Patchwork Use an std::vector for inline_states

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Submitter Simon Marchi
Date April 7, 2018, 2:42 p.m.
Message ID <20180407144205.20909-1-simon.marchi@polymtl.ca>
Download mbox | patch
Permalink /patch/26639/
State New
Headers show

Comments

Simon Marchi - April 7, 2018, 2:42 p.m.
This patch replaces VEC(inline_state) with std::vector<inline_state> and
adjusts the code that uses it.

gdb/ChangeLog:

	* 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/inline-frame.c | 113 +++++++++++++++++++++++------------------------------
 1 file changed, 48 insertions(+), 65 deletions(-)
Pedro Alves - April 7, 2018, 7:28 p.m.
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
Simon Marchi - April 7, 2018, 9:13 p.m.
On 2018-04-07 15:28, 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 ();
>  }

We actually have almost that already in common/gdb_vecs.h.  And I have 
no excuse not to know about it, since I added it.

I'll review my latest patches to see if there are more opportunities to 
use that.

Thanks,

Simon

Patch

diff --git a/gdb/inline-frame.c b/gdb/inline-frame.c
index a01961955949..37c6c1d57e5a 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;
+      inline_states.erase (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 ();