----------------------
- BUILD INSTRUCTIONS -
----------------------

Step 0: Build and install llvm
------------------------------

I'm assuming anyone reading this knows how to build and install llvm.
You need the latest llvm from the subversion repository.

Step 1: Build gcc
-----------------

Check out gcc from the gcc subversion repository:
  svn checkout svn://gcc.gnu.org/svn/gcc/trunk SomeLocalDir
Apply the patches in the gcc-patches subdirectory, if any.  Hopefully one day
the plugin will work with an unpatched gcc, but for the moment a few small
patches need to be applied.  Configure gcc with your favorite options.
Build gcc, and install it somewhere.

Darwin special: the gcc configure script thinks darwin doesn't support dynamic
libraries and concludes that plugins won't work.  Delete or improve the check.
If you improve it, please send your patch to the gcc developers!

Step 2: Build the plugin
------------------------

In the Makefile, set the GCCSOURCE_DIR variable to point to the place you
checked out the gcc repository, rather than to where I checked it out.
Set the GCCOBJECT_DIR to point to the place you built the repository.
Admire the awfulness of the build system, and make a mental note to rewrite
it properly.

Build the plugin using "make".  The end result of the build is a shared
library, dragonegg.so.

Darwin special: "-shared" doesn't result in a correct dynamic library on darwin,
use "-Wl,-flat_namespace -Wl,-undefined -Wl,suppress -dynamiclib" instead.

----------------------
- USAGE INSTRUCTIONS -
----------------------

Run gcc as usual, but pass -fplugin=./dragonegg.so as an extra command line
argument.  Make sure you use the gcc you installed above, not the system gcc!

Currently the plugin isn't capable of compiling much - you have been warned.


------------------
- USEFUL OPTIONS -
------------------

If you renamed dragonegg.so to something else, for example llvm.so, replace
-fplugin-arg-dragonegg with -fplugin-arg-llvm in the options below.

-fplugin-arg-dragonegg-emit-ir
  Output LLVM IR rather than target assembler.  You need to use -S with this,
  since otherwise GCC will pass the output to the system assembler (these don't
  usually understand LLVM IR).  It would be nice to fix this and have the option
  work with -c too but it's not clear how.  If you plan to read the IR then you
  probably want to use the -fverbose-asm flag as well (see below).

-fverbose-asm
  Annotate the target assembler with helpful comments.  Turns on the generation
  of helpful names (the same as in GCC tree dumps) in the LLVM IR.

-fstats
  Output both LLVM and GCC statistics.

-ftime-report
  Output both LLVM and GCC timing information.

-fno-ident
  If the ident global asm in the LLVM IR annoys you, use this to turn it off.

-fdump-rtl-all
  In the dump file, each function is output both as gimple and as LLVM IR.

-fplugin-arg-dragonegg-disable-llvm-optzns
  Do not perform any LLVM IR optimizations even if compiling at -O1, -O2 etc.

-fplugin-arg-dragonegg-enable-gcc-optzns
  Run the GCC tree optimizers as well as the LLVM IR optimizers.  Normally the
  GCC optimizers are disabled.

-fplugin-arg-dragonegg-save-gcc-output
  GCC assembler output is normally redirected to /dev/null so that it doesn't
  clash with the LLVM output.  This option causes GCC output to be written to
  a file instead.  Good for seeing which GCC output we've failed to turn off.