From 340da949ccde13f6506177e327ccc21f49f56d3b Mon Sep 17 00:00:00 2001
From: Richard Levitte <levitte@openssl.org>
Date: Sun, 28 Feb 2016 00:20:50 +0100
Subject: [PATCH] Make generation of dependency files more efficient when
 possible

When building with GNU C, clang or VMS C, it's more efficient to
generate dependency file and object file in one call rather than two.
Have the dependency output in a temporary file and compare it with the
previous one if available to see if replacement is waranted, thereby
avoiding unnecessary reconstruction of Makefile / descrip.mms.

Github issue #750

Reviewed-by: Rich Salz <rsalz@openssl.org>
---
 Configurations/descrip.mms.tmpl   | 14 +++++---------
 Configurations/unix-Makefile.tmpl | 11 ++++++-----
 2 files changed, 11 insertions(+), 14 deletions(-)

diff --git a/Configurations/descrip.mms.tmpl b/Configurations/descrip.mms.tmpl
index eb60b4ad81..b7e047ba7c 100644
--- a/Configurations/descrip.mms.tmpl
+++ b/Configurations/descrip.mms.tmpl
@@ -435,19 +435,15 @@ configdata.pm : {- sourcefile("Configurations", "descrip.mms.tmpl") -} $(SRCDIR)
       my $after = $unified_info{after}->{$obj.".OBJ"} || "\@ !";
 
       return <<"EOF";
-$obj.MMS : $deps
+$obj.OBJ : $deps
         ${before}
         SET DEFAULT $forward
-        \$(CC) \$(CFLAGS)${incs} /MMS=(FILE=${objd}${objn}.MMS,TARGET=$obj.OBJ) /NOOBJECT $srcs
-        SET DEFAULT $backward
-        ${after}
-        - PURGE $obj.MMS
-$obj.OBJ : $obj.MMS
-        ${before}
-        SET DEFAULT $forward
-        \$(CC) \$(CFLAGS)${incs} /OBJECT=${objd}${objn}.OBJ /REPOSITORY=$backward $srcs
+        \$(CC) \$(CFLAGS)${incs} /MMS=(FILE=${objd}${objn}.tmp-MMS,TARGET=$obj.OBJ) /OBJECT=${objd}${objn}.OBJ /REPOSITORY=$backward $srcs
         SET DEFAULT $backward
         ${after}
+        \@ PIPE ( \$(PERL) -e "use File::Compare qw/compare_text/; my \$x = compare_text(""$obj.MMS"",""$obj.tmp-MMS""); exit(0x10000000 + (\$x == 0));" || -
+                 RENAME $obj.tmp-MMS $obj.mms )
+        \@ IF F\$SEARCH("$obj.tmp-MMS") .NES. "" THEN DELETE $obj.tmp-MMS;*
         - PURGE $obj.OBJ
 EOF
   }
diff --git a/Configurations/unix-Makefile.tmpl b/Configurations/unix-Makefile.tmpl
index b9fc5f87e7..cff0023a3e 100644
--- a/Configurations/unix-Makefile.tmpl
+++ b/Configurations/unix-Makefile.tmpl
@@ -847,11 +847,12 @@ $obj$objext: $obj$depext
 EOF
       }
       return <<"EOF";
-$obj$depext: $deps
-	\$(CC) \$(CFLAGS) $ecflags$incs -MM -MF \$\@ -MQ $obj$objext $srcs
-	touch \$\@
-$obj$objext: $obj$depext
-	\$(CC) \$(CFLAGS) $ecflags$incs -c -o \$\@ $srcs
+$obj$objext: $deps
+	\$(CC) \$(CFLAGS) $ecflags$incs -MMD -MF $obj$depext.tmp -MT \$\@ -c -o \$\@ $srcs
+	\@touch $obj$depext.tmp
+	\@if ! cmp $obj$depext.tmp $obj$depext > /dev/null 2> /dev/null; then \\
+		mv $obj$depext.tmp $obj$depext; \\
+	fi
 EOF
   }
   # On Unix, we build shlibs from static libs, so we're ignoring the
-- 
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