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

[Ingo Molnar <mingo@elte.hu>]

* 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)