[Bug debug/94326] New: g++: error: pack.ii: ‘-fcompare-debug’ failure (length)

[Bug debug/94326] New: g++: error: pack.ii: ‘-fcompare-debug’ failure (length)

[marxin at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=94326

            Bug ID: 94326
           Summary: g++: error: pack.ii: ‘-fcompare-debug’ failure
                    (length)
           Product: gcc
           Version: 10.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: debug
          Assignee: unassigned at gcc dot gnu.org
          Reporter: marxin at gcc dot gnu.org
                CC: jakub at gcc dot gnu.org
  Target Milestone: ---

This one is very old (at least GCC 4.8.0):

$ cat pack.ii
template <typename = int> class A {
  const int &m_fn1() { return 0; }

public:
  template <typename _Kt> void m_fn2(_Kt) { m_fn1(); }
};
class B {
  A<> _M_t;

public:
  template <typename _Kt> auto m_fn3(_Kt p1) -> decltype(_M_t.m_fn2(p1)) {
    _M_t.m_fn2(p1);
  }
};
struct C {};
void operator<(C, int) {
  B a;
  a.m_fn3(C{});
}

$ g++ pack.ii -c -fcompare-debug -std=c++11
pack.ii: In instantiation of ‘const int& A< <template-parameter-1-1> >::m_fn1()
[with <template-parameter-1-1> = int]’:
pack.ii:5:45:   required from ‘void A< <template-parameter-1-1> >::m_fn2(_Kt)
[with _Kt = C; <template-parameter-1-1> = int]’
pack.ii:12:15:   required from ‘decltype
(((B*)this)->B::_M_t.A<>::m_fn2<_Kt>(p1)) B::m_fn3(_Kt) [with _Kt = C; decltype
(((B*)this)->B::_M_t.A<>::m_fn2<_Kt>(p1)) = void]’
pack.ii:18:14:   required from here
pack.ii:2:31: warning: returning reference to temporary [-Wreturn-local-addr]
    2 |   const int &m_fn1() { return 0; }
      |                               ^
g++: error: pack.ii: ‘-fcompare-debug’ failure (length)

[Bug debug/94326] g++: error: pack.ii: ‘-fcompare-debug’ failure (length)

[marxin at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=94326

Martin Liška <marxin at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Priority|P3                          |P2

[Bug debug/94326] g++: error: pack.ii: ‘-fcompare-debug’ failure (length)

[marxin at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=94326

Martin Liška <marxin at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
     Ever confirmed|0                           |1
             Status|UNCONFIRMED                 |NEW
   Last reconfirmed|                            |2020-03-25

[Bug c++/94326] g++: error: pack.ii: ‘-fcompare-debug’ failure (length)

[jakub at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=94326

Jakub Jelinek <jakub at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
          Component|debug                       |c++

--- Comment #1 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
Indeed, I think this started failing with
r0-114389-g4b6aaa996e0d8f5abac818315b6f77cb3596db98
before which it has been rejected with sorry message.
The bug isn't debug related in this case, but -w is affecting generated code.

[Bug c++/94326] g++: error: pack.ii: ‘-fcompare-debug’ failure (length)

[jakub at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=94326

--- Comment #2 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
$ rm -f pr94326.C.*; ./cc1plus -quiet -std=c++11 pr94326.C -Wreturn-local-addr
-da; grep REG_EH_REGION pr94326.C.*
pr94326.C: In instantiation of ‘const int& A< <template-parameter-1-1>
>::m_fn1() [with <template-parameter-1-1> = int]’:
pr94326.C:5:45:   required from ‘void A< <template-parameter-1-1> >::m_fn2(_Kt)
[with _Kt = C; <template-parameter-1-1> = int]’
pr94326.C:12:15:   required from ‘decltype
(((B*)this)->B::_M_t.A<>::m_fn2<_Kt>(p1)) B::m_fn3(_Kt) [with _Kt = C; decltype
(((B*)this)->B::_M_t.A<>::m_fn2<_Kt>(p1)) = void]’
pr94326.C:18:14:   required from here
pr94326.C:2:31: warning: returning reference to temporary [-Wreturn-local-addr]
    2 |   const int &m_fn1() { return 0; }
      |                               ^
$ rm -f pr94326.C.*; ./cc1plus -quiet -std=c++11 pr94326.C
-Wno-return-local-addr -da; grep REG_EH_REGION pr94326.C.*
pr94326.C.236r.expand:     (expr_list:REG_EH_REGION (const_int 0 [0])
pr94326.C.236r.expand:     (expr_list:REG_EH_REGION (const_int 0 [0])
pr94326.C.237r.vregs:     (expr_list:REG_EH_REGION (const_int 0 [0])
pr94326.C.238r.into_cfglayout:     (expr_list:REG_EH_REGION (const_int 0 [0])
pr94326.C.239r.jump:     (expr_list:REG_EH_REGION (const_int 0 [0])
pr94326.C.239r.jump:     (expr_list:REG_EH_REGION (const_int 0 [0])
pr94326.C.251r.reginfo:     (expr_list:REG_EH_REGION (const_int 0 [0])
pr94326.C.274r.outof_cfglayout:     (expr_list:REG_EH_REGION (const_int 0 [0])
pr94326.C.275r.split1:     (expr_list:REG_EH_REGION (const_int 0 [0])
pr94326.C.277r.dfinit:     (expr_list:REG_EH_REGION (const_int 0 [0])
pr94326.C.278r.mode_sw:     (expr_list:REG_EH_REGION (const_int 0 [0])
pr94326.C.279r.asmcons:     (expr_list:REG_EH_REGION (const_int 0 [0])
pr94326.C.284r.ira:            (expr_list:REG_EH_REGION (const_int 0 [0])
pr94326.C.285r.reload:     (expr_list:REG_EH_REGION (const_int 0 [0])
pr94326.C.292r.pro_and_epilogue:     (expr_list:REG_EH_REGION (const_int 0 [0])
pr94326.C.295r.jump2:     (expr_list:REG_EH_REGION (const_int 0 [0])
pr94326.C.306r.split4:     (expr_list:REG_EH_REGION (const_int 0 [0])
pr94326.C.307r.stack:     (expr_list:REG_EH_REGION (const_int 0 [0])
pr94326.C.308r.alignments:     (expr_list:REG_EH_REGION (const_int 0 [0])
pr94326.C.310r.mach:     (expr_list:REG_EH_REGION (const_int 0 [0])
pr94326.C.311r.barriers:     (expr_list:REG_EH_REGION (const_int 0 [0])
pr94326.C.316r.shorten:     (expr_list:REG_EH_REGION (const_int 0 [0])
pr94326.C.317r.nothrow:     (expr_list:REG_EH_REGION (const_int 0 [0])
pr94326.C.318r.dwarf2:     (expr_list:REG_EH_REGION (const_int 0 [0])
pr94326.C.319r.final:     (expr_list:REG_EH_REGION (const_int 0 [0])
pr94326.C.320r.dfinish:     (expr_list:REG_EH_REGION (const_int 0 [0])

[Bug c++/94326] g++: error: pack.ii: ‘-fcompare-debug’ failure (length)

[jakub at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=94326

Jakub Jelinek <jakub at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |jason at gcc dot gnu.org

--- Comment #3 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
And the reason for the differences is that with -Wno-return-local-addr (or -w
etc.) m_fn1 is marked TREE_NOTHROW (fndecl) in finish_function, while with
-Wreturn-local-addr (and without -w) it is not.
The difference is in cp_function_chain->can_throw , which set not set in the no
warning case, and is set in:
#0  set_flags_from_callee (call=<call_expr 0x7fffea958580>) at
../../gcc/cp/call.c:324
#1  0x0000000000966d3b in build_call_a (function=<call_expr 0x7fffea958580>,
n=2, argarray=0x7fffffffb1e0) at ../../gcc/cp/call.c:365
#2  0x000000000098936f in build_cxx_call (fn=<addr_expr 0x7fffea956f60>,
nargs=2, argarray=0x7fffffffb1e0, complain=128, orig_fndecl=<tree 0x0>)
    at ../../gcc/cp/call.c:9578
#3  0x00000000009877cc in build_over_call (cand=0x3763930, flags=3, complain=0)
at ../../gcc/cp/call.c:9082
#4  0x000000000098c868 in build_new_method_call_1 (instance=<component_ref
0x7fffea949b70>, fns=<overload 0x7fffea936c20>, 
    args=0x7fffffffb860 = {...}, conversion_path=<tree_binfo 0x7fffea93e5a0>,
flags=1, fn_p=0x0, complain=128) at ../../gcc/cp/call.c:10335
#5  0x000000000098cd56 in build_new_method_call (instance=<component_ref
0x7fffea949b70>, fns=<baselink 0x7fffea949ba0>, 
    args=0x7fffffffb860 = {...}, conversion_path=<tree 0x0>, flags=1, fn_p=0x0,
complain=128) at ../../gcc/cp/call.c:10410
#6  0x0000000000c41d6f in tsubst_copy_and_build (t=<call_expr 0x7fffea801188>,
args=<tree_vec 0x7fffea956360>, complain=128, in_decl=<tree 0x0>, 
    function_p=false, integral_constant_expression_p=false) at
../../gcc/cp/pt.c:19812
#7  0x0000000000c2ae69 in tsubst (t=<decltype_type 0x7fffea94f1f8>,
args=<tree_vec 0x7fffea956360>, complain=0, in_decl=<tree 0x0>)
    at ../../gcc/cp/pt.c:15746
#8  0x0000000000ac831c in dump_template_bindings (pp=0x34be940
<actual_pretty_printer>, parms=<tree 0x0>, args=<tree_vec 0x7fffea956360>, 
    typenames=0x7fffea950a28 = {...}) at ../../gcc/cp/error.c:414
#9  0x0000000000ace590 in dump_substitution (pp=0x34be940
<actual_pretty_printer>, t=<template_decl 0x7fffea81e980 m_fn3>, 
    template_parms=<tree_list 0x7fffea935e38>, template_args=<tree_vec
0x7fffea956360>, flags=132) at ../../gcc/cp/error.c:1560
#10 0x0000000000ad0138 in dump_function_decl (pp=0x34be940
<actual_pretty_printer>, t=<template_decl 0x7fffea81e980 m_fn3>, flags=132)
    at ../../gcc/cp/error.c:1718
#11 0x0000000000acd485 in dump_decl (pp=0x34be940 <actual_pretty_printer>,
t=<function_decl 0x7fffea95a700 m_fn3>, flags=132)
    at ../../gcc/cp/error.c:1290
#12 0x0000000000ad6ba8 in decl_to_string (decl=<function_decl 0x7fffea95a700
m_fn3>, verbose=1) at ../../gcc/cp/error.c:3092
#13 0x0000000000ada974 in cp_printer (pp=0x370bbb0, text=0x7fffffffc550,
spec=0x3721f62 "D", precision=0, wide=false, set_locus=false, 
    verbose=true, quoted=0x7fffffffc19f, buffer_ptr=0x3721d70) at
../../gcc/cp/error.c:4260
#14 0x00000000026f5fe2 in pp_format (pp=0x370bbb0, text=0x7fffffffc550) at
../../gcc/pretty-print.c:1458
#15 0x00000000026f63b2 in pp_format_verbatim (pp=0x370bbb0,
text=0x7fffffffc550) at ../../gcc/pretty-print.c:1519
#16 0x00000000026f6c1d in pp_verbatim (pp=0x370bbb0, msg=0x2813680 "required
from %q#D\n") at ../../gcc/pretty-print.c:1773
#17 0x0000000000ad8b73 in print_instantiation_partial_context_line
(context=0x36bc320 <global_diagnostic_context>, t=0x7fffea956440, 
    loc=2147483653, recursive_p=false) at ../../gcc/cp/error.c:3537
#18 0x0000000000ad8e6d in print_instantiation_partial_context
(context=0x36bc320 <global_diagnostic_context>, t0=0x7fffea936860,
loc=2147483653)
    at ../../gcc/cp/error.c:3625
#19 0x0000000000ad89fb in print_instantiation_full_context (context=0x36bc320
<global_diagnostic_context>) at ../../gcc/cp/error.c:3505
#20 0x0000000000ad8eec in maybe_print_instantiation_context (context=0x36bc320
<global_diagnostic_context>) at ../../gcc/cp/error.c:3642
#21 0x0000000000ad74c6 in cp_diagnostic_starter (context=0x36bc320
<global_diagnostic_context>, diagnostic=0x7fffffffc880)
    at ../../gcc/cp/error.c:3341
#22 0x00000000026cfced in diagnostic_report_diagnostic (context=0x36bc320
<global_diagnostic_context>, diagnostic=0x7fffffffc880)
    at ../../gcc/diagnostic.c:1160
#23 0x00000000026d02f2 in diagnostic_impl (richloc=0x7fffffffc8f0,
metadata=0x0, opt=635, gmsgid=0x284c5f8 "returning reference to temporary", 
    ap=0x7fffffffc9a0, kind=DK_WARNING) at ../../gcc/diagnostic.c:1309
#24 0x00000000026d0b70 in warning_at (location=247168, opt=635,
gmsgid=0x284c5f8 "returning reference to temporary")

i.e. when the warning is being emitted.
The call in question is
A<>::m_fn2<C> (&((struct B *) this)->_M_t, TARGET_EXPR <D.2226, p1>

So, shall set_flags_from_callee be setting cp_function_chain->can_throw (or
other flags) even in cp_unevaluated_operand ?  Or shouldn't tsubst or whatever
else sets cp_unevaluated_operand?  Something else?

[Bug c++/94326] g++: error: pack.ii: ‘-fcompare-debug’ failure (length)

[jakub at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=94326

--- Comment #4 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
--- gcc/cp/call.c.jj    2020-03-25 08:05:07.153731580 +0100
+++ gcc/cp/call.c       2020-03-26 15:03:42.432909693 +0100
@@ -333,11 +333,14 @@ set_flags_from_callee (tree call)
           && internal_fn_flags (CALL_EXPR_IFN (call)) & ECF_NOTHROW)
     nothrow = true;

-  if (!nothrow && at_function_scope_p () && cfun && cp_function_chain)
-    cp_function_chain->can_throw = 1;
+  if (cfun && cp_function_chain && !cp_unevaluated_operand)
+    {
+      if (!nothrow && at_function_scope_p ())
+       cp_function_chain->can_throw = 1;

-  if (decl && TREE_THIS_VOLATILE (decl) && cfun && cp_function_chain)
-    current_function_returns_abnormally = 1;
+      if (decl && TREE_THIS_VOLATILE (decl))
+       current_function_returns_abnormally = 1;
+    }

   TREE_NOTHROW (call) = nothrow;
 }

seems to work, but not sure if that is what we want.

[Bug c++/94326] g++: error: pack.ii: ‘-fcompare-debug’ failure (length)

[cvs-commit at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=94326

--- Comment #5 from CVS Commits <cvs-commit at gcc dot gnu.org> ---
The master branch has been updated by Jakub Jelinek <jakub@gcc.gnu.org>:

https://gcc.gnu.org/g:2eea00c518d5a72d0bdbc810ae675e7ad5fee414

commit r10-7411-g2eea00c518d5a72d0bdbc810ae675e7ad5fee414
Author: Jakub Jelinek <jakub@redhat.com>
Date:   Fri Mar 27 10:04:31 2020 +0100

    c++: Avoid calls in non-evaluated contexts affect whether function can or
can't throw [PR94326]

    The following testcase FAILs -fcompare-debug, because if we emit a
    -Wreturn-local-addr warning, we tsubst decltype in order to print the
    warning and as that function could throw, set_flags_from_callee during that
    sets cp_function_chain->can_throw and later on we don't set TREE_NOTHROW
    on foo.  While with -w or -Wno-return-local-addr, tsubst isn't called
during
    the warning_at, cp_function_chain->can_throw is kept clear and TREE_NOTHROW
    is set on foo.
    It isn't just a matter of the warning though, in
    int foo ();
    int bar () { return sizeof (foo ()); }
    int baz () { return sizeof (int); }
    I don't really see why we should mark only baz as TREE_NOTHROW and not bar
    too, when neither can really throw.

    2020-03-27  Jakub Jelinek  <jakub@redhat.com>

            PR c++/94326
            * call.c (set_flags_from_callee): Don't update
            cp_function_chain->can_throw or current_function_returns_abnormally
            if cp_unevaluated_operand.

            * g++.dg/other/pr94326.C: New test.

[Bug c++/94326] g++: error: pack.ii: ‘-fcompare-debug’ failure (length)

[jakub at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=94326

Jakub Jelinek <jakub at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
         Resolution|---                         |FIXED
             Status|NEW                         |RESOLVED

--- Comment #6 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
Fixed for 10+.