[PATCH] Make gcc3.3 Eliminate Unused Static Functions

From: Rusty Russell (rusty@rustcorp.com.au)
Date: Thu Jun 12 2003 - 19:17:05 EST

In discussions with akpm: it'd be nice to discard unused functions
(think CONFIG_PROC_FS=n) without needing to #ifdef around them.

Feedback welcome,

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

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: D: static int unusedfunc(void) { ... }; D: int otherfunc(void) D: { D: (void)unusedfunc; D: ... 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: 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: D: Earlier compilers don't understand this parameter, so we test for D: it at build time. D: D: Results (all with gcc 3.3) D: Without patch: D: -rwxrwxr-x 1 rusty rusty 5115166 Jun 13 09:17 vmlinux D: With patch: D: -rwxrwxr-x 1 rusty rusty 5115166 Jun 13 09:58 vmlinux D: Without patch (small unused function added): D: -rwxrwxr-x 1 rusty rusty 5115195 Jun 13 10:14 vmlinux D: 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 +213,13 @@ CFLAGS_KERNEL = AFLAGS_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) +-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 AFLAGS := -D__ASSEMBLY__ $(CPPFLAGS) export VERSION PATCHLEVEL SUBLEVEL EXTRAVERSION KERNELRELEASE ARCH \ - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/

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