[Automake-NG] [PATCH 2/2] [ng] perf: optimize 'am__strip_suffixes' for speed

[Stefano Lattarini]

This optimization offers some noticeable performance improvements for
packages having a lot of tests and using the Automake-provided parallel
testsuite harness; this is due to the fact that the internal automake
variable 'am__test_bases' used by it is calculated through a proper call
to 'am__strip_suffixes'.

More precisely, we have measured the times required to complete null
"make all", "make recheck" and "make check AM_LAZY_CHECK=yes"
invocations in a package with 5000 tests in the top-level directory
and other 5000 tests in a subdirectory.  Here are the results,
averaged on a several runs:

+ Before this patch:
  - "make all"                           2.7 seconds
  - "make recheck"                       3.9 seconds
  - "make check AM_LAZY_CHECK=yes"      15.2 seconds

+ After this patch:
  - "make all"                           0.4 seconds
  - "make recheck"                       1.7 seconds
  - "make check AM_LAZY_CHECK=yes"       7.2 seconds

+ In mainline automake (commit v1.12-75-gd89da9c):
  - "make all"                           0.9 seconds
  - "make recheck"                       3.5 seconds
  - "make check RECHECK_LOGS="          14.1 seconds

See also previous commit v1.12-233-g0010655 "[ng] check: memoize some
internal vars (avoid useless recalculation)" for another (weaker)
optimization.

The need for this optimization has been suggested by Bob Friesenhahn:
<http://lists.gnu.org/archive/html/automake-ng/2012-05/msg00045.html>

* lib/am/header-vars.am (am__strip_suffixes): Rewrite in a way
that allows much better performance.
(am__private_suffix): New internal variable, used by the new
implementation.
(am__strip_suffixes): Remove, it's not needed anymore.
* t/internals.tap: Adjust.

Signed-off-by: Stefano Lattarini <address@hidden>
---
 lib/am/header-vars.am |   23 +++++++++--------------
 t/internals.tap       |   41 +++++++++++------------------------------
 2 files changed, 20 insertions(+), 44 deletions(-)

diff --git a/lib/am/header-vars.am b/lib/am/header-vars.am
index 386df1f..10ff773 100644
--- a/lib/am/header-vars.am
+++ b/lib/am/header-vars.am
@@ -103,25 +103,20 @@ am__uniq = $(strip \
 am__memoize = $(or $(am__memoized_value/$1),$(strip \
   $(eval am__memoized_value/$1 := $$2))$(am__memoized_value/$1))
 
-## $(call am__strip_suffixes_0, SUFFIXES, WORD)
-## --------------------------------------------
-## Strip any of the SUFFIXES from WORD.  Even if WORD terminates with
-## several suffixes, only one is stripped: the first one that matches.
-am__strip_suffixes_0 = $(strip \
-  $(if $(strip $(1)), \
-    $(if $(filter %$(firstword $(1)), $(2)), \
-         $(patsubst %$(firstword $(1)), %, $(2)), \
-         $(call am__strip_suffixes_0, \
-               $(call am__strip_firstword, $(1)), $(2))), \
-    $(2)))
-
 ## $(call am__strip_suffixes, SUFFIXES, LIST)
 ## ------------------------------------------
 ## Strip any of the SUFFIXES from each of the entries of LIST.  Even if an
 ## entry of LIST terminates with several suffixes, only one is stripped:
 ## the first one that matches.
-am__strip_suffixes = \
-  $(foreach am__i,$(2),$(call am__strip_suffixes_0,$(1),$(am__i)))
+am__private_suffix = .,;&!@
+am__strip_suffixes = $(strip \
+  $(if \
+    $(strip $1), \
+      $(patsubst %$(am__private_suffix),%, \
+        $(call am__strip_suffixes, \
+          $(call am__strip_firstword,$1), \
+          $(patsubst %$(firstword $1),%$(am__private_suffix),$2))), \
+    $2))
 
 ## Some derived variables that have been found to be useful.
 pkgdatadir = $(datadir)/@PACKAGE@
diff --git a/t/internals.tap b/t/internals.tap
index 6d69166..f6ea954 100755
--- a/t/internals.tap
+++ b/t/internals.tap
@@ -19,7 +19,7 @@
 am_create_testdir=empty
 . ./defs || Exit 1
 
-plan_ 5
+plan_ 4
 
 cp "$am_amdir"/header-vars.am . \
   || fatal_ "fetching makefile fragment headers-vars.am"
@@ -74,32 +74,6 @@ test-uniq:
        test '$(call am__uniq,3 1 1 4 1 4 1 1)' = '3 1 4'
        test '$(call am__uniq,  1   3   1  )'   = '1 3'
 
-.PHONY: test-strip-suffixes0
-test-strip-suffixes0:
-       test '$(call am__strip_suffixes_0,,)'                 = ''
-       test '$(call am__strip_suffixes_0,        ,)'         = ''
-       test '$(call am__strip_suffixes_0,,       )'          = ''
-       test '$(call am__strip_suffixes_0,      ,         )'  = ''
-       test '$(call am__strip_suffixes_0,x,)'                = ''
-       test '$(call am__strip_suffixes_0,x,      )'          = ''
-       test '$(call am__strip_suffixes_0,x y,    )'          = ''
-       test '$(call am__strip_suffixes_0,,x)'                = 'x'
-       test '$(call am__strip_suffixes_0,       ,x)'         = 'x'
-       test '$(call am__strip_suffixes_0,.c,foo.c)'          = 'foo'
-       test '$(call am__strip_suffixes_0,.c .c++, bar.c++)'  = 'bar'
-       test '$(call am__strip_suffixes_0,.c .c++, bar.cxx)'  = 'bar.cxx'
-       test '$(call am__strip_suffixes_0,x,ax)'              = 'a'
-       test '$(call am__strip_suffixes_0,x,xa)'              = 'xa'
-       test '$(call am__strip_suffixes_0,x,xx)'              = 'x'
-       test '$(call am__strip_suffixes_0,x,xux)'             = 'xu'
-       test '$(call am__strip_suffixes_0, .a .b, x.a.a)'     = 'x.a'
-       test '$(call am__strip_suffixes_0, .a .b, x.a.b)'     = 'x.a'
-       test '$(call am__strip_suffixes_0, .a .b, x.b.a)'     = 'x.b'
-       test '$(call am__strip_suffixes_0, .a .b, x.b.b)'     = 'x.b'
-       # Corner cases: the *first* matched suffix is stripped
-       test '$(call am__strip_suffixes_0, .a .b.a, foo.b.a)' = 'foo.b'
-       test '$(call am__strip_suffixes_0, .b.a .a, foo.b.a)' = 'foo'
-
 .PHONY: test-strip-suffixes
 test-strip-suffixes:
        test '$(call am__strip_suffixes,,)'                 = ''
@@ -113,21 +87,28 @@ test-strip-suffixes:
        test '$(call am__strip_suffixes,.c,foo.c)'          = 'foo'
        test '$(call am__strip_suffixes,.foo,a.foo b.foo)'  = 'a b'
        test '$(call am__strip_suffixes, x y, ax ay ax)'    = 'a a a'
+       test '$(call am__strip_suffixes,x,ax)'              = 'a'
+       test '$(call am__strip_suffixes,x,xa)'              = 'xa'
+       test '$(call am__strip_suffixes,x,xx)'              = 'x'
+       test '$(call am__strip_suffixes,x,xux)'             = 'xu'
        test '$(call am__strip_suffixes, .c .c++, \
                foo.c bar.c++ baz.cxx zap.c)' = 'foo bar baz.cxx zap'
        test '$(call am__strip_suffixes, .a .b, \
                1.a.a 2.a.b 3.b.a 4.b.b)' = '1.a 2.a 3.b 4.b'
        # Corner cases: the *first* matched suffix is stripped
+       test '$(call am__strip_suffixes,.a .b,x.a.a)' = 'x.a'
+       test '$(call am__strip_suffixes,.a .b,x.a.b)' = 'x.a'
+       test '$(call am__strip_suffixes,.a .b,x.b.a)' = 'x.b'
+       test '$(call am__strip_suffixes,.a .b,x.b.b)' = 'x.b'
        test '$(call am__strip_suffixes, .a .b.a, foo.b.a bar.a)' \
-            = 'foo.b bar'
+             = 'foo.b bar'
        test '$(call am__strip_suffixes, .b.a .a, foo.b.a bar.a)' \
-            = 'foo bar'
+             = 'foo bar'
 END
 
 command_ok_  am__strip_firstword        $MAKE test-strip-firstword
 command_ok_  am__strip_lastword         $MAKE test-strip-lastword
 command_ok_  am__uniq                   $MAKE test-uniq
-command_ok_  am__test_strip_suffixes_0  $MAKE test-strip-suffixes0
 command_ok_  am__test_strip_suffixes    $MAKE test-strip-suffixes
 
 :
-- 
1.7.9.5