doc/guide/src/SSA.adoc

   1 SSA
   2 ===
   3
   4 <:SSA:> is an <:IntermediateLanguage:>, translated from <:SXML:> by
   5 <:ClosureConvert:>, optimized by <:SSASimplify:>, and translated by
   6 <:ToSSA2:> to <:SSA2:>.
   7
   8 == Description ==
   9
  10 <:SSA:> is a <:FirstOrder:>, <:SimplyTyped:> <:IntermediateLanguage:>.
  11 It is the main <:IntermediateLanguage:> used for optimizations.
  12
  13 An <:SSA:> program consists of a collection of datatype declarations,
  14 a sequence of global statements, and a collection of functions, along
  15 with a distinguished "main" function.  Each function consists of a
  16 collection of basic blocks, where each basic block is a sequence of
  17 statements ending with some control transfer.
  18
  19 == Implementation ==
  20
  21 * <!ViewGitFile(mlton,master,mlton/ssa/ssa.sig)>
  22 * <!ViewGitFile(mlton,master,mlton/ssa/ssa.fun)>
  23 * <!ViewGitFile(mlton,master,mlton/ssa/ssa-tree.sig)>
  24 * <!ViewGitFile(mlton,master,mlton/ssa/ssa-tree.fun)>
  25
  26 == Type Checking ==
  27
  28 Type checking (<!ViewGitFile(mlton,master,mlton/ssa/type-check.sig)>,
  29 <!ViewGitFile(mlton,master,mlton/ssa/type-check.fun)>) of a <:SSA:> program
  30 verifies the following:
  31
  32 * no duplicate definitions (tycons, cons, vars, labels, funcs)
  33 * no out of scope references (tycons, cons, vars, labels, funcs)
  34 * variable definitions dominate variable uses
  35 * case transfers are exhaustive and irredundant
  36 * `Enter`/`Leave` profile statements match
  37 * "traditional" well-typedness
  38
  39 == Details and Notes ==
  40
  41 SSA is an abbreviation for Static Single Assignment.
  42
  43 For some initial design discussion, see the thread at:
  44
  45 * http://mlton.org/pipermail/mlton/2001-August/019689.html
  46
  47 For some retrospectives, see the threads at:
  48
  49 * http://mlton.org/pipermail/mlton/2003-January/023054.html
  50 * http://mlton.org/pipermail/mlton/2007-February/029597.html