txscript: Add multisig redeem script extract bench.

txscript/bench_test.go

@@ -472,3 +472,20 @@ func BenchmarkCalcMultiSigStats(b *testing.B) {
 		}
 	}
 }
+
+// BenchmarkMultisigRedeemScript benchmarks how long it takes to extract the
+// redeem script for a very large script.
+func BenchmarkMultisigRedeemScript(b *testing.B) {
+	// NOTE: This isn't actually a p2sh multisig which the function being
+	// benchmarked expects, but it is acceptable for the purposes of the
+	// benchmark.
+	script, err := genComplexScript()
+	if err != nil {
+		b.Fatalf("failed to create benchmark script: %v", err)
+	}
+
+	b.ResetTimer()
+	for i := 0; i < b.N; i++ {
+		_, _ = MultisigRedeemScriptFromScriptSig(script)
+	}
+}