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

    * Jakub Jelinek <jakub@redhat.com> wrote:

    > > +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)
    > .

    indeed - updated patch below.

    Ingo

    Subject: allow gcc4 to optimize unit-at-a-time

    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 $(call cc-option,-fno-unit-at-a-time); fi ;)

    CFLAGS += $(cflags-y)

    -
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