atlas ~ # emerge --update --newuse --deep --with-bdeps=y @world
Calculating dependencies... done!
[ebuild  rR    ] dev-libs/icu-57.1  ABI_X86="32"
[ebuild  r  U  ] dev-libs/icu-58.1-r1 [57.1]
[ebuild  r  U #] sys-libs/ncurses-6.0-r1 [5.9-r5] USE="{-test%} -threads%"
[ebuild     U  ] dev-util/cmake-3.6.3 [3.5.2-r1]
[ebuild   R    ] dev-ruby/ffi-1.9.6-r2  RUBY_TARGETS="(-ruby20*) (-ruby22)"
[ebuild   R    ] virtual/ruby-ffi-3  RUBY_TARGETS="(-ruby20*)"
[ebuild   R    ] dev-ruby/rb-inotify-0.9.5-r1  RUBY_TARGETS="(-ruby20*)"
[ebuild   R    ] dev-ruby/listen-1.3.1-r3  RUBY_TARGETS="(-ruby20*)"
[ebuild   R    ] dev-ruby/sass-3.4.15  RUBY_TARGETS="(-ruby20*)"
[ebuild  rR    ] media-libs/harfbuzz-1.3.1  ABI_X86="32"
[ebuild  rR    ] sys-devel/llvm-3.7.1-r3  USE="clang*" ABI_X86="32"
[ebuild  N     ] sys-devel/clang-3.7.1-r100  USE="python static-analyzer -debug -multitarget" ABI_X86="(64) -32 (-x32)"
[ebuild     U  ] www-client/chromium-55.0.2883.75 [54.0.2840.100]

!!! Multiple package instances within a single package slot have been pulled
!!! into the dependency graph, resulting in a slot conflict:

sys-libs/ncurses:0

  (sys-libs/ncurses-6.0-r1:0/6::gentoo, ebuild scheduled for merge) pulled in by
    (no parents that aren't satisfied by other packages in this slot)

  (sys-libs/ncurses-5.9-r5:0/5::gentoo, installed) pulled in by
    >=sys-libs/ncurses-5.9-r3:0/5=[abi_x86_64(-)] required by (sys-libs/readline-6.3_p8-r3:0/0::gentoo, installed)
                             ^^^^^
    (and 45 more with the same problem)

dev-libs/icu:0

  (dev-libs/icu-58.1-r1:0/58.1::gentoo, ebuild scheduled for merge) pulled in by
    (no parents that aren't satisfied by other packages in this slot)

  (dev-libs/icu-57.1:0/57::gentoo, ebuild scheduled for merge) pulled in by
    dev-libs/icu:0/57= required by (media-libs/libvisio-0.1.5:0/0::gentoo, installed)
                ^^^^^^
    dev-libs/icu:0/57 required by (app-office/libreoffice-bin-5.1.4.2:0/0::gentoo, installed)
                ^^^^^
    (and 18 more with the same problems)

media-libs/harfbuzz:0

  (media-libs/harfbuzz-1.3.1:0/0.9.18::gentoo, ebuild scheduled for merge) pulled in by
    (no parents that aren't satisfied by other packages in this slot)

  (media-libs/harfbuzz-1.3.1:0/0.9.18::gentoo, installed) pulled in by
    (no parents that aren't satisfied by other packages in this slot)

sys-devel/llvm:0

  (sys-devel/llvm-3.7.1-r3:0/3.7.1::gentoo, ebuild scheduled for merge) pulled in by
    ~sys-devel/llvm-3.7.1[clang(-),debug=,multitarget?,python?,static-analyzer?,abi_x86_32(-)?,abi_x86_64(-)?,abi_x86_x32(-)?,abi_mips_n32(-)?,abi_mips_n64(-)?,abi_mips_o32(-)?,abi_ppc_32(-)?,abi_ppc_64(-)?,abi_s390_32(-)?,abi_s390_64(-)?] required by (sys-devel/clang-3.7.1-r100:0/3.7::gentoo, ebuild scheduled for merge)


  (sys-devel/llvm-3.7.1-r3:0/3.7.1::gentoo, installed) pulled in by
    (no parents that aren't satisfied by other packages in this slot)

NOTE: Use the '--verbose-conflicts' option to display parents omitted above

It may be possible to solve this problem by using package.mask to
prevent one of those packages from being selected. However, it is also
possible that conflicting dependencies exist such that they are
impossible to satisfy simultaneously.  If such a conflict exists in
the dependencies of two different packages, then those packages can
not be installed simultaneously. You may want to try a larger value of
the --backtrack option, such as --backtrack=30, in order to see if
that will solve this conflict automatically.

For more information, see MASKED PACKAGES section in the emerge man
page or refer to the Gentoo Handbook.


The following packages are causing rebuilds:

  (dev-libs/icu-58.1-r1:0/58.1::gentoo, ebuild scheduled for merge) causes rebuilds for:
    (media-libs/harfbuzz-1.3.1:0/0.9.18::gentoo, ebuild scheduled for merge)

The following USE changes are necessary to proceed:
 (see "package.use" in the portage(5) man page for more details)
# required by media-libs/mesa-12.0.1::gentoo
# required by media-libs/libepoxy-1.3.1::gentoo
# required by x11-libs/gtk+-3.20.9::gentoo
# required by @selected
# required by @world (argument)
>=sys-devel/llvm-3.7.1-r3 abi_x86_32
# required by dev-libs/libxml2-2.9.4::gentoo[icu]
# required by sys-devel/llvm-3.7.1-r3::gentoo[xml,clang]
# required by sys-devel/clang-3.7.1-r100::gentoo
=dev-libs/icu-57.1 abi_x86_32
# required by x11-libs/pango-1.40.3::gentoo
# required by www-client/chromium-55.0.2883.75::gentoo
# required by @selected
# required by @world (argument)
>=media-libs/harfbuzz-1.3.1 abi_x86_32

Use --autounmask-write to write changes to config files (honoring
CONFIG_PROTECT). Carefully examine the list of proposed changes,
paying special attention to mask or keyword changes that may expose
experimental or unstable packages.

!!! All ebuilds that could satisfy ">=dev-libs/icu-51.2-r1:0/57=[abi_x86_32(-),abi_x86_64(-)]" have been masked.
!!! One of the following masked packages is required to complete your request:
- dev-libs/icu-57.1::gentoo (masked by: )

(dependency required by "media-libs/harfbuzz-1.3.1::gentoo" [installed])
(dependency required by "@__auto_slot_operator_replace_installed__" [argument])
For more information, see the MASKED PACKAGES section in the emerge
man page or refer to the Gentoo Handbook.