[wasm] Fix checking of unreachable code (clear stack after unreachable).

src/wasm/function-body-decoder.cc

Index: src/wasm/function-body-decoder.cc
diff --git a/src/wasm/function-body-decoder.cc b/src/wasm/function-body-decoder.cc
index 7c95b5a672300eebed09d0fe7016ddd5f06a8cdb..a798ff8c24aa17fda92c7247471acb5c3315777f 100644
--- a/src/wasm/function-body-decoder.cc
+++ b/src/wasm/function-body-decoder.cc
@@ -1241,7 +1241,15 @@ class WasmFullDecoder : public WasmDecoder {
     if (pc_ > end_ && ok()) error("Beyond end of code");
   }
 
-  void EndControl() { ssa_env_->Kill(SsaEnv::kControlEnd); }
+  void EndControl() {
+    ssa_env_->Kill(SsaEnv::kControlEnd);
+    if (control_.empty()) {

[rossberg, 2017/01/19 12:55:11]

I suppose you could avoid spurious case distinctions like this by pushing a
control frame for the function block itself, so that the stack is never empty?

+      stack_.clear();
+    } else {
+      DCHECK_LE(control_.back().stack_depth, stack_.size());
+      stack_.resize(control_.back().stack_depth);
+    }
+  }
 
   void SetBlockType(Control* c, BlockTypeOperand& operand) {
     c->merge.arity = operand.arity;