[build, lto] Only accept -fuse-linker-plugin if linker supports -plugin (PR lto/46944)

[Rainer Orth]

Richard Guenther <rguenther@suse.de> writes:

> On Fri, 18 Mar 2011, Rainer Orth wrote:
>
>> Richard Guenther <richard.guenther@gmail.com> writes:
>> 
>> > It seemed to have disabled linker-plugin support for old binutils
>> > with --with-plugin-ld=/usr/local/bin/gold, explicit -fuse-linker-plugin says
>> > it is not supported.  The system linker does not have plugin support
>> > (nor gold).  /usr/local has gold from binutils 2.20.50.xxx.  So it seems that
>> >
>> >     # Allow -fuse-linker-plugin to enable plugin support in GNU gold 2.20.
>> >     elif test "$ld_is_gold" = yes -a "$ld_vers_major" -eq 2 -a
>> > "$ld_vers_minor" -eq 20; then
>> >       gcc_cv_lto_plugin=1
>> >     fi
>> >
>> > only allows explicit -fuse-linker-plugin for recent gold but based on checking
>> > the system linker version (instead of that of --with-plugin-ld).  I'd say
>> > allow explicit -fuse-linker-plugin always if --with-plugin-ld is specified.
>> 
>> Agreed.  I'll have a look and refrain from installing on 4.6 until this
>> is resolved.  I wasn't even aware of --with-plugin-ld, which isn't
>> documented in install.texi ;-(  This stuff seems insanely complicated to
>> me, though: which user is supposed to deal with such complications?
>
> It's sort of historic ... with plugin support for GNU ld we can probably
> drop this flag for 4.7 (eventually I'd even like to enforce the use
> of the plugin all the time or disable LTO, just for the sake of reducing
> the testing and bugreporting matrix ...).
>
> I just noticed the above with the LTO setup of our SPEC testers
> which are using somewhat old system tools.

Here's the patch I came up with.  It is on top of the previous one, so
if we want to backport to 4.6 later, both are necessary.

It also fixes a typo in the in_tree_ld case, which can never have worked.

Tested by i386-pc-solaris2.11 bootstraps with either Sun ld or gld 2.21,
and by configuring with Sun ld --with-plugin-ld=gld-2.21 and obvserving
HAVE_LTO_PLUGIN being set to 1.

Ok for mainline now and 4.6 after some soak time?

Thanks.
	Rainer


2011-03-19  Rainer Orth  <ro@CeBiTec.Uni-Bielefeld.DE>

	* configure.ac (gcc_cv_lto_plugin): Fix typo.
	Allow -fuse-linker-plugin for non-default plugin linker.
	* configure: Regenerate.

diff -r 916a52719d80 gcc/configure.ac
--- a/gcc/configure.ac	Sat Mar 19 08:54:19 2011 +0100
+++ b/gcc/configure.ac	Sun Mar 20 13:37:38 2011 +0100
@@ -3192,14 +3192,14 @@
 AC_MSG_CHECKING(linker plugin support)
 gcc_cv_lto_plugin=0
 if test -f liblto_plugin.la; then
-  if test $in_tree_ld = yes -a x"$ORIGINAL_PLUGIN_LD_FOR_TARGET=" = x"$gcc_cv_ld"; then
+  if test $in_tree_ld = yes -a x"$ORIGINAL_PLUGIN_LD_FOR_TARGET" = x"$gcc_cv_ld"; then
     if test "$gcc_cv_gld_major_version" -eq 2 -a "$gcc_cv_gld_minor_version" -ge 21 -o "$gcc_cv_gld_major_version" -gt 2; then
       gcc_cv_lto_plugin=2
     elif test "$ld_is_gold" = yes -a "$gcc_cv_gld_major_version" -eq 2 -a "$gcc_cv_gld_minor_version" -eq 20; then
       gcc_cv_lto_plugin=1
 
     fi
-  elif echo "$ld_ver" | grep GNU > /dev/null; then
+  elif test x"$ORIGINAL_PLUGIN_LD_FOR_TARGET" = x"$gcc_cv_ld" && echo "$ld_ver" | grep GNU > /dev/null; then
     # Require GNU ld or gold 2.21+ for plugin support by default.
     if test "$ld_vers_major" -eq 2 -a "$ld_vers_minor" -ge 21; then
       gcc_cv_lto_plugin=2
@@ -3207,6 +3207,10 @@
     elif test "$ld_is_gold" = yes -a "$ld_vers_major" -eq 2 -a "$ld_vers_minor" -eq 20; then
       gcc_cv_lto_plugin=1
     fi
+  elif test x"$ORIGINAL_PLUGIN_LD_FOR_TARGET" != x"$gcc_cv_ld"; then
+    # Allow -fuse-linker-plugin if plugin linker differs from
+    # default/specified linker.
+    gcc_cv_lto_plugin=1
   fi
 fi
 AC_DEFINE_UNQUOTED(HAVE_LTO_PLUGIN, $gcc_cv_lto_plugin,


-- 
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Rainer Orth, Center for Biotechnology, Bielefeld University