Per http://lists.qt-project.org/pipermail/development/2013-November/014085.html "Enabling SSE2 by default on x86 builds (32-bit)" Starting with Qt 5.3.0, x86 builds use SSE2 by default. Extra care needs to be taken so fedora's default i686 packaging includes libraries built with --no-sse2 NOTE: qt5-qtdeclarative had already included some minor hacks to support both see2-enabled and non-sse2 libraries. It will likely need to be reworked.
%changelog * Fri May 30 2014 Rex Dieter <rdieter> 5.3.0-6 - %%ix86: build -no-sse2 (#1103185) Here's the diff in the resulting qmodule.pri $ diff -u /usr/lib/qt5/mkspecs/qmodule.pri qmodule.pri --- /usr/lib/qt5/mkspecs/qmodule.pri 2014-05-22 08:57:41.000000000 -0500 +++ qmodule.pri 2014-05-30 09:26:28.296848196 -0500 @@ -1,4 +1,4 @@ -CONFIG += compile_examples system-sqlite qpa largefile nostrip sse2 sse3 ssse3 sse4_1 sse4_2 avx avx2 +CONFIG += compile_examples system-sqlite qpa largefile nostrip QT_BUILD_PARTS += libs tools examples QT_NO_DEFINES = IMAGEFORMAT_JPEG OPENVG TABLET XINPUT XKB ZLIB QT_QCONFIG_PATH = Next step(s): * consider building (some?) sse2-enabled libs too, install these to %{_libdir}/sse2/. Good candidates include: libQt5Core, libQt5Gui * verify how to do sse2-enabled builds for other qt5 pkgs. Something like "qmake-qt5 CONFIG+=sse2" ? * what about the other CONFIG items sse3 ssse3 sse4_1 sse4_2 avx avx2 ?
I've confirmed the current qt5-qtdeclarative sse2 solution still works As far as qtbase is concerned, only libQt5Gui uses some sse2-optimized routines. Building a sse2-enabled version of that could be considered for the future.
rex, i'm not sure if it's worth doing support old cpu these days. In my opinion we just drop it and only build qt with sse2 by default.
Then we need to get the project arch support policy changed (if not obvious, I disagree with enabling sse2 by default, if it's not supported distro-wide).
we will discuss it by next kde sig meeting. I would like to hear more comments from others how we handle this issue.
Fwiw, I'm still willing to help work on a special sse2-enabled libQt5Gui, as hinted in comment #2
I think the consensus from the meeting was to keep things as they are (with potential enhancements per comment #2), so I'll close this for now.