Fix visitBlock and add visitBlockStart in IRBuilder (#5959)

Visiting a block should push it onto the stack just like visiting any other
expression, but we previously had a `visitBlock` that introduced a new scope
instead. Fix `visitBlock` to behave as expected and introduce a new
`visitBlockStart` method to introduce a new scope.

Unfortunately this cannot be fully tested yet because the wat parser uses the
`makeXYZ` API intead of the `visit` API, but at least I updated `makeBlock` to
call `visitBlockStart`, so that is tested.

1 files changed, 7 insertions, 2 deletions

diff --git a/src/wasm/wasm-ir-builder.cpp b/src/wasm/wasm-ir-builder.cpp
index 6445cc3c9..bc3180423 100644
--- a/src/wasm/wasm-ir-builder.cpp
+++ b/src/wasm/wasm-ir-builder.cpp
@@ -233,7 +233,7 @@ Result<> IRBuilder::visitExpression(Expression* curr) {
 }
 
 Result<> IRBuilder::visitBlock(Block* curr) {
-  scopeStack.push_back({{}, curr});
+  // No children; pushing and finalizing will be handled by `visit`.
   return Ok{};
 }
 
@@ -281,6 +281,11 @@ Result<> IRBuilder::visitArrayNew(ArrayNew* curr) {
   return Ok{};
 }
 
+Result<> IRBuilder::visitBlockStart(Block* curr) {
+  scopeStack.push_back({{}, curr});
+  return Ok{};
+}
+
 Result<> IRBuilder::visitEnd() {
   if (scopeStack.empty() || !scopeStack.back().block) {
     return Err{"unexpected end"};
@@ -347,7 +352,7 @@ Result<> IRBuilder::makeBlock(Name label, Type type) {
   auto* block = wasm.allocator.alloc<Block>();
   block->name = label;
   block->type = type;
-  scopeStack.push_back({{}, block});
+  CHECK_ERR(visitBlockStart(block));
   return Ok{};
 }