| Message ID | 1283250838-13800-1-git-send-email-andi@firstfloor.org |
|---|---|
| State | New |
| Headers | show |
On 10-08-31 06:33 , Andi Kleen wrote: > @@ -2108,6 +2108,13 @@ to work around this, by choosing @code{BOOT_CFLAGS} to avoid the parts > of the stage1 compiler that were miscompiled, or by using @samp{make > bootstrap4} to increase the number of stages of bootstrap. > > +You can also use @code{BOOT_CFLAGS} to force an LTO bootstrap with > +@samp{BOOT_CFLAGS='-O2 -fwhopr=jobserver -fuse-linker-plugin -frandom-seed=1'}. > +Configure the compiler with @samp{--enable-stage1-languages=c,lto}. This > +will only work with the @command{gold} linker and if linker plugins are > +correctly configured. The @option{-frandom-seed=1} is needed to avoid > +bootstrap comparison failures. Could you add an explanation on why frandom-seed avoids the comparison failures? It's not immediately obvious. OK with that change. Diego.
On 08/31/2010 02:24 PM, Diego Novillo wrote: > On 10-08-31 06:33 , Andi Kleen wrote: > >> @@ -2108,6 +2108,13 @@ to work around this, by choosing >> @code{BOOT_CFLAGS} to avoid the parts >> of the stage1 compiler that were miscompiled, or by using @samp{make >> bootstrap4} to increase the number of stages of bootstrap. >> >> +You can also use @code{BOOT_CFLAGS} to force an LTO bootstrap with >> +@samp{BOOT_CFLAGS='-O2 -fwhopr=jobserver -fuse-linker-plugin >> -frandom-seed=1'}. >> +Configure the compiler with @samp{--enable-stage1-languages=c,lto}. This >> +will only work with the @command{gold} linker and if linker plugins are >> +correctly configured. The @option{-frandom-seed=1} is needed to avoid >> +bootstrap comparison failures. > > Could you add an explanation on why frandom-seed avoids the comparison > failures? It's not immediately obvious. > > OK with that change. No, config/bootstrap-lto.mk should be adjusted instead to use the options that Andi specifies. The doc change should be limited to the --enable-stage1-languages=c,lto part. Paolo
> No, config/bootstrap-lto.mk should be adjusted instead to use the > options that Andi specifies. The doc change should be limited to the > --enable-stage1-languages=c,lto part. The problem is that config/bootstrap-lto.mk doesn't work in the first place (and I don't know how to fix it). It never built for me. That is why I documented an alternative method. -Andi
On 08/31/2010 03:14 PM, Andi Kleen wrote: > >> No, config/bootstrap-lto.mk should be adjusted instead to use the >> options that Andi specifies. The doc change should be limited to the >> --enable-stage1-languages=c,lto part. > > The problem is that config/bootstrap-lto.mk doesn't work in the first place > (and I don't know how to fix it). It never built for me. > That is why I documented an alternative method. Have you tried s/-flto/flags-you-proposed-to-use-instead/ in that file? Paolo
On Aug 31, 2010, Andi Kleen <ak@linux.intel.com> wrote: >> No, config/bootstrap-lto.mk should be adjusted instead to use the >> options that Andi specifies. The doc change should be limited to >> the --enable-stage1-languages=c,lto part. > The problem is that config/bootstrap-lto.mk doesn't work in the first place > (and I don't know how to fix it). It never built for me. Somehow it worked for me. That said, I had lto in --enable-stage1-languages, but that was a mistake: it caused me to forget to adjust bootstrap-lto.mk to add lto to stage1 languages itself, which it should.
diff --git a/gcc/doc/install.texi b/gcc/doc/install.texi index fc9b988..e98675d 100644 --- a/gcc/doc/install.texi +++ b/gcc/doc/install.texi @@ -2108,6 +2108,13 @@ to work around this, by choosing @code{BOOT_CFLAGS} to avoid the parts of the stage1 compiler that were miscompiled, or by using @samp{make bootstrap4} to increase the number of stages of bootstrap. +You can also use @code{BOOT_CFLAGS} to force an LTO bootstrap with +@samp{BOOT_CFLAGS='-O2 -fwhopr=jobserver -fuse-linker-plugin -frandom-seed=1'}. +Configure the compiler with @samp{--enable-stage1-languages=c,lto}. This +will only work with the @command{gold} linker and if linker plugins are +correctly configured. The @option{-frandom-seed=1} is needed to avoid +bootstrap comparison failures. + @code{BOOT_CFLAGS} does not apply to bootstrapped target libraries. Since these are always compiled with the compiler currently being bootstrapped, you can use @code{CFLAGS_FOR_TARGET} to modify their @@ -2155,11 +2162,6 @@ Removes any @option{-O}-started option from @code{BOOT_CFLAGS}, and adds @item @samp{bootstrap-O3} Analogous to @code{bootstrap-O1}. -@item @samp{bootstrap-lto} -Enables Link-Time Optimization for host tools during bootstrapping. -@samp{BUILD_CONFIG=bootstrap-lto} is equivalent to adding -@option{-flto} to @samp{BOOT_CFLAGS}. - @item @samp{bootstrap-debug} Verifies that the compiler generates the same executable code, whether or not it is asked to emit debug information. To this end, this
From: Andi Kleen <ak@linux.intel.com> BUILD_CONFIG=bootstrap-lto does not work currently and causes build failures. Remove a reference to that in the install documentation and instead document a working method using BOOT_CFLAGS. Bootstrapped on x86-64 together with the -fwhopr=jobserver patchkit v2: Fix grammar/texinfo based on feedback Ok to commit? 2010-08-17 Andi Kleen <ak@linux.intel.com> * doc/install.texi (Building a native compiler): Remove reference to broken BUILD_CONFIG=bootstrap-lto. Document working method instead. --- gcc/doc/install.texi | 12 +++++++----- 1 files changed, 7 insertions(+), 5 deletions(-)