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The MicroC compiler

Coded in OCaml, this takes a highly stripped-down subset of C (ints,
bools, and void types, arithmetic, if-else, for, and while statements,
and user-defined functions) and compiles it into LLVM IR.

It needs the OCaml llvm library, which is most easily installed through opam.

Install LLVM and its development libraries, the m4 macro preprocessor,
and opam, then use opam to install llvm.

The version of the OCaml llvm library should match the version of the LLVM
system installed on your system.

In addition to print, which calls the C library function printf(),
this gratuitiously includes a primitive function "printbig," which
prints large ASCII-encoded characters.

The stock C compiler compiles printbig.o.  testall.sh runs the microc
executable on each testcase (.mc file) to produce a .ll file, invokes
"llc" (the LLVM compiler) to produce a .s (assembly) file, then
invokes "cc" (the stock C compiler) to assemble the .s file, link in
printbig.o, and generate an executable.  See testall.sh for details.

------------------------------
Installation under Ubuntu 15.10

LLVM 3.6 is the default under 15.10, so we ask for a matching version of the
OCaml library.

sudo apt-get install -y ocaml m4 llvm opam
opam init
opam install llvm.3.6 ocamlfind
eval `opam config env`

make
./testall.sh

------------------------------
Installation under Ubuntu 14.04

The default LLVM package is 3.4, so we install the matching OCaml
library using opam.  The default version of opam under 14.04 is too
old; we need to use a newer package.

sudo apt-get install m4 llvm software-properties-common

sudo add-apt-repository --yes ppa:avsm/ppa
sudo apt-get update -qq
sudo apt-get install -y opam
opam init

eval `opam config env`

opam install llvm.3.4 ocamlfind

------------------------------
Installation under OS X

1. Install Homebrew:

   ruby -e "$(curl -fsSL https://raw.githubusercontent.com/Homebrew/install/master/install)"

2. Verify Homebrew is installed correctly:

   brew doctor

3. Install opam:

   brew install opam

4. Set up opam:

   opam init

5. Install llvm:

   brew install llvm

   Take note of where brew places the llvm executables. It will show
   you the path to them under the CAVEATS section of the post-install
   terminal output. For me, they were in /usr/local/opt/llvm/bin. Also
   take note of the llvm version installed. For me, it was 3.6.2.

6. Have opam set up your enviroment:

   eval `opam config env`

7. Install the OCaml llvm library:

   opam install llvm.3.6 

   Ensure that the version of llvm you install here matches the
   version you installed via brew. Brew installed llvm version 3.6.2,
   so I install llvm.3.6 with opam.

   IF YOU HAVE PROBLEMS ON THIS STEP, it's probably because you are
   missing some external dependencies. Ensure that libffi is installed
   on your machine. It can be installed with

   brew install libffi

   If, after this, opam install llvm.3.6 is still not working, try
   running

   opam list --external --required-by=llvm.3.6

   This will list all of the external dependencies required by
   llvm.3.6. Install all the dependencies listed by this command.

   IF THE PREVIOUS STEPS DO NOT SOLVE THE ISSUE, it may be a problem
   with using your system's default version of llvm. Install a
   different version of llvm and opam install llvm with that version
   by running:

   brew install homebrew/versions/llvm37
   opam install llvm.3.7

   Where the number at the end of both commands is a version different 
   from the one your system currently has.

8. Create a symbolic link to the lli command:

   sudo ln -s /usr/local/opt/llvm/bin/lli /usr/bin/lli

   Create the symlink from wherever brew installs the llvm executables
   and place it in your bin. From step 5, I know that brew installed
   the lli executable in the folder, /usr/local/opt/llvm/bin/, so this
   is where I symlink to. Brew might install the lli executables in a
   different location for you, so make sure you symlink to the right
   directory.

   IF YOU GET OPERATION NOT PERMITTED ERROR, then this is probably a
   result of OSX's System Integrity Protection. 

   One way to get around this is to reboot your machine into recovery
   mode (by holding cmd-r when restarting). Open a terminal from
   recovery mode by going to Utilities -> Terminal, and enter the
   following commands:

   csrutil disable
   reboot
   
   After your machine has restarted, try the `ln....` command again,
   and it should succeed.

   IMPORTANT: the prevous step disables System Integrity Protection,
   which can leave your machine vulnerable. It's highly advisable to
   reenable System Integrity Protection when you are done by 
   rebooting your machine into recovery mode and entering the following
   command in the terminal:

   csrutil enable
   reboot

   Another solution is to update your path, e.g.,

   export PATH=$PATH:/usr/local/opt/llvm/bin

   A third solution is to modify the definition of LLI in testall.sh to
   point to the absolute path, e.g., LLI="/usr/local/opt/llvm/bin/lli"

9. To run and test, navigate to the MicroC folder. Once there, run

   make ; ./testall.sh

   MicroC should build without any complaints and all tests should
   pass.

   IF RUNNING ./testall.sh FAILS ON SOME TESTS, check to make sure you
   have symlinked the correct executable from your llvm installation.
   For example, if the executable is named lli-[version], then the 
   previous step should have looked something like:

   sudo ln -s /usr/local/opt/llvm/bin/lli-3.7 /usr/bin/lli   

   As before, you may also modify the path to lli in testall.sh

------------------------------
To run and test:

$ make
ocamlbuild -use-ocamlfind -pkgs llvm,llvm.analysis -cflags -w,+a-4 microc.native
Finished, 22 targets (0 cached) in 00:00:01.
cc    -c -o printbig.o printbig.c
$ ./testall.sh
test-arith1...OK
test-arith2...OK
test-arith3...OK
test-fib...OK
...
fail-while1...OK
fail-while2...OK