[RFC/Windows] Remember last tlb type for re-use in windows_get_tlb_type

["Pierre Muller" <pierre.muller@ics-cnrs.unistra.fr>]

  Each time, you examine the convenience variable
$_tlb on Windows executable
the function windows_get_tlb_type is called
and creates a new type.

  I copied this behavior from the internal variable _siginfo,
but I think that it is a big waste of time and memory to
regenerate it each time.
  Nevertheless, with multi-target GDB, you can possibly create
a type of windows-32 bit another for windows 64-bit
or even one for windows-CE.
  Thus I remember the last gdbarch passed
and return the remember type only if gdbarch did not change,
which is most of the time.

  I do not know if those kind of patches
are regarded as useful.

Comments welcome.


Pierre Muller

2010-04-19  Pierre Muller  <muller@ics.u-strasbg.fr>

	* windows-tdep.c (windows_get_tlb_type): Remember
	last GDBARCH and created type for re-use.

Index: windows-tdep.c
===================================================================
RCS file: /cvs/src/src/gdb/windows-tdep.c,v
retrieving revision 1.6
diff -u -p -r1.6 windows-tdep.c
--- windows-tdep.c	16 Apr 2010 07:49:35 -0000	1.6
+++ windows-tdep.c	19 Apr 2010 08:45:27 -0000
@@ -97,12 +97,18 @@ static int maint_display_all_tib = 0;
 static struct type *
 windows_get_tlb_type (struct gdbarch *gdbarch)
 {
+  static struct gdbarch *last_gdbarch = NULL;
+  static struct type *last_tlb_type = NULL;
   struct type *dword_ptr_type, *dword32_type, *void_ptr_type;
   struct type *peb_ldr_type, *peb_ldr_ptr_type;
   struct type *peb_type, *peb_ptr_type, *list_type, *list_ptr_type;
   struct type *module_list_ptr_type;
   struct type *tib_type, *seh_type, *tib_ptr_type, *seh_ptr_type;
 
+  /* Do not rebuild type if same gdbarch as last time.  */
+  if (last_tlb_type && last_gdbarch == gdbarch)
+    return last_tlb_type;
+  
   dword_ptr_type = arch_integer_type (gdbarch, gdbarch_ptr_bit (gdbarch),
 				 1, "DWORD_PTR");
   dword32_type = arch_integer_type (gdbarch, 32,
@@ -210,6 +216,9 @@ windows_get_tlb_type (struct gdbarch *gd
 			    TYPE_LENGTH (void_ptr_type), NULL);
   TYPE_TARGET_TYPE (tib_ptr_type) = tib_type;
 
+  last_tlb_type = tib_ptr_type;
+  last_gdbarch = gdbarch;
+
   return tib_ptr_type;
 }