btrace: Use binary search to find instruction.

Currently, btrace_find_insn_by_number will iterate over all function call
segments to find the one that contains the needed instruction.  This linear
search is too slow for the upcoming Python bindings that will use this
function to access instructions.  This patch introduces a vector in struct
btrace_thread_info that holds pointers to all recorded function segments and
allows to use binary search.

The proper solution is to turn the underlying tree into a vector of objects
and use indices for access.  This requires more work.  A patch set is
currently being worked on and will be published later.

Signed-off-by: Tim Wiederhake <tim.wiederhake@intel.com>

gdb/ChangeLog:
	* btrace.c (btrace_fetch): Copy function call segments pointer
	into a vector.
	(btrace_clear): Clear the vector.
	(btrace_find_insn_by_number): Use binary search to find the correct
	function call segment.
	* btrace.h (brace_fun_p): New typedef.
	(struct btrace_thread_info) <functions>: New field.

Change-Id: I8a7f67e80bfe4ff62c4192f74a2153a70bf2a035

1 files changed, 39 insertions, 6 deletions

diff --git a/gdb/btrace.c b/gdb/btrace.c
index 06122cd..95dc7ab 100644
--- a/gdb/btrace.c
+++ b/gdb/btrace.c
@@ -1839,13 +1839,19 @@ btrace_fetch (struct thread_info *tp)
   /* Compute the trace, provided we have any.  */
   if (!btrace_data_empty (&btrace))
     {
+      struct btrace_function *bfun;
+
       /* Store the raw trace data.  The stored data will be cleared in
 	 btrace_clear, so we always append the new trace.  */
       btrace_data_append (&btinfo->data, &btrace);
       btrace_maint_clear (btinfo);
 
+      VEC_truncate (btrace_fun_p, btinfo->functions, 0);
       btrace_clear_history (btinfo);
       btrace_compute_ftrace (tp, &btrace);
+
+      for (bfun = btinfo->begin; bfun != NULL; bfun = bfun->flow.next)
+	VEC_safe_push (btrace_fun_p, btinfo->functions, bfun);
     }
 
   do_cleanups (cleanup);
@@ -1868,6 +1874,8 @@ btrace_clear (struct thread_info *tp)
 
   btinfo = &tp->btrace;
 
+  VEC_free (btrace_fun_p, btinfo->functions);
+
   it = btinfo->begin;
   while (it != NULL)
     {
@@ -2458,20 +2466,45 @@ btrace_find_insn_by_number (struct btrace_insn_iterator *it,
 			    unsigned int number)
 {
   const struct btrace_function *bfun;
+  unsigned int upper, lower;
 
-  for (bfun = btinfo->end; bfun != NULL; bfun = bfun->flow.prev)
-    if (bfun->insn_offset <= number)
-      break;
+  if (VEC_empty (btrace_fun_p, btinfo->functions))
+      return 0;
 
-  if (bfun == NULL)
+  lower = 0;
+  bfun = VEC_index (btrace_fun_p, btinfo->functions, lower);
+  if (number < bfun->insn_offset)
     return 0;
 
-  if (bfun->insn_offset + ftrace_call_num_insn (bfun) <= number)
+  upper = VEC_length (btrace_fun_p, btinfo->functions) - 1;
+  bfun = VEC_index (btrace_fun_p, btinfo->functions, upper);
+  if (number >= bfun->insn_offset + ftrace_call_num_insn (bfun))
     return 0;
 
+  /* We assume that there are no holes in the numbering.  */
+  for (;;)
+    {
+      const unsigned int average = lower + (upper - lower) / 2;
+
+      bfun = VEC_index (btrace_fun_p, btinfo->functions, average);
+
+      if (number < bfun->insn_offset)
+	{
+	  upper = average - 1;
+	  continue;
+	}
+
+      if (number >= bfun->insn_offset + ftrace_call_num_insn (bfun))
+	{
+	  lower = average + 1;
+	  continue;
+	}
+
+      break;
+    }
+
   it->function = bfun;
   it->index = number - bfun->insn_offset;
-
   return 1;
 }