Re: Two observations using GDB 13 snapshot

[Eli Zaretskii <eliz@gnu.org>]

> Date: Tue, 3 Jan 2023 16:34:53 -0500
> Cc: tom@tromey.com, gdb-patches@sourceware.org, luis.machado@arm.com
> From: Simon Marchi <simark@simark.ca>
> 
> > In terms of the code, may be worth trying TOLOWER from
> > include/safe-ctype.h instead of tolower()
> 
> The tolower call is inside strcasecmp, we don't call tolower directly:
> 
> #0  0x77c348d5 in msvcrt!__crtLCMapStringA ()
>    from C:\WINDOWS\system32\msvcrt.dll
> #1  0x77c348cd in msvcrt!__crtLCMapStringA ()
>    from C:\WINDOWS\system32\msvcrt.dll
> #2  0x77c30045 in wmktemp () from C:\WINDOWS\system32\msvcrt.dll
> #3  0x77c1c992 in tolower () from C:\WINDOWS\system32\msvcrt.dll
> #4  0x77c462a1 in stricmp () from C:\WINDOWS\system32\msvcrt.dll
> #5  0x005107d3 in strcasecmp (__s2=<optimized out>, __s1=<optimized out>)
>     at d:/usr/include/strings.h:92
> #6  cooked_index_entry::operator< (this=<optimized out>, other=...)
>     at ./dwarf2/cooked-index.h:150
> 
> It would be interesting to change that strcasecmp call to strcmp, just
> to see if it makes an impact on the performance.  Whether or not that
> would be correct is another thing, but it would help see if that
> strcasecmp / tolower call is really at fault here.

Looks like indeed strcasecmp is the culprit.  With the patch below,
which replaces strcasecmp with a simple case-insensitive comparison
that only works with ASCII, the phase of reading symbols from gdb.exe
goes down to just 6 seconds, which is basically the same time as with
GDB 12.

--- gdb/dwarf2/cooked-index.h~0	2022-12-17 03:47:12.000000000 +0200
+++ gdb/dwarf2/cooked-index.h	2023-01-04 20:00:04.052250000 +0200
@@ -35,6 +35,8 @@
 #include "dwarf2/tag.h"
 #include "gdbsupport/range-chain.h"
 
+#define my_tolower(c) (('A' <= (c) && (c) <= 'Z') ? ((c) - 'A' + 'a') : (c))
+
 struct dwarf2_per_cu_data;
 
 /* Flags that describe an entry in the index.  */
@@ -147,7 +149,20 @@ struct cooked_index_entry : public alloc
      entries.  */
   bool operator< (const cooked_index_entry &other) const
   {
+#if 0
     return strcasecmp (canonical, other.canonical) < 0;
+#else
+    const unsigned char *s1 = (unsigned char *)canonical, *s2 = (unsigned char *)other.canonical;
+
+    while (my_tolower(*s1) == my_tolower(*s2))
+      {
+	if (*s1 == 0)
+	  return false;
+	s1++;
+	s2++;
+      }
+    return (int)my_tolower(*s1) < (int)my_tolower(*s2);
+#endif
   }
 
   /* The name as it appears in DWARF.  This always points into one of