wasm2c: implement the tail-call proposal

README.md

@@ -54,7 +54,7 @@ Wabt has been compiled to JavaScript via emscripten. Some of the functionality i
 | [simd][]              | `--disable-simd`            | ✓ | ✓ | ✓ | ✓ | ✓ | ✓ |
 | [threads][]           | `--enable-threads`          |   | ✓ | ✓ | ✓ | ✓ |   |
 | [multi-value][]       | `--disable-multi-value`     | ✓ | ✓ | ✓ | ✓ | ✓ | ✓ |
-| [tail-call][]         | `--enable-tail-call`        |   | ✓ | ✓ | ✓ | ✓ |   |
+| [tail-call][]         | `--enable-tail-call`        |   | ✓ | ✓ | ✓ | ✓ | ✓ |
 | [bulk memory][]       | `--disable-bulk-memory`     | ✓ | ✓ | ✓ | ✓ | ✓ | ✓ |
 | [reference types][]   | `--disable-reference-types` | ✓ | ✓ | ✓ | ✓ | ✓ | ✓ |
 | [annotations][]       | `--enable-annotations`      |   |   | ✓ |   |   |   |

include/wabt/c-writer.h

@@ -29,6 +29,7 @@ class Stream;
 
 struct WriteCOptions {
   std::string_view module_name;
+  Features features;
   /*
    * name_to_output_file_index takes const iterators to begin and end of a list
    * of all functions in the module, number of imported functions, and number of

include/wabt/ir.h

@@ -310,6 +310,13 @@ class FuncType : public TypeEntry {
   Type GetResultType(Index index) const { return sig.GetResultType(index); }
 
   FuncSignature sig;
+
+  // The BinaryReaderIR tracks whether a FuncType is the target of a tailcall
+  // (via a return_call_indirect). wasm2c (CWriter) uses this information to
+  // limit its output in some cases.
+  struct {
+    bool tailcall = false;
+  } features_used;
 };
 
 struct Field {
@@ -893,6 +900,13 @@ struct Func {
   BindingHash bindings;
   ExprList exprs;
   Location loc;
+
+  // For a subset of features, the BinaryReaderIR tracks whether they are
+  // actually used by the function. wasm2c (CWriter) uses this information to
+  // limit its output in some cases.
+  struct {
+    bool tailcall = false;
+  } features_used;
 };
 
 struct Global {

src/binary-reader-ir.cc

@@ -895,15 +895,29 @@ Result BinaryReaderIR::OnCallRefExpr() {
 }
 
 Result BinaryReaderIR::OnReturnCallExpr(Index func_index) {
+  if (current_func_) {
+    // syntactically, a return_call expr can occur in an init expression
+    // (outside a function)
+    current_func_->features_used.tailcall = true;
+  }
   return AppendExpr(
       std::make_unique<ReturnCallExpr>(Var(func_index, GetLocation())));
 }
 
 Result BinaryReaderIR::OnReturnCallIndirectExpr(Index sig_index,
                                                 Index table_index) {
+  if (current_func_) {
+    // syntactically, a return_call_indirect expr can occur in an init
+    // expression (outside a function)
+    current_func_->features_used.tailcall = true;
+  }
   auto expr = std::make_unique<ReturnCallIndirectExpr>();
   SetFuncDeclaration(&expr->decl, Var(sig_index, GetLocation()));
   expr->table = Var(table_index, GetLocation());
+  FuncType* type = module_->GetFuncType(Var(sig_index, GetLocation()));
+  if (type) {
+    type->features_used.tailcall = true;
+  }
   return AppendExpr(std::move(expr));
 }