ir: add faster serializer (#1694)

This Serializer which is implemented
external to the IR node definition
uses a StringBuilder to achieve about a
1.7x performance improvement when serializing.

Eventually, all implementations of the
`serialize` methd should be replaced with
a call to `Serializer.serialize`.

However, for this PR we keep the old
code in place in order to allow for easy
regression testing with the benchmark JAR
like this:
> java -cp utils/bin/firrtl-benchmark.jar \
  firrtl.benchmark.hot.SerializationBenchmark \
  ~/benchmarks/medium.pb 2 5 test

Co-authored-by: mergify[bot] <37929162+mergify[bot]@users.noreply.github.com>

1 files changed, 40 insertions, 0 deletions

diff --git a/benchmark/src/main/scala/firrtl/benchmark/hot/SerializationBenchmark.scala b/benchmark/src/main/scala/firrtl/benchmark/hot/SerializationBenchmark.scala
new file mode 100644
index 00000000..e6ef04ec
--- /dev/null
+++ b/benchmark/src/main/scala/firrtl/benchmark/hot/SerializationBenchmark.scala
@@ -0,0 +1,40 @@
+// See LICENSE for license details.
+package firrtl.benchmark.hot
+
+import firrtl.benchmark.util._
+import firrtl.ir.Serializer
+
+object SerializationBenchmark extends App {
+  val inputFile = args(0)
+  val warmup = args(1).toInt
+  val runs = args(2).toInt
+  val select = if(args.length > 3) args(3) else "o"
+
+  val input = filenameToCircuit(inputFile)
+
+  if(select == "n") {
+    println("Benchmarking new Serializer.serialize")
+    firrtl.benchmark.hot.util.benchmark(warmup, runs)(Serializer.serialize(input))
+  } else if(select == "o") {
+    println("Benchmarking legacy serialization")
+    firrtl.benchmark.hot.util.benchmark(warmup, runs)(input.serialize)
+  } else if(select.startsWith("test")) {
+    println("Testing the new serialization against the old one")
+    val o = input.serialize.split('\n').filterNot(_.trim.isEmpty)
+    val n = Serializer.serialize(input).split('\n').filterNot(_.trim.isEmpty)
+    val silent = select.endsWith("silent")
+
+    println(s"Old lines: ${o.length}")
+    println(s"New lines: ${n.length}")
+    o.zip(n).zipWithIndex.foreach { case ((ol, nl), ii) =>
+      if(ol != nl) {
+        println(s"❌@$ii OLD: |$ol|")
+        println(s"❌@$ii NEW: |$nl|")
+        throw new RuntimeException()
+      } else if(!silent) {
+        println(s"✅        |$ol")
+      }
+    }
+
+  }
+}