Patch: speed up compilations

[Tom Tromey]

This patch changes automake so that dependency-tracking compilations
in gcc3 mode are inlined.  This gives us a speedup in this common and
imho important case.

Unfortunately this patch isn't perfect :-(.  It regresses cxx2.test,
at least.

Alexandre, what do you think is the best way to fix the resulting
failure?  It looks like this:

/home/tromey/gnu/Auto/automake/automake/tests/../lib/am/depend2.am: 
am__fastdepCXX does not appear in AM_CONDITIONAL
FAIL: cxx2.test

The problem is that we get the missing AM_CONDITIONAL error before we
get the missing AC_PROG_CXX error.  The latter is much more
informative to the user, so just leaving things as-is isn't the best
idea.

Do you even think this is worthwhile?  I haven't quantified the
slowdown from using depcomp.  I'll put that on my to-do list...

Tom

Index: ChangeLog
from  Tom Tromey  <address@hidden>

        * m4/depend.m4 (_AM_DEPENDENCIES): Compute am__fastdep<compiler>
        conditional.
        * automake.in (handle_languages): Compute FASTDEP.
        * lib/am/depend2.am: Added %FASTDEP% mode.

Index: automake.in
===================================================================
RCS file: /cvs/automake/automake/automake.in,v
retrieving revision 1.1317
diff -u -r1.1317 automake.in
--- automake.in 3 Jul 2002 18:50:03 -0000 1.1317
+++ automake.in 5 Jul 2002 22:36:31 -0000
@@ -1717,11 +1717,14 @@
 
        my $AMDEP = (($use_dependencies && $lang->autodep ne 'no')
                     ? 'AMDEP' : 'FALSE');
+       my $FASTDEP = (($use_dependencies && $lang->autodep ne 'no')
+                      ? ('am__fastdep' . $fpfx) : 'FALSE');
 
        my %transform = ('EXT'     => $ext,
                         'PFX'     => $pfx,
                         'FPFX'    => $fpfx,
                         'AMDEP'   => $AMDEP,
+                        'FASTDEP' => $FASTDEP,
                         '-c'      => $lang->compile_flag || '',
                         'MORE-THAN-ONE'
                                   => (count_files_for_language ($lang->name) > 
1));
Index: lib/am/depend2.am
===================================================================
RCS file: /cvs/automake/automake/lib/am/depend2.am,v
retrieving revision 1.42
diff -u -r1.42 depend2.am
--- lib/am/depend2.am 26 Mar 2002 09:24:52 -0000 1.42
+++ lib/am/depend2.am 5 Jul 2002 22:36:33 -0000
@@ -29,9 +29,23 @@
 ## - if deps are on, %AMDEP% is mapped onto AMDEP,  and therefore
 ##   the `if AMDEP' chunk is prefix with @AMDEP_TRUE@ just like for any
 ##   other configure-time conditional.
+##
+## We do likewise for %FASTDEP%; this expands to an ordinary
+## configure-time conditional.  %FASTDEP% is used to speed up the
+## common case of building a package with gcc 3.x.  In this case we
+## can skip the use of depcomp and easily inline the dependency
+## tracking.
 
 ?GENERIC?%EXT%.o:
 ?!GENERIC?%OBJ%: %SOURCE%
+if %FASTDEP%
+## In fast-dep mode, we can always use -o.
+       if %COMPILE% -MT %OBJ% -MD -MP -MF "%DEPBASE%.Tpo" \
+         %-c% -o %OBJ% `test -f '%SOURCE%' || echo '$(srcdir)/'`%SOURCE%; \
+       then mv "%DEPBASE%.Tpo" "%DEPBASE%.Po"; \
+       else rm -f "%DEPBASE%.Tpo"; exit 1; \
+       fi
+else !%FASTDEP%
 if %AMDEP%
        source='%SOURCE%' object='%OBJ%' libtool=no @AMDEPBACKSLASH@
        depfile='%DEPBASE%.Po' tmpdepfile='%DEPBASE%.TPo' @AMDEPBACKSLASH@
@@ -39,9 +53,18 @@
 endif %AMDEP%
 ?-o?   %COMPILE% %-c% %-o% %OBJ% `test -f '%SOURCE%' || echo 
'$(srcdir)/'`%SOURCE%
 ?!-o?  %COMPILE% %-c% `test -f '%SOURCE%' || echo '$(srcdir)/'`%SOURCE%
+endif !%FASTDEP%
 
 ?GENERIC?%EXT%.obj:
 ?!GENERIC?%OBJOBJ%: %SOURCE%
+if %FASTDEP%
+## In fast-dep mode, we can always use -o.
+       if %COMPILE% -MT %OBJOBJ% -MD -MP -MF "%DEPBASE%.Tpo" \
+         %-c% -o %OBJOBJ% `cygpath -w %SOURCE%`; \
+       then mv "%DEPBASE%.Tpo" "%DEPBASE%.Po"; \
+       else rm -f "%DEPBASE%.Tpo"; exit 1; \
+       fi
+else !%FASTDEP%
 if %AMDEP%
        source='%SOURCE%' object='%OBJOBJ%' libtool=no @AMDEPBACKSLASH@
        depfile='%DEPBASE%.Po' tmpdepfile='%DEPBASE%.TPo' @AMDEPBACKSLASH@
@@ -49,15 +72,25 @@
 endif %AMDEP%
 ?-o?   %COMPILE% %-c% %-o% %OBJOBJ% `cygpath -w %SOURCE%`
 ?!-o?  %COMPILE% %-c% `cygpath -w %SOURCE%`
+endif !%FASTDEP%
 
 if %?LIBTOOL%
 ?GENERIC?%EXT%.lo:
 ?!GENERIC?%LTOBJ%: %SOURCE%
-if  %AMDEP%
+if %FASTDEP%
+## In fast-dep mode, we can always use -o.
+       if %COMPILE% -MT %LTOBJ% -MD -MP -MF "%DEPBASE%.Tpo" \
+         %-c% -o %LTOBJ% `test -f '%SOURCE%' || echo '$(srcdir)/'`%SOURCE% \
+       then mv "%DEPBASE%.Tpo" "%DEPBASE%.Po"; \
+       else rm -f "%DEPBASE%.Tpo"; exit 1; \
+       fi
+else !%FASTDEP%
+if %AMDEP%
        source='%SOURCE%' object='%LTOBJ%' libtool=yes @AMDEPBACKSLASH@
        depfile='%DEPBASE%.Plo' tmpdepfile='%DEPBASE%.TPlo' @AMDEPBACKSLASH@
        $(%FPFX%DEPMODE) $(depcomp) @AMDEPBACKSLASH@
-endif  %AMDEP%
+endif %AMDEP%
 ## We can always use `-o' with Libtool.
        %LTCOMPILE% %-c% -o %LTOBJ% `test -f '%SOURCE%' || echo 
'$(srcdir)/'`%SOURCE%
+endif !%FASTDEP%
 endif %?LIBTOOL%
Index: m4/depend.m4
===================================================================
RCS file: /cvs/automake/automake/m4/depend.m4,v
retrieving revision 1.25
diff -u -r1.25 depend.m4
--- m4/depend.m4 24 May 2002 10:36:16 -0000 1.25
+++ m4/depend.m4 5 Jul 2002 22:36:33 -0000
@@ -107,6 +107,9 @@
 fi
 ])
 AC_SUBST([$1DEPMODE], [depmode=$am_cv_$1_dependencies_compiler_type])
+AM_CONDITIONAL([am__fastdep$1], [
+  test "x$enable_dependency_tracking" != xno \
+  && test "$am_cv_$1_dependencies_compiler_type" = gcc3])
 ])