Re: [PATCH 01/12] use a shell function for _AC_PREPROC_IFELSE

[Eric Blake]

Paolo Bonzini <bonzini <at> gnu.org> writes:

> 
> So, this is the patch bomb for shell functions. 
> 
> I'm starting from four simple functions for _AC_*_IFELSE.  Together,
> they obtain most of the size reduction (10-15%) but slow down Autoconf
> by ~5%.

Slow down?  Not on my watch ;)

I'm squashing some changes on top of yours, and then I actually see a speedup 
of .5 or 1% (the lost time you were seeing was all the wasted parsing of the 
function body and computation of diversion numbers within AS_REQUIRE; now that 
the function body is hidden behind a macro name, and AS_REQUIRE is called less 
frequently, there is a net gain).  Here's what I'm about to push, provided that 
the testsuite currently in progress completes successfully.

From: Paolo Bonzini <address@hidden>
Date: Tue, 21 Oct 2008 08:55:05 -0600
Subject: [PATCH] Use a shell function for _AC_PREPROC_IFELSE.

* lib/autoconf/general.m4 (_AC_PREPROC_IFELSE_BODY): New macro.
(_AC_PREPROC_IFELSE): Use a shell function.
* lib/m4sugar/m4sh.m4 (AS_REQUIRE): Factor for faster execution.
* lib/m4sugar/m4sh.m4 (AS_REQUIRE_SHELL_FN): Bypass AS_REQUIRE if
function has already been provided.

Signed-off-by: Eric Blake <address@hidden>
---
 ChangeLog               |   10 ++++++++++
 lib/autoconf/general.m4 |   34 ++++++++++++++++++++++++----------
 lib/m4sugar/m4sh.m4     |   17 +++++++++++------
 3 files changed, 45 insertions(+), 16 deletions(-)

diff --git a/ChangeLog b/ChangeLog
index e57150e..e6759f4 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,13 @@
+2008-10-21  Paolo Bonzini  <address@hidden>
+       and Eric Blake  <address@hidden>
+
+       Use a shell function for _AC_PREPROC_IFELSE.
+       * lib/autoconf/general.m4 (_AC_PREPROC_IFELSE_BODY): New macro.
+       (_AC_PREPROC_IFELSE): Use a shell function.
+       * lib/m4sugar/m4sh.m4 (AS_REQUIRE): Factor for faster execution.
+       * lib/m4sugar/m4sh.m4 (AS_REQUIRE_SHELL_FN): Bypass AS_REQUIRE if
+       function has already been provided.
+
 2008-10-21  Eric Blake  <address@hidden>
 
        Add banners to generated files.
diff --git a/lib/autoconf/general.m4 b/lib/autoconf/general.m4
index 32c13f6..b5c720d 100644
--- a/lib/autoconf/general.m4
+++ b/lib/autoconf/general.m4
@@ -2377,6 +2377,23 @@ AC_DEFUN([AC_RUN_LOG],
 ## ------------------------ ##
 
 
+# _AC_PREPROC_IFELSE_BODY
+# -----------------------
+# Shell function body for _AC_PREPROC_IFELSE.
+m4_define([_AC_PREPROC_IFELSE_BODY],
+[  AS_LINENO_PUSH([$[]1])
+  AS_IF([_AC_DO_STDERR([$ac_cpp conftest.$ac_ext]) >/dev/null && {
+        test -z "$ac_[]_AC_LANG_ABBREV[]_preproc_warn_flag$ac_[]_AC_LANG_ABBREV
[]_werror_flag" ||
+        test ! -s conftest.err
+       }],
+    [ac_retval=0],
+    [_AC_MSG_LOG_CONFTEST
+    ac_retval=1])
+  rm -f conftest.err
+  AS_LINENO_POP
+  return $ac_retval
+])
+
 
 # _AC_PREPROC_IFELSE(PROGRAM, [ACTION-IF-TRUE], [ACTION-IF-FALSE])
 # ----------------------------------------------------------------
@@ -2385,18 +2402,15 @@ AC_DEFUN([AC_RUN_LOG],
 # This macro can be used during the selection of a preprocessor.
 # eval is necessary to expand ac_cpp.
 AC_DEFUN([_AC_PREPROC_IFELSE],
-[m4_ifvaln([$1], [AC_LANG_CONFTEST([$1])])dnl
-AS_IF([_AC_DO_STDERR([$ac_cpp conftest.$ac_ext]) >/dev/null && {
-        test -z "$ac_[]_AC_LANG_ABBREV[]_preproc_warn_flag$ac_[]_AC_LANG_ABBREV
[]_werror_flag" ||
-        test ! -s conftest.err
-       }],
-  [$2],
-  [_AC_MSG_LOG_CONFTEST
-  $3])
-rm -f conftest.err m4_ifval([$1], [conftest.$ac_ext])[]dnl
+[AC_REQUIRE_SHELL_FN([ac_func_]_AC_LANG_ABBREV[_try_cpp],
+  [AS_FUNCTION_DESCRIBE([ac_func_]_AC_LANG_ABBREV[_try_cpp], [LINENO],
+    [Try to preprocess conftest.$ac_ext, and return whether this succeeded.])],
+    [$0_BODY])]dnl
+[m4_ifvaln([$1], [AC_LANG_CONFTEST([$1])])]dnl
+[AS_IF([ac_func_[]_AC_LANG_ABBREV[]_try_cpp "$LINENO"], [$2], [$3])
+m4_ifvaln([$1], [rm -f conftest.$ac_ext])dnl
 ])# _AC_PREPROC_IFELSE
 
-
 # AC_PREPROC_IFELSE(PROGRAM, [ACTION-IF-TRUE], [ACTION-IF-FALSE])
 # ---------------------------------------------------------------
 # Try to preprocess PROGRAM.  Requires that the preprocessor for the
diff --git a/lib/m4sugar/m4sh.m4 b/lib/m4sugar/m4sh.m4
index 5ed52d4..9ef15f5 100644
--- a/lib/m4sugar/m4sh.m4
+++ b/lib/m4sugar/m4sh.m4
@@ -317,11 +317,14 @@ m4_divert_pop[]dnl
 # Note: we expand _m4_divert_desired before passing it to m4_divert_require,
 # otherwise we would need to use m4_pushdef and m4_popdef instead of
 # simply m4_define.
+#
+# Since $2 can be quite large, this is factored for faster execution, giving
+# either m4_require([$1], [$2]) or m4_divert_require(desired, [$1], [$2]).
 m4_defun([AS_REQUIRE],
-[m4_define([_m4_divert_desired], [m4_default_quoted([$3], [M4SH-INIT])])dnl
-m4_if(m4_eval(_m4_divert(_m4_divert_dump) <= _m4_divert(_m4_divert_desired)), 
1,
-      [m4_require([$1], [$2])],
-      [m4_divert_require(_m4_divert(_m4_divert_desired), [$1], [$2])])])
+[m4_define([_m4_divert_desired], [m4_default_quoted([$3], [M4SH-INIT])])]dnl
+[m4_if(m4_eval(_m4_divert(_m4_divert_dump) <= _m4_divert(_m4_divert_desired)),
+       1, [m4_require(],
+         [m4_divert_require(_m4_divert(_m4_divert_desired),]) [$1], [$2])])
 
 
 # AS_REQUIRE_SHELL_FN(NAME-TO-CHECK, COMMENT, BODY-TO-EXPAND,
@@ -333,12 +336,14 @@ m4_if(m4_eval(_m4_divert(_m4_divert_dump) <= _m4_divert
(_m4_divert_desired)), 1,
 # provided (often via AS_FUNCTION_DESCRIBE), it is listed with a
 # newline before the function name.
 m4_define([AS_REQUIRE_SHELL_FN],
+[m4_provide_if([AS_SHELL_FN_$1], [],
 [AS_REQUIRE([AS_SHELL_FN_$1],
-[m4_provide([AS_SHELL_FN_$1])m4_n([$2])$1 ()
+[m4_provide([AS_SHELL_FN_$1])
+m4_n([$2])$1 ()
 {
 $3
 } [#] $1
-], m4_default_quoted([$4], [M4SH-INIT-FN]))])
+], m4_default_quoted([$4], [M4SH-INIT-FN]))])])
 
 
 # _AS_RUN(TEST, [SHELL])
-- 
1.6.0.2