chore: go mod vendor / tidy

vendor/github.com/mmcloughlin/avo/pass/cfg.go

@@ -0,0 +1,81 @@
+package pass
+
+import (
+	"errors"
+	"fmt"
+
+	"github.com/mmcloughlin/avo/ir"
+)
+
+// LabelTarget populates the LabelTarget of the given function. This maps from
+// label name to the following instruction.
+func LabelTarget(fn *ir.Function) error {
+	target := map[ir.Label]*ir.Instruction{}
+	var pending []ir.Label
+	for _, node := range fn.Nodes {
+		switch n := node.(type) {
+		case ir.Label:
+			if _, found := target[n]; found {
+				return fmt.Errorf("duplicate label \"%s\"", n)
+			}
+			pending = append(pending, n)
+		case *ir.Instruction:
+			for _, label := range pending {
+				target[label] = n
+			}
+			pending = nil
+		}
+	}
+	if len(pending) != 0 {
+		return errors.New("function ends with label")
+	}
+	fn.LabelTarget = target
+	return nil
+}
+
+// CFG constructs the call-flow-graph for the function.
+func CFG(fn *ir.Function) error {
+	is := fn.Instructions()
+	n := len(is)
+
+	// Populate successors.
+	for i := 0; i < n; i++ {
+		cur := is[i]
+		var nxt *ir.Instruction
+		if i+1 < n {
+			nxt = is[i+1]
+		}
+
+		// If it's a branch, locate the target.
+		if cur.IsBranch {
+			lbl := cur.TargetLabel()
+			if lbl == nil {
+				return errors.New("no label for branch instruction")
+			}
+			target, found := fn.LabelTarget[*lbl]
+			if !found {
+				return fmt.Errorf("unknown label %q", *lbl)
+			}
+			cur.Succ = append(cur.Succ, target)
+		}
+
+		// Otherwise, could continue to the following instruction.
+		switch {
+		case cur.IsTerminal:
+		case cur.IsUnconditionalBranch():
+		default:
+			cur.Succ = append(cur.Succ, nxt)
+		}
+	}
+
+	// Populate predecessors.
+	for _, i := range is {
+		for _, s := range i.Succ {
+			if s != nil {
+				s.Pred = append(s.Pred, i)
+			}
+		}
+	}
+
+	return nil
+}