Re: [patch 02/2] allow gcc4 to optimize unit-at-a-time

[Jakub Jelinek <jakub@redhat.com>]

On Wed, Dec 28, 2005 at 12:47:01PM +0100, Ingo Molnar wrote:
> allow gcc4 compilers to optimize unit-at-a-time - which results in gcc
> having a wider scope when optimizing. This also results in smaller code
> when optimizing for size. (gcc4 does not have the stack footprint
> problem of gcc3 compilers.)
> 
> Signed-off-by: Ingo Molnar <mingo@elte.hu>
> Signed-off-by: Arjan van de Ven <arjan@infradead.org>
> ----
> 
>  arch/i386/Makefile |    6 +++---
>  1 files changed, 3 insertions(+), 3 deletions(-)
> 
> Index: linux/arch/i386/Makefile
> ===================================================================
> --- linux.orig/arch/i386/Makefile
> +++ linux/arch/i386/Makefile
> @@ -42,9 +42,9 @@ include $(srctree)/arch/i386/Makefile.cp
>  GCC_VERSION			:= $(call cc-version)
>  cflags-$(CONFIG_REGPARM) 	+= $(shell if [ $(GCC_VERSION) -ge 0300 ] ; then echo "-mregparm=3"; fi ;)
>  
> -# Disable unit-at-a-time mode, it makes gcc use a lot more stack
> -# due to the lack of sharing of stacklots.
> -CFLAGS += $(call cc-option,-fno-unit-at-a-time)
> +# Disable unit-at-a-time mode on pre-gcc-4.0 compilers, it makes gcc use
> +# a lot more stack due to the lack of sharing of stacklots:
> +CFLAGS				+= $(shell if [ $(GCC_VERSION) -lt 0400 ] ; then echo "-fno-unit-at-a-time"; fi ;)

-fno-unit-at-a-time option has been introduced in GCC 3.4 (and 3.3-hammer
branch).  So unless the minimum supported GCC version to compile kernel is
3.4+, you need to replace
echo "-fno-unit-at-a-time"
with
$(call cc-option,-fno-unit-at-a-time)
.

	Jakub