feat(furc): start working on ssa optimizations

Compute dominance frontiers.

Refs: #2

furc/include/furc/front/ssa.hpp

@@ -0,0 +1,32 @@
+#ifndef FURC_FRONT_SSA_HPP
+#define FURC_FRONT_SSA_HPP
+
+#include "furlang/ir/function.hpp"
+#include "furlang/ir/instruction.hpp"
+#include "furlang/ir/module.hpp"
+
+#include <memory>
+#include <unordered_map>
+#include <unordered_set>
+#include <vector>
+
+namespace furc {
+namespace front {
+
+class ssa {
+    using block_map_t = std::unordered_map<furlang::ir::block_index, std::vector<furlang::ir::block_index>>;
+public:
+    static void optimize(furlang::ir::module& mod);
+private:
+    static void optimize(const std::unique_ptr<furlang::ir::function>& func);
+
+    static void dfs_rpo(furlang::ir::block_index      block,
+        const block_map_t&                            successors,
+        std::unordered_set<furlang::ir::block_index>& visited,
+        std::vector<furlang::ir::block_index>&        rpo);
+};
+
+} // namespace front
+} // namespace furc
+
+#endif // FURC_FRONT_SSA_HPP