[PATCH 2/3] Eliminate unused functions for gcc 3.3+

From: Rusty Russell (rusty@rustcorp.com.au)
Date: Mon Jun 23 2003 - 04:12:15 EST

Name: Eliminate Unused Functions
Author: Rusty Russell
Status: Tested on 2.5.70-bk16

D: GCC 3.3 has the ability to eliminate unused static functions. This includes
D: code like this:
D: static int unusedfunc(void) { ... };
D: int otherfunc(void)
D: {
D: (void)unusedfunc;
D: ...
D: This means that macros can suppress the "unused" warning on functions
D: without preventing the function elimination. This should allow us to
D: remove a number of #ifdefs around unused functions.
D: Unfortunately, this elimination is only performed if
D: -finline-functions is used. In order to prevent GCC automatically
D: inlining anything, we also specify "--param max-inline-insns-auto=0".
D: Earlier compilers don't understand this parameter, so we test for
D: it at build time.
D: Results:
D: gcc 3.3 without patch:
D: -rwxrwxr-x 1 rusty rusty 5115166 Jun 13 09:17 vmlinux
D: gcc 3.3 with patch:
D: -rwxrwxr-x 1 rusty rusty 5115166 Jun 13 09:58 vmlinux
D: gcc 3.3 without patch (small unused function added):
D: -rwxrwxr-x 1 rusty rusty 5115195 Jun 13 10:14 vmlinux
D: gcc 3.3 with patch (small unused function added):
D: -rwxrwxr-x 1 rusty rusty 5115166 Jun 13 10:15 vmlinux

diff -urpN --exclude TAGS -X /home/rusty/devel/kernel/kernel-patches/current-dontdiff --minimal working-2.5.70-bk16-check_region/Makefile working-2.5.70-bk16-check_region-inline/Makefile
--- working-2.5.70-bk16-check_region/Makefile 2003-06-12 09:57:39.000000000 +1000
+++ working-2.5.70-bk16-check_region-inline/Makefile 2003-06-12 21:34:40.000000000 +1000
@@ -213,10 +213,12 @@ CFLAGS_KERNEL =
 NOSTDINC_FLAGS = -nostdinc -iwithprefix include
+# Needs gcc 3.3 or above to understand max-inline-insns-auto.
+INLINE_OPTS := $(shell $(CC) -o /non/existent/file -c --param max-inline-insns-auto=0 -xc /dev/null 2>&1 | grep /non/existent/file >/dev/null && echo -finline-functions --param max-inline-insns-auto=0)
 CPPFLAGS := -D__KERNEL__ -Iinclude
 CFLAGS := $(CPPFLAGS) -Wall -Wstrict-prototypes -Wno-trigraphs -O2 \
- -fno-strict-aliasing -fno-common
+ $(INLINE_OPTS) -fno-strict-aliasing -fno-common

  Anyone who quotes me in their sig is an idiot. -- Rusty Russell.
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