[analyzer PATCH] Restore bootstrap with g++ 4.8.

[analyzer PATCH] Restore bootstrap with g++ 4.8.

[Roger Sayle]

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This patch restores bootstrap when using g++ 4.8 as a host compiler.
Returning a std::unique_ptr requires a std::move on C++ compilers
(pre-C++17) that don't guarantee copy elision/return value optimization.

Bootstrapped on x86_64-pc-linux-gnu using both gcc 4.8.5 (system) and
gcc 10.2.1 (using "scl enable devetoolset-10") as host compilers.
Ok for mainline?


2024-06-07  Roger Sayle  <roger@nextmovesoftware.com>

gcc/analyzer/ChangeLog
        * constraint-manager.cc (equiv_class::make_dump_widget): Use
        std::move to return a std::unique_ptr.
        (bounded_ranges_constraint::make_dump_widget): Likewise.
        (constraint_manager::make_dump_widget): Likewise.
        * program_state.cc (sm_state_map::make_dump_widget): Likewise.
        (program_state::make_dump_widget): Likewise.
        * region-model.cc (region_to_value_map::make_dump_widget): Likewise.
        (region_model::make_dump_widget): Likewise.
        * region.cc (region::make_dump_widget): Likewise.
        * store.cc (binding_cluster::make_dump_widget): Likewise.
        (store::make_dump_widget): Likewise.
        * svalue.cc (svalue::make_dump_widget): Likewise.

Thanks in advance,
Roger
--


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diff --git a/gcc/analyzer/constraint-manager.cc b/gcc/analyzer/constraint-manager.cc
index 707385d..883f33b 100644
--- a/gcc/analyzer/constraint-manager.cc
+++ b/gcc/analyzer/constraint-manager.cc
@@ -1176,7 +1176,7 @@ equiv_class::make_dump_widget (const text_art::dump_widget_info &dwi,
       ec_widget->add_child (tree_widget::make (dwi, &pp));
     }
 
-  return ec_widget;
+  return std::move (ec_widget);
 }
 
 /* Generate a hash value for this equiv_class.
@@ -1500,7 +1500,7 @@ make_dump_widget (const text_art::dump_widget_info &dwi) const
     (tree_widget::from_fmt (dwi, nullptr,
 			    "ec%i bounded ranges", m_ec_id.as_int ()));
   m_ranges->add_to_dump_widget (*brc_widget.get (), dwi);
-  return brc_widget;
+  return std::move (brc_widget);
 }
 
 bool
@@ -1853,7 +1853,7 @@ constraint_manager::make_dump_widget (const text_art::dump_widget_info &dwi) con
   if (cm_widget->get_num_children () == 0)
     return nullptr;
 
-  return cm_widget;
+  return std::move (cm_widget);
 }
 
 /* Attempt to add the constraint LHS OP RHS to this constraint_manager.
diff --git a/gcc/analyzer/program-state.cc b/gcc/analyzer/program-state.cc
index dc2d4bd..efaf569 100644
--- a/gcc/analyzer/program-state.cc
+++ b/gcc/analyzer/program-state.cc
@@ -382,7 +382,7 @@ sm_state_map::make_dump_widget (const text_art::dump_widget_info &dwi,
       state_widget->add_child (tree_widget::make (dwi, pp));
     }
 
-  return state_widget;
+  return std::move (state_widget);
 }
 
 /* Return true if no states have been set within this map
@@ -1247,7 +1247,7 @@ program_state::make_dump_widget (const text_art::dump_widget_info &dwi) const
 	state_widget->add_child (smap->make_dump_widget (dwi, m_region_model));
   }
 
-  return state_widget;
+  return std::move (state_widget);
 }
 
 /* Update this program_state to reflect a top-level call to FUN.
diff --git a/gcc/analyzer/region-model.cc b/gcc/analyzer/region-model.cc
index d142d85..4fbc970 100644
--- a/gcc/analyzer/region-model.cc
+++ b/gcc/analyzer/region-model.cc
@@ -288,7 +288,7 @@ make_dump_widget (const text_art::dump_widget_info &dwi) const
       sval->dump_to_pp (pp, true);
       w->add_child (text_art::tree_widget::make (dwi, pp));
     }
-  return w;
+  return std::move (w);
 }
 
 /* Attempt to merge THIS with OTHER, writing the result
@@ -556,7 +556,7 @@ region_model::make_dump_widget (const text_art::dump_widget_info &dwi) const
 			       m_mgr->get_store_manager ()));
   model_widget->add_child (m_constraints->make_dump_widget (dwi));
   model_widget->add_child (m_dynamic_extents.make_dump_widget (dwi));
-  return model_widget;
+  return std::move (model_widget);
 }
 
 /* Assert that this object is valid.  */
diff --git a/gcc/analyzer/region.cc b/gcc/analyzer/region.cc
index 71bae97..050feb6 100644
--- a/gcc/analyzer/region.cc
+++ b/gcc/analyzer/region.cc
@@ -1119,7 +1119,7 @@ region::make_dump_widget (const text_art::dump_widget_info &dwi,
   if (m_parent)
     w->add_child (m_parent->make_dump_widget (dwi, "parent"));
 
-  return w;
+  return std::move (w);
 }
 
 void
diff --git a/gcc/analyzer/store.cc b/gcc/analyzer/store.cc
index d14cfa3..b20bc29 100644
--- a/gcc/analyzer/store.cc
+++ b/gcc/analyzer/store.cc
@@ -1489,7 +1489,7 @@ binding_cluster::make_dump_widget (const text_art::dump_widget_info &dwi,
 
       m_map.add_to_tree_widget (*cluster_widget, dwi);
 
-      return cluster_widget;
+      return std::move (cluster_widget);
     }
 }
 
@@ -2766,7 +2766,7 @@ store::make_dump_widget (const text_art::dump_widget_info &dwi,
       store_widget->add_child (std::move (parent_reg_widget));
     }
 
-  return store_widget;
+  return std::move (store_widget);
 }
 
 /* Get any svalue bound to REG, or NULL.  */
diff --git a/gcc/analyzer/svalue.cc b/gcc/analyzer/svalue.cc
index f1fd21e..b67780a 100644
--- a/gcc/analyzer/svalue.cc
+++ b/gcc/analyzer/svalue.cc
@@ -252,7 +252,7 @@ svalue::make_dump_widget (const text_art::dump_widget_info &dwi,
 
   add_dump_widget_children (*w, dwi);
 
-  return w;
+  return std::move (w);
 }
 
 /* If this svalue is a constant_svalue, return the underlying tree constant.

Re: [analyzer PATCH] Restore bootstrap with g++ 4.8.

[David Malcolm]

On Fri, 2024-06-07 at 19:40 +0100, Roger Sayle wrote:
> 
> This patch restores bootstrap when using g++ 4.8 as a host compiler.
> Returning a std::unique_ptr requires a std::move on C++ compilers
> (pre-C++17) that don't guarantee copy elision/return value
> optimization.
> 
> Bootstrapped on x86_64-pc-linux-gnu using both gcc 4.8.5 (system) and
> gcc 10.2.1 (using "scl enable devetoolset-10") as host compilers.
> Ok for mainline?

Yes, thanks.  Sorry for the breakage.

Dave

> 
> 
> 2024-06-07  Roger Sayle  <roger@nextmovesoftware.com>
> 
> gcc/analyzer/ChangeLog
>         * constraint-manager.cc (equiv_class::make_dump_widget): Use
>         std::move to return a std::unique_ptr.
>         (bounded_ranges_constraint::make_dump_widget): Likewise.
>         (constraint_manager::make_dump_widget): Likewise.
>         * program_state.cc (sm_state_map::make_dump_widget):
> Likewise.
>         (program_state::make_dump_widget): Likewise.
>         * region-model.cc (region_to_value_map::make_dump_widget):
> Likewise.
>         (region_model::make_dump_widget): Likewise.
>         * region.cc (region::make_dump_widget): Likewise.
>         * store.cc (binding_cluster::make_dump_widget): Likewise.
>         (store::make_dump_widget): Likewise.
>         * svalue.cc (svalue::make_dump_widget): Likewise.
> 
> Thanks in advance,
> Roger
> --
> 

Re: [analyzer PATCH] Restore bootstrap with g++ 4.8.

[Jonathan Wakely]

On 07/06/24 19:40 +0100, Roger Sayle wrote:
>
>This patch restores bootstrap when using g++ 4.8 as a host compiler.
>Returning a std::unique_ptr requires a std::move on C++ compilers
>(pre-C++17) that don't guarantee copy elision/return value optimization.

It doesn't though.  The C++17 guaranteed copy elision rules are not
relevant here.  This is about lookup for the constructor used in the
return statement, and whether that lookup considers the variable to be
an lvalue or an rvalue.  C++11 already says this is valid:

i#include <memory>

std::unique_ptr<int> f()
{
     std::unique_ptr<int> m;
     return m;
}

See C++11 12.8 [class.copy] p31:

   This elision of copy/move operations, called copy elision, is
   permitted in the following circumstances (which may be combined to
   eliminate multiple copies):

   - in a return statement in a function with a class return type, when
   the expression is the name of a non-volatile automatic object (other
   than a function or catch-clause parameter) with the same cv-
   unqualified type as the function return type, the copy/move
   operation can be omitted by constructing the automatic object
   directly into the function’s return value

and then p32:

   When the criteria for elision of a copy operation are met or would
   be met save for the fact that the source object is a function
   parameter, and the object to be copied is designated by an lvalue,
   overload resolution to select the constructor for the copy is first
   performed as if the object were designated by an rvalue.

The constructor isn't required to be elided in C++11, but the compiler
is required to use a move constructor instead of a copy constructor,
if a move constructor is available. So you don't need to use std::move
on the return value.

And the code above compiles fine with gcc 4.8.5 on CentOS 7 (and even
with 4.7.1).

So the std::move calls you've added are redundant, and will cause
-Wredundant-move warnings.

What's the error you were seeing?


>Bootstrapped on x86_64-pc-linux-gnu using both gcc 4.8.5 (system) and
>gcc 10.2.1 (using "scl enable devetoolset-10") as host compilers.
>Ok for mainline?
>
>
>2024-06-07  Roger Sayle  <roger@nextmovesoftware.com>
>
>gcc/analyzer/ChangeLog
>        * constraint-manager.cc (equiv_class::make_dump_widget): Use
>        std::move to return a std::unique_ptr.
>        (bounded_ranges_constraint::make_dump_widget): Likewise.
>        (constraint_manager::make_dump_widget): Likewise.
>        * program_state.cc (sm_state_map::make_dump_widget): Likewise.
>        (program_state::make_dump_widget): Likewise.
>        * region-model.cc (region_to_value_map::make_dump_widget): Likewise.
>        (region_model::make_dump_widget): Likewise.
>        * region.cc (region::make_dump_widget): Likewise.
>        * store.cc (binding_cluster::make_dump_widget): Likewise.
>        (store::make_dump_widget): Likewise.
>        * svalue.cc (svalue::make_dump_widget): Likewise.
>
>Thanks in advance,
>Roger
>--
>

>diff --git a/gcc/analyzer/constraint-manager.cc b/gcc/analyzer/constraint-manager.cc
>index 707385d..883f33b 100644
>--- a/gcc/analyzer/constraint-manager.cc
>+++ b/gcc/analyzer/constraint-manager.cc
>@@ -1176,7 +1176,7 @@ equiv_class::make_dump_widget (const text_art::dump_widget_info &dwi,
>       ec_widget->add_child (tree_widget::make (dwi, &pp));
>     }
>
>-  return ec_widget;
>+  return std::move (ec_widget);
> }
>
> /* Generate a hash value for this equiv_class.
>@@ -1500,7 +1500,7 @@ make_dump_widget (const text_art::dump_widget_info &dwi) const
>     (tree_widget::from_fmt (dwi, nullptr,
> 			    "ec%i bounded ranges", m_ec_id.as_int ()));
>   m_ranges->add_to_dump_widget (*brc_widget.get (), dwi);
>-  return brc_widget;
>+  return std::move (brc_widget);
> }
>
> bool
>@@ -1853,7 +1853,7 @@ constraint_manager::make_dump_widget (const text_art::dump_widget_info &dwi) con
>   if (cm_widget->get_num_children () == 0)
>     return nullptr;
>
>-  return cm_widget;
>+  return std::move (cm_widget);
> }
>
> /* Attempt to add the constraint LHS OP RHS to this constraint_manager.
>diff --git a/gcc/analyzer/program-state.cc b/gcc/analyzer/program-state.cc
>index dc2d4bd..efaf569 100644
>--- a/gcc/analyzer/program-state.cc
>+++ b/gcc/analyzer/program-state.cc
>@@ -382,7 +382,7 @@ sm_state_map::make_dump_widget (const text_art::dump_widget_info &dwi,
>       state_widget->add_child (tree_widget::make (dwi, pp));
>     }
>
>-  return state_widget;
>+  return std::move (state_widget);
> }
>
> /* Return true if no states have been set within this map
>@@ -1247,7 +1247,7 @@ program_state::make_dump_widget (const text_art::dump_widget_info &dwi) const
> 	state_widget->add_child (smap->make_dump_widget (dwi, m_region_model));
>   }
>
>-  return state_widget;
>+  return std::move (state_widget);
> }
>
> /* Update this program_state to reflect a top-level call to FUN.
>diff --git a/gcc/analyzer/region-model.cc b/gcc/analyzer/region-model.cc
>index d142d85..4fbc970 100644
>--- a/gcc/analyzer/region-model.cc
>+++ b/gcc/analyzer/region-model.cc
>@@ -288,7 +288,7 @@ make_dump_widget (const text_art::dump_widget_info &dwi) const
>       sval->dump_to_pp (pp, true);
>       w->add_child (text_art::tree_widget::make (dwi, pp));
>     }
>-  return w;
>+  return std::move (w);
> }
>
> /* Attempt to merge THIS with OTHER, writing the result
>@@ -556,7 +556,7 @@ region_model::make_dump_widget (const text_art::dump_widget_info &dwi) const
> 			       m_mgr->get_store_manager ()));
>   model_widget->add_child (m_constraints->make_dump_widget (dwi));
>   model_widget->add_child (m_dynamic_extents.make_dump_widget (dwi));
>-  return model_widget;
>+  return std::move (model_widget);
> }
>
> /* Assert that this object is valid.  */
>diff --git a/gcc/analyzer/region.cc b/gcc/analyzer/region.cc
>index 71bae97..050feb6 100644
>--- a/gcc/analyzer/region.cc
>+++ b/gcc/analyzer/region.cc
>@@ -1119,7 +1119,7 @@ region::make_dump_widget (const text_art::dump_widget_info &dwi,
>   if (m_parent)
>     w->add_child (m_parent->make_dump_widget (dwi, "parent"));
>
>-  return w;
>+  return std::move (w);
> }
>
> void
>diff --git a/gcc/analyzer/store.cc b/gcc/analyzer/store.cc
>index d14cfa3..b20bc29 100644
>--- a/gcc/analyzer/store.cc
>+++ b/gcc/analyzer/store.cc
>@@ -1489,7 +1489,7 @@ binding_cluster::make_dump_widget (const text_art::dump_widget_info &dwi,
>
>       m_map.add_to_tree_widget (*cluster_widget, dwi);
>
>-      return cluster_widget;
>+      return std::move (cluster_widget);
>     }
> }
>
>@@ -2766,7 +2766,7 @@ store::make_dump_widget (const text_art::dump_widget_info &dwi,
>       store_widget->add_child (std::move (parent_reg_widget));
>     }
>
>-  return store_widget;
>+  return std::move (store_widget);
> }
>
> /* Get any svalue bound to REG, or NULL.  */
>diff --git a/gcc/analyzer/svalue.cc b/gcc/analyzer/svalue.cc
>index f1fd21e..b67780a 100644
>--- a/gcc/analyzer/svalue.cc
>+++ b/gcc/analyzer/svalue.cc
>@@ -252,7 +252,7 @@ svalue::make_dump_widget (const text_art::dump_widget_info &dwi,
>
>   add_dump_widget_children (*w, dwi);
>
>-  return w;
>+  return std::move (w);
> }
>
> /* If this svalue is a constant_svalue, return the underlying tree constant.

Re: [analyzer PATCH] Restore bootstrap with g++ 4.8.

[Jonathan Wakely]

On 14/06/24 10:36 +0100, Jonathan Wakely wrote:
>On 07/06/24 19:40 +0100, Roger Sayle wrote:
>>
>>This patch restores bootstrap when using g++ 4.8 as a host compiler.
>>Returning a std::unique_ptr requires a std::move on C++ compilers
>>(pre-C++17) that don't guarantee copy elision/return value optimization.
>
>It doesn't though.  The C++17 guaranteed copy elision rules are not
>relevant here.  This is about lookup for the constructor used in the
>return statement, and whether that lookup considers the variable to be
>an lvalue or an rvalue.  C++11 already says this is valid:
>
>i#include <memory>
>
>std::unique_ptr<int> f()
>{
>    std::unique_ptr<int> m;
>    return m;
>}
>
>See C++11 12.8 [class.copy] p31:
>
>  This elision of copy/move operations, called copy elision, is
>  permitted in the following circumstances (which may be combined to
>  eliminate multiple copies):
>
>  - in a return statement in a function with a class return type, when
>  the expression is the name of a non-volatile automatic object (other
>  than a function or catch-clause parameter) with the same cv-
>  unqualified type as the function return type, the copy/move
>  operation can be omitted by constructing the automatic object
>  directly into the function’s return value
>
>and then p32:
>
>  When the criteria for elision of a copy operation are met or would
>  be met save for the fact that the source object is a function
>  parameter, and the object to be copied is designated by an lvalue,
>  overload resolution to select the constructor for the copy is first
>  performed as if the object were designated by an rvalue.
>
>The constructor isn't required to be elided in C++11, but the compiler
>is required to use a move constructor instead of a copy constructor,
>if a move constructor is available. So you don't need to use std::move
>on the return value.
>
>And the code above compiles fine with gcc 4.8.5 on CentOS 7 (and even
>with 4.7.1).
>
>So the std::move calls you've added are redundant, and will cause
>-Wredundant-move warnings.
>
>What's the error you were seeing?

I can reproduce it:

/home/test/src/gcc/gcc/analyzer/constraint-manager.cc: In member function ‘std::unique_ptr<text_art::widget> ana::equiv_class::make_dump_widget(const text_art::dump_widget_info&, unsigned int) const’:
/home/test/src/gcc/gcc/analyzer/constraint-manager.cc:1179:10: error: cannot bind ‘std::unique_ptr<text_art::tree_widget>’ lvalue to ‘std::unique_ptr<text_art::tree_widget>&&’
    return ec_widget;
           ^

Odd ... I'm looking into it ...

Re: [analyzer PATCH] Restore bootstrap with g++ 4.8.

[Jonathan Wakely]

On 14/06/24 11:26 +0100, Jonathan Wakely wrote:
>On 14/06/24 10:36 +0100, Jonathan Wakely wrote:
>>On 07/06/24 19:40 +0100, Roger Sayle wrote:
>>>
>>>This patch restores bootstrap when using g++ 4.8 as a host compiler.
>>>Returning a std::unique_ptr requires a std::move on C++ compilers
>>>(pre-C++17) that don't guarantee copy elision/return value optimization.
>>
>>It doesn't though.  The C++17 guaranteed copy elision rules are not
>>relevant here.  This is about lookup for the constructor used in the
>>return statement, and whether that lookup considers the variable to be
>>an lvalue or an rvalue.  C++11 already says this is valid:
>>
>>i#include <memory>
>>
>>std::unique_ptr<int> f()
>>{
>>   std::unique_ptr<int> m;
>>   return m;
>>}
>>
>>See C++11 12.8 [class.copy] p31:
>>
>> This elision of copy/move operations, called copy elision, is
>> permitted in the following circumstances (which may be combined to
>> eliminate multiple copies):
>>
>> - in a return statement in a function with a class return type, when
>> the expression is the name of a non-volatile automatic object (other
>> than a function or catch-clause parameter) with the same cv-
>> unqualified type as the function return type, the copy/move
>> operation can be omitted by constructing the automatic object
>> directly into the function’s return value
>>
>>and then p32:
>>
>> When the criteria for elision of a copy operation are met or would
>> be met save for the fact that the source object is a function
>> parameter, and the object to be copied is designated by an lvalue,
>> overload resolution to select the constructor for the copy is first
>> performed as if the object were designated by an rvalue.
>>
>>The constructor isn't required to be elided in C++11, but the compiler
>>is required to use a move constructor instead of a copy constructor,
>>if a move constructor is available. So you don't need to use std::move
>>on the return value.
>>
>>And the code above compiles fine with gcc 4.8.5 on CentOS 7 (and even
>>with 4.7.1).
>>
>>So the std::move calls you've added are redundant, and will cause
>>-Wredundant-move warnings.
>>
>>What's the error you were seeing?
>
>I can reproduce it:
>
>/home/test/src/gcc/gcc/analyzer/constraint-manager.cc: In member function ‘std::unique_ptr<text_art::widget> ana::equiv_class::make_dump_widget(const text_art::dump_widget_info&, unsigned int) const’:
>/home/test/src/gcc/gcc/analyzer/constraint-manager.cc:1179:10: error: cannot bind ‘std::unique_ptr<text_art::tree_widget>’ lvalue to ‘std::unique_ptr<text_art::tree_widget>&&’
>   return ec_widget;
>          ^
>
>Odd ... I'm looking into it ...

Ah, the problem here is that the function's return type is
std::unique_ptr<text_art::widget> but the return value is
std::unique_ptr<tree_widget> and that requires the converting
constructor, not the move constructor.

That *did* change after C++11, and isn't supported by G++ until 5.1

Is there a reason that function has to return unique_ptr<widget>
instead of unique_ptr<tree_widget>? The conversion to ptr-to-base
could happen at the call site (where you always have an rvalue)
instead of on the return value.

Re: [analyzer PATCH] Restore bootstrap with g++ 4.8.

[Jonathan Wakely]

On 14/06/24 11:37 +0100, Jonathan Wakely wrote:
>On 14/06/24 11:26 +0100, Jonathan Wakely wrote:
>>On 14/06/24 10:36 +0100, Jonathan Wakely wrote:
>>>On 07/06/24 19:40 +0100, Roger Sayle wrote:
>>>>
>>>>This patch restores bootstrap when using g++ 4.8 as a host compiler.
>>>>Returning a std::unique_ptr requires a std::move on C++ compilers
>>>>(pre-C++17) that don't guarantee copy elision/return value optimization.
>>>
>>>It doesn't though.  The C++17 guaranteed copy elision rules are not
>>>relevant here.  This is about lookup for the constructor used in the
>>>return statement, and whether that lookup considers the variable to be
>>>an lvalue or an rvalue.  C++11 already says this is valid:
>>>
>>>i#include <memory>
>>>
>>>std::unique_ptr<int> f()
>>>{
>>>  std::unique_ptr<int> m;
>>>  return m;
>>>}
>>>
>>>See C++11 12.8 [class.copy] p31:
>>>
>>>This elision of copy/move operations, called copy elision, is
>>>permitted in the following circumstances (which may be combined to
>>>eliminate multiple copies):
>>>
>>>- in a return statement in a function with a class return type, when
>>>the expression is the name of a non-volatile automatic object (other
>>>than a function or catch-clause parameter) with the same cv-
>>>unqualified type as the function return type, the copy/move
>>>operation can be omitted by constructing the automatic object
>>>directly into the function’s return value
>>>
>>>and then p32:
>>>
>>>When the criteria for elision of a copy operation are met or would
>>>be met save for the fact that the source object is a function
>>>parameter, and the object to be copied is designated by an lvalue,
>>>overload resolution to select the constructor for the copy is first
>>>performed as if the object were designated by an rvalue.
>>>
>>>The constructor isn't required to be elided in C++11, but the compiler
>>>is required to use a move constructor instead of a copy constructor,
>>>if a move constructor is available. So you don't need to use std::move
>>>on the return value.
>>>
>>>And the code above compiles fine with gcc 4.8.5 on CentOS 7 (and even
>>>with 4.7.1).
>>>
>>>So the std::move calls you've added are redundant, and will cause
>>>-Wredundant-move warnings.
>>>
>>>What's the error you were seeing?
>>
>>I can reproduce it:
>>
>>/home/test/src/gcc/gcc/analyzer/constraint-manager.cc: In member function ‘std::unique_ptr<text_art::widget> ana::equiv_class::make_dump_widget(const text_art::dump_widget_info&, unsigned int) const’:
>>/home/test/src/gcc/gcc/analyzer/constraint-manager.cc:1179:10: error: cannot bind ‘std::unique_ptr<text_art::tree_widget>’ lvalue to ‘std::unique_ptr<text_art::tree_widget>&&’
>>  return ec_widget;
>>         ^
>>
>>Odd ... I'm looking into it ...
>
>Ah, the problem here is that the function's return type is
>std::unique_ptr<text_art::widget> but the return value is
>std::unique_ptr<tree_widget> and that requires the converting
>constructor, not the move constructor.
>
>That *did* change after C++11, and isn't supported by G++ until 5.1

That changed with https://cplusplus.github.io/CWG/issues/1579.html
which is in C++14 and is a DR against C++11, but of course compilers
that implement the original C++11 rules don't support that DR.

Arguably, g++ should not give -Wredundant-move warnings here when
using the -std=c++11 dialect, because it's only redundant if the C++11
compiler implements that DR.

>Is there a reason that function has to return unique_ptr<widget>
>instead of unique_ptr<tree_widget>? The conversion to ptr-to-base
>could happen at the call site (where you always have an rvalue)
>instead of on the return value.

Changing the return type to match the return value would avoid the
issue entirely though, as it would be valid with all C++11 compilers.

Re: [analyzer PATCH] Restore bootstrap with g++ 4.8.

[Jonathan Wakely]

On 14/06/24 11:42 +0100, Jonathan Wakely wrote:
>On 14/06/24 11:37 +0100, Jonathan Wakely wrote:
>>On 14/06/24 11:26 +0100, Jonathan Wakely wrote:
>>>On 14/06/24 10:36 +0100, Jonathan Wakely wrote:
>>>>On 07/06/24 19:40 +0100, Roger Sayle wrote:
>>>>>
>>>>>This patch restores bootstrap when using g++ 4.8 as a host compiler.
>>>>>Returning a std::unique_ptr requires a std::move on C++ compilers
>>>>>(pre-C++17) that don't guarantee copy elision/return value optimization.
>>>>
>>>>It doesn't though.  The C++17 guaranteed copy elision rules are not
>>>>relevant here.  This is about lookup for the constructor used in the
>>>>return statement, and whether that lookup considers the variable to be
>>>>an lvalue or an rvalue.  C++11 already says this is valid:
>>>>
>>>>i#include <memory>
>>>>
>>>>std::unique_ptr<int> f()
>>>>{
>>>> std::unique_ptr<int> m;
>>>> return m;
>>>>}
>>>>
>>>>See C++11 12.8 [class.copy] p31:
>>>>
>>>>This elision of copy/move operations, called copy elision, is
>>>>permitted in the following circumstances (which may be combined to
>>>>eliminate multiple copies):
>>>>
>>>>- in a return statement in a function with a class return type, when
>>>>the expression is the name of a non-volatile automatic object (other
>>>>than a function or catch-clause parameter) with the same cv-
>>>>unqualified type as the function return type, the copy/move
>>>>operation can be omitted by constructing the automatic object
>>>>directly into the function’s return value
>>>>
>>>>and then p32:
>>>>
>>>>When the criteria for elision of a copy operation are met or would
>>>>be met save for the fact that the source object is a function
>>>>parameter, and the object to be copied is designated by an lvalue,
>>>>overload resolution to select the constructor for the copy is first
>>>>performed as if the object were designated by an rvalue.
>>>>
>>>>The constructor isn't required to be elided in C++11, but the compiler
>>>>is required to use a move constructor instead of a copy constructor,
>>>>if a move constructor is available. So you don't need to use std::move
>>>>on the return value.
>>>>
>>>>And the code above compiles fine with gcc 4.8.5 on CentOS 7 (and even
>>>>with 4.7.1).
>>>>
>>>>So the std::move calls you've added are redundant, and will cause
>>>>-Wredundant-move warnings.
>>>>
>>>>What's the error you were seeing?
>>>
>>>I can reproduce it:
>>>
>>>/home/test/src/gcc/gcc/analyzer/constraint-manager.cc: In member function ‘std::unique_ptr<text_art::widget> ana::equiv_class::make_dump_widget(const text_art::dump_widget_info&, unsigned int) const’:
>>>/home/test/src/gcc/gcc/analyzer/constraint-manager.cc:1179:10: error: cannot bind ‘std::unique_ptr<text_art::tree_widget>’ lvalue to ‘std::unique_ptr<text_art::tree_widget>&&’
>>> return ec_widget;
>>>        ^
>>>
>>>Odd ... I'm looking into it ...
>>
>>Ah, the problem here is that the function's return type is
>>std::unique_ptr<text_art::widget> but the return value is
>>std::unique_ptr<tree_widget> and that requires the converting
>>constructor, not the move constructor.
>>
>>That *did* change after C++11, and isn't supported by G++ until 5.1
>
>That changed with https://cplusplus.github.io/CWG/issues/1579.html

Which for the record was implemented in r5-1576-gfb682f9458c6cf (by
me, which I'd forgotten!)

>which is in C++14 and is a DR against C++11, but of course compilers
>that implement the original C++11 rules don't support that DR.
>
>Arguably, g++ should not give -Wredundant-move warnings here when
>using the -std=c++11 dialect, because it's only redundant if the C++11
>compiler implements that DR.
>
>>Is there a reason that function has to return unique_ptr<widget>
>>instead of unique_ptr<tree_widget>? The conversion to ptr-to-base
>>could happen at the call site (where you always have an rvalue)
>>instead of on the return value.
>
>Changing the return type to match the return value would avoid the
>issue entirely though, as it would be valid with all C++11 compilers.
>
>

[PATCH] analyzer: Fix g++ 4.8 bootstrap without using std::move to return std::unique_ptr

[Jonathan Wakely]

This builds successfully using both gcc-4.8.5 and gcc-13.3.1 as host
compiler.

OK for trunk if testing succeeds?

-- >8 --

Revert the changes in r15-1111-ge22b7f741ab54f and fix bootstrap with
GCC 4.8 a different way. The original problem is not related to C++17
guaranteed copy elision, it's related to Core DR 1579 [1], which was
part of C++14 but only implemented in G++ as a C++11 DR with
r5-1576-gfb682f9458c6cf (so GCC 4.8 doesn't implement it).

The original fix causes -Wredundant-move warnings with GCC trunk.

[1] https://cplusplus.github.io/CWG/issues/1579.html

gcc/analyzer/ChangeLog
	* constraint-manager.cc (equiv_class::make_dump_widget): Change
	return type to match return value and do not use std::move on
	return value.
	(bounded_ranges_constraint::make_dump_widget): Likewise.
	(constraint_manager::make_dump_widget): Likewise.
	* constraint-manager.h (equiv_class::make_dump_widget): Change
	return type.
	(bounded_ranges_constraint::make_dump_widget): Likewise.
	(constraint_manager::make_dump_widget): Likewise.
	* program-state.cc (sm_state_map::make_dump_widget): Likewise.
	(program_state::make_dump_widget): Likewise.
	* program-state.h (sm_state_map::make_dump_widget): Likewise.
	(program_state::make_dump_widget): Likewise.
	* region-model.cc (region_to_value_map::make_dump_widget): Likewise.
	(region_model::make_dump_widget): Likewise.
	* region-model.h (region_to_value_map::make_dump_widget): Likewise.
	(region_model::make_dump_widget): Likewise.
	* region.cc (region::make_dump_widget): Likewise.
	* region.h (region::make_dump_widget): Likewise.
	* store.cc (binding_cluster::make_dump_widget): Likewise.
	(store::make_dump_widget): Likewise.
	* store.h (binding_cluster::make_dump_widget): Likewise.
	(store::make_dump_widget): Likewise.
	* svalue.cc (svalue::make_dump_widget): Likewise.
	* svalue.h (svalue::make_dump_widget): Likewise.
---
 gcc/analyzer/constraint-manager.cc | 12 ++++++------
 gcc/analyzer/constraint-manager.h  |  6 +++---
 gcc/analyzer/program-state.cc      |  8 ++++----
 gcc/analyzer/program-state.h       |  4 ++--
 gcc/analyzer/region-model.cc       |  8 ++++----
 gcc/analyzer/region-model.h        |  4 ++--
 gcc/analyzer/region.cc             |  4 ++--
 gcc/analyzer/region.h              |  2 +-
 gcc/analyzer/store.cc              |  8 ++++----
 gcc/analyzer/store.h               |  4 ++--
 gcc/analyzer/svalue.cc             |  4 ++--
 gcc/analyzer/svalue.h              |  2 +-
 12 files changed, 33 insertions(+), 33 deletions(-)

diff --git a/gcc/analyzer/constraint-manager.cc b/gcc/analyzer/constraint-manager.cc
index a9d58c9cdcf..29539060ebd 100644
--- a/gcc/analyzer/constraint-manager.cc
+++ b/gcc/analyzer/constraint-manager.cc
@@ -1146,7 +1146,7 @@ equiv_class::to_json () const
   return ec_obj;
 }
 
-std::unique_ptr<text_art::widget>
+std::unique_ptr<text_art::tree_widget>
 equiv_class::make_dump_widget (const text_art::dump_widget_info &dwi,
 			       unsigned id) const
 {
@@ -1176,7 +1176,7 @@ equiv_class::make_dump_widget (const text_art::dump_widget_info &dwi,
       ec_widget->add_child (tree_widget::make (dwi, &pp));
     }
 
-  return std::move (ec_widget);
+  return ec_widget;
 }
 
 /* Generate a hash value for this equiv_class.
@@ -1491,7 +1491,7 @@ bounded_ranges_constraint::to_json () const
   return con_obj;
 }
 
-std::unique_ptr<text_art::widget>
+std::unique_ptr<text_art::tree_widget>
 bounded_ranges_constraint::
 make_dump_widget (const text_art::dump_widget_info &dwi) const
 {
@@ -1500,7 +1500,7 @@ make_dump_widget (const text_art::dump_widget_info &dwi) const
     (tree_widget::from_fmt (dwi, nullptr,
 			    "ec%i bounded ranges", m_ec_id.as_int ()));
   m_ranges->add_to_dump_widget (*brc_widget.get (), dwi);
-  return std::move (brc_widget);
+  return brc_widget;
 }
 
 bool
@@ -1829,7 +1829,7 @@ constraint_manager::to_json () const
   return cm_obj;
 }
 
-std::unique_ptr<text_art::widget>
+std::unique_ptr<text_art::tree_widget>
 constraint_manager::make_dump_widget (const text_art::dump_widget_info &dwi) const
 {
   using text_art::tree_widget;
@@ -1853,7 +1853,7 @@ constraint_manager::make_dump_widget (const text_art::dump_widget_info &dwi) con
   if (cm_widget->get_num_children () == 0)
     return nullptr;
 
-  return std::move (cm_widget);
+  return cm_widget;
 }
 
 /* Attempt to add the constraint LHS OP RHS to this constraint_manager.
diff --git a/gcc/analyzer/constraint-manager.h b/gcc/analyzer/constraint-manager.h
index 31556aebc7a..81e9c7ec035 100644
--- a/gcc/analyzer/constraint-manager.h
+++ b/gcc/analyzer/constraint-manager.h
@@ -273,7 +273,7 @@ public:
 
   json::object *to_json () const;
 
-  std::unique_ptr<text_art::widget>
+  std::unique_ptr<text_art::tree_widget>
   make_dump_widget (const text_art::dump_widget_info &dwi,
 		    unsigned id) const;
 
@@ -408,7 +408,7 @@ public:
 
   void add_to_hash (inchash::hash *hstate) const;
 
-  std::unique_ptr<text_art::widget>
+  std::unique_ptr<text_art::tree_widget>
   make_dump_widget (const text_art::dump_widget_info &dwi) const;
 
   equiv_class_id m_ec_id;
@@ -444,7 +444,7 @@ public:
 
   json::object *to_json () const;
 
-  std::unique_ptr<text_art::widget>
+  std::unique_ptr<text_art::tree_widget>
   make_dump_widget (const text_art::dump_widget_info &dwi) const;
 
   const equiv_class &get_equiv_class_by_index (unsigned idx) const
diff --git a/gcc/analyzer/program-state.cc b/gcc/analyzer/program-state.cc
index cb9c3888002..c42fc752350 100644
--- a/gcc/analyzer/program-state.cc
+++ b/gcc/analyzer/program-state.cc
@@ -309,7 +309,7 @@ sm_state_map::to_json () const
 /* Make a text_art::tree_widget describing this sm_state_map,
    using MODEL if non-null to describe svalues.  */
 
-std::unique_ptr<text_art::widget>
+std::unique_ptr<text_art::tree_widget>
 sm_state_map::make_dump_widget (const text_art::dump_widget_info &dwi,
 				const region_model *model) const
 {
@@ -382,7 +382,7 @@ sm_state_map::make_dump_widget (const text_art::dump_widget_info &dwi,
       state_widget->add_child (tree_widget::make (dwi, pp));
     }
 
-  return std::move (state_widget);
+  return state_widget;
 }
 
 /* Return true if no states have been set within this map
@@ -1229,7 +1229,7 @@ program_state::to_json (const extrinsic_state &ext_state) const
 }
 
 
-std::unique_ptr<text_art::widget>
+std::unique_ptr<text_art::tree_widget>
 program_state::make_dump_widget (const text_art::dump_widget_info &dwi) const
 {
   using text_art::tree_widget;
@@ -1247,7 +1247,7 @@ program_state::make_dump_widget (const text_art::dump_widget_info &dwi) const
 	state_widget->add_child (smap->make_dump_widget (dwi, m_region_model));
   }
 
-  return std::move (state_widget);
+  return state_widget;
 }
 
 /* Update this program_state to reflect a top-level call to FUN.
diff --git a/gcc/analyzer/program-state.h b/gcc/analyzer/program-state.h
index 7e751386b21..322ca8d0f11 100644
--- a/gcc/analyzer/program-state.h
+++ b/gcc/analyzer/program-state.h
@@ -119,7 +119,7 @@ public:
 
   json::object *to_json () const;
 
-  std::unique_ptr<text_art::widget>
+  std::unique_ptr<text_art::tree_widget>
   make_dump_widget (const text_art::dump_widget_info &dwi,
 		    const region_model *model) const;
 
@@ -233,7 +233,7 @@ public:
 
   json::object *to_json (const extrinsic_state &ext_state) const;
 
-  std::unique_ptr<text_art::widget>
+  std::unique_ptr<text_art::tree_widget>
   make_dump_widget (const text_art::dump_widget_info &dwi) const;
 
   void push_frame (const extrinsic_state &ext_state, const function &fun);
diff --git a/gcc/analyzer/region-model.cc b/gcc/analyzer/region-model.cc
index 7969055a59c..4d6e16cf0f4 100644
--- a/gcc/analyzer/region-model.cc
+++ b/gcc/analyzer/region-model.cc
@@ -258,7 +258,7 @@ region_to_value_map::to_json () const
   return map_obj;
 }
 
-std::unique_ptr<text_art::widget>
+std::unique_ptr<text_art::tree_widget>
 region_to_value_map::
 make_dump_widget (const text_art::dump_widget_info &dwi) const
 {
@@ -288,7 +288,7 @@ make_dump_widget (const text_art::dump_widget_info &dwi) const
       sval->dump_to_pp (pp, true);
       w->add_child (text_art::tree_widget::make (dwi, pp));
     }
-  return std::move (w);
+  return w;
 }
 
 /* Attempt to merge THIS with OTHER, writing the result
@@ -532,7 +532,7 @@ region_model::to_json () const
   return model_obj;
 }
 
-std::unique_ptr<text_art::widget>
+std::unique_ptr<text_art::tree_widget>
 region_model::make_dump_widget (const text_art::dump_widget_info &dwi) const
 {
   using text_art::tree_widget;
@@ -556,7 +556,7 @@ region_model::make_dump_widget (const text_art::dump_widget_info &dwi) const
 			       m_mgr->get_store_manager ()));
   model_widget->add_child (m_constraints->make_dump_widget (dwi));
   model_widget->add_child (m_dynamic_extents.make_dump_widget (dwi));
-  return std::move (model_widget);
+  return model_widget;
 }
 
 /* Assert that this object is valid.  */
diff --git a/gcc/analyzer/region-model.h b/gcc/analyzer/region-model.h
index f57d2069b3b..4683c1a4314 100644
--- a/gcc/analyzer/region-model.h
+++ b/gcc/analyzer/region-model.h
@@ -179,7 +179,7 @@ public:
 
   json::object *to_json () const;
 
-  std::unique_ptr<text_art::widget>
+  std::unique_ptr<text_art::tree_widget>
   make_dump_widget (const text_art::dump_widget_info &dwi) const;
 
   bool can_merge_with_p (const region_to_value_map &other,
@@ -288,7 +288,7 @@ class region_model
 
   json::object *to_json () const;
 
-  std::unique_ptr<text_art::widget>
+  std::unique_ptr<text_art::tree_widget>
   make_dump_widget (const text_art::dump_widget_info &dwi) const;
 
   void validate () const;
diff --git a/gcc/analyzer/region.cc b/gcc/analyzer/region.cc
index 2eabda41941..d110b0eef35 100644
--- a/gcc/analyzer/region.cc
+++ b/gcc/analyzer/region.cc
@@ -1076,7 +1076,7 @@ region::maybe_print_for_user (pretty_printer *pp,
 /* Use DWI to create a text_art::widget describing this region in
    a tree-like form, using PREFIX as a prefix (e.g. for field names).  */
 
-std::unique_ptr<text_art::widget>
+std::unique_ptr<text_art::tree_widget>
 region::make_dump_widget (const text_art::dump_widget_info &dwi,
 			  const char *prefix) const
 {
@@ -1101,7 +1101,7 @@ region::make_dump_widget (const text_art::dump_widget_info &dwi,
   if (m_parent)
     w->add_child (m_parent->make_dump_widget (dwi, "parent"));
 
-  return std::move (w);
+  return w;
 }
 
 void
diff --git a/gcc/analyzer/region.h b/gcc/analyzer/region.h
index 211dd3458c0..ffc05e034f1 100644
--- a/gcc/analyzer/region.h
+++ b/gcc/analyzer/region.h
@@ -182,7 +182,7 @@ public:
   bool maybe_print_for_user (pretty_printer *pp,
 			     const region_model &model) const;
 
-  std::unique_ptr<text_art::widget>
+  std::unique_ptr<text_art::tree_widget>
   make_dump_widget (const text_art::dump_widget_info &dwi,
 		    const char *prefix = nullptr) const;
 
diff --git a/gcc/analyzer/store.cc b/gcc/analyzer/store.cc
index f58b84ef946..284866c7eff 100644
--- a/gcc/analyzer/store.cc
+++ b/gcc/analyzer/store.cc
@@ -1451,7 +1451,7 @@ binding_cluster::to_json () const
   return cluster_obj;
 }
 
-std::unique_ptr<text_art::widget>
+std::unique_ptr<text_art::tree_widget>
 binding_cluster::make_dump_widget (const text_art::dump_widget_info &dwi,
 				   store_manager *mgr) const
 {
@@ -1489,7 +1489,7 @@ binding_cluster::make_dump_widget (const text_art::dump_widget_info &dwi,
 
       m_map.add_to_tree_widget (*cluster_widget, dwi);
 
-      return std::move (cluster_widget);
+      return cluster_widget;
     }
 }
 
@@ -2710,7 +2710,7 @@ store::to_json () const
   return store_obj;
 }
 
-std::unique_ptr<text_art::widget>
+std::unique_ptr<text_art::tree_widget>
 store::make_dump_widget (const text_art::dump_widget_info &dwi,
 			 store_manager *mgr) const
 {
@@ -2769,7 +2769,7 @@ store::make_dump_widget (const text_art::dump_widget_info &dwi,
       store_widget->add_child (std::move (parent_reg_widget));
     }
 
-  return std::move (store_widget);
+  return store_widget;
 }
 
 /* Get any svalue bound to REG, or NULL.  */
diff --git a/gcc/analyzer/store.h b/gcc/analyzer/store.h
index affb6e218a6..af9ea4172a2 100644
--- a/gcc/analyzer/store.h
+++ b/gcc/analyzer/store.h
@@ -617,7 +617,7 @@ public:
 
   json::object *to_json () const;
 
-  std::unique_ptr<text_art::widget>
+  std::unique_ptr<text_art::tree_widget>
   make_dump_widget (const text_art::dump_widget_info &dwi,
 		    store_manager *mgr) const;
 
@@ -760,7 +760,7 @@ public:
 
   json::object *to_json () const;
 
-  std::unique_ptr<text_art::widget>
+  std::unique_ptr<text_art::tree_widget>
   make_dump_widget (const text_art::dump_widget_info &dwi,
 		    store_manager *mgr) const;
 
diff --git a/gcc/analyzer/svalue.cc b/gcc/analyzer/svalue.cc
index cad6b7dd3cd..c82aa107b3c 100644
--- a/gcc/analyzer/svalue.cc
+++ b/gcc/analyzer/svalue.cc
@@ -230,7 +230,7 @@ svalue::maybe_print_for_user (pretty_printer *pp,
    (a) print_dump_widget_label, to populate the text of a tree_widget, and
    (b) add_dump_widget_children, to add children to the tree_widget.  */
 
-std::unique_ptr<text_art::widget>
+std::unique_ptr<text_art::tree_widget>
 svalue::make_dump_widget (const text_art::dump_widget_info &dwi,
 			  const char *prefix) const
 {
@@ -252,7 +252,7 @@ svalue::make_dump_widget (const text_art::dump_widget_info &dwi,
 
   add_dump_widget_children (*w, dwi);
 
-  return std::move (w);
+  return w;
 }
 
 /* If this svalue is a constant_svalue, return the underlying tree constant.
diff --git a/gcc/analyzer/svalue.h b/gcc/analyzer/svalue.h
index e5503a54177..bc2374fe889 100644
--- a/gcc/analyzer/svalue.h
+++ b/gcc/analyzer/svalue.h
@@ -107,7 +107,7 @@ public:
 
   json::value *to_json () const;
 
-  std::unique_ptr<text_art::widget>
+  std::unique_ptr<text_art::tree_widget>
   make_dump_widget (const dump_widget_info &dwi,
 		    const char *prefix = nullptr) const;
 
-- 
2.45.1

Re: [PATCH] analyzer: Fix g++ 4.8 bootstrap without using std::move to return std::unique_ptr

[David Malcolm]

On Fri, 2024-06-14 at 13:57 +0100, Jonathan Wakely wrote:
> This builds successfully using both gcc-4.8.5 and gcc-13.3.1 as host
> compiler.
> 
> OK for trunk if testing succeeds?

Yes, thanks!

Dave