diff --git a/README.md b/README.md
index c031e16..d8fd3d2 100644
--- a/README.md
+++ b/README.md
@@ -1,10 +1,5 @@
 # analysisutil
 
-[![godoc.org][godoc-badge]][godoc]
+[![PkgGoDev](https://pkg.go.dev/badge/github.com/gostaticanalysis/analysisutil)](https://pkg.go.dev/github.com/gostaticanalysis/analysisutil)
 
 Utilities for x/tools/go/analysis package.
-
-<!-- links -->
-[godoc]: https://godoc.org/github.com/gostaticanalysis/analysisutil
-[godoc-badge]: https://img.shields.io/badge/godoc-reference-4F73B3.svg?style=flat-square&label=%20godoc.org
-
diff --git a/ssa.go b/ssa.go
index ce3af58..79cec17 100644
--- a/ssa.go
+++ b/ssa.go
@@ -72,7 +72,7 @@ func returnsInBlock(b *ssa.BasicBlock, done map[*ssa.BasicBlock]bool) (rets []*s
 }
 
 // BinOp returns binary operator values which are contained in the block b.
-func BinOp(b *ssa.BasicBlock) ([]*ssa.BinOp) {
+func BinOp(b *ssa.BasicBlock) []*ssa.BinOp {
 	var binops []*ssa.BinOp
 	for _, instr := range b.Instrs {
 		if binop, ok := instr.(*ssa.BinOp); ok {
@@ -81,3 +81,60 @@ func BinOp(b *ssa.BasicBlock) ([]*ssa.BinOp) {
 	}
 	return binops
 }
+
+// Used returns an instruction which uses the value in the instructions.
+func Used(v ssa.Value, instrs []ssa.Instruction) ssa.Instruction {
+	if len(instrs) == 0 || v.Referrers() == nil {
+		return nil
+	}
+
+	for _, instr := range instrs {
+		if used := usedInInstr(v, instr); used != nil {
+			return used
+		}
+	}
+
+	return nil
+}
+
+func usedInInstr(v ssa.Value, instr ssa.Instruction) ssa.Instruction {
+	switch instr := instr.(type) {
+	case *ssa.MakeClosure:
+		return usedInClosure(v, instr)
+	default:
+		operands := instr.Operands(nil)
+		for _, x := range operands {
+			if x != nil && *x == v {
+				return instr
+			}
+		}
+	}
+	return nil
+}
+
+func usedInClosure(v ssa.Value, instr *ssa.MakeClosure) ssa.Instruction {
+	fn, _ := instr.Fn.(*ssa.Function)
+	if fn == nil {
+		return nil
+	}
+
+	var fv *ssa.FreeVar
+	for i := range instr.Bindings {
+		if instr.Bindings[i] == v {
+			fv = fn.FreeVars[i]
+			break
+		}
+	}
+
+	if fv == nil {
+		return nil
+	}
+
+	for _, b := range fn.Blocks {
+		if used := Used(fv, b.Instrs); used != nil {
+			return used
+		}
+	}
+
+	return nil
+}
diff --git a/ssa_test.go b/ssa_test.go
index 4d7ccfd..7f7e98b 100644
--- a/ssa_test.go
+++ b/ssa_test.go
@@ -5,6 +5,9 @@ import (
 	"testing"
 
 	"github.com/gostaticanalysis/analysisutil"
+	"golang.org/x/tools/go/analysis"
+	"golang.org/x/tools/go/analysis/analysistest"
+	"golang.org/x/tools/go/analysis/passes/buildssa"
 	"golang.org/x/tools/go/ssa"
 )
 
@@ -97,3 +100,27 @@ func Test_BinOp(t *testing.T) {
 		})
 	}
 }
+
+func TestUsed(t *testing.T) {
+	a := &analysis.Analyzer{
+		Name:     "used",
+		Requires: []*analysis.Analyzer{buildssa.Analyzer},
+		Run: func(pass *analysis.Pass) (interface{}, error) {
+			srcFuncs := pass.ResultOf[buildssa.Analyzer].(*buildssa.SSA).SrcFuncs
+			for _, f := range srcFuncs {
+				if len(f.Params) != 1 {
+					continue
+				}
+				v := f.Params[0]
+				for _, b := range f.Blocks {
+					if analysisutil.Used(v, b.Instrs) != nil {
+						pass.Reportf(v.Pos(), "used")
+					}
+				}
+			}
+			return nil, nil
+		},
+	}
+	testdata := analysistest.TestData()
+	analysistest.Run(t, testdata, a, "used")
+}
diff --git a/testdata/src/used/used.go b/testdata/src/used/used.go
new file mode 100644
index 0000000..90e60e8
--- /dev/null
+++ b/testdata/src/used/used.go
@@ -0,0 +1,48 @@
+package used
+
+var (
+	N int
+	V interface{}
+)
+
+func f1(v interface{}) { // want "used"
+	println(v)
+}
+
+func f2(v interface{}) {} // unsed
+
+func f3(v interface{}) { // unsed
+	{
+		v := 100
+		println(v)
+	}
+}
+
+func f4(v interface{}) { // want "used"
+	V = v
+}
+
+func f5(v interface{}) { // want "used"
+	if N == 0 {
+		return
+	}
+	V = v
+}
+
+func f6(v interface{}) { // want "used"
+	func() {
+		println(v)
+	}()
+}
+
+func f7(v interface{}) { // want "used"
+	go func() {
+		println(v)
+	}()
+}
+
+func f8(v interface{}) { // want "used"
+	defer func() {
+		println(v)
+	}()
+}