Subzero: Use -filetype instead of -ias and -elf-writer.

README.rst

 Subzero - Fast code generator for PNaCl bitcode
 ===============================================
 
 Building
 --------
 
 Subzero is set up to be built within the Native Client tree.  Follow the
 `Developing PNaCl
 <https://sites.google.com/a/chromium.org/dev/nativeclient/pnacl/developing-pnacl>`_
 instructions, in particular the section on building PNaCl sources.  This will
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     ``-help`` -- Show available arguments and possible values.  (Note: this
     unfortunately also pulls in some LLVM-specific options that are reported but
     that Subzero doesn't use.)
 
     ``-notranslate`` -- Suppress the ICE translation phase, which is useful if
     ICE is missing some support.
 
     ``-target=<TARGET>`` -- Set the target architecture.  The default is x8632.
     Future targets include x8664, arm32, and arm64.
 
-    ``-integrated-as=0|1`` -- Disable/enable the integrated assembler.
+    ``-filetype=obj|asm|iasm`` -- Select the output file type.  ``obj`` is a
+    native ELF file, ``asm`` is a textual assembly file, and ``iasm`` is a
+    low-level textual assembly file demonstrating the integrated assembler.
 
     ``-O<LEVEL>`` -- Set the optimization level.  Valid levels are ``2``, ``1``,
     ``0``, ``-1``, and ``m1``.  Levels ``-1`` and ``m1`` are synonyms, and
     represent the minimum optimization and worst code quality, but fastest code
     generation.
 
     ``-verbose=<list>`` -- Set verbosity flags.  This argument allows a
     comma-separated list of values.  The default is ``none``, and the value
     ``inst,pred`` will roughly match the .ll bitcode file.  Of particular use
     are ``all`` and ``none``.
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 The Subzero-translated symbols are specially mangled to avoid multiple
 definition errors from the linker.  Both translated versions are linked together
 with a driver program that calls each version of each unit test with a variety
 of interesting inputs and compares the results for equality.  The cross tests
 are currently invoked by running the ``runtests.sh`` script.
 
 A convenient way to run both the lit tests and the cross tests is::
 
     make -f Makefile.standalone check
 
-Assembling ``llvm2ice`` output
-------------------------------
+Assembling ``llvm2ice`` output as needed
+----------------------------------------
 
-Currently ``llvm2ice`` produces textual assembly code in a structure suitable
-for input to ``llvm-mc``.  An object file can be produced using the command::
+``llvm2ice`` can now produce a native ELF binary using ``-filetype=obj``.
+
+``llvm2ice`` can also produce textual assembly code in a structure suitable for
+input to ``llvm-mc``, using ``-filetype=asm`` or ``-filetype=iasm``.  An object
+file can then be produced using the command::
 
     llvm-mc -arch=x86 -filetype=obj -o=MyObj.o
 
-In the future, the integrated assembler will directly produce ELF object files.
-
 Building a translated binary
 ----------------------------
 
 There is a helper script, ``pydir/szbuild.py``, that translates a finalized pexe
 into a fully linked executable.  Run it with ``-help`` for extensive
 documentation.
 
 By default, ``szbuild.py`` builds an executable using only Subzero translation,
 but it can also be used to produce hybrid Subzero/``llc`` binaries (``llc`` is
 the name of the LLVM translator) for bisection-based debugging.  In bisection
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 * Global, linear-scan register allocation.
 
 * Advanced phi lowering after target lowering and global register allocation,
   via edge splitting, topological sorting of the parallel moves, and final local
   register allocation.
 
 * Stack slot coalescing to reduce frame size.
 
 * Branch optimization to reduce the number of branches to the following block.