[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/ExpressionBuilder.cpp

@@ -0,0 +1,53 @@
+#include "Function.h"
+#include "decompiler/IR/IR.h"
+#include "ExpressionStack.h"
+
+namespace {
+bool expressionize_begin(IR_Begin* begin, LinkedObjectFile& file) {
+  ExpressionStack stack;
+  // todo - this might need to run multiple times?
+  for (auto& op : begin->forms) {
+    op->expression_stack(stack, file);
+  }
+  begin->forms = stack.get_result();
+  return true;
+}
+}  // namespace
+
+bool Function::build_expression(LinkedObjectFile& file) {
+  if (!ir) {
+    return false;
+  }
+
+  try {
+    // first we get a list of begins, which are where we can build up expressions.
+    // we want to start with innermost begins because we'll probably need to do some fixing up
+    // or more complicated analysis to do as good as possible on outer begins.
+    auto all_children = ir->get_all_ir(file);
+    std::vector<IR_Begin*> all_begins;
+    for (auto i = all_children.size(); i-- > 0;) {
+      auto as_begin = dynamic_cast<IR_Begin*>(all_children.at(i).get());
+      if (as_begin) {
+        all_begins.push_back(as_begin);
+      }
+    }
+
+    // the top level may also be a begin
+    auto as_begin = dynamic_cast<IR_Begin*>(ir.get());
+    if (as_begin) {
+      all_begins.push_back(as_begin);
+    }
+
+    // turn each begin into an expression
+    for (auto b : all_begins) {
+      if (!expressionize_begin(b, file)) {
+        return false;
+      }
+    }
+  } catch (std::exception& e) {
+    printf("build_expression failed on %s due to %s\n", guessed_name.to_string().c_str(), e.what());
+    return false;
+  }
+
+  return true;
+}