Subzero - Fast code generator for PNaCl bitcode
===============================================

Building
--------

You must have LLVM trunk source code available and built.  See
http://llvm.org/docs/GettingStarted.html#getting-started-quickly-a-summary for
guidance.

Set variables ``LLVM_SRC_PATH`` and ``LLVM_BIN_PATH`` to point to the
appropriate directories in the LLVM source and build directories.  These can be
set as environment variables, or you can modify the top-level Makefile.

Run ``make`` at the top level to build the main target ``llvm2ice``.

``llvm2ice``
------------

The ``llvm2ice`` program uses the LLVM infrastructure to parse an LLVM bitcode
file and translate it into ICE.  It then invokes ICE's translate method to lower
it to target-specific machine code, dumping the IR at various stages of the
translation.

The program can be run as follows::

    ../llvm2ice ./ir_samples/<file>.ll
    ../llvm2ice ./tests_lit/llvm2ice_tests/<file>.ll

At this time, ``llvm2ice`` accepts a few arguments:

    ``-help`` -- Show available arguments and possible values.

    ``-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.

    ``-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``.

    ``-o <FILE>`` -- Set the assembly output file name.  Default is stdout.

    ``-log <FILE>`` -- Set the file name for diagnostic output (whose level is
    controlled by ``-verbose``).  Default is stdout.

See ir_samples/README.rst for more details.

Running the test suite
----------------------

Subzero uses the LLVM ``lit`` testing tool for its test suite, which lives in
``tests_lit``. To execute the test suite, first build Subzero, and then run::

    python <path_to_lit.py> -sv tests_lit

``path_to_lit`` is the direct path to the lit script in the LLVM source
(``$LLVM_SRC_PATH/utils/lit/lit.py``).

The above ``lit`` execution also needs the LLVM binary path in the
``LLVM_BIN_PATH`` env var.

Assuming the LLVM paths are set up, ``make check`` is a convenient way to run
the test suite.

Assembling ``llvm2ice`` output
------------------------------

Currently ``llvm2ice`` produces textual assembly code in a structure suitable
for input to ``llvm-mc`` and currently using "intel" assembly syntax.  The first
line of output is a convenient comment indicating how to pipe the output to
``llvm-mc`` to produce object code.