QLocale: make qstrnto(u)ll not have output arguments

That is, return everything in the return argument. On the SysV ABI, that
means everything gets returned in registers, in both 32- and 64-bit
platforms (unlike QtPrivate::ParsedNumber). There's a minor but
perceptible performance improvement in parsing strings and byte arrays.

Before:
Parsed string   "42"    "1234"  "-1548860221"
Clock (ns)      16.673  18.878  25.517
CPU cycles      46.548  52.704  71.243
Instructions    201     233     331

After:
Parsed string   "42"    "1234"  "-1548860221"
Clock (ns)      15.577  17.998  24.198
CPU cycles      43.491  49.942  67.552
Instructions    179     211     308

On my Core i7-1165G7 @ 2.80 GHz, the 22-23 instruction gain per
iteration results in half the expected clock gain in runtime (22 /
2.8 GHz = 7.8 ns) because of a slightly lower instruction per cycle
rate. That's acceptable because we need less speculative execution.

Pick-to: 6.4
Task-number: QTBUG-107788
Change-Id: I07ec23f3cb174fb197c3fffd17220fd64d473cc0
Reviewed-by: Edward Welbourne <edward.welbourne@qt.io>

1 files changed, 12 insertions, 11 deletions

diff --git a/src/corelib/time/qtimezoneprivate_tz.cpp b/src/corelib/time/qtimezoneprivate_tz.cpp
index 099bccb071..d7c529ad10 100644
--- a/src/corelib/time/qtimezoneprivate_tz.cpp
+++ b/src/corelib/time/qtimezoneprivate_tz.cpp
@@ -392,27 +392,28 @@ static int parsePosixTime(const char *begin, const char *end)
     int hour, min = 0, sec = 0;
 
     const int maxHour = 137; // POSIX's extended range.
-    bool ok = false;
-    const char *cut = begin;
-    hour = qstrntoll(begin, end - begin, &cut, 10, &ok);
-    if (!ok || hour < -maxHour || hour > maxHour || cut > begin + 2)
+    auto r = qstrntoll(begin, end - begin, 10);
+    hour = r.result;
+    if (!r.ok() || hour < -maxHour || hour > maxHour || r.endptr > begin + 2)
         return INT_MIN;
-    begin = cut;
+    begin = r.endptr;
     if (begin < end && *begin == ':') {
         // minutes
         ++begin;
-        min = qstrntoll(begin, end - begin, &cut, 10, &ok);
-        if (!ok || min < 0 || min > 59 || cut > begin + 2)
+        r = qstrntoll(begin, end - begin, 10);
+        min = r.result;
+        if (!r.ok() || min < 0 || min > 59 || r.endptr > begin + 2)
             return INT_MIN;
 
-        begin = cut;
+        begin = r.endptr;
         if (begin < end && *begin == ':') {
             // seconds
             ++begin;
-            sec = qstrntoll(begin, end - begin, &cut, 10, &ok);
-            if (!ok || sec < 0 || sec > 59 || cut > begin + 2)
+            r = qstrntoll(begin, end - begin, 10);
+            sec = r.result;
+            if (!r.ok() || sec < 0 || sec > 59 || r.endptr > begin + 2)
                 return INT_MIN;
-            begin = cut;
+            begin = r.endptr;
         }
     }