From 64a0ca2512199c55e51ec90dbd3ec7d563472255 Mon Sep 17 00:00:00 2001
From: Jack Koenig
Date: Tue, 31 Aug 2021 13:31:33 -0700
Subject: Handle references better in ANTLR Parser

Tweak the grammar to handle references without left-recursion. Also
split references and subreferences out from the regular expression rule
to make their parsing more efficient.
---
 src/main/antlr4/FIRRTL.g4 | 22 ++++++++++++++--------
 1 file changed, 14 insertions(+), 8 deletions(-)

(limited to 'src/main/antlr4')

diff --git a/src/main/antlr4/FIRRTL.g4 b/src/main/antlr4/FIRRTL.g4
index f5116485..d40c6560 100644
--- a/src/main/antlr4/FIRRTL.g4
+++ b/src/main/antlr4/FIRRTL.g4
@@ -99,9 +99,9 @@ stmt
   | mdir 'mport' id '=' id '[' exp ']' exp info?
   | 'inst' id 'of' id info?
   | 'node' id '=' exp info?
-  | exp '<=' exp info?
-  | exp '<-' exp info?
-  | exp 'is' 'invalid' info?
+  | ref '<=' exp info?
+  | ref '<-' exp info?
+  | ref 'is' 'invalid' info?
   | when
   | 'stop(' exp exp intLit ')' stmtName? info?
   | 'printf(' exp exp StringLit ( exp)* ')' stmtName? info?
@@ -167,16 +167,22 @@ ruw
 exp
   : 'UInt' ('<' intLit '>')? '(' intLit ')'
   | 'SInt' ('<' intLit '>')? '(' intLit ')'
-  | id    // Ref
-  | exp '.' fieldId
-  | exp '.' DoubleLit // TODO Workaround for #470
-  | exp '[' intLit ']'
-  | exp '[' exp ']'
+  | ref
   | 'mux(' exp exp exp ')'
   | 'validif(' exp exp ')'
   | primop exp* intLit*  ')'
   ;
 
+ref
+  : id subref?
+  ;
+
+subref
+  : '.' fieldId subref?
+  | '.' DoubleLit subref? // TODO Workaround for #470
+  | '[' (intLit | exp) ']' subref?
+  ;
+
 id
   : Id
   | keywordAsId
-- 
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