On Fri, Feb 28, 2025 at 02:33:04PM +0000, Bruce Richardson wrote: > On Thu, Feb 27, 2025 at 05:52:17PM -0800, Andre Muezerie wrote: > > This patchset allows users to specify the CPU for which the generated > > code should be optimized for by passing the CPU name. > > > > MSVC does not provide this functionality natively, so logic was > > added. This additional logic relies on a table which stores instruction > > set availability (like AXV512F) for different CPUs. > > To make it easier to update this table a new devtool is introduced > > with this patch. The new tool generates the table entries for all CPUs > > listed in an input file using a recent version of the compiler, which > > has all the information needed. This reduces enormously the amount > > of work needed to update the table in msvc/meson.build and makes the > > process much less error prone. > > > > Signed-off-by: Andre Muezerie <andre...@linux.microsoft.com> > > --- > > devtools/dump-cpu-flags/README.md | 25 +++++ > > devtools/dump-cpu-flags/cpu-names.txt | 120 +++++++++++++++++++++ > > devtools/dump-cpu-flags/dump-cpu-flags.cpp | 119 ++++++++++++++++++++ > > devtools/dump-cpu-flags/dump-cpu-flags.py | 41 +++++++ > > 4 files changed, 305 insertions(+) > > create mode 100644 devtools/dump-cpu-flags/README.md > > create mode 100644 devtools/dump-cpu-flags/cpu-names.txt > > create mode 100644 devtools/dump-cpu-flags/dump-cpu-flags.cpp > > create mode 100644 devtools/dump-cpu-flags/dump-cpu-flags.py > > > > diff --git a/devtools/dump-cpu-flags/README.md > > b/devtools/dump-cpu-flags/README.md > > new file mode 100644 > > index 0000000000..3db69f9f8f > > --- /dev/null > > +++ b/devtools/dump-cpu-flags/README.md > > @@ -0,0 +1,25 @@ > > +# Generating updated CPU flags > > + > > +File `config\x86\msvc\meson.build` has a table with flags indicating > > instruction set support for a variety of CPU types. > > + > > +Script `dump-cpu-flags.py` can be used to generate updated entries for > > this table. > > + > > +The CPU names are stored in file `cpu-names.txt`, which is consumed by > > `dump-cpu-flags.py`. The formatting used in that file is described at the > > top of the file itself. > > + > > +The script relies on the information embedded in the g++ compiler. This > > means that an updated table can automatically be generated by switching to > > a newer version of the compiler. This avoids the need to manually edit the > > entries, which is error prone. With the script the table entries can just > > copied and pasted into `meson.build`. The only thing that might need to be > > done is adding new CPU names to cpu-names.txt, when new CPUs are released. > > + > > +**NOTE**: CPUs not known to the compiler will result in errors, which can > > be ignored (`dump-cpu-flags.py` will ignore these errors and continue). For > > best results use the latest g++ compiler available. > > + > > +Below is a sample output, where an error was logged because the compiler > > did not know about a CPU named ‘raptorlake’. > > + > > +```sh > > +$ ./dump-cpu-flags.py > > + 'x86-64-v2': [], > > + 'x86-64-v3': ['AVX', 'AVX2'], > > + 'x86-64-v4': ['AVX', 'AVX2', 'AVX512F', 'AVX512VL', 'AVX512BW', > > 'AVX512DQ', 'AVX512CD'], > > + 'alderlake': ['AVX', 'PCLMUL', 'RDRND', 'AVX2', 'RDSEED', 'AES', > > 'VPCLMULQDQ', 'GFNI'], > > +cc1plus: error: bad value (‘raptorlake’) for ‘-march=’ switch > > +cc1plus: note: valid arguments to ‘-march=’ switch are: nocona core2 > > nehalem corei7 westmere sandybridge... > > + 'silvermont': ['PCLMUL', 'RDRND'], > > + 'slm': ['PCLMUL', 'RDRND'], > > +``` > > \ No newline at end of file > > How about having the tool output a valid meson.build file, that can then be > used directly without copy-paste. While I know such a thing would end up > with us having deep subdir structures, it could be just loaded from e.g. > config/x86/msvc/cpu-flags/meson.build, for example. > > /Bruce
That's an interesting idea. It could be done, but when I think that this table will probably get updated no more than once per release I don't see much reason to to come up with something more sofisticated. Sometimes it's better to keep things simple.
