chore: go mod vendor / tidy

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

@@ -0,0 +1,123 @@
+package pass
+
+import (
+	"github.com/mmcloughlin/avo/ir"
+	"github.com/mmcloughlin/avo/operand"
+)
+
+// PruneJumpToFollowingLabel removes jump instructions that target an
+// immediately following label.
+func PruneJumpToFollowingLabel(fn *ir.Function) error {
+	for i := 0; i+1 < len(fn.Nodes); i++ {
+		node := fn.Nodes[i]
+		next := fn.Nodes[i+1]
+
+		// This node is an unconditional jump.
+		inst, ok := node.(*ir.Instruction)
+		if !ok || !inst.IsBranch || inst.IsConditional {
+			continue
+		}
+
+		target := inst.TargetLabel()
+		if target == nil {
+			continue
+		}
+
+		// And the jump target is the immediately following node.
+		lbl, ok := next.(ir.Label)
+		if !ok || lbl != *target {
+			continue
+		}
+
+		// Then the jump is unnecessary and can be removed.
+		fn.Nodes = deletenode(fn.Nodes, i)
+		i--
+	}
+
+	return nil
+}
+
+// PruneDanglingLabels removes labels that are not referenced by any branches.
+func PruneDanglingLabels(fn *ir.Function) error {
+	// Count label references.
+	count := map[ir.Label]int{}
+	for _, n := range fn.Nodes {
+		i, ok := n.(*ir.Instruction)
+		if !ok || !i.IsBranch {
+			continue
+		}
+
+		target := i.TargetLabel()
+		if target == nil {
+			continue
+		}
+
+		count[*target]++
+	}
+
+	// Look for labels with no references.
+	for i := 0; i < len(fn.Nodes); i++ {
+		node := fn.Nodes[i]
+		lbl, ok := node.(ir.Label)
+		if !ok {
+			continue
+		}
+
+		if count[lbl] == 0 {
+			fn.Nodes = deletenode(fn.Nodes, i)
+			i--
+		}
+	}
+
+	return nil
+}
+
+// PruneSelfMoves removes move instructions from one register to itself.
+func PruneSelfMoves(fn *ir.Function) error {
+	return removeinstructions(fn, func(i *ir.Instruction) bool {
+		switch i.Opcode {
+		case "MOVB", "MOVW", "MOVL", "MOVQ":
+		default:
+			return false
+		}
+
+		return operand.IsRegister(i.Operands[0]) && operand.IsRegister(i.Operands[1]) && i.Operands[0] == i.Operands[1]
+	})
+}
+
+// removeinstructions deletes instructions from the given function which match predicate.
+func removeinstructions(fn *ir.Function, predicate func(*ir.Instruction) bool) error {
+	// Removal of instructions has the potential to invalidate CFG structures.
+	// Clear them to prevent accidental use of stale structures after this pass.
+	invalidatecfg(fn)
+
+	for i := 0; i < len(fn.Nodes); i++ {
+		n := fn.Nodes[i]
+
+		inst, ok := n.(*ir.Instruction)
+		if !ok || !predicate(inst) {
+			continue
+		}
+
+		fn.Nodes = deletenode(fn.Nodes, i)
+	}
+
+	return nil
+}
+
+// deletenode deletes node i from nodes and returns the resulting slice.
+func deletenode(nodes []ir.Node, i int) []ir.Node {
+	n := len(nodes)
+	copy(nodes[i:], nodes[i+1:])
+	nodes[n-1] = nil
+	return nodes[:n-1]
+}
+
+// invalidatecfg clears CFG structures.
+func invalidatecfg(fn *ir.Function) {
+	fn.LabelTarget = nil
+	for _, i := range fn.Instructions() {
+		i.Pred = nil
+		i.Succ = nil
+	}
+}