[wasm2wat] Write select type immediate (#1451)

The main fix is in `wat-writer.cc`, where the type immediate was never
being printed. But I've also included a change to how `select` type
immediates are represented in wabt.

Previously, a bare `select` instruction would be stored with the type
`Type::Any`. This is not a real wasm type, and is primarily used for
type validation. The spec instead considers this form of `select` to
have an empty type immediate, which is closer to the `Type::Void` type.

This commit now uses `Type::Void` (or an empty `TypeVector`) to
represent the bare `select` instruction.

Fixes #1444.

7 files changed, 16 insertions, 10 deletions

diff --git a/src/binary-reader-ir.cc b/src/binary-reader-ir.cc
index d1a4ecf2..b1cb9115 100644
--- a/src/binary-reader-ir.cc
+++ b/src/binary-reader-ir.cc
@@ -935,7 +935,7 @@ Result BinaryReaderIR::OnReturnExpr() {
 }
 
 Result BinaryReaderIR::OnSelectExpr(Type result_type) {
-  return AppendExpr(MakeUnique<SelectExpr>(TypeVector{result_type}));
+  return AppendExpr(MakeUnique<SelectExpr>(result_type.GetInlineVector()));
 }
 
 Result BinaryReaderIR::OnGlobalSetExpr(Index global_index) {
diff --git a/src/binary-reader.cc b/src/binary-reader.cc
index 9780e39c..02579eb6 100644
--- a/src/binary-reader.cc
+++ b/src/binary-reader.cc
@@ -643,7 +643,7 @@ Result BinaryReader::ReadFunctionBody(Offset end_offset) {
       }
 
       case Opcode::Select:
-        CALLBACK(OnSelectExpr, Type::Any);
+        CALLBACK(OnSelectExpr, Type::Void);
         CALLBACK0(OnOpcodeBare);
         break;
 
diff --git a/src/binary-writer.cc b/src/binary-writer.cc
index b574402c..fd2b0c24 100644
--- a/src/binary-writer.cc
+++ b/src/binary-writer.cc
@@ -700,8 +700,7 @@ void BinaryWriter::WriteExpr(const Func* func, const Expr* expr) {
       break;
     case ExprType::Select: {
       auto* select_expr = cast<SelectExpr>(expr);
-      if (select_expr->result_type.size() == 1 &&
-          select_expr->result_type[0] == Type::Any) {
+      if (select_expr->result_type.empty()) {
         WriteOpcode(stream_, Opcode::Select);
       } else {
         WriteOpcode(stream_, Opcode::SelectT);
diff --git a/src/type-checker.cc b/src/type-checker.cc
index a025a4a8..0304a09f 100644
--- a/src/type-checker.cc
+++ b/src/type-checker.cc
@@ -716,7 +716,7 @@ Result TypeChecker::OnSelect(Type expected) {
   result |= PeekAndCheckType(0, Type::I32);
   result |= PeekType(1, &type1);
   result |= PeekType(2, &type2);
-  if (expected == Type::Any) {
+  if (expected == Type::Void) {
     if (type1.IsRef() || type2.IsRef()) {
       result = Result::Error;
     } else {
diff --git a/src/validator.cc b/src/validator.cc
index 8884059e..e23d5be1 100644
--- a/src/validator.cc
+++ b/src/validator.cc
@@ -464,8 +464,13 @@ Result Validator::OnReturnCallIndirectExpr(ReturnCallIndirectExpr* expr) {
 }
 
 Result Validator::OnSelectExpr(SelectExpr* expr) {
-  assert(expr->result_type.size());
-  result_ |= validator_.OnSelect(expr->loc, expr->result_type[0]);
+  Type result_type;
+  if (expr->result_type.empty()) {
+    result_type = Type::Void;
+  } else {
+    result_type = expr->result_type[0];
+  }
+  result_ |= validator_.OnSelect(expr->loc, result_type);
   // TODO: Existing behavior fails when select fails.
 #if 0
   return Result::Ok;
diff --git a/src/wast-parser.cc b/src/wast-parser.cc
index 88189f0a..bbe31744 100644
--- a/src/wast-parser.cc
+++ b/src/wast-parser.cc
@@ -1736,8 +1736,6 @@ Result WastParser::ParsePlainInstr(std::unique_ptr<Expr>* out_expr) {
           MatchLpar(TokenType::Result)) {
         CHECK_RESULT(ParseValueTypeList(&result));
         EXPECT(Rpar);
-      } else {
-        result.push_back(Type::Any);
       }
       out_expr->reset(new SelectExpr(result, loc));
       break;
diff --git a/src/wat-writer.cc b/src/wat-writer.cc
index 9431df7f..d8d6e9eb 100644
--- a/src/wat-writer.cc
+++ b/src/wat-writer.cc
@@ -854,7 +854,11 @@ Result WatWriter::ExprVisitorDelegate::OnReturnCallIndirectExpr(
 }
 
 Result WatWriter::ExprVisitorDelegate::OnSelectExpr(SelectExpr* expr) {
-  writer_->WritePutsNewline(Opcode::Select_Opcode.GetName());
+  writer_->WritePutsSpace(Opcode::Select_Opcode.GetName());
+  if (!expr->result_type.empty()) {
+    writer_->WriteTypes(expr->result_type, "result");
+  }
+  writer_->WriteNewline(NO_FORCE_NEWLINE);
   return Result::Ok;
 }