[speex-dev] libspeex/SSE Intrinsics with GCC 3.3.x

[Ralph Giles]

On Fri, Apr 02, 2004 at 12:33:13AM -0500, Jean-Marc Valin wrote:

> Do you have any sample code for that? Also, how do you tell autoconf to
> append '-msse' without running into problems when CFLAGS is not set (and
> usually defaults to -g -O2, but not always).

Example patch attached. It only tries if the use passes --enable-sse; 
testing by target arch as Aron suggested is another reasonable approach. 
However, the -msse cflag test fails on powerpc-unknown-linux-gnu so it 
might be safe just to switch the default value of the --enable-sse arg.

AC_PROG_CC tries to find a compiler and then checks whether it's 
actually gcc. If so it automatically adds '-g -O2' to the CFLAGS.
That's the origin of those two flags.

The patch includes an explicit call to AC_PROG_CC since it uses its 
cache results; however AM_PROG_LIBTOOL and possibly other macros will 
call it if it's not been called explicitly when they're invoked.)

There are some options here; the -msse check could be conditional on gcc 
being detected, the way -O3 is. These flags are pretty much never 
portable, but it probably doesn't hurt to try.

The patch as written results in CFLAGS="-g -O2  -O3 -msee" if it 
succeeds. You can avoid the duplicate optimization levels by saying 
something like:

      if test $ac_cv_prog_gcc = yes; then
        dnl remove any existing gcc -On flag
        oldcflags=`echo $old_cflags | sed -e 's/-O.//'`
        OPT_CFLAGS="$OPT_CFLAGS -O3"
      fi
      OPT_CFLAGS="$OPT_CFLAGS -msse"

instead.

So perhaps not so simple, but writing expert systems in sh never is.

 -r

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