| Message ID | CAPUDrwdV-vTgjFXjuyALZp-E_DY_4f+vKCpbTFHkmeuzg4LrxA@mail.gmail.com |
|---|---|
| State | New |
| Headers | show |
On 25 October 2017 at 07:15, Dale Curtis <dalecurtis@chromium.org> wrote: > Technically _tzcnt* intrinsics are only available when the BMI > instruction set is present. However the instruction encoding > degrades to "rep bsf" on older processors. > > Clang for Windows debatably restricts the _tzcnt* instrinics behind > the __BMI__ architecture define, so check for its presence or > exclude the usage of these intrinics when clang is present. > > See also: > https://ffmpeg.org/pipermail/ffmpeg-devel/2015-November/183404.html > https://bugs.llvm.org/show_bug.cgi?id=30506 > http://lists.llvm.org/pipermail/cfe-dev/2016-October/051034.html > > Signed-off-by: Dale Curtis <dalecurtis@chromium.org LGTM
On Thu, Oct 26, 2017 at 03:39:57AM +1100, Matt Oliver wrote: > On 25 October 2017 at 07:15, Dale Curtis <dalecurtis@chromium.org> wrote: > > > Technically _tzcnt* intrinsics are only available when the BMI > > instruction set is present. However the instruction encoding > > degrades to "rep bsf" on older processors. > > > > Clang for Windows debatably restricts the _tzcnt* instrinics behind > > the __BMI__ architecture define, so check for its presence or > > exclude the usage of these intrinics when clang is present. > > > > See also: > > https://ffmpeg.org/pipermail/ffmpeg-devel/2015-November/183404.html > > https://bugs.llvm.org/show_bug.cgi?id=30506 > > http://lists.llvm.org/pipermail/cfe-dev/2016-October/051034.html > > > > Signed-off-by: Dale Curtis <dalecurtis@chromium.org > > > LGTM will apply thanks [...]
From 123a60bdcf99cab6b6e6bd31a463a29bc49598f0 Mon Sep 17 00:00:00 2001 From: Dale Curtis <dalecurtis@chromium.org> Date: Tue, 24 Oct 2017 13:03:59 -0700 Subject: [PATCH] Don't use _tzcnt instrinics with clang for windows w/o BMI. Technically _tzcnt* intrinsics are only available when the BMI instruction set is present. However the instruction encoding degrades to "rep bsf" on older processors. Clang for Windows debatably restricts the _tzcnt* instrinics behind the __BMI__ architecture define, so check for its presence or exclude the usage of these intrinics when clang is present. See also: https://ffmpeg.org/pipermail/ffmpeg-devel/2015-November/183404.html https://bugs.llvm.org/show_bug.cgi?id=30506 http://lists.llvm.org/pipermail/cfe-dev/2016-October/051034.html Signed-off-by: Dale Curtis <dalecurtis@chromium.org> --- libavutil/x86/intmath.h | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-) diff --git a/libavutil/x86/intmath.h b/libavutil/x86/intmath.h index e83971c084..40743fd13e 100644 --- a/libavutil/x86/intmath.h +++ b/libavutil/x86/intmath.h @@ -47,7 +47,8 @@ static av_always_inline av_const int ff_log2_x86(unsigned int v) # endif # define ff_log2_16bit av_log2 -#if defined(__INTEL_COMPILER) || (defined(_MSC_VER) && (_MSC_VER >= 1700)) +#if defined(__INTEL_COMPILER) || (defined(_MSC_VER) && (_MSC_VER >= 1700) && \ + (defined(__BMI__) || !defined(__clang__))) # define ff_ctz(v) _tzcnt_u32(v) # if ARCH_X86_64 -- 2.15.0.rc0.271.g36b669edcc-goog
Technically _tzcnt* intrinsics are only available when the BMI instruction set is present. However the instruction encoding degrades to "rep bsf" on older processors. Clang for Windows debatably restricts the _tzcnt* instrinics behind the __BMI__ architecture define, so check for its presence or exclude the usage of these intrinics when clang is present. See also: https://ffmpeg.org/pipermail/ffmpeg-devel/2015-November/183404.html https://bugs.llvm.org/show_bug.cgi?id=30506 http://lists.llvm.org/pipermail/cfe-dev/2016-October/051034.html Signed-off-by: Dale Curtis <dalecurtis@chromium.org>