Fixing arena chunk reuse.

src/alloy/arena.cc

@@ -45,13 +45,14 @@ void Arena::DebugFill() {
 
 void* Arena::Alloc(size_t size) {
   if (active_chunk_) {
-    if (active_chunk_->capacity - active_chunk_->offset < size) {
+    if (active_chunk_->capacity - active_chunk_->offset < size + 4096) {
       Chunk* next = active_chunk_->next;
       if (!next) {
         XEASSERT(size < chunk_size_); // need to support larger chunks
         next = new Chunk(chunk_size_);
         active_chunk_->next = next;
       }
+      next->offset = 0;
       active_chunk_ = next;
     }
   } else {

src/alloy/hir/hir_builder.cc

@@ -72,6 +72,7 @@ int HIRBuilder::Finalize() {
         // Sometimes VC++ generates functions with bl at the end even if they
         // will never return. Just add a return to satisfy things.
         XELOGW("Fall-through out of the function.");
+        Trap();
         Return();
         current_block_ = NULL;
         break;