QtPrivate::isLatin1: fix SSE2 non-SSE4.1 code

The implementation was broken. The "high" in PUNPCKHBW's "unpack high
data" means the high 64-bit of the 128-bit, not the high byte of a 16-
bit word. This never worked. It always passed for me because I don't
build non-SSE4.2 code (too old, no longer relevant).

So just use the working version of simdTestMask.

Pick-to: 5.15 5.12
Change-Id: I35a1b4d0a19a43149daefffd16284542f0de3fa3
Reviewed-by: Allan Sandfeld Jensen <allan.jensen@qt.io>

1 files changed, 1 insertions, 20 deletions

diff --git a/src/corelib/text/qstring.cpp b/src/corelib/text/qstring.cpp
index b63b980e72..82cdeec1a3 100644
--- a/src/corelib/text/qstring.cpp
+++ b/src/corelib/text/qstring.cpp
@@ -564,31 +564,12 @@ bool QtPrivate::isLatin1(QStringView s) noexcept
     const QChar *ptr = s.begin();
     const QChar *end = s.end();
 
-#if defined(__SSE4_1__)
+#ifdef __SSE2__
     const char *ptr8 = reinterpret_cast<const char *>(ptr);
     const char *end8 = reinterpret_cast<const char *>(end);
     if (!simdTestMask(ptr8, end8, 0xff00ff00))
         return false;
     ptr = reinterpret_cast<const QChar *>(ptr8);
-#elif defined(__SSE2__)
-    // Testing if every other byte is non-zero can be done efficiently by
-    // using PUNPCKHBW (unpack high order bytes) and comparing that to zero.
-    while (ptr + 32 < end) {
-        __m128i data1 = _mm_loadu_si128(reinterpret_cast<const __m128i *>(ptr));
-        __m128i data2 = _mm_loadu_si128(reinterpret_cast<const __m128i *>(ptr + 16));
-        __m128i high = _mm_unpackhi_epi8(data1, data2);
-        __m128i comparison = _mm_cmpeq_epi16(high, _mm_setzero_si128());
-        if (_mm_movemask_epi8(comparison))
-            return false;
-        ptr += 16;
-    }
-    if (ptr + 16 < end) {
-        __m128i data1 = _mm_loadu_si128(reinterpret_cast<const __m128i *>(ptr));
-        __m128i high = _mm_unpackhi_epi8(data1, data1);
-        __m128i comparison = _mm_cmpeq_epi16(high, _mm_setzero_si128());
-        if (_mm_movemask_epi8(comparison))
-            return false;
-    }
 #endif
 
     while (ptr != end) {