Configure: Improve incremental build time

When Makefile/opensslconf.h is unchanged, don't write it at all.

Currently every time Configure is executed, these files are overwritten.
Makefile leads to regeneration of buildinf.h, and opensslconf.h is itself
a central header.

As a result, Configure triggers full rebuild, even if nothing is changed.

Reviewed-by: Rich Salz <rsalz@openssl.org>
Reviewed-by: Richard Levitte <levitte@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/1370)

1 files changed, 24 insertions, 5 deletions

diff --git a/Configure b/Configure
index c39f71a179..c26c9d78cd 100755
--- a/Configure
+++ b/Configure
@@ -7,6 +7,7 @@ eval 'exec perl -S $0 ${1+"$@"}'
 
 require 5.000;
 use strict;
+use File::Compare;
 
 # see INSTALL for instructions.
 
@@ -1792,8 +1793,16 @@ while (<IN>)
 	}
 close(IN);
 close(OUT);
-rename($Makefile,"$Makefile.bak") || die "unable to rename $Makefile\n" if -e $Makefile;
-rename("$Makefile.new",$Makefile) || die "unable to rename $Makefile.new\n";
+if ((compare($Makefile, "$Makefile.new"))
+	or file_newer('Configure', $Makefile)
+	or file_newer('config', $Makefile)
+	or file_newer('Makefile.org', $Makefile))
+	{
+	rename($Makefile,"$Makefile.bak") || die "unable to rename $Makefile\n" if -e $Makefile;
+	rename("$Makefile.new",$Makefile) || die "unable to rename $Makefile.new\n";
+	}
+else
+	{ unlink("$Makefile.new"); }
 
 print "CC            =$cc\n";
 print "CFLAG         =$cflags\n";
@@ -1985,9 +1994,13 @@ print OUT "#ifdef  __cplusplus\n";
 print OUT "}\n";
 print OUT "#endif\n";
 close(OUT);
-rename("crypto/opensslconf.h","crypto/opensslconf.h.bak") || die "unable to rename crypto/opensslconf.h\n" if -e "crypto/opensslconf.h";
-rename("crypto/opensslconf.h.new","crypto/opensslconf.h") || die "unable to rename crypto/opensslconf.h.new\n";
-
+if (compare("crypto/opensslconf.h.new","crypto/opensslconf.h"))
+	{
+	rename("crypto/opensslconf.h","crypto/opensslconf.h.bak") || die "unable to rename crypto/opensslconf.h\n" if -e "crypto/opensslconf.h";
+	rename("crypto/opensslconf.h.new","crypto/opensslconf.h") || die "unable to rename crypto/opensslconf.h.new\n";
+	}
+else
+	{ unlink("crypto/opensslconf.h.new"); }
 
 # Fix the date
 
@@ -2289,3 +2302,9 @@ sub test_sanity
 	print STDERR "No sanity errors detected!\n" if $errorcnt == 0;
 	return $errorcnt;
 	}
+
+sub file_newer
+	{
+	my ($file1, $file2) = @_;
+	return (stat($file1))[9] > (stat($file2))[9]
+	}