Regions

The CFG is organized as a tree of SESE (Single Entry, Single Exit) regions. Each region contains an ordered sequence of basic blocks and child regions.

Region Kinds

Nesting and Implicit Capture

Regions nest to form a tree. Values defined in an outer region are visible in inner regions via implicit capture (VPlan style). There is no explicit capture list — the live-in set is computed on demand.

func @example(int) -> int {
  bb0:
    v0 = iconst 10       // v0 defined in function body

  region loop {
    bb1(v1: int):
      v2 = add v1, v0    // v0 captured implicitly from outer scope
      ...
  }
}

Loop Regions

A loop region’s entry block is the loop header. The continue terminator transfers control back to the loop header, passing new values for the header’s block arguments. Exiting a loop is done by branching to a block outside the loop region.