[libav-devel] [PATCH 1/3] configure: speed up flatten_extralibs_wrapper()

James Almer jamrial at gmail.com
Mon Sep 17 04:52:59 CEST 2018


From: Avi Halachmi <avihpit at yahoo.com>

x50 - x200 faster.

Currently configure spends 50-70% of its runtime inside a single
function: flatten_extralibs[_wrapper] - which does string processing.

During its run, nearly 20K command substitutions (subshells) are used,
including its callees unique() and resolve(), which is the reason
for its lengthy run.

This commit avoids all subshells during its execution, speeding it up
by about two orders of magnitude, and reducing the overall configure
runtime by 50-70% .

resolve() is rewritten to avoid subshells, and in unique() and
flatten_extralibs() we inline the filter[_out] functionality.

Note that logically, unique functionality has more than one possible
output (depending on which of the recurring items is kept). As it
turns out, other parts expect the last recurring item to be kept
(which was the original behavior of uniqie()). This patch preservs
its output order.

Signed-off-by: James Almer <jamrial at gmail.com>
---
 configure | 46 +++++++++++++++++++++++++++++++++-------------
 1 file changed, 33 insertions(+), 13 deletions(-)

diff --git a/configure b/configure
index 48e8536b0..be348e881 100755
--- a/configure
+++ b/configure
@@ -689,22 +689,37 @@ prepend(){
     eval "$var=\"$* \$$var\""
 }
 
+reverse () {
+    eval '
+        reverse_out=
+        for v in $'$1'; do
+            reverse_out="$v $reverse_out"
+        done
+        '$1'=$reverse_out
+    '
+}
+
+# keeps the last occurence of each non-unique item
 unique(){
-    var=$1
-    uniq_list=""
-    for tok in $(eval echo \$$var); do
-        uniq_list="$(filter_out $tok $uniq_list) $tok"
+    unique_out=
+    eval unique_in=\$$1
+    reverse unique_in
+    for v in $unique_in; do
+        # " $unique_out" +space such that every item is surrounded with spaces
+        case " $unique_out" in *" $v "*) continue; esac  # already in list
+        unique_out="$unique_out$v "
     done
-    eval "$var=\"${uniq_list}\""
+    reverse unique_out
+    eval $1=\$unique_out
 }
 
 resolve(){
-    var=$1
-    tmpvar=
-    for entry in $(eval echo \$$var); do
-        tmpvar="$tmpvar $(eval echo \$${entry})"
+    resolve_out=
+    eval resolve_in=\$$1
+    for v in $resolve_in; do
+        eval 'resolve_out="$resolve_out$'$v' "'
     done
-    eval "$var=\"${tmpvar}\""
+    eval $1=\$resolve_out
 }
 
 add_cppflags(){
@@ -5097,14 +5112,19 @@ check_deps $CONFIG_LIST       \
            $ALL_COMPONENTS    \
 
 flatten_extralibs(){
-    unset nested_entries
+    nested_entries=
     list_name=$1
     eval list=\$${1}
     for entry in $list; do
         entry_copy=$entry
         resolve entry_copy
-        append nested_entries $(filter '*_extralibs' $entry_copy)
-        flat_entries=$(filter_out '*_extralibs' $entry_copy)
+        flat_entries=
+        for e in $entry_copy; do
+            case $e in
+                *_extralibs) nested_entries="$nested_entries$e ";;
+                          *) flat_entries="$flat_entries$e ";;
+            esac
+        done
         eval $entry="\$flat_entries"
     done
     append $list_name "$nested_entries"
-- 
2.19.0



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