feat(furc/ssa): implement renaming

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

furc/src/front/ssa.cpp

@@ -0,0 +1,253 @@
+#include "furc/front/ssa.hpp"
+
+#include "furlang/ir/instruction.hpp"
+#include "furlang/ir/operand.hpp"
+
+#include <algorithm>
+#include <cstddef>
+#include <functional>
+#include <memory>
+#include <stack>
+#include <unordered_map>
+#include <unordered_set>
+#include <vector>
+
+namespace furc::front {
+
+void ssa::optimize(furlang::ir::module& mod) {
+    for (const auto& func : mod.functions()) {
+        ssa::optimize(func);
+    }
+}
+
+void ssa::optimize(const std::unique_ptr<furlang::ir::function>& func) {
+    block_map_t predecessors;
+    block_map_t successors;
+
+    std::unordered_map<furlang::ir::register_t, std::unordered_set<furlang::ir::block_index>> regSites;
+    std::unordered_map<furlang::ir::block_index, std::unordered_set<furlang::ir::register_t>> regUses;
+
+    std::unordered_map<furlang::ir::block_index, furlang::ir::block_index> idoms;
+
+    std::unordered_map<furlang::ir::register_t, std::uint32_t>                          regVers;
+    std::unordered_map<furlang::ir::register_t, std::stack<std::uint32_t>>              regVerStacks;
+    std::unordered_map<furlang::ir::block_index, std::vector<furlang::ir::block_index>> domTree;
+
+    for (furlang::ir::block_index i = 0; i < func->blocks().size(); ++i) {
+        const auto& block = func->blocks()[i];
+
+        for (const auto& instr : block->instructions()) {
+            if (instr->has_destination()) {
+                if (instr->destination().type() == furlang::ir::operand_t::Register) {
+                    regSites[instr->destination().reg()].insert(i);
+                }
+            }
+
+            for (const furlang::ir::operand* src : instr->sources()) {
+                if (src->type() != furlang::ir::operand_t::Register) continue;
+                regUses[i].insert(src->reg());
+            }
+        }
+
+        const auto& exit = block->exit();
+        switch (exit->type()) {
+        case furlang::ir::instruction_t::Branch: {
+            const auto& br = dynamic_cast<const furlang::ir::branch_instruction&>(*exit);
+            predecessors[br.block()].push_back(i);
+            successors[i].push_back(br.block());
+        } break;
+        case furlang::ir::instruction_t::BranchCond: {
+            const auto& br = dynamic_cast<const furlang::ir::branch_cond_instruction&>(*exit);
+            predecessors[br.if_block()].push_back(i);
+            predecessors[br.else_block()].push_back(i);
+            successors[i].push_back(br.if_block());
+            successors[i].push_back(br.else_block());
+        } break;
+        default: break;
+        }
+    }
+
+    std::unordered_set<furlang::ir::block_index> visited;
+    std::vector<furlang::ir::block_index>        rpoOrder;
+    dfs_rpo(0, successors, visited, rpoOrder);
+    std::reverse(rpoOrder.begin(), rpoOrder.end());
+
+    std::unordered_map<furlang::ir::block_index, std::size_t> rpoIndex;
+    for (std::size_t i = 0; i < rpoOrder.size(); ++i) {
+        rpoIndex[rpoOrder[i]] = i;
+    }
+
+    auto intersect = [&](furlang::ir::block_index block1, furlang::ir::block_index block2) {
+        while (block1 != block2) {
+            while (rpoIndex[block1] > rpoIndex[block2]) {
+                block1 = idoms[block1];
+            }
+            while (rpoIndex[block2] > rpoIndex[block1]) {
+                block2 = idoms[block2];
+            }
+        }
+        return block1;
+    };
+
+    auto entry   = rpoOrder.front();
+    idoms[entry] = entry;
+
+    bool changed = true;
+    while (changed) {
+        changed = false;
+
+        for (std::size_t i = 1; i < rpoOrder.size(); ++i) {
+            auto block = rpoOrder[i];
+
+            furlang::ir::block_index newIdom = 0;
+            bool                     found   = false;
+            for (auto pred : predecessors[block]) {
+                if (idoms.find(pred) == idoms.end()) continue;
+                if (!found) {
+                    newIdom = pred;
+                    found   = true;
+                } else {
+                    newIdom = intersect(pred, newIdom);
+                }
+            }
+
+            if (idoms.find(block) == idoms.end() || idoms[block] != newIdom) {
+                idoms[block] = newIdom;
+                changed      = true;
+            }
+        }
+    }
+
+    std::unordered_map<furlang::ir::block_index, std::unordered_set<furlang::ir::block_index>> df;
+    for (auto block : rpoOrder) {
+        df[block] = std::unordered_set<furlang::ir::block_index>{};
+    }
+
+    for (auto block : rpoOrder) {
+        if (predecessors[block].size() < 2) continue;
+
+        for (auto pred : predecessors[block]) {
+            auto runner = pred;
+            while (runner != idoms[block]) {
+                df[runner].insert(block);
+                runner = idoms[runner];
+            }
+        }
+    }
+
+    std::unordered_map<furlang::ir::block_index, std::unordered_set<furlang::ir::register_t>> phis;
+
+    for (const auto& [reg, blocks] : regSites) {
+        std::vector<furlang::ir::block_index> worklist(blocks.begin(), blocks.end());
+
+        std::unordered_set<furlang::ir::block_index> added;
+        while (!worklist.empty()) {
+            auto block = worklist.back();
+            worklist.pop_back();
+            for (auto frontier : df[block]) {
+                if (added.find(frontier) != added.end()) continue;
+                phis[frontier].insert(reg);
+                added.insert(frontier);
+                if (blocks.find(frontier) == blocks.end()) {
+                    worklist.push_back(frontier);
+                }
+            }
+        }
+    }
+
+    for (furlang::ir::block_index i = 0; i < func->blocks().size(); ++i) {
+        if (phis.find(i) == phis.end()) continue;
+        const auto& block = func->blocks()[i];
+        const auto& preds = predecessors[i];
+
+        for (auto reg : phis[i]) {
+            if (regUses[i].find(reg) == regUses[i].end()) continue;
+
+            auto phiInstr = std::make_unique<furlang::ir::phi_instruction>(reg);
+            for (auto pred : preds) {
+                phiInstr->labels().emplace_back(furlang::ir::operand::new_reg(reg), pred);
+            }
+            block->instructions().emplace(block->instructions().begin(), std::move(phiInstr));
+        }
+    }
+
+    for (const auto& [block, idom] : idoms) {
+        if (block != idom) domTree[idom].push_back(block);
+    }
+
+    std::function<void(furlang::ir::block_index)> renameBlock = [&](furlang::ir::block_index blockIndex) -> void {
+        std::unordered_map<furlang::ir::register_t, std::uint32_t> pushed;
+
+        const auto& block = func->blocks()[blockIndex];
+        for (auto& instr : block->instructions()) {
+            if (instr->type() != furlang::ir::instruction_t::Phi) continue;
+            auto          orig             = instr->destination().reg();
+            std::uint32_t newVer           = regVers[orig]++;
+            instr->destination().reg().ver = newVer;
+            regVerStacks[orig].push(newVer);
+            ++pushed[orig];
+        }
+
+        for (auto& instr : block->instructions()) {
+            if (instr->type() == furlang::ir::instruction_t::Phi) continue;
+
+            for (auto& operand : instr->sources()) {
+                if (operand->type() != furlang::ir::operand_t::Register) continue;
+                auto orig = operand->reg();
+                if (!regVerStacks[orig].empty()) {
+                    operand->reg().ver = regVerStacks[orig].top();
+                }
+            }
+
+            if (instr->has_destination() || instr->destination().type() == furlang::ir::operand_t::Register) {
+                auto          orig             = instr->destination().reg();
+                std::uint32_t newVer           = regVers[orig]++;
+                instr->destination().reg().ver = newVer;
+                regVerStacks[orig].push(newVer);
+                ++pushed[orig];
+            }
+        }
+
+        for (auto succIndex : successors[blockIndex]) {
+            const auto& succ = func->blocks()[succIndex];
+            for (auto& instr : succ->instructions()) {
+                if (instr->type() != furlang::ir::instruction_t::Phi) break;
+                auto& phi = dynamic_cast<furlang::ir::phi_instruction&>(*instr);
+                for (auto& [op, bl] : phi.labels()) {
+                    if (bl != blockIndex) continue;
+                    if (regVerStacks[op.reg()].empty()) continue;
+                    op.reg().ver = regVerStacks[op.reg()].top();
+                }
+            }
+        }
+
+        for (const auto& child : domTree[blockIndex]) {
+            renameBlock(child);
+        }
+
+        for (const auto& [reg, count] : pushed) {
+            for (std::uint32_t i = 0; i < count; ++i) {
+                regVerStacks[reg].pop();
+            }
+        }
+    };
+
+    renameBlock(entry);
+}
+
+void ssa::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) {
+    visited.insert(block);
+    if (auto it = successors.find(block); it != successors.end()) {
+        for (auto successor : it->second) {
+            if (visited.find(successor) == visited.end()) {
+                dfs_rpo(successor, successors, visited, rpo);
+            }
+        }
+    }
+    rpo.push_back(block);
+}
+
+} // namespace furc::front

furc/src/main.cpp

@@ -3,6 +3,7 @@
 #include "furc/ast/program.hpp"
 #include "furc/front/ir_generator.hpp"
 #include "furc/front/parser.hpp"
+#include "furc/front/ssa.hpp"
 
 #include <iostream>
 
@@ -34,6 +35,8 @@ int main(void) {
         program->accept(generator);
 
         auto module = std::move(generator.move_module());
+        furc::front::ssa::optimize(module);
+
         std::cout << "Generated IR:\n";
         for (const auto& function : module.functions()) {
             std::cout << function->name() << ":\n";

furlang/include/furlang/ir/instruction.hpp

@@ -6,6 +6,9 @@
 #include <cstdint>
 #include <optional>
 #include <ostream>
+#include <stdexcept>
+#include <utility>
+#include <vector>
 
 namespace furlang {
 namespace ir {
@@ -21,6 +24,7 @@ enum class instruction_t {
     Branch,     /**< Branch */
     BranchCond, /**< Conditional branch */
     Return,     /**< Return */
+    Phi,        /**< Phi function */
 };
 
 /**
@@ -66,6 +70,41 @@ public:
      * @return The type.
      */
     virtual instruction_t type() const = 0;
+
+    /**
+     * @brief Returns whether this instruction has a destination operand.
+     *
+     * @return true if this instruction has the destination operand.
+     */
+    virtual bool has_destination() const { return false; }
+
+    /**
+     * @brief Returns destination operand of this instruction.
+     *
+     * @return The destination operand.
+     */
+    virtual operand& destination() { throw std::runtime_error("instruction type mismatch"); }
+
+    /**
+     * @brief Returns destination operand of this instruction.
+     *
+     * @return The destination operand.
+     */
+    virtual const operand& destination() const { throw std::runtime_error("instruction type mismatch"); }
+
+    /**
+     * @brief Returns a list of source operands of this instruction.
+     *
+     * @return The list of source operands.
+     */
+    virtual std::vector<operand*> sources() { return {}; }
+
+    /**
+     * @brief Returns a list of source operands of this instruction.
+     *
+     * @return The list of source operands.
+     */
+    virtual std::vector<const operand*> sources() const { return {}; }
 public:
     /**
      * @brief Prints an instruction to an output stream.
@@ -158,18 +197,39 @@ public:
     instruction_t type() const override { return instruction_t::Assign; }
 
     /**
-     * @brief Returns this instruction's source.
+     * @brief Returns whether this instruction has a destination operand.
      *
-     * @return The source.
+     * @return true
      */
-    const operand& source() const { return m_source; }
+    bool has_destination() const override { return true; }
 
     /**
      * @brief Returns this instruction's destination.
      *
      * @return The destination.
      */
-    const operand& destination() const { return m_destination; }
+    operand& destination() override { return m_destination; }
+
+    /**
+     * @brief Returns this instruction's destination.
+     *
+     * @return The destination.
+     */
+    const operand& destination() const override { return m_destination; }
+
+    /**
+     * @brief Returns a list of this instruction's source operands.
+     *
+     * @return The list of source operands.
+     */
+    std::vector<operand*> sources() override { return { &m_source }; }
+
+    /**
+     * @brief Returns a list of this instruction's source operands.
+     *
+     * @return The list of source operands.
+     */
+    std::vector<const operand*> sources() const override { return { &m_source }; }
 private:
     operand m_source;
     operand m_destination;
@@ -253,6 +313,16 @@ public:
      */
     instruction_t type() const override { return instruction_t::BinaryOp; }
 
+    bool has_destination() const override { return true; }
+
+    operand& destination() override { return m_dst; }
+
+    const operand& destination() const override { return m_dst; }
+
+    std::vector<operand*> sources() override { return { &m_lhs, &m_rhs }; }
+
+    std::vector<const operand*> sources() const override { return { &m_lhs, &m_rhs }; }
+
     /**
      * @brief Returns this instruction's operation type.
      *
@@ -442,6 +512,16 @@ public:
      */
     instruction_t type() const override { return instruction_t::Return; }
 
+    std::vector<operand*> sources() override {
+        if (m_value.has_value()) return { &*m_value };
+        return {};
+    }
+
+    std::vector<const operand*> sources() const override {
+        if (m_value.has_value()) return { &*m_value };
+        return {};
+    }
+
     /**
      * @brief Returns this instruction's return value operand.
      *
@@ -458,7 +538,83 @@ protected:
     }
 };
 
+/**
+ * @brief Phi instruction
+ *
+ * Used to implement the phi node in the SSA graph.
+ */
+class phi_instruction final : public instruction {
+public:
+    phi_instruction(register_operand dst)
+      : m_dst(operand::new_reg(dst)) {}
+
+    ~phi_instruction() override = default;
+
+    /**
+     * @brief Move constructor.
+     */
+    phi_instruction(phi_instruction&&) noexcept = default;
+
+    /**
+     * @brief Move constructor.
+     */
+    phi_instruction& operator=(phi_instruction&&) noexcept = default;
+
+    phi_instruction(const phi_instruction&) = delete;
+
+    phi_instruction& operator=(const phi_instruction&) = delete;
+public:
+    /**
+     * @brief Returns this instruction's type.
+     *
+     * @return instruction_t::Phi.
+     */
+    instruction_t type() const override { return instruction_t::Phi; }
+
+    /**
+     * @brief Returns this instruction's destination register.
+     *
+     * @return The register.
+     */
+    operand& destination() override { return m_dst; }
+
+    /**
+     * @brief Returns this instruction's destination register.
+     *
+     * @return The register.
+     */
+    const operand& destination() const override { return m_dst; }
+
+    /**
+     * @brief Returns this instruction's labels.
+     *
+     * @return The labels.
+     */
+    std::vector<std::pair<operand, block_index>>& labels() { return m_labels; }
+
+    /**
+     * @brief Returns this instruction's labels.
+     *
+     * @return The labels.
+     */
+    const std::vector<std::pair<operand, block_index>>& labels() const { return m_labels; }
+private:
+    operand                                      m_dst;
+    std::vector<std::pair<operand, block_index>> m_labels;
+protected:
+    std::ostream& print(std::ostream& os) const override {
+        os << "phi " << m_dst << " =";
+        bool first = true;
+        for (const auto& pair : m_labels) {
+            if (!first) os << ',';
+            first = false;
+            os << ' ' << pair.second << ": " << pair.first;
+        }
+        return os;
+    }
+};
+
 } // namespace ir
 } // namespace furlang
 
-#endif // FURLANG_IR_INSTRUCTION_HPP
+#endif // FURLANG_IR_INSTRUCTION_HPP

furlang/include/furlang/ir/operand.hpp

@@ -19,11 +19,33 @@ enum class operand_t {
     String,   /**< String */
 };
 
+/**
+ * @brief Alias to a register type.
+ */
+using register_t = std::uint32_t;
+
 /**
  * @brief Register operand alias.
  * @see operand_t::Register
  */
-using register_operand = std::uint32_t;
+struct register_operand {
+    register_t    reg;
+    std::uint32_t ver = 0;
+
+    register_operand(register_t reg)
+      : reg(reg) {}
+
+    register_operand(register_t reg, std::uint32_t ver)
+      : reg(reg), ver(ver) {}
+
+    operator std::uint32_t&() { return reg; }
+    operator const std::uint32_t&() const { return reg; }
+
+    friend std::ostream& operator<<(std::ostream& os, const register_operand& op) {
+        return os << op.reg << '_' << op.ver;
+    }
+};
+
 /**
  * @brief Variable operand alias.
  * @see operand_t::Variable
@@ -102,6 +124,19 @@ public:
     operand(const operand&)            = delete;
     operand& operator=(const operand&) = delete;
 public:
+    /**
+     * @brief Construct a new register operand.
+     *
+     * @param value Value of the new register operand.
+     * @return The register operand.
+     */
+    static operand new_reg(register_t value) {
+        operand operand;
+        operand.m_type      = operand_t::Register;
+        operand.m_value.reg = { value, 0 };
+        return operand;
+    }
+
     /**
      * @brief Construct a new register operand.
      *
@@ -163,6 +198,13 @@ public:
      */
     operand_t type() const { return m_type; }
 
+    /**
+     * @brief Returns this operand's register value.
+     *
+     * @return The register value.
+     */
+    register_operand& reg() { return m_value.reg; }
+
     /**
      * @brief Returns this operand's register value.
      *
@@ -228,4 +270,4 @@ private:
 } // namespace ir
 } // namespace furlang
 
-#endif // FURLANG_IR_OPERAND_HPP
+#endif // FURLANG_IR_OPERAND_HPP