Resetting the builder arena. May be a bug or two here still.

src/alloy/hir/hir_builder.cc

@@ -42,6 +42,10 @@ void HIRBuilder::Reset() {
   next_value_ordinal_ = 0;
   block_head_ = block_tail_ = NULL;
   current_block_ = NULL;
+#if XE_DEBUG
+  arena_->DebugFill();
+#endif
+  arena_->Reset();
 }
 
 int HIRBuilder::Finalize() {
@@ -319,6 +323,19 @@ void HIRBuilder::InsertLabel(Label* label, Instr* prev_instr) {
   }
 }
 
+void HIRBuilder::ResetLabelTags() {
+  // TODO(benvanik): make this faster?
+  auto block = block_head_;
+  while (block) {
+    auto label = block->label_head;
+    while (label) {
+      label->tag = 0;
+      label = label->next;
+    }
+    block = block->next;
+  }
+}
+
 Block* HIRBuilder::AppendBlock() {
   Block* block = arena_->Alloc<Block>();
   block->arena = arena_;

src/alloy/hir/hir_builder.h

@@ -13,6 +13,7 @@
 #include <alloy/core.h>
 #include <alloy/hir/block.h>
 #include <alloy/hir/instr.h>
+#include <alloy/hir/label.h>
 #include <alloy/hir/opcodes.h>
 #include <alloy/hir/value.h>
 
@@ -47,6 +48,7 @@ public:
   Label* NewLabel();
   void MarkLabel(Label* label, Block* block = 0);
   void InsertLabel(Label* label, Instr* prev_instr);
+  void ResetLabelTags();
 
   // static allocations:
   // Value* AllocStatic(size_t length);