From 7c601e6b7b7696b24ce5f5715fa14dbb91c71d6e Mon Sep 17 00:00:00 2001
From: Jan Maria Matejka <mq@ucw.cz>
Date: Wed, 29 Nov 2017 11:38:01 +0100
Subject: [PATCH] Filter: recursion to loop

It was supposed to do tail-recursion in interpret() but it didn't
compile as such. Converting it to loop makes a significant filter
performance improvement for flat filters.
---
 filter/filter.c | 10 +++-------
 1 file changed, 3 insertions(+), 7 deletions(-)

diff --git a/filter/filter.c b/filter/filter.c
index db90941f..85721dbd 100644
--- a/filter/filter.c
+++ b/filter/filter.c
@@ -633,15 +633,13 @@ static struct f_val
 interpret(struct f_inst *what)
 {
   struct symbol *sym;
-  struct f_val v1, v2, res, *vp;
+  struct f_val v1, v2, res = { .type = T_VOID }, *vp;
   unsigned u1, u2;
   int i;
   u32 as;
 
+  for ( ; what; what = what->next) {
   res.type = T_VOID;
-  if (!what)
-    return res;
-
   switch(what->fi_code) {
   case FI_COMMA:
     TWOARGS;
@@ -1510,9 +1508,7 @@ interpret(struct f_inst *what)
 
   default:
     bug( "Unknown instruction %d (%c)", what->fi_code, what->fi_code & 0xff);
-  }
-  if (what->next)
-    return interpret(what->next);
+  }}
   return res;
 }