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Re: [PATCH 2/2] Support slim LTO bootstrap
- From: Richard Biener <richard dot guenther at gmail dot com>
- To: Andi Kleen <andi at firstfloor dot org>
- Cc: GCC Patches <gcc-patches at gcc dot gnu dot org>, Andi Kleen <ak at linux dot intel dot com>
- Date: Mon, 1 Sep 2014 13:43:08 +0200
- Subject: Re: [PATCH 2/2] Support slim LTO bootstrap
- Authentication-results: sourceware.org; auth=none
- References: <1409496686-14681-1-git-send-email-andi at firstfloor dot org> <1409496686-14681-2-git-send-email-andi at firstfloor dot org> <1409496686-14681-3-git-send-email-andi at firstfloor dot org>
On Sun, Aug 31, 2014 at 4:51 PM, Andi Kleen <andi@firstfloor.org> wrote:
> From: Andi Kleen <ak@linux.intel.com>
>
> Change the bootstrap-lto config file to use slim (non fat) LTO..
> Speeds up the LTO bootstrap by ~18% on a 4 core system.
>
> This requires using gcc-ar/ranlib in post stage 1 builds, so these
> are passed to all sub builds.
>
> v2: Change existing config file as requested by Honza.
>
> config/:
>
> 2014-08-31 Andi Kleen <ak@linux.intel.com>
>
> * bootstrap-lto.mk: Implement slim bootstrap.
> /:
>
> 2014-08-31 Andi Kleen <ak@linux.intel.com>
>
> * Makefile.tpl (POSTSTAGE1_HOST_EXPORTS): Add LTO_EXPORTS.
> POSTSTAGE1_FLAGS_TO_PASS): Add LTO_FLAGS_TO_PASS.
> * Makefile.in: Regenerate.
> ---
> Makefile.in | 2 ++
> Makefile.tpl | 2 ++
> config/bootstrap-lto-slim.mk | 13 +++++++++++++
> config/bootstrap-lto.mk | 16 +++++++++++-----
> 4 files changed, 28 insertions(+), 5 deletions(-)
> create mode 100644 config/bootstrap-lto-slim.mk
>
> diff --git a/Makefile.in b/Makefile.in
> index add8cf6..d6105b3 100644
> --- a/Makefile.in
> +++ b/Makefile.in
> @@ -257,6 +257,7 @@ POSTSTAGE1_HOST_EXPORTS = \
> $(XGCC_FLAGS_FOR_TARGET) $$TFLAGS"; export CC; \
> CC_FOR_BUILD="$$CC"; export CC_FOR_BUILD; \
> $(POSTSTAGE1_CXX_EXPORT) \
> + $(LTO_EXPORTS) \
> GNATBIND="$$r/$(HOST_SUBDIR)/prev-gcc/gnatbind"; export GNATBIND; \
> LDFLAGS="$(POSTSTAGE1_LDFLAGS) $(BOOT_LDFLAGS)"; export LDFLAGS; \
> HOST_LIBS="$(POSTSTAGE1_LIBS)"; export HOST_LIBS;
> @@ -828,6 +829,7 @@ POSTSTAGE1_FLAGS_TO_PASS = \
> GNATBIND="$${GNATBIND}" \
> LDFLAGS="$${LDFLAGS}" \
> HOST_LIBS="$${HOST_LIBS}" \
> + $(LTO_FLAGS_TO_PASS) \
> "`echo 'ADAFLAGS=$(BOOT_ADAFLAGS)' | sed -e s'/[^=][^=]*=$$/XFOO=/'`"
>
> # Flags to pass down to makes which are built with the target environment.
> diff --git a/Makefile.tpl b/Makefile.tpl
> index 00dba36..f7c7e38 100644
> --- a/Makefile.tpl
> +++ b/Makefile.tpl
> @@ -260,6 +260,7 @@ POSTSTAGE1_HOST_EXPORTS = \
> $(XGCC_FLAGS_FOR_TARGET) $$TFLAGS"; export CC; \
> CC_FOR_BUILD="$$CC"; export CC_FOR_BUILD; \
> $(POSTSTAGE1_CXX_EXPORT) \
> + $(LTO_EXPORTS) \
> GNATBIND="$$r/$(HOST_SUBDIR)/prev-gcc/gnatbind"; export GNATBIND; \
> LDFLAGS="$(POSTSTAGE1_LDFLAGS) $(BOOT_LDFLAGS)"; export LDFLAGS; \
> HOST_LIBS="$(POSTSTAGE1_LIBS)"; export HOST_LIBS;
> @@ -633,6 +634,7 @@ POSTSTAGE1_FLAGS_TO_PASS = \
> GNATBIND="$${GNATBIND}" \
> LDFLAGS="$${LDFLAGS}" \
> HOST_LIBS="$${HOST_LIBS}" \
> + $(LTO_FLAGS_TO_PASS) \
> "`echo 'ADAFLAGS=$(BOOT_ADAFLAGS)' | sed -e s'/[^=][^=]*=$$/XFOO=/'`"
>
> # Flags to pass down to makes which are built with the target environment.
> diff --git a/config/bootstrap-lto-slim.mk b/config/bootstrap-lto-slim.mk
> new file mode 100644
> index 0000000..9e065e1
> --- /dev/null
> +++ b/config/bootstrap-lto-slim.mk
> @@ -0,0 +1,13 @@
> +# This option enables LTO for stage2 and stage3 in slim mode
> +
> +STAGE2_CFLAGS += -flto=jobserver -frandom-seed=1
> +STAGE3_CFLAGS += -flto=jobserver -frandom-seed=1
> +STAGEprofile_CFLAGS += -fno-lto
> +
> +# assumes the host supports the linker plugin
> +LTO_AR = $$r/$(HOST_SUBDIR)/prev-gcc/gcc-ar$(exeext) -B$$r/$(HOST_SUBDIR)/prev-gcc/
> +LTO_RANLIB = $$r/$(HOST_SUBDIR)/prev-gcc/gcc-ranlib$(exeext) -B$$r/$(HOST_SUBDIR)/prev-gcc/
> +
-ffat-lto-objects is automatically active for hosts not supporting the
linker plugin. Is gcc-ar$(exeext) unconditionally built and found
on such hosts? Will gcc-ar work without finding a linker plugin
on such hosts?
As I think the non-linker-plugin path is not really interesting the
patch is ok as-is. Just be prepared to followup with a fix for
such hosts (darwin I suppose, and other non-ELF hosts).
Thanks,
Richard.
> +LTO_EXPORTS = AR="$(LTO_AR)"; export AR; \
> + RANLIB="$(LTO_RANLIB)"; export RANLIB;
> +LTO_FLAGS_TO_PASS = AR="$(LTO_AR)" RANLIB="$(LTO_RANLIB)"
> diff --git a/config/bootstrap-lto.mk b/config/bootstrap-lto.mk
> index 27bad15..9e065e1 100644
> --- a/config/bootstrap-lto.mk
> +++ b/config/bootstrap-lto.mk
> @@ -1,7 +1,13 @@
> -# This option enables LTO for stage2 and stage3.
> -# FIXME: Our build system is not yet able to use gcc-ar wrapper, so we need
> -# to go with -ffat-lto-objects.
> +# This option enables LTO for stage2 and stage3 in slim mode
>
> -STAGE2_CFLAGS += -flto=jobserver -frandom-seed=1 -ffat-lto-objects
> -STAGE3_CFLAGS += -flto=jobserver -frandom-seed=1 -ffat-lto-objects
> +STAGE2_CFLAGS += -flto=jobserver -frandom-seed=1
> +STAGE3_CFLAGS += -flto=jobserver -frandom-seed=1
> STAGEprofile_CFLAGS += -fno-lto
> +
> +# assumes the host supports the linker plugin
> +LTO_AR = $$r/$(HOST_SUBDIR)/prev-gcc/gcc-ar$(exeext) -B$$r/$(HOST_SUBDIR)/prev-gcc/
> +LTO_RANLIB = $$r/$(HOST_SUBDIR)/prev-gcc/gcc-ranlib$(exeext) -B$$r/$(HOST_SUBDIR)/prev-gcc/
> +
> +LTO_EXPORTS = AR="$(LTO_AR)"; export AR; \
> + RANLIB="$(LTO_RANLIB)"; export RANLIB;
> +LTO_FLAGS_TO_PASS = AR="$(LTO_AR)" RANLIB="$(LTO_RANLIB)"
> --
> 2.0.4
>