doc/guide/src/ToMachine.adoc

   1 ToMachine
   2 =========
   3
   4 <:ToMachine:> is a translation pass from the <:RSSA:>
   5 <:IntermediateLanguage:> to the <:Machine:> <:IntermediateLanguage:>.
   6
   7 == Description ==
   8
   9 This pass converts from a <:RSSA:> program into a <:Machine:> program.
  10
  11 It uses <:AllocateRegisters:>, <:Chunkify:>, and <:ParallelMove:>.
  12
  13 == Implementation ==
  14
  15 * <!ViewGitFile(mlton,master,mlton/backend/backend.sig)>
  16 * <!ViewGitFile(mlton,master,mlton/backend/backend.fun)>
  17
  18 == Details and Notes ==
  19
  20 Because the MLton runtime system is shared by all <:Codegen:codegens>, it is most
  21 convenient to decide on stack layout _before_ any <:Codegen:codegen> takes over.
  22 In particular, we compute all the stack frame info for each <:RSSA:>
  23 function, including stack size, <:GarbageCollection:garbage collector>
  24 masks for each frame, etc.  To do so, the <:Machine:>
  25 <:IntermediateLanguage:> imagines an abstract machine with an infinite
  26 number of (pseudo-)registers of every size.  A liveness analysis
  27 determines, for each variable, whether or not it is live across a
  28 point where the runtime system might take over (for example, any
  29 garbage collection point) or a non-tail call to another <:RSSA:>
  30 function.  Those that are live go on the stack, while those that
  31 aren't live go into psuedo-registers.  From this information, we know
  32 all we need to about each stack frame.  On the downside, nothing
  33 further on is allowed to change this stack info; it is set in stone.