[Decompiler] WIP: Stack Spills (#382)

* set up types

* cleaned up type analysis and got things working through atomic ops

* expression working, need types

* improved types and names

* getting close

* finish up dma-disasm

* fix

decompiler/util/StackSpillMap.h

@@ -0,0 +1,40 @@
+#pragma once
+
+#include <unordered_map>
+#include <vector>
+#include <string>
+
+namespace decompiler {
+/*!
+ * Memory on the stack used to spill a register.
+ * This just has a size/is_signed? and doesn't know anything about types.
+ */
+struct StackSpillSlot {
+  int offset = -1;         // relative to sp
+  int size = -1;           // bytes
+  bool is_signed = false;  // set to false for quadwords/doublewords
+
+  bool operator==(const StackSpillSlot& other) const {
+    return offset == other.offset && size == other.size && is_signed == other.is_signed;
+  }
+
+  bool operator!=(const StackSpillSlot& other) const { return !((*this) == other); }
+
+  std::string print() const;
+};
+
+/*!
+ * Map of StackSpillSlots for a function.
+ */
+class StackSpillMap {
+ public:
+  void add_access(const StackSpillSlot& access);
+  void finalize();
+  const StackSpillSlot& lookup(int offset) const;
+  int size() const;
+  const std::unordered_map<int, StackSpillSlot>& map() const { return m_slot_map; }
+
+ private:
+  std::unordered_map<int, StackSpillSlot> m_slot_map;
+};
+}  // namespace decompiler