Commit 9ab34fe7 authored Jan 14, 2006 by Ingo Molnar Committed by Linus Torvalds Jan 14, 2006

[PATCH] enable unit-at-a-time optimisations for gcc4



Allow gcc4 compilers to optimize unit-at-a-time.

This flag enables gcc to "see" the entire C file before making optimisation
decisions such as inline, which results in gcc making better decisions.  One
of the immediate effects of this is that static functions that are used only
once now get inlined.

gcc 3.4 has this flag as well, however gcc 3.x have a problem with inlining
and stacks and as a result, enabling this flag there would cause excessive and
unacceptable stack use.  This problem is fixed in the gcc 4.x series.  The
x86-64 architecture already enables this feature so it's well tested already.

Signed-off-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Arjan van de Ven <arjan@infradead.org>
Acked-by: Jeff Garzik <jgarzik@pobox.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

parent 40fc55cb

arch/i386/Makefile

+3 −3

Original line number	Original line	Diff line number	Diff line
	@@ -42,9 +42,9 @@ include $(srctree)/arch/i386/Makefile.cpu
	cflags-$(CONFIG_REGPARM) += $(shell if [ $(call cc-version) -ge 0300 ] ; then \		cflags-$(CONFIG_REGPARM) += $(shell if [ $(call cc-version) -ge 0300 ] ; then \
	echo "-mregparm=3"; fi ;)		echo "-mregparm=3"; fi ;)

	# Disable unit-at-a-time mode, it makes gcc use a lot more stack		# Disable unit-at-a-time mode on pre-gcc-4.0 compilers, it makes gcc use
	# due to the lack of sharing of stacklots.		# a lot more stack due to the lack of sharing of stacklots:
	CFLAGS += $(call cc-option,-fno-unit-at-a-time)		CFLAGS += $(shell if [ $(call cc-version) -lt 0400 ] ; then echo $(call cc-option,-fno-unit-at-a-time); fi ;)

	CFLAGS += $(cflags-y)		CFLAGS += $(cflags-y)

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