go/src/cmd/compile/internal/loopvar/loopvar.go

type VarAndLoop …

// ForCapture transforms for and range loops that declare variables that might be
// captured by a closure or escaped to the heap, using a syntactic check that
// conservatively overestimates the loops where capture occurs, but still avoids
// transforming the (large) majority of loops. It returns the list of names
// subject to this change, that may (once transformed) be heap allocated in the
// process. (This allows checking after escape analysis to call out any such
// variables, in case it causes allocation/performance problems).
//
// The decision to transform loops is normally encoded in the For/Range loop node
// field DistinctVars but is also dependent on base.LoopVarHash, and some values
// of base.Debug.LoopVar (which is set per-package).  Decisions encoded in DistinctVars
// are preserved across inlining, so if package a calls b.F and loops in b.F are
// transformed, then they are always transformed, whether b.F is inlined or not.
//
// Per-package, the debug flag settings that affect this transformer:
//
// base.LoopVarHash != nil => use hash setting to govern transformation.
// note that LoopVarHash != nil sets base.Debug.LoopVar to 1 (unless it is >= 11, for testing/debugging).
//
// base.Debug.LoopVar == 11 => transform ALL loops ignoring syntactic/potential escape. Do not log, can be in addition to GOEXPERIMENT.
//
// The effect of GOEXPERIMENT=loopvar is to change the default value (0) of base.Debug.LoopVar to 1 for all packages.
func ForCapture(fn *ir.Func) []VarAndLoop { … }

// forAllDefInInitUpdate applies "do" to all the defining assignments in the Init clause of a ForStmt.
// This abstracts away some of the boilerplate from the already complex and verbose for-3-clause case.
func forAllDefInInitUpdate(x *ir.ForStmt, do func(z ir.Node, update *ir.Node)) { … }

// forAllDefInInit is forAllDefInInitUpdate without the update option.
func forAllDefInInit(x *ir.ForStmt, do func(z ir.Node)) { … }

// rewriteNodes applies editNodes to all statement lists in fn.
func rewriteNodes(fn *ir.Func, editNodes func(c ir.Nodes) ir.Nodes) { … }

func LogTransformations(transformed []VarAndLoop) { … }