(air quotes) "register allocation" without spills.

src/alloy/hir/hir_builder.cc

@@ -419,6 +419,7 @@ Value* HIRBuilder::AllocValue(TypeName type) {
   value->flags = 0;
   value->def = NULL;
   value->use_head = NULL;
+  value->last_use = NULL;
   value->tag = NULL;
   value->reg = -1;
   return value;
@@ -432,6 +433,7 @@ Value* HIRBuilder::CloneValue(Value* source) {
   value->constant.v128 = source->constant.v128;
   value->def = NULL;
   value->use_head = NULL;
+  value->last_use = NULL;
   value->tag = NULL;
   value->reg = -1;
   return value;

src/alloy/hir/value.h

@@ -70,6 +70,8 @@ public:
 
   Instr*    def;
   Use*      use_head;
+  // NOTE: for performance reasons this is not maintained during construction.
+  Instr*    last_use;
 
   // TODO(benvanik): remove to shrink size.
   void*     tag;