            Bug ID: 60756
           Summary: var-tracking selects wrong registers
           Product: gcc
           Version: unknown
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: debug
          Assignee: unassigned at gcc dot gnu.org
          Reporter: rth at gcc dot gnu.org

The smallest example I can find is gcc.dg/guality/param-3.c.

The parameter "str" is passed in x0+x1, and immediately copied into
the call-saved registers x22+x23, where they stay for the duration
of the function.

But var-tracking works (or appears to work) back-to-front, taking
the location of the variable from the src rather than the dest of
a copy.  Thus we get

(note 43 1 44 (var_location str (reg:TI 0 x0 [ str ])) NOTE_INSN_VAR_LOCATION)
...
(note 35 34 28 NOTE_INSN_PROLOGUE_END)
(insn 28 35 46 (set (reg:DI 22 x22 [orig:75 str ] [75])
        (reg:DI 0 x0 [ str ])) z.c:18 34 {*movdi_aarch64}
     (expr_list:REG_DEAD (reg:DI 0 x0 [ str ])
        (nil)))
(note 46 28 29 (var_location str (reg:TI 0 x0 [ str ])) NOTE_INSN_VAR_LOCATION)
(insn 29 46 3 (set (reg:DI 23 x23 [ str+8 ])
        (reg:DI 1 x1 [ str+8 ])) z.c:18 34 {*movdi_aarch64}
     (expr_list:REG_DEAD (reg:DI 1 x1 [ str+8 ])
        (nil)))
...
(insn 8 5 47 (set (reg:SI 0 x0)
        (reg:SI 2 x2 [orig:76 a ] [76])) z.c:19 33 {*movsi_aarch64}
     (nil))
(note 47 8 9 (var_location str (nil)) NOTE_INSN_VAR_LOCATION)
...
(note 53 16 26 (var_location str (nil)) NOTE_INSN_VAR_LOCATION)
(insn 26 53 54 (set (reg:DI 0 x0)
        (reg:DI 22 x22 [orig:75 str ] [75])) z.c:21 34 {*movdi_aarch64}
     (expr_list:REG_DEAD (reg:DI 22 x22 [orig:75 str ] [75])
        (nil)))
(note 55 54 27 (var_location str (reg:TI 22 x22 [orig:75 str ] [75]))
NOTE_INSN_VAR_LOCATION)

where we have the initial prologue describing str as residing in x0,
a clobber of x0 and the death of str, then the copy of str back to
an outgoing parameter and suddenly str is once again live in x22.

At minimum it would seem that taking DECL_RTL into account when
examining these assignments would be a good start.  When copying into
its canonical location, it would seem a great time to alter the
live range.

[Bug c++/60755] lambda capturing `this` doesn't honor const qualifier of the enclosing member function

[momchil.velikov at gmail dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=60755

Momchil Velikov <momchil.velikov at gmail dot com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |momchil.velikov at gmail dot com

--- Comment #2 from Momchil Velikov <momchil.velikov at gmail dot com> ---
Possible duplicate of http://gcc.gnu.org/bugzilla/show_bug.cgi?id=60463

[Bug c++/60755] lambda capturing `this` doesn't honor const qualifier of the enclosing member function

[jason at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=60755

--- Comment #3 from Jason Merrill <jason at gcc dot gnu.org> ---
Author: jason
Date: Fri May  9 20:07:45 2014
New Revision: 210292

URL: http://gcc.gnu.org/viewcvs?rev=210292&root=gcc&view=rev
Log:
    PR c++/60463
    PR c++/60755
    * lambda.c (lambda_expr_this_capture): Add new parameter
    add_capture_p controlling whether the functions will try to
    capture 'this' via the default capture.
    (maybe_resolve_dummy): Likewise.
    * cp-tree.h: Adjust prototypes.
    * call.c, semantics.c: Change callers of these functions.
    * call.c (build_new_method_call_1): Use the actual 'this' that
    would be potentially captured for the overload resolution, instead
    of the dummy object.

Added:
    trunk/gcc/testsuite/g++.dg/cpp0x/lambda/lambda-const-this.C
Modified:
    trunk/gcc/cp/ChangeLog
    trunk/gcc/cp/call.c
    trunk/gcc/cp/cp-tree.h
    trunk/gcc/cp/lambda.c
    trunk/gcc/cp/semantics.c

[Bug c++/60755] lambda capturing `this` doesn't honor const qualifier of the enclosing member function

[paolo.carlini at oracle dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=60755

Paolo Carlini <paolo.carlini at oracle dot com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |RESOLVED
         Resolution|---                         |FIXED
   Target Milestone|---                         |4.10.0

--- Comment #4 from Paolo Carlini <paolo.carlini at oracle dot com> ---
I think we can close this as fixed in 4.10.0.

[Bug c++/60755] lambda capturing `this` doesn't honor const qualifier of the enclosing member function

[jason at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=60755

--- Comment #5 from Jason Merrill <jason at gcc dot gnu.org> ---
Author: jason
Date: Mon Sep 22 19:22:11 2014
New Revision: 215478

URL: https://gcc.gnu.org/viewcvs?rev=215478&root=gcc&view=rev
Log:
    PR c++/63320
    PR c++/60463
    PR c++/60755
    * lambda.c (maybe_resolve_dummy, lambda_expr_this_capture): Handle
    not finding 'this'.

Added:
    trunk/gcc/testsuite/g++.dg/cpp0x/lambda/lambda-this19.C
Modified:
    trunk/gcc/cp/ChangeLog
    trunk/gcc/cp/lambda.c
    trunk/gcc/testsuite/g++.dg/cpp0x/lambda/lambda-ice3.C