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.

1 files changed, 2 insertions, 2 deletions

diff --git a/build.sc b/build.sc
index 59e6d4c0..de5922d8 100644
--- a/build.sc
+++ b/build.sc
@@ -139,7 +139,7 @@ class firrtlCrossModule(val crossScalaVersion: String)
           antlrSource().path.toString,
           "-package",
           "firrtl.antlr",
-          "-no-listener",
+          "-listener",
           "-visitor",
           antlrSource().path.toString
         ).call()
@@ -152,7 +152,7 @@ class firrtlCrossModule(val crossScalaVersion: String)
           antlrSource().path.toString,
           "-package",
           "firrtl.antlr",
-          "-no-listener",
+          "-listener",
           "-visitor",
           antlrSource().path.toString
         ).call()