1 files changed, 53 insertions, 0 deletions
diff --git a/src/math/big/escape_test.go b/src/math/big/escape_test.go
new file mode 100644
index 0000000000..1e757f55ab
--- /dev/null
+++ b/src/math/big/escape_test.go
@@ -0,0 +1,53 @@
+// Copyright 2025 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package big
+
+import (
+	"internal/testenv"
+	"math/rand"
+	"os/exec"
+	"strings"
+	"testing"
+)
+
+func TestEscape(t *testing.T) {
+	testenv.MustHaveGoBuild(t)
+	// The multiplication routines create many temporary Int values,
+	// expecting them to be stack-allocated. Make sure none escape to the heap.
+	out, err := exec.Command("go", "build", "-gcflags=-m").CombinedOutput()
+	if err != nil {
+		t.Fatalf("go build -gcflags=-m: %v\n%s", err, out)
+	}
+	for line := range strings.Lines(string(out)) {
+		if strings.Contains(line, "natmul.go") && strings.Contains(line, "Int") && strings.Contains(line, "escapes") {
+			t.Error(strings.TrimSpace(line))
+		}
+	}
+}
+
+func TestMulAlloc(t *testing.T) {
+	r := rand.New(rand.NewSource(1234))
+	sizes := []int{karatsubaThreshold / 2, karatsubaThreshold}
+	for _, size := range sizes {
+		x := randInt(r, uint(size))
+		y := randInt(r, uint(size))
+		z := &Int{abs: make(nat, 2*uint(size))}
+		if n := testing.AllocsPerRun(10, func() { z.Mul(x, y) }); n >= 1 {
+			t.Errorf("Mul(len %d, len %d) allocates %.2f objects", size, size, n)
+		}
+	}
+}
+
+func TestSqrAlloc(t *testing.T) {
+	r := rand.New(rand.NewSource(1234))
+	sizes := []int{basicSqrThreshold / 2, basicSqrThreshold, karatsubaSqrThreshold}
+	for _, size := range sizes {
+		x := randInt(r, uint(size))
+		z := &Int{abs: make(nat, 2*uint(size))}
+		if n := testing.AllocsPerRun(10, func() { z.Mul(x, x) }); n >= 1 {
+			t.Errorf("Mul(len %d with itself) allocates %.2f objects", size, n)
+		}
+	}
+}