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imcc is the Intermediate Code Compiler for Parrot.
The language it compiles is currently termed Parrot
Intermediate Language (PIR).

Why? Writing a compiler is a large undertaking. We are trying
to take some of the load off of potential language designers,
including the designers of the Perl6 compiler. We can provide a
common back-end for Parrot that does:

   Register Allocation and Spillage
   Constant folding and expression evaluation
   Instruction selection
   Bytecode generation

This way, language designers can get right to work on

   Tokenizing, parsing, type checking AST/DAG production

Then they can simply feed PIR to imcc which will compile
directly to Parrot bytecode.

So far, all the compiler does is register allocation and spilling. I like
Steve Muchnick's MIR language, and I'm taking a few things from it.

I expect the IR compiler to be FAST, simple, and maintainable,
and never develop featuritis; however I want it to be adequate
for all languages targetting parrot. Did I mention that it
needs to be FAST?

Register Allocation

  The allocator uses graph-coloring and du-chains to assign registers
  to lexicals and symbolic temporaries. One weakness of the allocator
  is the lack of branch analysis. A brute force method is used in the
  du-chain computation where we assume any symbol is live from the time
  it was first used until either the last time it was used or the last
  branch instruction. This is being replaced with directed graphs of
  basic blocks and flow analysis.


  We break the instructions into a directed graph of basic blocks.
  The plan is to translate to SSA form to make optimizations easier.

Why C and Bison?

  Until Perl6 compiles itself (and does it fast), a Bison parser is
the easiest to maintain. An additional, important benefit, is
C-based parsers are pretty darn fast. Currently assembling
Parrot on the fly is still relatively slow.

Instructions not known to imcc are looked up in parrot's
op_info_table and must have the proper amount and types of

Please mail with bug-reports or patches.

Original Author:

Melvin Smith <>, <>

Contributing Authors:

Angel Faus <> ... CFG, life analysis
Sean O'Rourke <>   ... anyop, iANY
Leopold Toetsch <>  ... major rewrite
                                     numerous bugfixes/cleanup/rewrite
                                     run parrot code inside imcc
Juergen Boemmels <> Macro preprocessor

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