Re: [gentoo-dev] Re: Move x86/amd64 CPU extensions USE flags to a new USE_EXPAND variable

[Francesco R]

2010/12/13 Ryan Hill <dirtyepic@g.o>

> On Sun, 12 Dec 2010 09:01:13 -0400
> "Sergio D. Rodríguez Inclan" <srinclan@×××××.com> wrote:
>
> >   El 12/12/2010 02:46 a.m., Ryan Hill escribió:
> > > I think the fewer sources of magic USE flags the better.  Maybe we
> could
> > > document how to figure out what instruction sets a processor supports
> in the
> > > handbook instead.
>
> > A good manual would be greatly appreciated :)
>
> I wrote a guide a couple weeks ago that might be a good starting point.
>
> http://en.gentoo-wiki.com/wiki/Hardware_CFLAGS
>
>
if I read correctly the article on the wiki it does circa what the script
reported below does.
would be possible to adopt something similar for automatic C*FLAGS selection
if someone step in willing to take the pain to mantain it.

#!/usr/bin/python
# Copyright 2010 Gentoo Foundation
# Distributed under the terms of the GNU General Public License v2
# Author: Francesco Riosa
# extrapolated from http://en.gentoo-wiki.com/wiki/Hardware_CFLAGS, errors
are mine

# kate: encoding utf-8; eol unix
# kate: indent-width 4; mixedindent off; replace-tabs on;
# kate: remove-trailing-space on; space-indent on

# echo "int main() { return 0; }" | gcc -march=native -v -E - 2>&1 | grep
march
# echo "int main() { return 0; }" | gcc -march=core2 -v -Q -x c - 2>&1

"""
example output:
./hw-cflags.py
extrapolating flags for gcc-4.4.5
  useful flags: -march=core2 -msse4.1 --param l1-cache-size=32 --param
l1-cache-line-size=64 --param l2-cache-size=2048 -mtune=generic
  redundant:    -mcx16 -msahf

extrapolating flags for gcc-4.5.1
  useful flags: -march=core2 -msse4.1 --param l1-cache-size=32 --param
l1-cache-line-size=64 --param l2-cache-size=2048 -mtune=core2
  redundant:    -mcx16 -msahf
"""

import os
import time
import fnmatch
from subprocess import Popen, PIPE

GCC_PATH = '/usr/bin/'
GCC_LIST = fnmatch.filter(os.listdir(GCC_PATH), 'gcc-[0-9].*')
GCC_LIST.sort()

def extract_flags(gcccmd, header):
    # get output from gcc
    buf = ''
    devnul = open('/dev/null', 'w')
    p = Popen(gcccmd, stdin=PIPE, stdout=devnul, stderr=PIPE)
    p.stdin.write("""int main() { return 0; }""")
    p.stdin.close()
    while p.poll() is None:
        t = p.stderr.read()
        buf = "buf%s" % t
        time.sleep(0.01)
    p.stderr.close()
    devnul.close()

    # parse it
    flags = []
    add = False
    for line in buf.split('\n'):
        if line.startswith(header):
            add = True
            flags += line.strip().split(' ')
            continue
        if add:
            if line.startswith(' '):
                flags += line.strip().split(' ')
            else:
                break

    # extract flags we are interested in
    t = []
    march = ''
    mtune = '-mtune=generic'
    for i in xrange(len(flags)):
        if flags[i].startswith('-m'):
            if flags[i].startswith('-mtune'):
                mtune = flags[i]
            elif flags[i].startswith('-march'):
                march = flags[i]
            else:
                t.append(flags[i])
        elif flags[i] == '--param':
            t.append("%s %s" % (flags[i], flags[i+1]))
    flags = t

    return march, mtune, flags


for gcc in GCC_LIST:

    print "extrapolating flags for %s" % gcc

    gcccmd = [ GCC_PATH + gcc, '-march=native', '-v', '-E', '-', ]
    header='COLLECT_GCC_OPTIONS'
    march, mtune, flags_native = extract_flags(gcccmd, header)

    gcccmd = [ GCC_PATH + gcc, march, '-v', '-Q', '-x', 'c', '-', ]
    header='options enabled:'
    t, t, flags_enabled = extract_flags(gcccmd, header)

    redundant_flags = []
    useful_flags = []

    for x in flags_native:
        if x in flags_enabled:
            redundant_flags.append(x)
        else:
            useful_flags.append(x)

    if gcc < "gcc-4.5.0":
        mtune = '-mtune=generic'

    print "  useful flags: %s %s %s " % (march, " ".join(useful_flags),
mtune)
    print "  redundant:    %s" % " ".join(redundant_flags)
    print