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