[PATCH 0/3] Type equality refactor and instrumentation

[PATCH 0/3] Type equality refactor and instrumentation

[Giuliano Procida]

Hi Dodji.

This series refactors various operator== methods making their common
functionality evident.

The first patch is just a prelude to make the second smaller.

The second patch does the refactoring. I'm not attached to the name
'equality_helper'.

The third patch is not intended for direct inclusion in libabigail but
builds on the refactoring to investigate how equality and canonical
types work in practice. It identifies some potential discrepancies,
but they may be entirely expected.

In general, it can be risky to define operator== in a way where
reflexivity, symmetry and transitivity do not obviously hold or can be
sensitive to small code changes or in way where equality, say for
class_decl_sptr, can be affected by something like canonicalisation.
More instrumentation could be added to check behaviour.

Giuliano Procida (3):
  abg-ir.cc: Tidy some operator== definitions
  abg-ir.cc: Refactor operator== methods with helper
  Add some type equality paranoia.

 src/abg-ir.cc | 185 +++++++++++++++++++++++++++++---------------------
 1 file changed, 106 insertions(+), 79 deletions(-)

-- 
2.27.0.383.g050319c2ae-goog

[PATCH 1/3] abg-ir.cc: Tidy some operator== definitions

[Giuliano Procida]

Many of the operator== definitions in this source file follow the same
pattern:

- the address of the argument is dynamic_cast to type of 'this'
- naked canonical type pointers are compared, if both present
- the types are compared structurally with 'equals'

In a couple of cases extra work is done to fetch the canonical type
of the definition of a declaration.

This commit adjusts a few cases so they more closely follow the common
form. This is to make the next refactoring trivial.

There are no behavioural changes.

	* src/abg-irc.cc (scope_type_decl::operator==): Compare naked
	canonical type pointers instead of the shared pointers.
	(qualified_type_def::operator==): Remove excess blank line.
	(function_type::operator==): Do dynamic_cast and check of
	argument before comparing naked canonical type pointers.
	(class_or_union::operator==): Eliminate temporary reference.
	(class_decl::operator==): Likewise.
	(union_decl::operator==): Likewise.

Signed-off-by: Giuliano Procida <gprocida@google.com>
---
 src/abg-ir.cc | 22 +++++++++-------------
 1 file changed, 9 insertions(+), 13 deletions(-)

diff --git a/src/abg-ir.cc b/src/abg-ir.cc
index 37f6bbdf..41e2f00e 100644
--- a/src/abg-ir.cc
+++ b/src/abg-ir.cc
@@ -12872,8 +12872,8 @@ scope_type_decl::operator==(const decl_base& o) const
   if (!other)
     return false;
 
-  if (get_canonical_type() && other->get_canonical_type())
-    return get_canonical_type().get() == other->get_canonical_type().get();
+  if (get_naked_canonical_type() && other->get_naked_canonical_type())
+    return get_naked_canonical_type() == other->get_naked_canonical_type();
 
   return equals(*this, *other, 0);
 }
@@ -13243,7 +13243,6 @@ qualified_type_def::operator==(const decl_base& o) const
   if (get_naked_canonical_type() && other->get_naked_canonical_type())
     return get_naked_canonical_type() == other->get_naked_canonical_type();
 
-
   return equals(*this, *other, 0);
 }
 
@@ -16723,16 +16722,16 @@ function_type::get_cached_name(bool internal) const
 bool
 function_type::operator==(const type_base& other) const
 {
+  const function_type* o = dynamic_cast<const function_type*>(&other);
+  if (!o)
+    return false;
+
   type_base* canonical_type = get_naked_canonical_type();
   type_base* other_canonical_type = other.get_naked_canonical_type();
 
   if (canonical_type && other_canonical_type)
     return canonical_type == other_canonical_type;
 
-  const function_type* o = dynamic_cast<const function_type*>(&other);
-  if (!o)
-    return false;
-
   return equals(*this, *o, 0);
 }
 
@@ -19111,8 +19110,7 @@ class_or_union::operator==(const decl_base& other) const
   if (canonical_type && other_canonical_type)
     return canonical_type == other_canonical_type;
 
-  const class_or_union& o = *op;
-  return equals(*this, o, 0);
+  return equals(*this, *op, 0);
 }
 
 /// Equality operator.
@@ -20966,8 +20964,7 @@ class_decl::operator==(const decl_base& other) const
   if (canonical_type && other_canonical_type)
     return canonical_type == other_canonical_type;
 
-  const class_decl& o = *op;
-  return equals(*this, o, 0);
+  return equals(*this, *op, 0);
 }
 
 /// Equality operator for class_decl.
@@ -21755,8 +21752,7 @@ union_decl::operator==(const decl_base& other) const
   if (canonical_type && other_canonical_type)
     return canonical_type == other_canonical_type;
 
-  const union_decl &o = *op;
-  return equals(*this, o, 0);
+  return equals(*this, *op, 0);
 }
 
 /// Equality operator for union_decl.
-- 
2.27.0.383.g050319c2ae-goog

[PATCH 2/3] abg-ir.cc: Refactor operator== methods with helper

[Giuliano Procida]

Many of the operator== definitions in this source file follow the same
pattern:

- the address of the argument is dynamic_cast to type of 'this'
- naked canonical type pointers are compared, if both present
- the types are compared structurally with 'equals'

In a couple of cases extra work is done to fetch the canonical type
of the definition of a declaration.

This commit refactors all the common logic into a couple of templated
helper functions.

There are no behavioural changes.

	* src/abg-ir.cc (equality_helper): Add an overloaded function
	to perform the common actions needed for operator==. The first
	overload takes two extra canonical type pointer arguments
	while the second obtains these from the types being compared.
	(type_decl::operator==): Call equality_helper to perform
	canonical type pointer and 'equals' comparisons.
	(scope_type_decl::operator==): Likewise.
	(qualified_type_def::operator==): Likewise.
	(pointer_type_def::operator==): Likewise.
	(reference_type_def::operator==): Likewise.
	(array_type_def::subrange_type::operator==): Likewise.
	(array_type_def::operator==): Likewise.
	(enum_type_decl::operator==): Likewise.
	(typedef_decl::operator==): Likewise.
	(function_type::operator==): Likewise.
	(class_or_union::operator==): Likewise.
	(class_decl::operator==): Likewise.
	(union_decl::operator==): Likewise.

Signed-off-by: Giuliano Procida <gprocida@google.com>
---
 src/abg-ir.cc | 104 ++++++++++++++------------------------------------
 1 file changed, 29 insertions(+), 75 deletions(-)

diff --git a/src/abg-ir.cc b/src/abg-ir.cc
index 41e2f00e..4b7e180d 100644
--- a/src/abg-ir.cc
+++ b/src/abg-ir.cc
@@ -651,6 +651,22 @@ struct type_name_comp
   {return operator()(type_base_sptr(l), type_base_sptr(r));}
 }; // end struct type_name_comp
 
+template<typename T>
+bool equality_helper(const T* lptr, const T* rptr,
+		     const type_base* lcanon,
+		     const type_base* rcanon)
+{
+  return lcanon && rcanon ? lcanon == rcanon : equals(*lptr, *rptr, 0);
+}
+
+template<typename T>
+bool equality_helper(const T* lptr, const T* rptr)
+{
+  return equality_helper(lptr, rptr,
+			 lptr->get_naked_canonical_type(),
+			 rptr->get_naked_canonical_type());
+}
+
 /// Getter of all types types sorted by their pretty representation.
 ///
 /// @return a sorted vector of all types sorted by their pretty
@@ -12690,11 +12706,7 @@ type_decl::operator==(const decl_base& o) const
   const type_decl* other = dynamic_cast<const type_decl*>(&o);
   if (!other)
     return false;
-
-  if (get_naked_canonical_type() && other->get_naked_canonical_type())
-    return get_naked_canonical_type() == other->get_naked_canonical_type();
-
-  return equals(*this, *other, 0);
+  return equality_helper(this, other);
 }
 
 /// Return true if both types equals.
@@ -12871,11 +12883,7 @@ scope_type_decl::operator==(const decl_base& o) const
   const scope_type_decl* other = dynamic_cast<const scope_type_decl*>(&o);
   if (!other)
     return false;
-
-  if (get_naked_canonical_type() && other->get_naked_canonical_type())
-    return get_naked_canonical_type() == other->get_naked_canonical_type();
-
-  return equals(*this, *other, 0);
+  return equality_helper(this, other);
 }
 
 /// Equality operator between two scope_type_decl.
@@ -13239,11 +13247,7 @@ qualified_type_def::operator==(const decl_base& o) const
     dynamic_cast<const qualified_type_def*>(&o);
   if (!other)
     return false;
-
-  if (get_naked_canonical_type() && other->get_naked_canonical_type())
-    return get_naked_canonical_type() == other->get_naked_canonical_type();
-
-  return equals(*this, *other, 0);
+  return equality_helper(this, other);
 }
 
 /// Equality operator for qualified types.
@@ -13610,14 +13614,7 @@ pointer_type_def::operator==(const decl_base& o) const
   const pointer_type_def* other = is_pointer_type(&o);
   if (!other)
     return false;
-
-  type_base* canonical_type = get_naked_canonical_type();
-  type_base* other_canonical_type = other->get_naked_canonical_type();
-
-  if (canonical_type && other_canonical_type)
-    return canonical_type == other_canonical_type;
-
-  return equals(*this, *other, 0);
+  return equality_helper(this, other);
 }
 
 /// Return true iff both instances of pointer_type_def are equal.
@@ -13921,14 +13918,7 @@ reference_type_def::operator==(const decl_base& o) const
     dynamic_cast<const reference_type_def*>(&o);
   if (!other)
     return false;
-
-  type_base* canonical_type = get_naked_canonical_type();
-  type_base* other_canonical_type = other->get_naked_canonical_type();
-
-  if (canonical_type && other_canonical_type)
-    return canonical_type == other_canonical_type;
-
-  return equals(*this, *other, 0);
+  return equality_helper(this, other);
 }
 
 /// Equality operator of the @ref reference_type_def type.
@@ -14470,11 +14460,7 @@ array_type_def::subrange_type::operator==(const decl_base& o) const
     dynamic_cast<const subrange_type*>(&o);
   if (!other)
     return false;
-
-  if (get_naked_canonical_type() && other->get_naked_canonical_type())
-    return get_naked_canonical_type() == other->get_naked_canonical_type();
-
-  return equals(*this, *other, 0);
+  return equality_helper(this, other);
 }
 
 /// Equality operator.
@@ -14792,11 +14778,7 @@ array_type_def::operator==(const decl_base& o) const
     dynamic_cast<const array_type_def*>(&o);
   if (!other)
     return false;
-
-  if (get_naked_canonical_type() && other->get_naked_canonical_type())
-    return get_naked_canonical_type() == other->get_naked_canonical_type();
-
-  return equals(*this, *other, 0);
+  return equality_helper(this, other);
 }
 
 bool
@@ -15272,11 +15254,7 @@ enum_type_decl::operator==(const decl_base& o) const
   const enum_type_decl* op = dynamic_cast<const enum_type_decl*>(&o);
   if (!op)
     return false;
-
-  if (get_naked_canonical_type() && op->get_naked_canonical_type())
-    return get_naked_canonical_type() == op->get_naked_canonical_type();
-
-  return equals(*this, *op, 0);
+  return equality_helper(this, op);
 }
 
 /// Equality operator.
@@ -15626,11 +15604,7 @@ typedef_decl::operator==(const decl_base& o) const
   const typedef_decl* other = dynamic_cast<const typedef_decl*>(&o);
   if (!other)
     return false;
-
-  if (get_naked_canonical_type() && other->get_naked_canonical_type())
-    return get_naked_canonical_type() == other->get_naked_canonical_type();
-
-  return equals(*this, *other, 0);
+  return equality_helper(this, other);
 }
 
 /// Equality operator
@@ -16725,14 +16699,7 @@ function_type::operator==(const type_base& other) const
   const function_type* o = dynamic_cast<const function_type*>(&other);
   if (!o)
     return false;
-
-  type_base* canonical_type = get_naked_canonical_type();
-  type_base* other_canonical_type = other.get_naked_canonical_type();
-
-  if (canonical_type && other_canonical_type)
-    return canonical_type == other_canonical_type;
-
-  return equals(*this, *o, 0);
+  return equality_helper(this, o);
 }
 
 /// Return a copy of the pretty representation of the current @ref
@@ -19107,10 +19074,7 @@ class_or_union::operator==(const decl_base& other) const
     other_canonical_type =
       op->get_naked_definition_of_declaration()->get_naked_canonical_type();
 
-  if (canonical_type && other_canonical_type)
-    return canonical_type == other_canonical_type;
-
-  return equals(*this, *op, 0);
+  return equality_helper(this, op, canonical_type, other_canonical_type);
 }
 
 /// Equality operator.
@@ -20961,10 +20925,7 @@ class_decl::operator==(const decl_base& other) const
     other_canonical_type =
       op->get_naked_definition_of_declaration()->get_naked_canonical_type();
 
-  if (canonical_type && other_canonical_type)
-    return canonical_type == other_canonical_type;
-
-  return equals(*this, *op, 0);
+  return equality_helper(this, op, canonical_type, other_canonical_type);
 }
 
 /// Equality operator for class_decl.
@@ -21745,14 +21706,7 @@ union_decl::operator==(const decl_base& other) const
   const union_decl* op = dynamic_cast<const union_decl*>(&other);
   if (!op)
     return false;
-
-  type_base *canonical_type = get_naked_canonical_type(),
-    *other_canonical_type = op->get_naked_canonical_type();
-
-  if (canonical_type && other_canonical_type)
-    return canonical_type == other_canonical_type;
-
-  return equals(*this, *op, 0);
+  return equality_helper(this, op);
 }
 
 /// Equality operator for union_decl.
-- 
2.27.0.383.g050319c2ae-goog

Re: [PATCH 2/3] abg-ir.cc: Refactor operator== methods with helper

[Dodji Seketeli]

[-- Attachment #1: Type: text/plain, Size: 6193 bytes --]

Giuliano Procida <gprocida@google.com> a écrit:

> Many of the operator== definitions in this source file follow the same
> pattern:
>
> - the address of the argument is dynamic_cast to type of 'this'
> - naked canonical type pointers are compared, if both present
> - the types are compared structurally with 'equals'
>
> In a couple of cases extra work is done to fetch the canonical type
> of the definition of a declaration.
>
> This commit refactors all the common logic into a couple of templated
> helper functions.
>
> There are no behavioural changes.
>
> 	* src/abg-ir.cc (equality_helper): Add an overloaded function
> 	to perform the common actions needed for operator==. The first
> 	overload takes two extra canonical type pointer arguments
> 	while the second obtains these from the types being compared.
> 	(type_decl::operator==): Call equality_helper to perform
> 	canonical type pointer and 'equals' comparisons.
> 	(scope_type_decl::operator==): Likewise.
> 	(qualified_type_def::operator==): Likewise.
> 	(pointer_type_def::operator==): Likewise.
> 	(reference_type_def::operator==): Likewise.
> 	(array_type_def::subrange_type::operator==): Likewise.
> 	(array_type_def::operator==): Likewise.
> 	(enum_type_decl::operator==): Likewise.
> 	(typedef_decl::operator==): Likewise.
> 	(function_type::operator==): Likewise.
> 	(class_or_union::operator==): Likewise.
> 	(class_decl::operator==): Likewise.
> 	(union_decl::operator==): Likewise.
>
> Signed-off-by: Giuliano Procida <gprocida@google.com>
> ---
>  src/abg-ir.cc | 104 ++++++++++++++------------------------------------
>  1 file changed, 29 insertions(+), 75 deletions(-)
>
> diff --git a/src/abg-ir.cc b/src/abg-ir.cc
> index 41e2f00e..4b7e180d 100644
> --- a/src/abg-ir.cc
> +++ b/src/abg-ir.cc
> @@ -651,6 +651,22 @@ struct type_name_comp
>    {return operator()(type_base_sptr(l), type_base_sptr(r));}
>  }; // end struct type_name_comp
>  
> +template<typename T>
> +bool equality_helper(const T* lptr, const T* rptr,
> +		     const type_base* lcanon,
> +		     const type_base* rcanon)
> +{
> +  return lcanon && rcanon ? lcanon == rcanon : equals(*lptr, *rptr, 0);
> +}
> +
> +template<typename T>
> +bool equality_helper(const T* lptr, const T* rptr)
> +{

As done already throughout the code, the return type of functions should
be on their own line, please.

The name of the function should start on its own line as well.  This
makes searching for the definition of the function easy by typing a
regular expression like "^equality_helper".

Also, to make the code somewhat self documented, I try to have all
function names contain a "verb".  That forces us to give a name that
tells what the function /does/. equality_helper is not quite useful in
that respect.  Essentially, what the function does is that it tries to
compare the types canonically (i.e, using their canonical types) if
possible.  Otherwise, it falls back to structural comparison.

So I'd rather call this something like try_canonical_compare.

Last but not least, all function definitions should come documented,
please.

I have adjusted this accordingly and a patch that you'll find at the end
of this message.

> +  return equality_helper(lptr, rptr,
> +			 lptr->get_naked_canonical_type(),
> +			 rptr->get_naked_canonical_type());
> +}
> +
>  /// Getter of all types types sorted by their pretty representation.
>  ///
>  /// @return a sorted vector of all types sorted by their pretty
> @@ -12690,11 +12706,7 @@ type_decl::operator==(const decl_base& o) const
>    const type_decl* other = dynamic_cast<const type_decl*>(&o);
>    if (!other)
>      return false;
> -
> -  if (get_naked_canonical_type() && other->get_naked_canonical_type())

Something to keep in mind is that there are times when we need to debug
some possibly tricky issues related to type comparison.  Especially, we
want to see why two types are (for instance) deemed different by
libabigail.  That is, we want to know why the types have different
canonical types.

A simple way to know this is to step in the debugger at this point and
then make the debugger jump to the "return equals()" line below.  That
way, we force the code to take structural equality path in the
debugger.  We can thus step and see why the structural equality code
decided that the two types are different (and thus that their canonical
types are different).

Yours changes in equality_helper are making this important debubbing
much more difficult.  So I have taken that into account in how I
adjusted the try_canonical_compare function.

> -    return get_naked_canonical_type() == other->get_naked_canonical_type();
> -
> -  return equals(*this, *other, 0);
> +  return equality_helper(this, other);
>  }

[...]


>  /// Return a copy of the pretty representation of the current @ref
> @@ -19107,10 +19074,7 @@ class_or_union::operator==(const decl_base& other) const
>      other_canonical_type =
>        op->get_naked_definition_of_declaration()->get_naked_canonical_type();
>  
> -  if (canonical_type && other_canonical_type)
> -    return canonical_type == other_canonical_type;
> -
> -  return equals(*this, *op, 0);
> +  return equality_helper(this, op, canonical_type, other_canonical_type);

By massaging the code above this line, it's possible to call the second
overload of equality_helper (just like what all the other spots are
doing) and thus do away with the first overload of equality_helper.  My
amended patch does this.

>  }
>  
>  /// Equality operator.
> @@ -20961,10 +20925,7 @@ class_decl::operator==(const decl_base& other) const
>      other_canonical_type =
>        op->get_naked_definition_of_declaration()->get_naked_canonical_type();
>  
> -  if (canonical_type && other_canonical_type)
> -    return canonical_type == other_canonical_type;
> -
> -  return equals(*this, *op, 0);
> +  return equality_helper(this, op, canonical_type, other_canonical_type);

Likewise.

>  }

[...]

Here is the amended patch that I'd be for applying.  I have also
adjusted its commit log.  Thanks.


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From cd06d651b8fca32a8385ff152bae972763e95b26 Mon Sep 17 00:00:00 2001
From: Giuliano Procida <gprocida@google.com>
Date: Wed, 8 Jul 2020 10:53:14 +0100
Subject: [PATCH] abg-ir.cc: Refactor operator== methods with helper function

Many of the operator== definitions in this source file follow the same
pattern:

- First, canonical comparison is attempted if canonical types are
  present.
- Otherwise, the comparison is performed structurally using the
  'equals' function.

This commit refactors the common logic into a templated helper
function named "try_canonical_compare".

There are no behavioural changes.

	* src/abg-ir.cc (try_canonical_compare): New template function.
	(type_decl::operator==): Use it here.
	(scope_type_decl::operator==): Likewise.
	(qualified_type_def::operator==): Likewise.
	(pointer_type_def::operator==): Likewise.
	(reference_type_def::operator==): Likewise.
	(array_type_def::subrange_type::operator==): Likewise.
	(array_type_def::operator==): Likewise.
	(enum_type_decl::operator==): Likewise.
	(typedef_decl::operator==): Likewise.
	(function_type::operator==): Likewise.
	(class_or_union::operator==): Likewise.
	(class_decl::operator==): Likewise.
	(union_decl::operator==): Likewise.

Signed-off-by: Giuliano Procida <gprocida@google.com>
Signed-off-by: Dodji Seketeli <dodji@redhat.com>
---
 src/abg-ir.cc | 166 +++++++++++++++++++++-------------------------------------
 1 file changed, 59 insertions(+), 107 deletions(-)

diff --git a/src/abg-ir.cc b/src/abg-ir.cc
index f6eb285..ac837da 100644
--- a/src/abg-ir.cc
+++ b/src/abg-ir.cc
@@ -651,6 +651,25 @@ struct type_name_comp
   {return operator()(type_base_sptr(l), type_base_sptr(r));}
 }; // end struct type_name_comp
 
+/// Compare two types by comparing their canonical types if present.
+///
+/// If the canonical types are not present (because the types have not
+/// yet been canonicalized, for instance) then the types are compared
+/// structurally.
+///
+/// @param l the first type to take into account in the comparison.
+///
+/// @param r the second type to take into account in the comparison.
+template<typename T>
+bool
+try_canonical_compare(const T *l, const T *r)
+{
+  if (const type_base *lc = l->get_naked_canonical_type())
+    if (const type_base *rc = r->get_naked_canonical_type())
+      return lc == rc;
+  return equals(*l, *r, 0);
+}
+
 /// Getter of all types types sorted by their pretty representation.
 ///
 /// @return a sorted vector of all types sorted by their pretty
@@ -12904,11 +12923,7 @@ type_decl::operator==(const decl_base& o) const
   const type_decl* other = dynamic_cast<const type_decl*>(&o);
   if (!other)
     return false;
-
-  if (get_naked_canonical_type() && other->get_naked_canonical_type())
-    return get_naked_canonical_type() == other->get_naked_canonical_type();
-
-  return equals(*this, *other, 0);
+  return try_canonical_compare(this, other);
 }
 
 /// Return true if both types equals.
@@ -13085,11 +13100,7 @@ scope_type_decl::operator==(const decl_base& o) const
   const scope_type_decl* other = dynamic_cast<const scope_type_decl*>(&o);
   if (!other)
     return false;
-
-  if (get_naked_canonical_type() && other->get_naked_canonical_type())
-    return get_naked_canonical_type() == other->get_naked_canonical_type();
-
-  return equals(*this, *other, 0);
+  return try_canonical_compare(this, other);
 }
 
 /// Equality operator between two scope_type_decl.
@@ -13453,11 +13464,7 @@ qualified_type_def::operator==(const decl_base& o) const
     dynamic_cast<const qualified_type_def*>(&o);
   if (!other)
     return false;
-
-  if (get_naked_canonical_type() && other->get_naked_canonical_type())
-    return get_naked_canonical_type() == other->get_naked_canonical_type();
-
-  return equals(*this, *other, 0);
+  return try_canonical_compare(this, other);
 }
 
 /// Equality operator for qualified types.
@@ -13824,14 +13831,7 @@ pointer_type_def::operator==(const decl_base& o) const
   const pointer_type_def* other = is_pointer_type(&o);
   if (!other)
     return false;
-
-  type_base* canonical_type = get_naked_canonical_type();
-  type_base* other_canonical_type = other->get_naked_canonical_type();
-
-  if (canonical_type && other_canonical_type)
-    return canonical_type == other_canonical_type;
-
-  return equals(*this, *other, 0);
+  return try_canonical_compare(this, other);
 }
 
 /// Return true iff both instances of pointer_type_def are equal.
@@ -14135,14 +14135,7 @@ reference_type_def::operator==(const decl_base& o) const
     dynamic_cast<const reference_type_def*>(&o);
   if (!other)
     return false;
-
-  type_base* canonical_type = get_naked_canonical_type();
-  type_base* other_canonical_type = other->get_naked_canonical_type();
-
-  if (canonical_type && other_canonical_type)
-    return canonical_type == other_canonical_type;
-
-  return equals(*this, *other, 0);
+  return try_canonical_compare(this, other);
 }
 
 /// Equality operator of the @ref reference_type_def type.
@@ -14684,11 +14677,7 @@ array_type_def::subrange_type::operator==(const decl_base& o) const
     dynamic_cast<const subrange_type*>(&o);
   if (!other)
     return false;
-
-  if (get_naked_canonical_type() && other->get_naked_canonical_type())
-    return get_naked_canonical_type() == other->get_naked_canonical_type();
-
-  return equals(*this, *other, 0);
+  return try_canonical_compare(this, other);
 }
 
 /// Equality operator.
@@ -15006,11 +14995,7 @@ array_type_def::operator==(const decl_base& o) const
     dynamic_cast<const array_type_def*>(&o);
   if (!other)
     return false;
-
-  if (get_naked_canonical_type() && other->get_naked_canonical_type())
-    return get_naked_canonical_type() == other->get_naked_canonical_type();
-
-  return equals(*this, *other, 0);
+  return try_canonical_compare(this, other);
 }
 
 bool
@@ -15485,11 +15470,7 @@ enum_type_decl::operator==(const decl_base& o) const
   const enum_type_decl* op = dynamic_cast<const enum_type_decl*>(&o);
   if (!op)
     return false;
-
-  if (get_naked_canonical_type() && op->get_naked_canonical_type())
-    return get_naked_canonical_type() == op->get_naked_canonical_type();
-
-  return equals(*this, *op, 0);
+  return try_canonical_compare(this, op);
 }
 
 /// Equality operator.
@@ -15839,11 +15820,7 @@ typedef_decl::operator==(const decl_base& o) const
   const typedef_decl* other = dynamic_cast<const typedef_decl*>(&o);
   if (!other)
     return false;
-
-  if (get_naked_canonical_type() && other->get_naked_canonical_type())
-    return get_naked_canonical_type() == other->get_naked_canonical_type();
-
-  return equals(*this, *other, 0);
+  return try_canonical_compare(this, other);
 }
 
 /// Equality operator
@@ -16934,14 +16911,7 @@ function_type::operator==(const type_base& other) const
   const function_type* o = dynamic_cast<const function_type*>(&other);
   if (!o)
     return false;
-
-  type_base* canonical_type = get_naked_canonical_type();
-  type_base* other_canonical_type = other.get_naked_canonical_type();
-
-  if (canonical_type && other_canonical_type)
-    return canonical_type == other_canonical_type;
-
-  return equals(*this, *o, 0);
+  return try_canonical_compare(this, o);
 }
 
 /// Return a copy of the pretty representation of the current @ref
@@ -19201,29 +19171,22 @@ class_or_union::operator==(const decl_base& other) const
   if (!op)
     return false;
 
-  type_base *canonical_type = get_naked_canonical_type(),
-    *other_canonical_type = op->get_naked_canonical_type();
-
-  // If this is a declaration only class with no canonical class, use
-  // the canonical type of the definition, if any.
-  if (!canonical_type
-      && get_is_declaration_only()
-      && get_naked_definition_of_declaration())
-    canonical_type = is_class_or_union_type
-      (get_naked_definition_of_declaration())->get_naked_canonical_type();
+  // If this is a decl-only type (and thus with no canonical type),
+  // use the canonical type of the definition, if any.
+  const class_or_union *l = 0;
+  if (get_is_declaration_only())
+    l = dynamic_cast<const class_or_union*>(get_naked_definition_of_declaration());
+  if (l == 0)
+    l = this;
 
   // Likewise for the other class.
-  if (!other_canonical_type
-      && op->get_is_declaration_only()
-      && op->get_naked_definition_of_declaration())
-    other_canonical_type =
-      is_class_or_union_type
-      (op->get_naked_definition_of_declaration())->get_naked_canonical_type();
+  const class_or_union *r = 0;
+  if (op->get_is_declaration_only())
+    r = dynamic_cast<const class_or_union*>(op->get_naked_definition_of_declaration());
+  if (r == 0)
+    r = op;
 
-  if (canonical_type && other_canonical_type)
-    return canonical_type == other_canonical_type;
-
-  return equals(*this, *op, 0);
+  return try_canonical_compare(l, r);
 }
 
 /// Equality operator.
@@ -21032,30 +20995,26 @@ class_decl::operator==(const decl_base& other) const
   if (!op)
     return false;
 
-  type_base *canonical_type = get_naked_canonical_type(),
-    *other_canonical_type = op->get_naked_canonical_type();
+  // If this is a decl-only type (and thus with no canonical type),
+  // use the canonical type of the definition, if any.
+  const class_decl *l = 0;
+  if (get_is_declaration_only())
+    l = dynamic_cast<const class_decl*>(get_naked_definition_of_declaration());
+  if (l == 0)
+    l = this;
 
-  // If this is a declaration only class with no canonical class, use
-  // the canonical type of the definition, if any.
-  if (!canonical_type
-      && get_is_declaration_only()
-      && get_naked_definition_of_declaration())
-    canonical_type =
-      is_class_type
-      (get_naked_definition_of_declaration())->get_naked_canonical_type();
+  ABG_ASSERT(l);
 
-  // Likewise for the other class.
-  if (!other_canonical_type
-      && op->get_is_declaration_only()
-      && op->get_naked_definition_of_declaration())
-    other_canonical_type =
-      is_class_type
-      (op->get_naked_definition_of_declaration())->get_naked_canonical_type();
+  // Likewise for the other type.
+  const class_decl *r = 0;
+  if (op->get_is_declaration_only())
+    r = dynamic_cast<const class_decl*>(op->get_naked_definition_of_declaration());
+  if (r == 0)
+    r = op;
 
-  if (canonical_type && other_canonical_type)
-    return canonical_type == other_canonical_type;
+  ABG_ASSERT(r);
 
-  return equals(*this, *op, 0);
+  return try_canonical_compare(l, r);
 }
 
 /// Equality operator for class_decl.
@@ -21836,14 +21795,7 @@ union_decl::operator==(const decl_base& other) const
   const union_decl* op = dynamic_cast<const union_decl*>(&other);
   if (!op)
     return false;
-
-  type_base *canonical_type = get_naked_canonical_type(),
-    *other_canonical_type = op->get_naked_canonical_type();
-
-  if (canonical_type && other_canonical_type)
-    return canonical_type == other_canonical_type;
-
-  return equals(*this, *op, 0);
+  return try_canonical_compare(this, op);
 }
 
 /// Equality operator for union_decl.
-- 
1.8.3.1


[-- Attachment #3: Type: text/plain, Size: 13 bytes --]


-- 
		Dodji

Re: [PATCH 2/3] abg-ir.cc: Refactor operator== methods with helper

[Giuliano Procida]

Hi.

On Mon, 27 Jul 2020 at 08:56, Dodji Seketeli <dodji@seketeli.org> wrote:
>
> Giuliano Procida <gprocida@google.com> a écrit:
>
> > Many of the operator== definitions in this source file follow the same
> > pattern:
> >
> > - the address of the argument is dynamic_cast to type of 'this'
> > - naked canonical type pointers are compared, if both present
> > - the types are compared structurally with 'equals'
> >
> > In a couple of cases extra work is done to fetch the canonical type
> > of the definition of a declaration.
> >
> > This commit refactors all the common logic into a couple of templated
> > helper functions.
> >
> > There are no behavioural changes.
> >
> >       * src/abg-ir.cc (equality_helper): Add an overloaded function
> >       to perform the common actions needed for operator==. The first
> >       overload takes two extra canonical type pointer arguments
> >       while the second obtains these from the types being compared.
> >       (type_decl::operator==): Call equality_helper to perform
> >       canonical type pointer and 'equals' comparisons.
> >       (scope_type_decl::operator==): Likewise.
> >       (qualified_type_def::operator==): Likewise.
> >       (pointer_type_def::operator==): Likewise.
> >       (reference_type_def::operator==): Likewise.
> >       (array_type_def::subrange_type::operator==): Likewise.
> >       (array_type_def::operator==): Likewise.
> >       (enum_type_decl::operator==): Likewise.
> >       (typedef_decl::operator==): Likewise.
> >       (function_type::operator==): Likewise.
> >       (class_or_union::operator==): Likewise.
> >       (class_decl::operator==): Likewise.
> >       (union_decl::operator==): Likewise.
> >
> > Signed-off-by: Giuliano Procida <gprocida@google.com>
> > ---
> >  src/abg-ir.cc | 104 ++++++++++++++------------------------------------
> >  1 file changed, 29 insertions(+), 75 deletions(-)
> >
> > diff --git a/src/abg-ir.cc b/src/abg-ir.cc
> > index 41e2f00e..4b7e180d 100644
> > --- a/src/abg-ir.cc
> > +++ b/src/abg-ir.cc
> > @@ -651,6 +651,22 @@ struct type_name_comp
> >    {return operator()(type_base_sptr(l), type_base_sptr(r));}
> >  }; // end struct type_name_comp
> >
> > +template<typename T>
> > +bool equality_helper(const T* lptr, const T* rptr,
> > +                  const type_base* lcanon,
> > +                  const type_base* rcanon)
> > +{
> > +  return lcanon && rcanon ? lcanon == rcanon : equals(*lptr, *rptr, 0);
> > +}
> > +
> > +template<typename T>
> > +bool equality_helper(const T* lptr, const T* rptr)
> > +{
>
> As done already throughout the code, the return type of functions should
> be on their own line, please.

Of course. Sorry.

> The name of the function should start on its own line as well.  This
> makes searching for the definition of the function easy by typing a
> regular expression like "^equality_helper".
>
> Also, to make the code somewhat self documented, I try to have all
> function names contain a "verb".  That forces us to give a name that
> tells what the function /does/. equality_helper is not quite useful in
> that respect.  Essentially, what the function does is that it tries to
> compare the types canonically (i.e, using their canonical types) if
> possible.  Otherwise, it falls back to structural comparison.
>
> So I'd rather call this something like try_canonical_compare.

Yes, the name wasn't ideal.

> Last but not least, all function definitions should come documented,
> please.

Oops.

> I have adjusted this accordingly and a patch that you'll find at the end
> of this message.
>
> > +  return equality_helper(lptr, rptr,
> > +                      lptr->get_naked_canonical_type(),
> > +                      rptr->get_naked_canonical_type());
> > +}
> > +
> >  /// Getter of all types types sorted by their pretty representation.
> >  ///
> >  /// @return a sorted vector of all types sorted by their pretty
> > @@ -12690,11 +12706,7 @@ type_decl::operator==(const decl_base& o) const
> >    const type_decl* other = dynamic_cast<const type_decl*>(&o);
> >    if (!other)
> >      return false;
> > -
> > -  if (get_naked_canonical_type() && other->get_naked_canonical_type())
>
> Something to keep in mind is that there are times when we need to debug
> some possibly tricky issues related to type comparison.  Especially, we
> want to see why two types are (for instance) deemed different by
> libabigail.  That is, we want to know why the types have different
> canonical types.
>
> A simple way to know this is to step in the debugger at this point and
> then make the debugger jump to the "return equals()" line below.  That
> way, we force the code to take structural equality path in the
> debugger.  We can thus step and see why the structural equality code
> decided that the two types are different (and thus that their canonical
> types are different).
>
> Yours changes in equality_helper are making this important debubbing
> much more difficult.  So I have taken that into account in how I
> adjusted the try_canonical_compare function.

That's a shame. One motivation was to make it easier to perform bulk
checks against canonical and structural equality logic. I see your
tweaks to a couple of the functions enable a uniform calling path
into the helper, allowing the removal of the second overload.

> > -    return get_naked_canonical_type() == other->get_naked_canonical_type();
> > -
> > -  return equals(*this, *other, 0);
> > +  return equality_helper(this, other);
> >  }
>
> [...]
>
>
> >  /// Return a copy of the pretty representation of the current @ref
> > @@ -19107,10 +19074,7 @@ class_or_union::operator==(const decl_base& other) const
> >      other_canonical_type =
> >        op->get_naked_definition_of_declaration()->get_naked_canonical_type();
> >
> > -  if (canonical_type && other_canonical_type)
> > -    return canonical_type == other_canonical_type;
> > -
> > -  return equals(*this, *op, 0);
> > +  return equality_helper(this, op, canonical_type, other_canonical_type);
>
> By massaging the code above this line, it's possible to call the second
> overload of equality_helper (just like what all the other spots are
> doing) and thus do away with the first overload of equality_helper.  My
> amended patch does this.
>
> >  }
> >
> >  /// Equality operator.
> > @@ -20961,10 +20925,7 @@ class_decl::operator==(const decl_base& other) const
> >      other_canonical_type =
> >        op->get_naked_definition_of_declaration()->get_naked_canonical_type();
> >
> > -  if (canonical_type && other_canonical_type)
> > -    return canonical_type == other_canonical_type;
> > -
> > -  return equals(*this, *op, 0);
> > +  return equality_helper(this, op, canonical_type, other_canonical_type);
>
> Likewise.
>
> >  }
>
> [...]
>
> Here is the amended patch that I'd be for applying.  I have also
> adjusted its commit log.  Thanks.
>

It looks good to me.

Giuliano.

>
> --
>                 Dodji

Re: [PATCH 2/3] abg-ir.cc: Refactor operator== methods with helper

[Dodji Seketeli]

Giuliano Procida <gprocida@google.com> a écrit:

[...]

> It looks good to me.

Applied to master, thanks!

-- 
		Dodji

[PATCH 3/3] Add some type equality paranoia.

[Giuliano Procida]

This commit is an attempt to answer the question "how do canonical
types relate to type equality?" and in particular "are they just an
optimisation?". It adds some instrumentation to the equality_helper
methods.

- they take an extra line (__LINE__) argument
- both canonical type pointer and plain comparisons are done
- comparisons are skipped if the pointers are identical
- in-progress comparisons are recorded to avoid infinite recursion
- discrepancies are logged

The commit also adds some comments to reflect behaviour seen in
practice with libabigail's test suite.

Note that this is not quite cross-checking canonical pointer
comparison with deep equality as the (recursive) equality tests are
themselves influenced by canonical pointer comparisons in the
direction of considering more things to be equal.

Note that thread-local storage is used to avoid corruption of the
comparison stack. This is not portable to older compilers in its
current form.

While the behaviour should be the same, the code runs much more slowly
and there can be considerable logging to stderr depending on what you
choose to log.

Signed-off-by: Giuliano Procida <gprocida@google.com>
---
 src/abg-ir.cc | 111 ++++++++++++++++++++++++++++++++++++++++++--------
 1 file changed, 94 insertions(+), 17 deletions(-)

diff --git a/src/abg-ir.cc b/src/abg-ir.cc
index 4b7e180d..e797a341 100644
--- a/src/abg-ir.cc
+++ b/src/abg-ir.cc
@@ -651,18 +651,81 @@ struct type_name_comp
   {return operator()(type_base_sptr(l), type_base_sptr(r));}
 }; // end struct type_name_comp
 
+class hold
+{
+ public:
+  hold(const void* l, const void* r)
+    : p_(std::make_pair(l, r))
+  {
+    st_.push_back(p_);
+  }
+  ~hold()
+  {
+    ABG_ASSERT(st_.size());
+    ABG_ASSERT(st_.back() == p_);
+    st_.pop_back();
+  }
+  static bool has(const void* l, const void* r)
+  {
+    return find(st_.begin(), st_.end(), std::make_pair(l, r)) != st_.end();
+  }
+ private:
+  const std::pair<const void *, const void *> p_;
+  thread_local static std::vector<std::pair<const void*, const void*>> st_;
+};
+
+thread_local std::vector<std::pair<const void*, const void*>> hold::st_;
+
+const bool debug_equality = true;
+
 template<typename T>
-bool equality_helper(const T* lptr, const T* rptr,
+bool equality_helper(size_t line, const T* lptr, const T* rptr,
 		     const type_base* lcanon,
 		     const type_base* rcanon)
 {
-  return lcanon && rcanon ? lcanon == rcanon : equals(*lptr, *rptr, 0);
+  if (debug_equality)
+    {
+      // Short cut equality with identical pointers to avoid wasteful deep
+      // comparisons.
+      if (lptr == rptr)
+	return true;
+      // Record outcome of canonical type pointer comparison.
+      char c = lcanon ? rcanon ? lcanon == rcanon ? '1' : '0' : 'L' : rcanon ? 'R' : 'X';
+      // If we are already holding this pair of type_base pointers we should
+      // assume they are equal in recursive calls.
+      bool held = hold::has(lptr, rptr);
+      bool eq;
+      if (held)
+	eq = true;
+      else
+	{
+	  hold it(static_cast<const void *>(lptr),
+		  static_cast<const void *>(rptr));
+	  eq = equals(*lptr, *rptr, 0);
+	}
+      // Record outcome of plain comparison.
+      char p = held ? 'H' : eq ? '1' : '0';
+      if (c + p == '0' + '1')
+	{
+	  // Avoid tearing the output.
+	  std::ostringstream os;
+	  os << line << " canon=" << c << " plain=" << p
+	     << " '" << lptr->get_cached_pretty_representation(true)
+	     << "' '" << rptr->get_cached_pretty_representation(true) << "'\n";
+	  std::cerr << os.str();
+	}
+      return lcanon && rcanon ? lcanon == rcanon : eq;
+    }
+  else
+    {
+      return lcanon && rcanon ? lcanon == rcanon : equals(*lptr, *rptr, 0);
+    }
 }
 
 template<typename T>
-bool equality_helper(const T* lptr, const T* rptr)
+bool equality_helper(size_t line, const T* lptr, const T* rptr)
 {
-  return equality_helper(lptr, rptr,
+  return equality_helper(line, lptr, rptr,
 			 lptr->get_naked_canonical_type(),
 			 rptr->get_naked_canonical_type());
 }
@@ -12706,7 +12769,7 @@ type_decl::operator==(const decl_base& o) const
   const type_decl* other = dynamic_cast<const type_decl*>(&o);
   if (!other)
     return false;
-  return equality_helper(this, other);
+  return equality_helper(__LINE__, this, other);
 }
 
 /// Return true if both types equals.
@@ -12883,7 +12946,7 @@ scope_type_decl::operator==(const decl_base& o) const
   const scope_type_decl* other = dynamic_cast<const scope_type_decl*>(&o);
   if (!other)
     return false;
-  return equality_helper(this, other);
+  return equality_helper(__LINE__, this, other);
 }
 
 /// Equality operator between two scope_type_decl.
@@ -13247,7 +13310,7 @@ qualified_type_def::operator==(const decl_base& o) const
     dynamic_cast<const qualified_type_def*>(&o);
   if (!other)
     return false;
-  return equality_helper(this, other);
+  return equality_helper(__LINE__, this, other);
 }
 
 /// Equality operator for qualified types.
@@ -13614,7 +13677,8 @@ pointer_type_def::operator==(const decl_base& o) const
   const pointer_type_def* other = is_pointer_type(&o);
   if (!other)
     return false;
-  return equality_helper(this, other);
+  // Sometimes canonically distinct but compare as equal.
+  return equality_helper(__LINE__, this, other);
 }
 
 /// Return true iff both instances of pointer_type_def are equal.
@@ -13918,7 +13982,7 @@ reference_type_def::operator==(const decl_base& o) const
     dynamic_cast<const reference_type_def*>(&o);
   if (!other)
     return false;
-  return equality_helper(this, other);
+  return equality_helper(__LINE__, this, other);
 }
 
 /// Equality operator of the @ref reference_type_def type.
@@ -14460,7 +14524,7 @@ array_type_def::subrange_type::operator==(const decl_base& o) const
     dynamic_cast<const subrange_type*>(&o);
   if (!other)
     return false;
-  return equality_helper(this, other);
+  return equality_helper(__LINE__, this, other);
 }
 
 /// Equality operator.
@@ -14778,7 +14842,8 @@ array_type_def::operator==(const decl_base& o) const
     dynamic_cast<const array_type_def*>(&o);
   if (!other)
     return false;
-  return equality_helper(this, other);
+  // Sometimes canonically distinct but compare as equal.
+  return equality_helper(__LINE__, this, other);
 }
 
 bool
@@ -15254,7 +15319,8 @@ enum_type_decl::operator==(const decl_base& o) const
   const enum_type_decl* op = dynamic_cast<const enum_type_decl*>(&o);
   if (!op)
     return false;
-  return equality_helper(this, op);
+  // Sometimes canonically distinct but compare as equal.
+  return equality_helper(__LINE__, this, op);
 }
 
 /// Equality operator.
@@ -15604,7 +15670,9 @@ typedef_decl::operator==(const decl_base& o) const
   const typedef_decl* other = dynamic_cast<const typedef_decl*>(&o);
   if (!other)
     return false;
-  return equality_helper(this, other);
+  // Sometimes canonically distinct but compare as equal.
+  // Sometimes canonically equal but compare as distinct.
+  return equality_helper(__LINE__, this, other);
 }
 
 /// Equality operator
@@ -16699,7 +16767,9 @@ function_type::operator==(const type_base& other) const
   const function_type* o = dynamic_cast<const function_type*>(&other);
   if (!o)
     return false;
-  return equality_helper(this, o);
+  // Sometimes canonically distinct but compare as equal.
+  // Sometimes canonically equal but compare as distinct.
+  return equality_helper(__LINE__, this, o);
 }
 
 /// Return a copy of the pretty representation of the current @ref
@@ -19074,7 +19144,9 @@ class_or_union::operator==(const decl_base& other) const
     other_canonical_type =
       op->get_naked_definition_of_declaration()->get_naked_canonical_type();
 
-  return equality_helper(this, op, canonical_type, other_canonical_type);
+  // Or should this just be definition_of_declaration equality?
+  // Sometimes canonically equal but compare as distinct.
+  return equality_helper(__LINE__, this, op, canonical_type, other_canonical_type);
 }
 
 /// Equality operator.
@@ -20925,7 +20997,10 @@ class_decl::operator==(const decl_base& other) const
     other_canonical_type =
       op->get_naked_definition_of_declaration()->get_naked_canonical_type();
 
-  return equality_helper(this, op, canonical_type, other_canonical_type);
+  // Or should this just be definition_of_declaration equality?
+  // Sometimes canonically distinct but compare as equal.
+  // Sometimes canonically equal but compare as distinct.
+  return equality_helper(__LINE__, this, op, canonical_type, other_canonical_type);
 }
 
 /// Equality operator for class_decl.
@@ -21706,7 +21781,9 @@ union_decl::operator==(const decl_base& other) const
   const union_decl* op = dynamic_cast<const union_decl*>(&other);
   if (!op)
     return false;
-  return equality_helper(this, op);
+  // Sometimes canonically distinct but compare as equal.
+  // Sometimes canonically equal but compare as distinct.
+  return equality_helper(__LINE__, this, op);
 }
 
 /// Equality operator for union_decl.
-- 
2.27.0.383.g050319c2ae-goog

Re: [PATCH 0/3] Type equality refactor and instrumentation

[Dodji Seketeli]

Hello Giuliano,

Giuliano Procida <gprocida@google.com> a écrit:

> Hi Dodji.
>
> This series refactors various operator== methods making their common
> functionality evident.
>
> The first patch is just a prelude to make the second smaller.
>
> The second patch does the refactoring. I'm not attached to the name
> 'equality_helper'.

Thank you for working on this.

I have looked into these first two patches and they look good to me in general.
I'll post their individual review as usual, shortly.

> The third patch is not intended for direct inclusion in libabigail but
> builds on the refactoring to investigate how equality and canonical
> types work in practice. It identifies some potential discrepancies,
> but they may be entirely expected.

In it's current form, I'd rather hold the inclusion of this one for now.
It's super intrusive, clutters the code quite a bit and I am not really
sure about its practical use at the moment.

> In general, it can be risky to define operator== in a way where
> reflexivity, symmetry and transitivity do not obviously hold or can be
> sensitive to small code changes or in way where equality, say for
> class_decl_sptr, can be affected by something like canonicalisation.
> More instrumentation could be added to check behaviour.

The comparison code is tricky.  The number one reason for this is that
it has to be fast.  So yes, it's risky.

One category of tests that are "simple" to perform and in practise are
quite powerful to detect and debug potential comparison issues are
"identity tests".  That is, comparing a binary against itself and
requiring that the result be the empty set.  This is why the option
"--abidiff" was added to abidw.

So I tend to favor schemes that keep the code the less cluttered and the
most "debuggable" as possible, as opposed to adding a lot of
instrumentation.  I guess some balance has to found there.

Cheers,

-- 
		Dodji

Re: [PATCH 0/3] Type equality refactor and instrumentation

[Giuliano Procida]

Hi Dodji.

On Mon, 27 Jul 2020 at 08:33, Dodji Seketeli <dodji@seketeli.org> wrote:
>
> Hello Giuliano,
>
> Giuliano Procida <gprocida@google.com> a écrit:
>
> > Hi Dodji.
> >
> > This series refactors various operator== methods making their common
> > functionality evident.
> >
> > The first patch is just a prelude to make the second smaller.
> >
> > The second patch does the refactoring. I'm not attached to the name
> > 'equality_helper'.
>
> Thank you for working on this.
>
> I have looked into these first two patches and they look good to me in general.
> I'll post their individual review as usual, shortly.
>
> > The third patch is not intended for direct inclusion in libabigail but
> > builds on the refactoring to investigate how equality and canonical
> > types work in practice. It identifies some potential discrepancies,
> > but they may be entirely expected.
>
> In it's current form, I'd rather hold the inclusion of this one for now.
> It's super intrusive, clutters the code quite a bit and I am not really
> sure about its practical use at the moment.

The code is absolutely not intended to be committed to master.
On top of the obvious impact on the code, tests were still running
after 60h with this turned on!

> > In general, it can be risky to define operator== in a way where
> > reflexivity, symmetry and transitivity do not obviously hold or can be
> > sensitive to small code changes or in way where equality, say for
> > class_decl_sptr, can be affected by something like canonicalisation.
> > More instrumentation could be added to check behaviour.
>
> The comparison code is tricky.  The number one reason for this is that
> it has to be fast.  So yes, it's risky.
>
> One category of tests that are "simple" to perform and in practise are
> quite powerful to detect and debug potential comparison issues are
> "identity tests".  That is, comparing a binary against itself and
> requiring that the result be the empty set.  This is why the option
> "--abidiff" was added to abidw.
>
> So I tend to favor schemes that keep the code the less cluttered and the
> most "debuggable" as possible, as opposed to adding a lot of
> instrumentation.  I guess some balance has to found there.

This was intended for one-off (or occasional) instrumentation. Running with
the instrumentation, I noticed various places where canonical and structural
comparison differ. If the comparisons are happening during canonicalisation
then things may be temporarily off. Or I may have a bug in the instrumentation.

At any rate, the commit adds code comments showing where certain discrepancies
were noted during "make check". For example, function_type nodes sometimes
compare as canonically equal but not "structurally" and vice versa.
"Structurally"
is not really fully structurally as recursive calls attempt canonical comparison
first.

If there are any you think are of concern, let me know and I can investigate
further and open a bug with findings.

I've reworked my series to account for your version of the second commit.
The instrumentation commit can be found amongst the changes in
https://github.com/myxoid/libabigail/commits/type-equality-paranoia

Regards,
Giuliano.

> Cheers,
>
> --
>                 Dodji