Make try body start with 'do' (#2846)

In WebAssembly/exception-handling#52, We decided to put `try` bodies in
a `do` clause to be more consistent with `catch`.

- Before
```wast
(try
  ...
  (catch
    ...
  )
)
```

- After
```wast
(try
  (do
    ...
  )
  (catch
    ...
  )
)
```

Another upside of this change is when there are multiple instructions
within a `try` body, we no longer need to wrap them in a `block`.

1 files changed, 9 insertions, 2 deletions

diff --git a/src/passes/Print.cpp b/src/passes/Print.cpp
index a87eae325..0839b3feb 100644
--- a/src/passes/Print.cpp
+++ b/src/passes/Print.cpp
@@ -1930,9 +1930,11 @@ struct PrintSExpression : public OverriddenVisitor<PrintSExpression> {
   }
   // try-catch-end is written in the folded wat format as
   // (try
+  //  (do
   //   ...
+  //  )
   //  (catch
-  //    ...
+  //   ...
   //  )
   // )
   // The parenthesis wrapping 'catch' is just a syntax and does not affect
@@ -1941,7 +1943,12 @@ struct PrintSExpression : public OverriddenVisitor<PrintSExpression> {
     o << '(';
     PrintExpressionContents(currFunction, o).visit(curr);
     incIndent();
-    maybePrintImplicitBlock(curr->body, false);
+    doIndent(o, indent);
+    o << "(do";
+    incIndent();
+    maybePrintImplicitBlock(curr->body, true);
+    decIndent();
+    o << "\n";
     doIndent(o, indent);
     o << "(catch";
     incIndent();