Fix branching out of loops and improve tracking

wasm-ast/src/builder.rs

@@ -82,6 +82,24 @@ impl<'a> TypeInfo<'a> {
 		self.arity_of(*adjusted)
 	}
 
+	fn block_arity_of(&self, typ: BlockType) -> Arity {
+		match typ {
+			BlockType::NoResult => Arity {
+				num_param: 0,
+				num_result: 0,
+			},
+			BlockType::Value(_) => Arity {
+				num_param: 0,
+				num_result: 1,
+			},
+			BlockType::TypeIndex(i) => {
+				let id = i.try_into().unwrap();
+
+				self.arity_of(id)
+			}
+		}
+	}
+
 	fn func_of_import(import: &ImportEntry) -> Option<usize> {
 		if let &External::Function(i) = import.external() {
 			Some(i.try_into().unwrap())
@@ -110,17 +128,35 @@ impl<'a> TypeInfo<'a> {
 	}
 }
 
+enum BlockVariant {
+	Forward,
+	Backward,
+	If,
+	Else,
+}
+
+enum BlockData {
+	Forward { num_result: usize },
+	Backward { num_param: usize },
+	If { num_result: usize, typ: BlockType },
+	Else { num_result: usize },
+}
+
+impl Default for BlockData {
+	fn default() -> Self {
+		BlockData::Forward { num_result: 0 }
+	}
+}
+
 #[derive(Default)]
 struct StatList {
 	stack: Vec<Expression>,
 	code: Vec<Statement>,
 	last: Option<Terminator>,
 
-	num_result: usize,
-	num_param: usize,
+	block_data: BlockData,
 	num_stack: usize,
 	num_previous: usize,
-	is_else: bool,
 }
 
 impl StatList {
@@ -376,26 +412,29 @@ impl<'a> Builder<'a> {
 		}
 	}
 
-	fn start_block(&mut self, typ: BlockType, stat: Statement) {
-		let (num_param, num_result) = match typ {
-			BlockType::NoResult => (0, 0),
-			BlockType::Value(_) => (0, 1),
-			BlockType::TypeIndex(i) => {
-				let id = i.try_into().unwrap();
-				let arity = self.type_info.arity_of(id);
-
-				(arity.num_param, arity.num_result)
-			}
-		};
+	fn start_block(&mut self, typ: BlockType, variant: BlockVariant) {
+		let Arity {
+			num_param,
+			num_result,
+		} = self.type_info.block_arity_of(typ);
 
 		let mut old = std::mem::take(&mut self.target);
 
 		old.leak_all();
-		old.code.push(stat);
+
+		self.target.block_data = match variant {
+			BlockVariant::Forward => BlockData::Forward { num_result },
+			BlockVariant::Backward => BlockData::Backward { num_param },
+			BlockVariant::If => BlockData::If { num_result, typ },
+			BlockVariant::Else => {
+				old.pop_len(num_result);
+				old.push_temporary(num_param);
+
+				BlockData::Else { num_result }
+			}
+		};
 
 		self.target.stack = old.pop_len(num_param);
-		self.target.num_result = num_result;
-		self.target.num_param = num_param;
 		self.target.num_previous = old.num_previous + old.stack.len();
 
 		old.push_temporary(num_result);
@@ -404,22 +443,15 @@ impl<'a> Builder<'a> {
 	}
 
 	fn start_else(&mut self) {
-		let mut temp = StatList {
-			num_result: self.target.num_result,
-			num_param: self.target.num_param,
-			num_stack: self.target.num_stack,
-			num_previous: self.target.num_previous,
-			is_else: true,
-			..Default::default()
+		let typ = if let BlockData::If { typ, .. } = self.target.block_data {
+			typ
+		} else {
+			unreachable!()
 		};
 
-		temp.push_temporary(temp.num_param);
-
+		self.target.leak_all();
 		self.end_block();
-
-		let old = std::mem::replace(&mut self.target, temp);
-
-		self.pending.push(old);
+		self.start_block(typ, BlockVariant::Else);
 	}
 
 	fn end_block(&mut self) {
@@ -428,13 +460,26 @@ impl<'a> Builder<'a> {
 
 		self.target.num_stack = now.num_stack;
 
-		match self.target.code.last_mut().unwrap() {
-			Statement::Forward(data) => *data = now.into(),
-			Statement::Backward(data) => *data = now.into(),
-			Statement::If(data) if !now.is_else => data.truthy = now.into(),
-			Statement::If(data) if now.is_else => data.falsey = Some(now.into()),
-			_ => unreachable!(),
+		let stat = match now.block_data {
+			BlockData::Forward { .. } => Statement::Forward(now.into()),
+			BlockData::Backward { .. } => Statement::Backward(now.into()),
+			BlockData::If { .. } => Statement::If(If {
+				cond: self.target.pop_required(),
+				truthy: now.into(),
+				falsey: None,
+			}),
+			BlockData::Else { .. } => {
+				if let Statement::If(v) = self.target.code.last_mut().unwrap() {
+					v.falsey = Some(now.into());
+				} else {
+					unreachable!()
 				}
+
+				return;
+			}
+		};
+
+		self.target.code.push(stat);
 	}
 
 	fn get_relative_block(&self, index: usize) -> Option<&StatList> {
@@ -447,7 +492,15 @@ impl<'a> Builder<'a> {
 
 	fn get_br_terminator(&self, target: usize) -> Br {
 		let (par_start, par_result) = match self.get_relative_block(target) {
-			Some(v) => (v.num_previous, v.num_result),
+			Some(v) => (
+				v.num_previous,
+				match v.block_data {
+					BlockData::Forward { num_result } => num_result,
+					BlockData::Backward { num_param } => num_param,
+					BlockData::If { num_result, .. } => num_result,
+					BlockData::Else { num_result } => num_result,
+				},
+			),
 			None => (0, self.num_result),
 		};
 
@@ -534,26 +587,18 @@ impl<'a> Builder<'a> {
 			}
 			Inst::Nop => {}
 			Inst::Block(typ) => {
-				let stat = Statement::Forward(Forward::default());
-
-				self.start_block(typ, stat);
+				self.start_block(typ, BlockVariant::Forward);
 			}
 			Inst::Loop(typ) => {
-				let stat = Statement::Backward(Backward::default());
-
-				self.start_block(typ, stat);
+				self.start_block(typ, BlockVariant::Backward);
 			}
 			Inst::If(typ) => {
-				let stat = Statement::If(If {
-					cond: self.target.pop_required(),
-					truthy: Forward::default(),
-					falsey: None,
-				});
+				let cond = self.target.pop_required();
 
-				self.start_block(typ, stat);
+				self.start_block(typ, BlockVariant::If);
+				self.pending.last_mut().unwrap().stack.push(cond);
 			}
 			Inst::Else => {
-				self.target.leak_all();
 				self.start_else();
 			}
 			Inst::End => {
@@ -726,7 +771,7 @@ impl<'a> Builder<'a> {
 	fn build_stat_list(&mut self, list: &[Instruction], num_result: usize) -> StatList {
 		self.nested_unreachable = 0;
 		self.num_result = num_result;
-		self.target.num_result = num_result;
+		self.target.block_data = BlockData::Forward { num_result };
 
 		for inst in list.iter().take(list.len() - 1) {
 			if self.nested_unreachable == 0 {