Commit 814f63ec authored by Peter Kümmel's avatar Peter Kümmel Committed by Thomas Petazzoni
Browse files

toolchain: add link-time-optimization support 



Add a new option BR2_GCC_ENABLE_LTO that builds gcc and binutils with
LTO support.

Individual packages still have to enable LTO explicitly by passing '-flto' to
GCC, which passes it on to the linker. This option does not add that flag
globally. Some packages detect if the compiler supports LTO and enable the flag
if it does.

To support LTO, ar and ranlib must be called with an argument which triggers the
usage of the LTO plugin. Since GCC doesn't call these tools itself, it instead
provides wrappers for ar and ranlib that pass the LTO arguments. This way
existing Makefiles don't need to be changed for LTO support. However, these
wrappers are called <tuple>-gcc-ar which matches the pattern to link to the
buildroot wrapper in the external toolchain logic. So the external toolchain
logic is updated to provide the correct symlink.

[Thomas:
  - Add a separate BR2_BINUTILS_ENABLE_LTO option to enable LTO
    support in binutils. This is a blind option, selected by
    BR2_GCC_ENABLE_LTO. It just avoids having binutils.mk poke
    directly into gcc Config.in options.
  - Remove the check on the AVR32 special gcc version, which we don't
    support anymore.
  - Adapt the help text of the LTO Config.in option to no longer
    mention "Since version 4.5", since we only support gcc >= 4.5 in
    Buildroot anyway.
  - Fix typo in toolchain-external.mk comment.]

Signed-off-by: default avatarPeter Kümmel <syntheticpp@gmx.net>
Signed-off-by: default avatarThomas Petazzoni <thomas.petazzoni@free-electrons.com>
parent 518cdabb

package/binutils/Config.in.host

+3 −0
Original line number Diff line number Diff line
@@ -38,6 +38,9 @@ config BR2_BINUTILS_VERSION 
	default "2.24"		if BR2_BINUTILS_VERSION_2_24

	default "2.25"		if BR2_BINUTILS_VERSION_2_25



config BR2_BINUTILS_ENABLE_LTO

	bool



config BR2_BINUTILS_EXTRA_CONFIG_OPTIONS

	string "Additional binutils options"

	default ""

package/binutils/binutils.mk

+4 −0
Original line number Diff line number Diff line
@@ -96,5 +96,9 @@ BINUTILS_PRE_PATCH_HOOKS += BINUTILS_XTENSA_PRE_PATCH 
HOST_BINUTILS_PRE_PATCH_HOOKS += BINUTILS_XTENSA_PRE_PATCH

endif



ifeq ($(BR2_BINUTILS_ENABLE_LTO),y)

HOST_BINUTILS_CONF_OPTS += --enable-plugins --enable-lto

endif



$(eval $(autotools-package))

$(eval $(host-autotools-package))

package/gcc/Config.in.host

+7 −0
Original line number Diff line number Diff line
@@ -116,6 +116,13 @@ config BR2_GCC_ENABLE_TLS 
	  Enable the compiler to generate code for accessing

	  thread local storage variables



config BR2_GCC_ENABLE_LTO

	bool "Enable compiler link-time-optimization support"

	select BR2_BINUTILS_ENABLE_LTO

	help

	  This option enables link-time optimization (LTO) support in

	  gcc.



config BR2_GCC_ENABLE_OPENMP

	bool "Enable compiler OpenMP support"

	depends on !BR2_PTHREADS_NONE && !BR2_arc && !BR2_microblaze

package/gcc/gcc.mk

+4 −0
Original line number Diff line number Diff line
@@ -132,6 +132,10 @@ else 
HOST_GCC_COMMON_CONF_OPTS += --disable-tls

endif



ifeq ($(BR2_GCC_ENABLE_LTO),y)

HOST_GCC_COMMON_CONF_OPTS += --enable-plugins --enable-lto

endif



ifeq ($(BR2_GCC_ENABLE_LIBMUDFLAP),y)

HOST_GCC_COMMON_CONF_OPTS += --enable-libmudflap

else

toolchain/toolchain-external/toolchain-external.mk

+8 −0
Original line number Diff line number Diff line
@@ -647,12 +647,20 @@ endif 
# Build toolchain wrapper for preprocessor, C and C++ compiler and setup

# symlinks for everything else. Skip gdb symlink when we are building our

# own gdb to prevent two gdb's in output/host/usr/bin.

# When the link-time-optimazation flag '-flto' is used, then the compiler

# and binutils have to support lto. ar/ranlib need to be called with the

# lto plugin. The wrappers *-gcc-ar and *-gcc-ranlib provided by GCC could

# be used as drop-ins for ar/runlib when Makefiles are used which do not

# pass the lto arguments.

define TOOLCHAIN_EXTERNAL_INSTALL_WRAPPER

	$(Q)$(call MESSAGE,"Building ext-toolchain wrapper")

	mkdir -p $(HOST_DIR)/usr/bin; cd $(HOST_DIR)/usr/bin; \

	for i in $(TOOLCHAIN_EXTERNAL_CROSS)*; do \

		base=$${i##*/}; \

		case "$$base" in \

		*-ar|*-ranlib|*-nm) \

			ln -sf $$(echo $$i | sed 's%^$(HOST_DIR)%../..%') .; \

			;; \

		*cc|*cc-*|*++|*++-*|*cpp) \

			ln -sf ext-toolchain-wrapper $$base; \

			;; \