[PATCH] gdb: fix nan in scoped_time_it output

[simon.marchi@polymtl.ca]

From: Simon Marchi <simon.marchi@efficios.com>

With "maintenance set per-command time on", a scope that takes less
than a millisecond prints:

  Time for "...": wall 0.000, user 0.000, sys 0.000, user+sys 0.000, -nan % CPU

The durations are converted to an integer millisecond count before the
CPU usage is computed, so a sub-millisecond scope truncates the wall
time to zero, and the division produces a NaN (or an infinity, if the
CPU time is not zero).  We don't really care about sub-millisecond
durations for the purpose of this tool, so just add a check for
`wall_ms == 0`, and report the CPU usage as 0% if true.  This is purely
cosmetic.

Change-Id: Iaf682bef4b537d6dbb58e82f7727c0ea079088aa
---
 gdb/maint.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/gdb/maint.c b/gdb/maint.c
index 8027429e6d39..22954f624efe 100644
--- a/gdb/maint.c
+++ b/gdb/maint.c
@@ -1230,7 +1230,8 @@ scoped_time_it::~scoped_time_it ()
 		     "user+sys %.03f, %.01f %% CPU\n",
 		     m_what, wall_ms / 1000.0, user_ms / 1000.0,
 		     sys_ms / 1000.0, user_plus_sys_ms / 1000.0,
-		     user_plus_sys_ms * 100.0 / wall_ms);
+		     (wall_ms == 0
+		      ? 0.0 : user_plus_sys_ms * 100.0 / wall_ms));
   gdb_stdlog->write_async_safe (str.data (), str.size ());
 }
 

base-commit: 421bec796fa3a06179856da870a13cf71ddf5df2
-- 
2.55.0