Add br_on_exn instruction (#1016)

It takes two u32 immediates: the branch depth and an exception index. The
stack signature is `[expect_ref] -> [except_ref]`, so the `except_ref`
can be tested easily against multiple exception types.

1 files changed, 10 insertions, 0 deletions

diff --git a/src/wast-parser.cc b/src/wast-parser.cc
index 64071faf..66e83a8c 100644
--- a/src/wast-parser.cc
+++ b/src/wast-parser.cc
@@ -111,6 +111,7 @@ bool IsPlainInstr(TokenType token_type) {
     case TokenType::Select:
     case TokenType::Br:
     case TokenType::BrIf:
+    case TokenType::BrOnExn:
     case TokenType::BrTable:
     case TokenType::Return:
     case TokenType::ReturnCall:
@@ -1368,6 +1369,15 @@ Result WastParser::ParsePlainInstr(std::unique_ptr<Expr>* out_expr) {
       CHECK_RESULT(ParsePlainInstrVar<BrIfExpr>(loc, out_expr));
       break;
 
+    case TokenType::BrOnExn: {
+      Consume();
+      auto expr = MakeUnique<BrOnExnExpr>(loc);
+      CHECK_RESULT(ParseVar(&expr->label_var));
+      CHECK_RESULT(ParseVar(&expr->event_var));
+      *out_expr = std::move(expr);
+      break;
+    }
+
     case TokenType::BrTable: {
       Consume();
       auto expr = MakeUnique<BrTableExpr>(loc);