Patchwork Use an std::vector for inline_states

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Submitter Simon Marchi
Date April 7, 2018, 11:21 p.m.
Message ID <da7e881e-9178-fa33-16f3-0e0cf7da76d2@polymtl.ca>
Download mbox | patch
Permalink /patch/26642/
State New
Headers show

Comments

Simon Marchi - April 7, 2018, 11:21 p.m.
On 2018-04-07 03:28 PM, Pedro Alves wrote:
> On 04/07/2018 03:42 PM, Simon Marchi wrote:
> 
>>  /* Locate saved inlined frame state for PTID, if it exists
>>     and is valid.  */
>> @@ -66,43 +70,29 @@ static VEC(inline_state_s) *inline_states;
>>  static struct inline_state *
>>  find_inline_frame_state (ptid_t ptid)
>>  {
> 
>> -	  if (current_pc != state->saved_pc)
>> -	    {
>> -	      /* PC has changed - this context is invalid.  Use the
>> -		 default behavior.  */
>> -	      VEC_unordered_remove (inline_state_s, inline_states, ix);
>> -	      return NULL;
> 
> ...
> 
>> -  state = VEC_safe_push (inline_state_s, inline_states, NULL);
>> -  memset (state, 0, sizeof (*state));
>> -  state->ptid = ptid;
>> +      inline_states.erase (state_it);
> 
> The patch looks good, though it made me realize that when we're
> replacing VEC_unordered_remove with std::vector::erase, we're introducing
> a pessimization, which makes me ponder about having an utility/replacement
> for VEC_unordered_remove that works with std::vector and alikes.
> I.e., a function that removes an element from a vector simply by moving
> the last element to the now-vacant position.  That's more efficient
> than erase, because it avoids having to copy/move the remaining
> elements, making it O(1).
> 
> Something like:
> 
>  template<typename Vector>
>  void
>  unordered_erase (Vector &v, typename Vector::const_iterator pos)
>  {
>      *pos = std::move (v.back ());
>      v.pop_back ();
>  }
> 
> Thanks,
> Pedro Alves
> 

How about this (modulo the fact that unordered_remove should be renamed to
unordered_erase to align with the STL)?


From a7c9bbe86dd2e75c826e0ac0d10db97de7b802d0 Mon Sep 17 00:00:00 2001
From: Simon Marchi <simon.marchi@polymtl.ca>
Date: Sat, 7 Apr 2018 10:42:05 -0400
Subject: [PATCH] Use an std::vector for inline_states

This patch replaces VEC(inline_state) with std::vector<inline_state> and
adjusts the code that uses it.

gdb/ChangeLog:

	* common/gdb_vecs.h (unordered_remove): Add overload that takes
	an iterator.
	* inline-frame.c: Include <algorithm>.
	(struct inline_state): Add constructor.
	(inline_state_s): Remove.
	(DEF_VEC_O(inline_state_s)): Remove.
	(inline_states): Change type to std::vector.
	(find_inline_frame_state): Adjust to std::vector.
	(allocate_inline_frame_state): Remove.
	(clear_inline_frame_state): Adjust to std::vector.
	(skip_inline_frames): Adjust to std::vector.
---
 gdb/common/gdb_vecs.h |  22 +++++++---
 gdb/inline-frame.c    | 113 +++++++++++++++++++++-----------------------------
 2 files changed, 65 insertions(+), 70 deletions(-)
Pedro Alves - April 8, 2018, 5:29 p.m.
On 04/08/2018 12:21 AM, Simon Marchi wrote:

> 
>  /* Forget about any hidden inlined functions in PTID, which is new or
> @@ -112,36 +102,34 @@ allocate_inline_frame_state (ptid_t ptid)
>  void
>  clear_inline_frame_state (ptid_t ptid)
>  {

...

> -  for (ix = 0; VEC_iterate (inline_state_s, inline_states, ix, state); ix++)
> -    if (ptid_equal (state->ptid, ptid))
> -      {
> -	VEC_unordered_remove (inline_state_s, inline_states, ix);
> -	return;
> -      }
> +  auto it = std::find_if (inline_states.begin (), inline_states.end (),
> +			  [&ptid] (const inline_state &state)
> +			    {
> +			      return ptid == state.ptid;
> +			    });
> +
> +  if (it != inline_states.end ())
> +    inline_states.erase (it);

Should this erase be unordered_remove as well?

Otherwise LGTM.

Thanks,
Pedro Alves
Pedro Alves - April 9, 2018, 9:10 a.m.
Hi,

I remembered now that I forgot so point at something that I had wanted
to mention before.

It's that I think that this:

> +template <typename T>
> +T
> +unordered_remove (std::vector<T> &vec, typename std::vector<T>::iterator it)
> +{

won't work as is with gdb::def_vector/gdb::byte_vector, because the above
assumes std::vector has a single template parameter, while in reality it
has two.  

I think this can either be fixed by adding an allocator template parameter
to unordered_remove:

 template<typename T, typename A>
 void
 unordered_erase (std::vector<T, A> &v, 
                  typename std::vector<T, A>::iterator pos)

or by making the whole vector/container type a template like in
my example:

 template<typename Vector>
 void
 unordered_erase (Vector &v, typename Vector::iterator pos)

Thanks,
Pedro Alves
Simon Marchi - April 9, 2018, 7:45 p.m.
On 2018-04-09 05:10, Pedro Alves wrote:
> Hi,
> 
> I remembered now that I forgot so point at something that I had wanted
> to mention before.
> 
> It's that I think that this:
> 
>> +template <typename T>
>> +T
>> +unordered_remove (std::vector<T> &vec, typename 
>> std::vector<T>::iterator it)
>> +{
> 
> won't work as is with gdb::def_vector/gdb::byte_vector, because the 
> above
> assumes std::vector has a single template parameter, while in reality 
> it
> has two.
> 
> I think this can either be fixed by adding an allocator template 
> parameter
> to unordered_remove:
> 
>  template<typename T, typename A>
>  void
>  unordered_erase (std::vector<T, A> &v,
>                   typename std::vector<T, A>::iterator pos)
> 
> or by making the whole vector/container type a template like in
> my example:
> 
>  template<typename Vector>
>  void
>  unordered_erase (Vector &v, typename Vector::iterator pos)

That sounds like a good change, but let's do it as a separate patch (as 
renaming the functions).

I was wondering if it would also be worthwhile to have an equivalent of 
std::remove_if that doesn't preserve the order of the remaining elements 
(which could have been used in this patch).

I pushed my patch in, including the missing usage of unordered_remove 
that you pointed out in your other message.

Thanks,

Simon

Patch

diff --git a/gdb/common/gdb_vecs.h b/gdb/common/gdb_vecs.h
index 141d05e0189a..3e461dca4838 100644
--- a/gdb/common/gdb_vecs.h
+++ b/gdb/common/gdb_vecs.h
@@ -47,6 +47,22 @@  extern void dirnames_to_char_ptr_vec_append
 extern std::vector<gdb::unique_xmalloc_ptr<char>>
   dirnames_to_char_ptr_vec (const char *dirnames);

+/* Remove the element pointed by iterator IT from VEC, not preserving the order
+   of the remaining elements.  Return the removed element.  */
+
+template <typename T>
+T
+unordered_remove (std::vector<T> &vec, typename std::vector<T>::iterator it)
+{
+  gdb_assert (it >= vec.begin () && it < vec.end ());
+
+  T removed = std::move (*it);
+  *it = std::move (vec.back ());
+  vec.pop_back ();
+
+  return removed;
+}
+
 /* Remove the element at position IX from VEC, not preserving the order of the
    remaining elements.  Return the removed element.  */

@@ -56,11 +72,7 @@  unordered_remove (std::vector<T> &vec, typename std::vector<T>::size_type ix)
 {
   gdb_assert (ix < vec.size ());

-  T removed = std::move (vec[ix]);
-  vec[ix] = std::move (vec.back ());
-  vec.pop_back ();
-
-  return removed;
+  return unordered_remove (vec, vec.begin () + ix);
 }

 /* Remove the element at position IX from VEC, preserving the order the
diff --git a/gdb/inline-frame.c b/gdb/inline-frame.c
index a01961955949..4333a3d82b05 100644
--- a/gdb/inline-frame.c
+++ b/gdb/inline-frame.c
@@ -27,6 +27,7 @@ 
 #include "symtab.h"
 #include "vec.h"
 #include "frame.h"
+#include <algorithm>

 /* We need to save a few variables for every thread stopped at the
    virtual call site of an inlined function.  If there was always a
@@ -34,6 +35,12 @@ 
    keep our own list.  */
 struct inline_state
 {
+  inline_state (ptid_t ptid_, int skipped_frames_, CORE_ADDR saved_pc_,
+		symbol *skipped_symbol_)
+    : ptid (ptid_), skipped_frames (skipped_frames_), saved_pc (saved_pc_),
+      skipped_symbol (skipped_symbol_)
+  {}
+
   /* The thread this data relates to.  It should be a currently
      stopped thread; we assume thread IDs never change while the
      thread is stopped.  */
@@ -55,10 +62,7 @@  struct inline_state
   struct symbol *skipped_symbol;
 };

-typedef struct inline_state inline_state_s;
-DEF_VEC_O(inline_state_s);
-
-static VEC(inline_state_s) *inline_states;
+static std::vector<inline_state> inline_states;

 /* Locate saved inlined frame state for PTID, if it exists
    and is valid.  */
@@ -66,43 +70,29 @@  static VEC(inline_state_s) *inline_states;
 static struct inline_state *
 find_inline_frame_state (ptid_t ptid)
 {
-  struct inline_state *state;
-  int ix;
-
-  for (ix = 0; VEC_iterate (inline_state_s, inline_states, ix, state); ix++)
-    {
-      if (ptid_equal (state->ptid, ptid))
-	{
-	  struct regcache *regcache = get_thread_regcache (ptid);
-	  CORE_ADDR current_pc = regcache_read_pc (regcache);
-
-	  if (current_pc != state->saved_pc)
-	    {
-	      /* PC has changed - this context is invalid.  Use the
-		 default behavior.  */
-	      VEC_unordered_remove (inline_state_s, inline_states, ix);
-	      return NULL;
-	    }
-	  else
-	    return state;
-	}
-    }
+  auto state_it = std::find_if (inline_states.begin (), inline_states.end (),
+				[&ptid] (const inline_state &state)
+				  {
+				    return ptid == state.ptid;
+				  });

-  return NULL;
-}
+  if (state_it == inline_states.end ())
+    return nullptr;

-/* Allocate saved inlined frame state for PTID.  */
+  inline_state &state = *state_it;
+  struct regcache *regcache = get_thread_regcache (ptid);
+  CORE_ADDR current_pc = regcache_read_pc (regcache);

-static struct inline_state *
-allocate_inline_frame_state (ptid_t ptid)
-{
-  struct inline_state *state;
+  if (current_pc != state.saved_pc)
+    {
+      /* PC has changed - this context is invalid.  Use the
+	 default behavior.  */

-  state = VEC_safe_push (inline_state_s, inline_states, NULL);
-  memset (state, 0, sizeof (*state));
-  state->ptid = ptid;
+      unordered_remove (inline_states, state_it);
+      return nullptr;
+    }

-  return state;
+  return &state;
 }

 /* Forget about any hidden inlined functions in PTID, which is new or
@@ -112,36 +102,34 @@  allocate_inline_frame_state (ptid_t ptid)
 void
 clear_inline_frame_state (ptid_t ptid)
 {
-  struct inline_state *state;
-  int ix;
-
-  if (ptid_equal (ptid, minus_one_ptid))
+  if (ptid == minus_one_ptid)
     {
-      VEC_free (inline_state_s, inline_states);
+      inline_states.clear ();
       return;
     }

-  if (ptid_is_pid (ptid))
+  if (ptid.is_pid ())
     {
-      VEC (inline_state_s) *new_states = NULL;
-      int pid = ptid_get_pid (ptid);
-
-      for (ix = 0;
-	   VEC_iterate (inline_state_s, inline_states, ix, state);
-	   ix++)
-	if (pid != ptid_get_pid (state->ptid))
-	  VEC_safe_push (inline_state_s, new_states, state);
-      VEC_free (inline_state_s, inline_states);
-      inline_states = new_states;
+      int pid = ptid.pid ();
+      auto it = std::remove_if (inline_states.begin (), inline_states.end (),
+				[pid] (const inline_state &state)
+				  {
+				    return pid == state.ptid.pid ();
+				  });
+
+      inline_states.erase (it, inline_states.end ());
+
       return;
     }

-  for (ix = 0; VEC_iterate (inline_state_s, inline_states, ix, state); ix++)
-    if (ptid_equal (state->ptid, ptid))
-      {
-	VEC_unordered_remove (inline_state_s, inline_states, ix);
-	return;
-      }
+  auto it = std::find_if (inline_states.begin (), inline_states.end (),
+			  [&ptid] (const inline_state &state)
+			    {
+			      return ptid == state.ptid;
+			    });
+
+  if (it != inline_states.end ())
+    inline_states.erase (it);
 }

 static void
@@ -303,16 +291,14 @@  block_starting_point_at (CORE_ADDR pc, const struct block *block)
 void
 skip_inline_frames (ptid_t ptid)
 {
-  CORE_ADDR this_pc;
   const struct block *frame_block, *cur_block;
   struct symbol *last_sym = NULL;
   int skip_count = 0;
-  struct inline_state *state;

   /* This function is called right after reinitializing the frame
      cache.  We try not to do more unwinding than absolutely
      necessary, for performance.  */
-  this_pc = get_frame_pc (get_current_frame ());
+  CORE_ADDR this_pc = get_frame_pc (get_current_frame ());
   frame_block = block_for_pc (this_pc);

   if (frame_block != NULL)
@@ -341,10 +327,7 @@  skip_inline_frames (ptid_t ptid)
     }

   gdb_assert (find_inline_frame_state (ptid) == NULL);
-  state = allocate_inline_frame_state (ptid);
-  state->skipped_frames = skip_count;
-  state->saved_pc = this_pc;
-  state->skipped_symbol = last_sym;
+  inline_states.emplace_back (ptid, skip_count, this_pc, last_sym);

   if (skip_count != 0)
     reinit_frame_cache ();