Add basic exception handling support (#2282)

This adds basic support for exception handling instructions, according
to the spec:
https://github.com/WebAssembly/exception-handling/blob/master/proposals/Exceptions.md

This PR includes support for:
- Binary reading/writing
- Wast reading/writing
- Stack IR
- Validation
- binaryen.js + C API
- Few IR routines: branch-utils, type-updating, etc
- Few passes: just enough to make `wasm-opt -O` pass
- Tests

This PR does not include support for many optimization passes, fuzzer,
or interpreter. They will be follow-up PRs.

Try-catch construct is modeled in Binaryen IR in a similar manner to
that of if-else: each of try body and catch body will contain a block,
which can be omitted if there is only a single instruction. This block
will not be emitted in wast or binary, as in if-else. As in if-else,
`class Try` contains two expressions each for try body and catch body,
and `catch` is not modeled as an instruction. `exnref` value pushed by
`catch` is get by `pop` instruction.

`br_on_exn` is special: it returns different types of values when taken
and not taken. We make `exnref`, the type `br_on_exn` pushes if not
taken, as `br_on_exn`'s type.

1 files changed, 7 insertions, 1 deletions

diff --git a/scripts/gen-s-parser.py b/scripts/gen-s-parser.py
index 615febd7d..c98388ad8 100755
--- a/scripts/gen-s-parser.py
+++ b/scripts/gen-s-parser.py
@@ -423,7 +423,13 @@ instructions = [
     ("f32x4.convert_i32x4_s",   "makeUnary(s, UnaryOp::ConvertSVecI32x4ToVecF32x4)"),
     ("f32x4.convert_i32x4_u",   "makeUnary(s, UnaryOp::ConvertUVecI32x4ToVecF32x4)"),
     ("f64x2.convert_i64x2_s",   "makeUnary(s, UnaryOp::ConvertSVecI64x2ToVecF64x2)"),
-    ("f64x2.convert_i64x2_u",   "makeUnary(s, UnaryOp::ConvertUVecI64x2ToVecF64x2)")
+    ("f64x2.convert_i64x2_u",   "makeUnary(s, UnaryOp::ConvertUVecI64x2ToVecF64x2)"),
+    # exception handling instructions
+    ("try",                  "makeTry(s)"),
+    ("throw",                "makeThrow(s)"),
+    ("catch",                "makeCatch(s)"),
+    ("rethrow",              "makeRethrow(s)"),
+    ("br_on_exn",            "makeBrOnExn(s)")
 ]