LTO bootstrap compare errors for ARM64

[Venkataramanan Kumar]

Hi,

I am trying to bootstrap of GCC 4.9 FSF branch with LTO on native
Aarch64 ,  The bootstrap build results in compare errors.

Command line.
------------------------
gcc-4_9/configure  --with-build-config=bootstrap-lto  --disable-werror
--enable-languages=c,c++,fortran --prefix=/work/vekumar/ltoinstall/
--with-gmp=/work//vekumar/installpre/installdir/--with-mpfr=/work//vekumar/installpre/installdir/
--with-mpc=/work/GCC_Team/vekumar/installpre/installdir/
--disable-werror --enable-languages=c,c++,fortran

Result
----------
--snip--
Comparing stages 2 and 3
warning: gcc/cc1plus-checksum.o differs
warning: gcc/cc1-checksum.o differs
Bootstrap comparison failure!
gcc/gimple.o differs
gcc/tree-diagnostic.o differs
gcc/gengtype-state.o differs
gcc/tree-vectorizer.o differs
gcc/passes.o differs
gcc/dumpfile.o differs
gcc/tree-cfg.o differs
gcc/tree-eh.o differs
gcc/reload1.o differs
gcc/ipa.o differs
gcc/build/gengtype-state.o differs
gcc/build/ggc-none.o differs
gcc/build/genconfig.o differs
gcc/build/genpeep.o differs
gcc/cp/parser.o differs
libcpp/files.o differs
libcpp/line-map.o differs
libcpp/expr.o differs
libcpp/directives.o differs
libcpp/traditional.o differs
libcpp/pch.o differs
libcpp/macro.o differs
make[2]: *** [compare] Error 1
---snip---

As a First step I compared the "objump -D" dump between
"stage2-gcc/gimple.o"  and "stage3-gcc/gimple.o".  Differences are in
LTO sections .gnu.lto_.decls.0, .gnu.lto_.symtab.
Ref: http://paste.ubuntu.com/7949238/

No differences when when using "objdump -d".

Next I passed "-save-temps" to stage2 and stage3 builds and compared
the assembly files. The differences are in strings dumped via .ascii
and ,string directives.

Next I checked the flags passed to the stage 2 and stage 3 builds. It
is same and below is the flag set being passed.

-save-temps -O2 -g -flto -flto=jobserver -frandom-seed=1
-ffat-lto-objects -DIN_GCC    -fno-exceptions -fno-rtti
-fasynchronous-unwind-tables -W -Wall -Wno-narrowing -Wwrite-strings
-Wcast-qual -Wmissing-forma        t-attribute -pedantic
-Wno-long-long -Wno-variadic-macros -Wno-overlength-strings

 Can you please suggest on how to fix/debug further these comparison
failures in GCC 4.9?

regards,
Venkat.