Trac #29453: Detect and use the system fflas-ffpack

This package already has an spkg-configure.m4 file and some distro
information, but we can't yet detect and use the system copy. Here's
hoping everyone ships the pkg-config file.

URL: https://trac.sagemath.org/29453
Reported by: mjo
Ticket author(s): Michael Orlitzky
Reviewer(s): Matthias Koeppe

Author: Release Manager

build/pkgs/fflas_ffpack/distros/arch.txt

@@ -0,0 +1 @@
+fflas-ffpack

build/pkgs/fflas_ffpack/distros/conda.txt

@@ -0,0 +1 @@
+fflas-ffpack

build/pkgs/fflas_ffpack/distros/gentoo.txt

@@ -0,0 +1 @@
+sci-libs/fflas-ffpack

build/pkgs/fflas_ffpack/distros/opensuse.txt

@@ -0,0 +1 @@
+fflas-ffpack

build/pkgs/fflas_ffpack/spkg-configure.m4

@@ -1,16 +1,34 @@
 SAGE_SPKG_CONFIGURE([fflas_ffpack], [
-  dnl A check for a system package is not implemented yet.
-  sage_spkg_install_fflas_ffpack=yes
-
-  dnl https://github.com/linbox-team/fflas-ffpack/blob/master/macros/instr_set.m4
-  dnl discovers these flags from the processor but fails to check whether
-  dnl compiler (and assembler) actually support these instruction sets.
-
-  AX_CHECK_COMPILE_FLAG([-mavx512f -mavx512vl -mavx512dq], [], [
-    AS_VAR_APPEND([SAGE_CONFIGURE_FFLAS_FFPACK], [" --disable-avx512f --disable-avx512vl --disable-avx512dq"])
+  # fflas-lapack uses whatever multi-precision library givaro uses,
+  # either gmp or mpir.
+  SAGE_SPKG_DEPCHECK([atlas givaro gmp mpir openblas], [
+    # If our dependencies come from the system, then we can use
+    # the system fflas-ffpack, too. Use pkg-config to find a
+    # recentish version, if there is one.
+    PKG_CHECK_MODULES([FFLAS_FFPACK],
+                      [fflas-ffpack >= 2.4.0],
+                      [sage_spkg_install_fflas_ffpack=no],
+                      [sage_spkg_install_fflas_ffpack=yes])
+  ],
+  [ # Some of its dependencies are installed as SPKGs, so install the
+    # fflas-ffpack SPKG as well.
+    sage_spkg_install_fflas_ffpack=yes
   ])
-  m4_foreach([ISFLAG], [fma, fma4], [
-    AX_CHECK_COMPILE_FLAG([-m]ISFLAG, [], [AS_VAR_APPEND]([SAGE_CONFIGURE_FFLAS_FFPACK], [" --disable-]ISFLAG[ "]))
+],[],[],[
+  # Run this AFTER the check above, unconditionally, so that in particular
+  # it gets run if the user passes --without-system-fflas-ffpack to the
+  # ./configure script.
+  AS_IF([test "x$sage_spkg_install_fflas_ffpack" = "xyes"],[
+    dnl https://github.com/linbox-team/fflas-ffpack/blob/master/macros/instr_set.m4
+    dnl discovers these flags from the processor but fails to check whether
+    dnl compiler (and assembler) actually support these instruction sets.
+
+    AX_CHECK_COMPILE_FLAG([-mavx512f -mavx512vl -mavx512dq], [], [
+      AS_VAR_APPEND([SAGE_CONFIGURE_FFLAS_FFPACK], [" --disable-avx512f --disable-avx512vl --disable-avx512dq"])
+    ])
+    m4_foreach([ISFLAG], [fma, fma4], [
+      AX_CHECK_COMPILE_FLAG([-m]ISFLAG, [], [AS_VAR_APPEND]([SAGE_CONFIGURE_FFLAS_FFPACK], [" --disable-]ISFLAG[ "]))
+    ])
+    AC_SUBST([SAGE_CONFIGURE_FFLAS_FFPACK])
   ])
-  AC_SUBST([SAGE_CONFIGURE_FFLAS_FFPACK])
 ])