From 17250fba841ae3129dc798c0bc48d10200be18ae Mon Sep 17 00:00:00 2001
From: Jack Koenig
Date: Tue, 31 Aug 2021 14:10:29 -0700
Subject: Use ANTLR Listener to save memory during parsing

The ANTLR-generated concrete syntax tree (CST) takes up much more memory
than the parsed .fir file. By using a Listener, we can construct the
FIRRTL AST live with CST construction and null out the CST as we consume
pieces of it. Not only does this improve performance, it drastically
reduces max memory use for the parser.
---
 src/main/scala/firrtl/parser/Listener.scala | 38 +++++++++++++++++++++++++++++
 1 file changed, 38 insertions(+)
 create mode 100644 src/main/scala/firrtl/parser/Listener.scala

(limited to 'src/main/scala/firrtl/parser')

diff --git a/src/main/scala/firrtl/parser/Listener.scala b/src/main/scala/firrtl/parser/Listener.scala
new file mode 100644
index 00000000..ffaa22b2
--- /dev/null
+++ b/src/main/scala/firrtl/parser/Listener.scala
@@ -0,0 +1,38 @@
+// SPDX-License-Identifier: Apache-2.0
+
+package firrtl.parser
+
+import firrtl.antlr.{FIRRTLParser, _}
+import firrtl.Visitor
+import firrtl.Parser.InfoMode
+import firrtl.ir._
+
+import scala.collection.mutable
+import scala.concurrent.{Await, Future}
+import scala.concurrent.duration.Duration
+
+private[firrtl] class Listener(infoMode: InfoMode) extends FIRRTLBaseListener {
+  private var main: Option[String] = None
+  private var info: Option[Info] = None
+  private val modules = mutable.ArrayBuffer.empty[DefModule]
+
+  private val visitor = new Visitor(infoMode)
+
+  override def exitModule(ctx: FIRRTLParser.ModuleContext): Unit = {
+    val m = visitor.visitModule(ctx)
+    ctx.children = null // Null out to save memory
+    modules += m
+  }
+
+  override def exitCircuit(ctx: FIRRTLParser.CircuitContext): Unit = {
+    info = Some(visitor.visitInfo(Option(ctx.info), ctx))
+    main = Some(ctx.id.getText)
+    ctx.children = null // Null out to save memory
+  }
+
+  def getCircuit: Circuit = {
+    require(main.nonEmpty)
+    val mods = modules.toSeq
+    Circuit(info.get, mods, main.get)
+  }
+}
-- 
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