Fix detection of F16C for the Intel compiler (again) and Visual Studio

Neither the Intel compiler nor Visual C++ have a dedicated switch to enable F16C support, like GCC and Clang do. So we used the AVX switch for that in commit 8241d51, as it was the closest, lowest denominator. That was incorrect and insufficient. The Intel compiler silently miscompiles the intrinsics with -xAVX, making calls to out-of-line functions like _mm_cvtps_ph, which don't exist. So we actually have to use AVX2 support to generate correct code. That might be a problem later, since Ivy Bridge supports F16C but not AVX2. Visual C++ is able to generate F16C code with just -arch:AVX. Either way, since there's no dedicated command-line switch, there's also no dedicated preprocessor macro. We're using __AVX2__ for both compilers, as that's a sufficient condition to indicate a processor that supports F16C. Change-Id: I27b55fdf514247549455fffd14b205b8d8b86da7 Reviewed-by: Allan Sandfeld Jensen <[email protected]>
spj0124 · Apr 6, 2017 · 280e321 · 280e321
1 parent c817b33
commit 280e321
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Showing 5 changed files with 7 additions and 5 deletions.
diff --git a/mkspecs/common/msvc-version.conf b/mkspecs/common/msvc-version.conf
@@ -49,6 +49,8 @@ greaterThan(QMAKE_MSC_VER, 1799) {
     QMAKE_CFLAGS       += -FS
     QMAKE_CXXFLAGS     += -FS
 
+    QMAKE_CFLAGS_F16C   = -arch:AVX
+
     equals(QMAKE_MSC_VER, 1800) {
         QMAKE_CFLAGS_RELEASE += -Zc:strictStrings
         QMAKE_CFLAGS_RELEASE_WITH_DEBUGINFO += -Zc:strictStrings

diff --git a/mkspecs/linux-icc/qmake.conf b/mkspecs/linux-icc/qmake.conf
@@ -42,7 +42,7 @@ QMAKE_CFLAGS_AVX512PF  += -xMIC-AVX512
 QMAKE_CFLAGS_AVX512DQ  += -xCORE-AVX512
 QMAKE_CFLAGS_AVX512BW  += -xCORE-AVX512
 QMAKE_CFLAGS_AVX512VL  += -xCORE-AVX512
-QMAKE_CFLAGS_F16C      += -xAVX
+QMAKE_CFLAGS_F16C      += $$QMAKE_CFLAGS_AVX2
 
 QMAKE_CXX               = icpc
 QMAKE_CXXFLAGS          = $$QMAKE_CFLAGS

diff --git a/mkspecs/macx-icc/qmake.conf b/mkspecs/macx-icc/qmake.conf
@@ -40,7 +40,7 @@ QMAKE_CFLAGS_AVX512PF  += -xMIC-AVX512
 QMAKE_CFLAGS_AVX512DQ  += -xCORE-AVX512
 QMAKE_CFLAGS_AVX512BW  += -xCORE-AVX512
 QMAKE_CFLAGS_AVX512VL  += -xCORE-AVX512
-QMAKE_CFLAGS_F16C      += -xAVX
+QMAKE_CFLAGS_F16C      += $$QMAKE_CFLAGS_AVX2
 
 QMAKE_CXX               = icpc
 QMAKE_CXXFLAGS          = $$QMAKE_CFLAGS

diff --git a/mkspecs/win32-icc/qmake.conf b/mkspecs/win32-icc/qmake.conf
@@ -33,7 +33,7 @@ QMAKE_CFLAGS_AVX512PF  += -QxMIC-AVX512
 QMAKE_CFLAGS_AVX512DQ  += -QxCORE-AVX512
 QMAKE_CFLAGS_AVX512BW  += -QxCORE-AVX512
 QMAKE_CFLAGS_AVX512VL  += -QxCORE-AVX512
-QMAKE_CFLAGS_F16C       = -QxAVX
+QMAKE_CFLAGS_F16C       = $$QMAKE_CFLAGS_AVX2
 
 QMAKE_CXX               = $$QMAKE_CC
 QMAKE_CXXFLAGS          = $$QMAKE_CFLAGS /Zc:forScope

diff --git a/src/corelib/global/qfloat16.h b/src/corelib/global/qfloat16.h
@@ -117,7 +117,7 @@ QT_WARNING_PUSH
 QT_WARNING_DISABLE_CLANG("-Wc99-extensions")
 inline qfloat16::qfloat16(float f) Q_DECL_NOTHROW
 {
-#if defined(QT_COMPILER_SUPPORTS_F16C) && defined(__F16C__)
+#if defined(QT_COMPILER_SUPPORTS_F16C) && (defined(__F16C__) || defined(__AVX2__))
     __m128 packsingle = _mm_set_ss(f);
     __m128i packhalf = _mm_cvtps_ph(packsingle, 0);
     b16 = _mm_extract_epi16(packhalf, 0);
@@ -135,7 +135,7 @@ QT_WARNING_POP
 
 inline qfloat16::operator float() const Q_DECL_NOTHROW
 {
-#if defined(QT_COMPILER_SUPPORTS_F16C) && defined(__F16C__)
+#if defined(QT_COMPILER_SUPPORTS_F16C) && (defined(__F16C__) || defined(__AVX2__))
     __m128i packhalf = _mm_cvtsi32_si128(b16);
     __m128 packsingle = _mm_cvtph_ps(packhalf);
     return _mm_cvtss_f32(packsingle);