[prev in list] [next in list] [prev in thread] [next in thread] 

List:       buildroot
Subject:    [Buildroot] [PATCH v2 1/1] toolchain: add link-time-optimization support
From:       Peter Kümmel <syntheticpp () gmx ! net>
Date:       2015-03-06 12:34:06
Message-ID: 1425645246-3800-1-git-send-email-syntheticpp () gmx ! net
[Download RAW message or body]

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.

Signed-off-by: Peter Kümmel <syntheticpp@gmx.net>
---

Changes vor v2:
    - update commit message
    - UI text change for BR2_GCC_ENABLE_LTO

 package/binutils/binutils.mk                       | 4 ++++
 package/gcc/Config.in.host                         | 7 +++++++
 package/gcc/gcc.mk                                 | 4 ++++
 toolchain/toolchain-external/toolchain-external.mk | 8 ++++++++
 4 files changed, 23 insertions(+)

diff --git a/package/binutils/binutils.mk b/package/binutils/binutils.mk
index 9e99253..daa8c45 100644
--- a/package/binutils/binutils.mk
+++ b/package/binutils/binutils.mk
@@ -96,5 +96,9 @@ BINUTILS_PRE_PATCH_HOOKS += BINUTILS_XTENSA_PRE_PATCH
 HOST_BINUTILS_PRE_PATCH_HOOKS += BINUTILS_XTENSA_PRE_PATCH
 endif
 
+ifeq ($(BR2_GCC_ENABLE_LTO),y)
+HOST_BINUTILS_CONF_OPTS += --enable-plugins --enable-lto
+endif
+
 $(eval $(autotools-package))
 $(eval $(host-autotools-package))
diff --git a/package/gcc/Config.in.host b/package/gcc/Config.in.host
index e07d881..fe8bfdf 100644
--- a/package/gcc/Config.in.host
+++ b/package/gcc/Config.in.host
@@ -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"
+	depends on !BR2_GCC_VERSION_4_2_2_AVR32_2_1_5
+	help
+	  Since version 4.5, GCC supports link-time optimization (LTO).
+	  Select this option to turn on LTO support in GCC.
+
 config BR2_GCC_ENABLE_OPENMP
 	bool "Enable compiler OpenMP support"
 	depends on !BR2_PTHREADS_NONE && !BR2_arc && !BR2_microblaze
diff --git a/package/gcc/gcc.mk b/package/gcc/gcc.mk
index ffac15c..b5d2ddb 100644
--- a/package/gcc/gcc.mk
+++ b/package/gcc/gcc.mk
@@ -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
diff --git a/toolchain/toolchain-external/toolchain-external.mk \
b/toolchain/toolchain-external/toolchain-external.mk index 78138d3..3eaf934 \
                100644
--- a/toolchain/toolchain-external/toolchain-external.mk
+++ b/toolchain/toolchain-external/toolchain-external.mk
@@ -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 needs 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; \
 			;; \
-- 
2.3.0

_______________________________________________
buildroot mailing list
buildroot@busybox.net
http://lists.busybox.net/mailman/listinfo/buildroot


[prev in list] [next in list] [prev in thread] [next in thread]