factor/basis/compiler/cfg/ssa/destruction/destruction-docs.factor

USING: compiler.cfg compiler.cfg.instructions
compiler.cfg.ssa.destruction.private help.markup help.syntax ;
IN: compiler.cfg.ssa.destruction

HELP: cleanup-cfg
{ $values { "cfg" cfg } }
{ $description "In this step, " { $link ##parallel-copy } " instructions are substituted with more concreete " { $link ##copy } " instructions. " { $link ##phi } " instructions are removed here." } ;

ARTICLE: "compiler.cfg.ssa.destruction" "SSA Destruction"
"Because of the design of the register allocator, this pass has three peculiar properties."
{ $list
  "Instead of renaming vreg usages in the CFG, a map from vregs to canonical representatives is computed. This allows the register allocator to use the original SSA names to get reaching definitions."
  { "Useless " { $link ##copy } " instructions, and all " { $link ##phi } " instructions, are eliminated, so the register allocator does not have to remove any redundant operations." }
  { "This pass computes live sets and fills out the " { $slot "gc-roots" } " slots of GC maps with " { $vocab-link "compiler.cfg.liveness" } ", so the linear scan register allocator does not need to compute liveness again." }
} ;

ABOUT: "compiler.cfg.ssa.destruction"