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, 16 insertions, 13 deletions

diff --git a/src/corelib/io/qstorageinfo_unix.cpp b/src/corelib/io/qstorageinfo_unix.cpp
index 5f3fa32482..be3bf0252d 100644
--- a/src/corelib/io/qstorageinfo_unix.cpp
+++ b/src/corelib/io/qstorageinfo_unix.cpp
@@ -451,32 +451,35 @@ inline bool QStorageIterator::next()
     const char *const stop = ptr + len - 1;
 
     // parse the line
-    bool ok;
     mnt.mnt_freq = 0;
     mnt.mnt_passno = 0;
 
-    mnt.mount_id = qstrntoll(ptr, stop - ptr, const_cast<const char **>(&ptr), 10, &ok);
-    if (!ok)
+    auto r = qstrntoll(ptr, stop - ptr, 10);
+    if (!r.ok())
         return false;
+    mnt.mount_id = r.result;
 
-    int parent_id = qstrntoll(ptr, stop - ptr, const_cast<const char **>(&ptr), 10, &ok);
-    Q_UNUSED(parent_id);
-    if (!ok)
+    r = qstrntoll(r.endptr, stop - r.endptr, 10);
+    if (!r.ok())
         return false;
+    int parent_id = r.result;
+    Q_UNUSED(parent_id);
 
-    int rdevmajor = qstrntoll(ptr, stop - ptr, const_cast<const char **>(&ptr), 10, &ok);
-    if (!ok)
+    r = qstrntoll(r.endptr, stop - r.endptr, 10);
+    if (!r.ok())
         return false;
-    if (*ptr != ':')
+    if (*r.endptr != ':')
         return false;
-    int rdevminor = qstrntoll(ptr + 1, stop - ptr - 1, const_cast<const char **>(&ptr), 10, &ok);
-    if (!ok)
+    int rdevmajor = r.result;
+    r = qstrntoll(r.endptr + 1, stop - r.endptr - 1, 10);
+    if (!r.ok())
         return false;
-    mnt.rdev = makedev(rdevmajor, rdevminor);
+    mnt.rdev = makedev(rdevmajor, r.result);
 
-    if (*ptr != ' ')
+    if (*r.endptr != ' ')
         return false;
 
+    ptr = const_cast<char *>(r.endptr);
     mnt.subvolume = ++ptr;
     ptr = parseMangledPath(ptr);
     if (!ptr)