[Decompiler] Experimental Expression Stack (#157)

* begin framework for expressions

* more

* clean up warnings

* small fixes

* update

* wip type prop improvements

* see if nasm works

* fix format strings

decompiler/Function/ExpressionStack.cpp

@@ -0,0 +1,80 @@
+#include "third-party/fmt/core.h"
+#include "ExpressionStack.h"
+
+std::string ExpressionStack::StackEntry::print(LinkedObjectFile& file) {
+  return fmt::format("d: {} {} <- {}", display, destination.to_charp(), source->print(file));
+}
+
+std::string ExpressionStack::print(LinkedObjectFile& file) {
+  std::string result;
+  for (auto& x : m_stack) {
+    result += x.print(file);
+    result += '\n';
+  }
+  return result;
+}
+
+void ExpressionStack::set(Register reg, std::shared_ptr<IR> value) {
+  StackEntry entry;
+  entry.display = true;  // by default, we should display everything!
+  entry.destination = reg;
+  entry.source = std::move(value);
+  m_stack.push_back(entry);
+}
+
+bool ExpressionStack::is_single_expression() {
+  int count = 0;
+  for (auto& e : m_stack) {
+    if (e.display) {
+      count++;
+    }
+  }
+  return count == 1;
+}
+
+std::shared_ptr<IR> ExpressionStack::get(Register reg) {
+  // see if the stack top is this register...
+  if (!display_stack_empty()) {
+    auto& top = get_display_stack_top();
+    if (top.destination == reg) {
+      // yep. We can compact!
+      top.display = false;
+      return top.source;
+    }
+  }
+  return std::make_shared<IR_Register>(reg, -1);
+}
+
+std::vector<std::shared_ptr<IR>> ExpressionStack::get_result() {
+  std::vector<std::shared_ptr<IR>> result;
+
+  for (auto& e : m_stack) {
+    if (!e.display) {
+      continue;
+    }
+    auto dst_reg = std::make_shared<IR_Register>(e.destination, -1);
+    auto op = std::make_shared<IR_Set>(IR_Set::EXPR, dst_reg, e.source);
+    result.push_back(op);
+  }
+
+  return result;
+}
+
+bool ExpressionStack::display_stack_empty() {
+  for (auto& e : m_stack) {
+    if (e.display) {
+      return false;
+    }
+  }
+  return true;
+}
+
+ExpressionStack::StackEntry& ExpressionStack::get_display_stack_top() {
+  for (size_t i = m_stack.size(); i-- > 0;) {
+    auto& entry = m_stack.at(i);
+    if (entry.display) {
+      return entry;
+    }
+  }
+  assert(false);
+}