2 files changed, 96 insertions, 5 deletions

diff --git a/src/wasm.cpp b/src/wasm.cpp
new file mode 100644
index 000000000..2157992e3
--- /dev/null
+++ b/src/wasm.cpp
@@ -0,0 +1,84 @@
+/*
+ * Copyright 2016 WebAssembly Community Group participants
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#include "wasm.h"
+#include "wasm-traversal.h"
+#include "ast_utils.h"
+
+namespace wasm {
+
+struct BlockTypeSeeker : public PostWalker<BlockTypeSeeker, Visitor<BlockTypeSeeker>> {
+  Block* target; // look for this one
+  WasmType type = unreachable;
+
+  BlockTypeSeeker(Block* target) : target(target) {}
+
+  void noteType(WasmType other) {
+    // once none, stop. it then indicates a poison value, that must not be consumed
+    // and ignore unreachable
+    if (type != none) {
+      if (other == none) {
+        type = none;
+      } else if (other != unreachable) {
+        type = other;
+      }
+    }
+  }
+
+  void visitBreak(Break *curr) {
+    if (curr->name == target->name) {
+      noteType(curr->value ? curr->value->type : none);
+    }
+  }
+
+  void visitSwitch(Switch *curr) {
+    for (auto name : curr->targets) {
+      if (name == target->name) noteType(curr->value ? curr->value->type : none);
+    }
+  }
+
+  void visitBlock(Block *curr) {
+    if (curr == target) {
+      if (curr->list.size() > 0) noteType(curr->list.back()->type);
+    } else {
+      type = unreachable; // ignore all breaks til now, they were captured by someone with the same name
+    }
+  }
+};
+
+void Block::finalize() {
+  if (list.size() > 0) {
+    auto last = list.back()->type;
+    if (last != unreachable) {
+      // well that was easy
+      type = last;
+      return;
+    }
+  }
+  if (!name.is()) {
+    // that was rather silly
+    type = unreachable;
+    return;
+  }
+  // oh no this is hard
+  BlockTypeSeeker seeker(this);
+  Expression* temp = this;
+  seeker.walk(temp);
+  type = seeker.type;
+}
+
+} // namespace wasm
+
diff --git a/src/wasm.h b/src/wasm.h
index b5dee81b8..b13011bae 100644
--- a/src/wasm.h
+++ b/src/wasm.h
@@ -833,11 +833,13 @@ public:
   Name name;
   ExpressionList list;
 
-  void finalize() {
-    if (list.size() > 0) {
-      type = list.back()->type;
-    }
+  // set the type of a block if you already know it
+  void finalize(WasmType type_) {
+    type = type;
   }
+
+  // set the type of a block based on its contents. this scans the block, so it is not fast
+  void finalize();
 };
 
 class If : public SpecificExpression<Expression::IfId> {
@@ -877,6 +879,12 @@ public:
   Name name;
   Expression *value;
   Expression *condition;
+
+  void finalize() {
+    if (condition) {
+      type = none;
+    }
+  }
 };
 
 class Switch : public SpecificExpression<Expression::SwitchId> {
@@ -1022,7 +1030,6 @@ public:
     if (isRelational()) {
       type = i32;
     } else {
-      assert(left->type != unreachable && right->type != unreachable ? left->type == right->type : true);
       type = getReachableWasmType(left->type, right->type);
     }
   }