[Bug c++/99281] New: internal compiler error: in assign_temp, at function.c:984

[Bug c++/99281] New: internal compiler error: in assign_temp, at function.c:984

[jonathan.poelen at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=99281

            Bug ID: 99281
           Summary: internal compiler error: in assign_temp, at
                    function.c:984
           Product: gcc
           Version: 10.2.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: jonathan.poelen at gmail dot com
  Target Milestone: ---

g++ -std=c++17 test.cpp
during RTL pass: expand
test.cpp: In function ‘int main()’:
test.cpp:27:5: internal compiler error: in assign_temp, at function.c:984
   27 |     pack_type<X>{get(1)};
      |     ^~~~~~~~~~~~~~~~~~~~

Compile with -O1 or higher.

struct Data
{
    Data() {}
    ~Data() {}

    long long i;
};

struct X
{
    Data a;
    int b;
};

template<class T>
X get(T const&)
{
    return X{};
}

template<class... Ts>
struct pack_type : Ts...
{};

int main()
{
    pack_type<X>{get(1)};
}

[Bug c++/99281] internal compiler error: in assign_temp, at function.c:984

[rguenth at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=99281

Richard Biener <rguenth at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Keywords|                            |ice-on-valid-code
     Ever confirmed|0                           |1
             Status|UNCONFIRMED                 |NEW
   Last reconfirmed|                            |2021-02-26

--- Comment #1 from Richard Biener <rguenth at gcc dot gnu.org> ---
Confirmed.  We're building a temporary of type X which we shouldn't do when
expanding

get<int> (&D.2164) [return slot optimization]

and we run into

#2  0x0000000000fd165a in expand_call (exp=<call_expr 0x7ffff66ed818>, 
    target=0x0, ignore=0) at /home/rguenther/src/gcc3/gcc/calls.c:3878
3873            else
3874              {
3875                /* For variable-sized objects, we must be called with a
target
3876                   specified.  If we were to allocate space on the stack
here,
3877                   we would have no way of knowing when to free it.  */
3878                rtx d = assign_temp (rettype, 1, 1);
3879                structure_value_addr = XEXP (d, 0);
3880                target = 0;

because target is NULL when we come via

#7  0x0000000001197afe in expand_assignment (to=<component_ref 0x7ffff66d9390>,
from=<call_expr 0x7ffff66ed818>, 
    nontemporal=false) at /home/rguenther/src/gcc3/gcc/expr.c:5482
5481              else
5482                result = store_field (to_rtx, bitsize, bitpos,
5483                                      bitregion_start, bitregion_end,
5484                                      mode1, from, get_alias_set (to),
5485                                      nontemporal, reversep);

and the large conditional on

  /* If the structure is in a register or if the component
     is a bit field, we cannot use addressing to access it.
     Use bit-field techniques or SUBREG to store in it.  */

somehow misfires on this, specifically there is

          /* And except for bitwise copying of TREE_ADDRESSABLE types,
             where the FIELD_DECL has the right bitsize, but TREE_TYPE (exp)
             includes some extra padding.  store_expr / expand_expr will in
             that case call get_inner_reference that will have the bitsize
             we check here and thus the block move will not clobber the
             padding that shouldn't be clobbered.  In the future we could
             replace the TREE_ADDRESSABLE check with a check that
             get_base_address needs to live in memory.  */
          && (!TREE_ADDRESSABLE (TREE_TYPE (exp))
              || TREE_CODE (exp) != COMPONENT_REF
              || !multiple_p (bitsize, BITS_PER_UNIT)
              || !multiple_p (bitpos, BITS_PER_UNIT)
              || !poly_int_tree_p (DECL_SIZE (TREE_OPERAND (exp, 1)),
                                   &decl_bitsize)
              || maybe_ne (decl_bitsize, bitsize)))

maybe sth as simple as the following works (instead of for return-slot-opt
we can also test !TREE_ADDRESSABLE here or boht for the testcase)

diff --git a/gcc/expr.c b/gcc/expr.c
index 86dc1b6c973..54007ac0efe 100644
--- a/gcc/expr.c
+++ b/gcc/expr.c
@@ -7214,7 +7214,10 @@ store_field (rtx target, poly_int64 bitsize, poly_int64
bitpos,
              || !multiple_p (bitpos, BITS_PER_UNIT)
              || !poly_int_tree_p (DECL_SIZE (TREE_OPERAND (exp, 1)),
                                   &decl_bitsize)
-             || maybe_ne (decl_bitsize, bitsize)))
+             || maybe_ne (decl_bitsize, bitsize))
+         /* A call with return-slot-opt must not need bitfield operations.  */
+         && (TREE_CODE (exp) != CALL_EXPR
+             || !CALL_EXPR_RETURN_SLOT_OPT (exp)))
       /* If we are expanding a MEM_REF of a non-BLKmode non-addressable
          decl we must use bitfield operations.  */
       || (known_size_p (bitsize)


note clang warns

t.ii:27:5: warning: expression result unused [-Wunused-value]
    pack_type<X>{get(1)};
    ^           ~~~~~~~~

[Bug c++/99281] internal compiler error: in assign_temp, at function.c:984

[rguenth at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=99281

Richard Biener <rguenth at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Assignee|unassigned at gcc dot gnu.org      |rguenth at gcc dot gnu.org
             Status|NEW                         |ASSIGNED

--- Comment #2 from Richard Biener <rguenth at gcc dot gnu.org> ---
Posted a patch.

[Bug c++/99281] internal compiler error: in assign_temp, at function.c:984

[cvs-commit at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=99281

--- Comment #3 from CVS Commits <cvs-commit at gcc dot gnu.org> ---
The master branch has been updated by Richard Biener <rguenth@gcc.gnu.org>:

https://gcc.gnu.org/g:c173346aac4a66ad3747f380f2f0c97d2dbf8973

commit r11-7420-gc173346aac4a66ad3747f380f2f0c97d2dbf8973
Author: Richard Biener <rguenther@suse.de>
Date:   Fri Feb 26 08:45:36 2021 +0100

    middle-end/99281 - avoid bitfield stores into addressable types

    This avoids doing bitfield stores into the return object of calls
    when using return-slot optimization and the type is addressable.
    Instead we have to pass down the original target RTX to the call
    expansion which otherwise tries to create a new temporary.

    2021-02-26  Richard Biener  <rguenther@suse.de>

            PR middle-end/99281
            * expr.c (store_field): For calls with return-slot optimization
            and addressable return type expand the store directly.

            * g++.dg/pr99218.C: New testcase.

[Bug c++/99281] internal compiler error: in assign_temp, at function.c:984

[rguenth at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=99281

Richard Biener <rguenth at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
      Known to work|                            |11.0
      Known to fail|11.0                        |

--- Comment #4 from Richard Biener <rguenth at gcc dot gnu.org> ---
Fixed on trunk, it's not a regression, the testcase is still rejected by GCC
6.5
and it ICEs with 7.1.0 already (at -O0).  I'm still leaving this open for
eventual backporting to at least GCC 10 where it was reported against.

[Bug c++/99281] internal compiler error: in assign_temp, at function.c:984

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=99281

Andrew Pinski <pinskia at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|ASSIGNED                    |RESOLVED
         Resolution|---                         |FIXED
   Target Milestone|---                         |11.0

--- Comment #5 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
GCC 10.x has long been closed for new patches so closing as fixed for GCC 11.