1 files changed, 642 insertions, 0 deletions

diff --git a/src/shader_recompiler/frontend/maxwell/control_flow.cpp b/src/shader_recompiler/frontend/maxwell/control_flow.cpp
new file mode 100644
index 000000000..1a954a509
--- /dev/null
+++ b/src/shader_recompiler/frontend/maxwell/control_flow.cpp
@@ -0,0 +1,642 @@
+// Copyright 2021 yuzu Emulator Project
+// Licensed under GPLv2 or any later version
+// Refer to the license.txt file included.
+
+#include <algorithm>
+#include <array>
+#include <optional>
+#include <string>
+#include <utility>
+
+#include <fmt/format.h>
+
+#include "shader_recompiler/exception.h"
+#include "shader_recompiler/frontend/maxwell/control_flow.h"
+#include "shader_recompiler/frontend/maxwell/decode.h"
+#include "shader_recompiler/frontend/maxwell/indirect_branch_table_track.h"
+#include "shader_recompiler/frontend/maxwell/location.h"
+
+namespace Shader::Maxwell::Flow {
+namespace {
+struct Compare {
+    bool operator()(const Block& lhs, Location rhs) const noexcept {
+        return lhs.begin < rhs;
+    }
+
+    bool operator()(Location lhs, const Block& rhs) const noexcept {
+        return lhs < rhs.begin;
+    }
+
+    bool operator()(const Block& lhs, const Block& rhs) const noexcept {
+        return lhs.begin < rhs.begin;
+    }
+};
+
+u32 BranchOffset(Location pc, Instruction inst) {
+    return pc.Offset() + static_cast<u32>(inst.branch.Offset()) + 8u;
+}
+
+void Split(Block* old_block, Block* new_block, Location pc) {
+    if (pc <= old_block->begin || pc >= old_block->end) {
+        throw InvalidArgument("Invalid address to split={}", pc);
+    }
+    *new_block = Block{};
+    new_block->begin = pc;
+    new_block->end = old_block->end;
+    new_block->end_class = old_block->end_class;
+    new_block->cond = old_block->cond;
+    new_block->stack = old_block->stack;
+    new_block->branch_true = old_block->branch_true;
+    new_block->branch_false = old_block->branch_false;
+    new_block->function_call = old_block->function_call;
+    new_block->return_block = old_block->return_block;
+    new_block->branch_reg = old_block->branch_reg;
+    new_block->branch_offset = old_block->branch_offset;
+    new_block->indirect_branches = std::move(old_block->indirect_branches);
+
+    const Location old_begin{old_block->begin};
+    Stack old_stack{std::move(old_block->stack)};
+    *old_block = Block{};
+    old_block->begin = old_begin;
+    old_block->end = pc;
+    old_block->end_class = EndClass::Branch;
+    old_block->cond = IR::Condition(true);
+    old_block->stack = old_stack;
+    old_block->branch_true = new_block;
+    old_block->branch_false = nullptr;
+}
+
+Token OpcodeToken(Opcode opcode) {
+    switch (opcode) {
+    case Opcode::PBK:
+    case Opcode::BRK:
+        return Token::PBK;
+    case Opcode::PCNT:
+    case Opcode::CONT:
+        return Token::PBK;
+    case Opcode::PEXIT:
+    case Opcode::EXIT:
+        return Token::PEXIT;
+    case Opcode::PLONGJMP:
+    case Opcode::LONGJMP:
+        return Token::PLONGJMP;
+    case Opcode::PRET:
+    case Opcode::RET:
+    case Opcode::CAL:
+        return Token::PRET;
+    case Opcode::SSY:
+    case Opcode::SYNC:
+        return Token::SSY;
+    default:
+        throw InvalidArgument("{}", opcode);
+    }
+}
+
+bool IsAbsoluteJump(Opcode opcode) {
+    switch (opcode) {
+    case Opcode::JCAL:
+    case Opcode::JMP:
+    case Opcode::JMX:
+        return true;
+    default:
+        return false;
+    }
+}
+
+bool HasFlowTest(Opcode opcode) {
+    switch (opcode) {
+    case Opcode::BRA:
+    case Opcode::BRX:
+    case Opcode::EXIT:
+    case Opcode::JMP:
+    case Opcode::JMX:
+    case Opcode::KIL:
+    case Opcode::BRK:
+    case Opcode::CONT:
+    case Opcode::LONGJMP:
+    case Opcode::RET:
+    case Opcode::SYNC:
+        return true;
+    case Opcode::CAL:
+    case Opcode::JCAL:
+        return false;
+    default:
+        throw InvalidArgument("Invalid branch {}", opcode);
+    }
+}
+
+std::string NameOf(const Block& block) {
+    if (block.begin.IsVirtual()) {
+        return fmt::format("\"Virtual {}\"", block.begin);
+    } else {
+        return fmt::format("\"{}\"", block.begin);
+    }
+}
+} // Anonymous namespace
+
+void Stack::Push(Token token, Location target) {
+    entries.push_back({
+        .token = token,
+        .target{target},
+    });
+}
+
+std::pair<Location, Stack> Stack::Pop(Token token) const {
+    const std::optional<Location> pc{Peek(token)};
+    if (!pc) {
+        throw LogicError("Token could not be found");
+    }
+    return {*pc, Remove(token)};
+}
+
+std::optional<Location> Stack::Peek(Token token) const {
+    const auto it{std::find_if(entries.rbegin(), entries.rend(),
+                               [token](const auto& entry) { return entry.token == token; })};
+    if (it == entries.rend()) {
+        return std::nullopt;
+    }
+    return it->target;
+}
+
+Stack Stack::Remove(Token token) const {
+    const auto it{std::find_if(entries.rbegin(), entries.rend(),
+                               [token](const auto& entry) { return entry.token == token; })};
+    const auto pos{std::distance(entries.rbegin(), it)};
+    Stack result;
+    result.entries.insert(result.entries.end(), entries.begin(), entries.end() - pos - 1);
+    return result;
+}
+
+bool Block::Contains(Location pc) const noexcept {
+    return pc >= begin && pc < end;
+}
+
+Function::Function(ObjectPool<Block>& block_pool, Location start_address)
+    : entrypoint{start_address} {
+    Label& label{labels.emplace_back()};
+    label.address = start_address;
+    label.block = block_pool.Create(Block{});
+    label.block->begin = start_address;
+    label.block->end = start_address;
+    label.block->end_class = EndClass::Branch;
+    label.block->cond = IR::Condition(true);
+    label.block->branch_true = nullptr;
+    label.block->branch_false = nullptr;
+}
+
+CFG::CFG(Environment& env_, ObjectPool<Block>& block_pool_, Location start_address,
+         bool exits_to_dispatcher_)
+    : env{env_}, block_pool{block_pool_}, program_start{start_address}, exits_to_dispatcher{
+                                                                            exits_to_dispatcher_} {
+    if (exits_to_dispatcher) {
+        dispatch_block = block_pool.Create(Block{});
+        dispatch_block->begin = {};
+        dispatch_block->end = {};
+        dispatch_block->end_class = EndClass::Exit;
+        dispatch_block->cond = IR::Condition(true);
+        dispatch_block->stack = {};
+        dispatch_block->branch_true = nullptr;
+        dispatch_block->branch_false = nullptr;
+    }
+    functions.emplace_back(block_pool, start_address);
+    for (FunctionId function_id = 0; function_id < functions.size(); ++function_id) {
+        while (!functions[function_id].labels.empty()) {
+            Function& function{functions[function_id]};
+            Label label{function.labels.back()};
+            function.labels.pop_back();
+            AnalyzeLabel(function_id, label);
+        }
+    }
+    if (exits_to_dispatcher) {
+        const auto last_block{functions[0].blocks.rbegin()};
+        dispatch_block->begin = last_block->end + 1;
+        dispatch_block->end = last_block->end + 1;
+        functions[0].blocks.insert(*dispatch_block);
+    }
+}
+
+void CFG::AnalyzeLabel(FunctionId function_id, Label& label) {
+    if (InspectVisitedBlocks(function_id, label)) {
+        // Label address has been visited
+        return;
+    }
+    // Try to find the next block
+    Function* const function{&functions[function_id]};
+    Location pc{label.address};
+    const auto next_it{function->blocks.upper_bound(pc, Compare{})};
+    const bool is_last{next_it == function->blocks.end()};
+    Block* const next{is_last ? nullptr : &*next_it};
+    // Insert before the next block
+    Block* const block{label.block};
+    // Analyze instructions until it reaches an already visited block or there's a branch
+    bool is_branch{false};
+    while (!next || pc < next->begin) {
+        is_branch = AnalyzeInst(block, function_id, pc) == AnalysisState::Branch;
+        if (is_branch) {
+            break;
+        }
+        ++pc;
+    }
+    if (!is_branch) {
+        // If the block finished without a branch,
+        // it means that the next instruction is already visited, jump to it
+        block->end = pc;
+        block->cond = IR::Condition{true};
+        block->branch_true = next;
+        block->branch_false = nullptr;
+    }
+    // Function's pointer might be invalid, resolve it again
+    // Insert the new block
+    functions[function_id].blocks.insert(*block);
+}
+
+bool CFG::InspectVisitedBlocks(FunctionId function_id, const Label& label) {
+    const Location pc{label.address};
+    Function& function{functions[function_id]};
+    const auto it{
+        std::ranges::find_if(function.blocks, [pc](auto& block) { return block.Contains(pc); })};
+    if (it == function.blocks.end()) {
+        // Address has not been visited
+        return false;
+    }
+    Block* const visited_block{&*it};
+    if (visited_block->begin == pc) {
+        throw LogicError("Dangling block");
+    }
+    Block* const new_block{label.block};
+    Split(visited_block, new_block, pc);
+    function.blocks.insert(it, *new_block);
+    return true;
+}
+
+CFG::AnalysisState CFG::AnalyzeInst(Block* block, FunctionId function_id, Location pc) {
+    const Instruction inst{env.ReadInstruction(pc.Offset())};
+    const Opcode opcode{Decode(inst.raw)};
+    switch (opcode) {
+    case Opcode::BRA:
+    case Opcode::JMP:
+    case Opcode::RET:
+        if (!AnalyzeBranch(block, function_id, pc, inst, opcode)) {
+            return AnalysisState::Continue;
+        }
+        switch (opcode) {
+        case Opcode::BRA:
+        case Opcode::JMP:
+            AnalyzeBRA(block, function_id, pc, inst, IsAbsoluteJump(opcode));
+            break;
+        case Opcode::RET:
+            block->end_class = EndClass::Return;
+            break;
+        default:
+            break;
+        }
+        block->end = pc;
+        return AnalysisState::Branch;
+    case Opcode::BRK:
+    case Opcode::CONT:
+    case Opcode::LONGJMP:
+    case Opcode::SYNC: {
+        if (!AnalyzeBranch(block, function_id, pc, inst, opcode)) {
+            return AnalysisState::Continue;
+        }
+        const auto [stack_pc, new_stack]{block->stack.Pop(OpcodeToken(opcode))};
+        block->branch_true = AddLabel(block, new_stack, stack_pc, function_id);
+        block->end = pc;
+        return AnalysisState::Branch;
+    }
+    case Opcode::KIL: {
+        const Predicate pred{inst.Pred()};
+        const auto ir_pred{static_cast<IR::Pred>(pred.index)};
+        const IR::Condition cond{inst.branch.flow_test, ir_pred, pred.negated};
+        AnalyzeCondInst(block, function_id, pc, EndClass::Kill, cond);
+        return AnalysisState::Branch;
+    }
+    case Opcode::PBK:
+    case Opcode::PCNT:
+    case Opcode::PEXIT:
+    case Opcode::PLONGJMP:
+    case Opcode::SSY:
+        block->stack.Push(OpcodeToken(opcode), BranchOffset(pc, inst));
+        return AnalysisState::Continue;
+    case Opcode::BRX:
+    case Opcode::JMX:
+        return AnalyzeBRX(block, pc, inst, IsAbsoluteJump(opcode), function_id);
+    case Opcode::EXIT:
+        return AnalyzeEXIT(block, function_id, pc, inst);
+    case Opcode::PRET:
+        throw NotImplementedException("PRET flow analysis");
+    case Opcode::CAL:
+    case Opcode::JCAL: {
+        const bool is_absolute{IsAbsoluteJump(opcode)};
+        const Location cal_pc{is_absolute ? inst.branch.Absolute() : BranchOffset(pc, inst)};
+        // Technically CAL pushes into PRET, but that's implicit in the function call for us
+        // Insert the function into the list if it doesn't exist
+        const auto it{std::ranges::find(functions, cal_pc, &Function::entrypoint)};
+        const bool exists{it != functions.end()};
+        const FunctionId call_id{exists ? static_cast<size_t>(std::distance(functions.begin(), it))
+                                        : functions.size()};
+        if (!exists) {
+            functions.emplace_back(block_pool, cal_pc);
+        }
+        block->end_class = EndClass::Call;
+        block->function_call = call_id;
+        block->return_block = AddLabel(block, block->stack, pc + 1, function_id);
+        block->end = pc;
+        return AnalysisState::Branch;
+    }
+    default:
+        break;
+    }
+    const Predicate pred{inst.Pred()};
+    if (pred == Predicate{true} || pred == Predicate{false}) {
+        return AnalysisState::Continue;
+    }
+    const IR::Condition cond{static_cast<IR::Pred>(pred.index), pred.negated};
+    AnalyzeCondInst(block, function_id, pc, EndClass::Branch, cond);
+    return AnalysisState::Branch;
+}
+
+void CFG::AnalyzeCondInst(Block* block, FunctionId function_id, Location pc,
+                          EndClass insn_end_class, IR::Condition cond) {
+    if (block->begin != pc) {
+        // If the block doesn't start in the conditional instruction
+        // mark it as a label to visit it later
+        block->end = pc;
+        block->cond = IR::Condition{true};
+        block->branch_true = AddLabel(block, block->stack, pc, function_id);
+        block->branch_false = nullptr;
+        return;
+    }
+    // Create a virtual block and a conditional block
+    Block* const conditional_block{block_pool.Create()};
+    Block virtual_block{};
+    virtual_block.begin = block->begin.Virtual();
+    virtual_block.end = block->begin.Virtual();
+    virtual_block.end_class = EndClass::Branch;
+    virtual_block.stack = block->stack;
+    virtual_block.cond = cond;
+    virtual_block.branch_true = conditional_block;
+    virtual_block.branch_false = nullptr;
+    // Save the contents of the visited block in the conditional block
+    *conditional_block = std::move(*block);
+    // Impersonate the visited block with a virtual block
+    *block = std::move(virtual_block);
+    // Set the end properties of the conditional instruction
+    conditional_block->end = pc + 1;
+    conditional_block->end_class = insn_end_class;
+    // Add a label to the instruction after the conditional instruction
+    Block* const endif_block{AddLabel(conditional_block, block->stack, pc + 1, function_id)};
+    // Branch to the next instruction from the virtual block
+    block->branch_false = endif_block;
+    // And branch to it from the conditional instruction if it is a branch or a kill instruction
+    // Kill instructions are considered a branch because they demote to a helper invocation and
+    // execution may continue.
+    if (insn_end_class == EndClass::Branch || insn_end_class == EndClass::Kill) {
+        conditional_block->cond = IR::Condition{true};
+        conditional_block->branch_true = endif_block;
+        conditional_block->branch_false = nullptr;
+    }
+    // Finally insert the condition block into the list of blocks
+    functions[function_id].blocks.insert(*conditional_block);
+}
+
+bool CFG::AnalyzeBranch(Block* block, FunctionId function_id, Location pc, Instruction inst,
+                        Opcode opcode) {
+    if (inst.branch.is_cbuf) {
+        throw NotImplementedException("Branch with constant buffer offset");
+    }
+    const Predicate pred{inst.Pred()};
+    if (pred == Predicate{false}) {
+        return false;
+    }
+    const bool has_flow_test{HasFlowTest(opcode)};
+    const IR::FlowTest flow_test{has_flow_test ? inst.branch.flow_test.Value() : IR::FlowTest::T};
+    if (pred != Predicate{true} || flow_test != IR::FlowTest::T) {
+        block->cond = IR::Condition(flow_test, static_cast<IR::Pred>(pred.index), pred.negated);
+        block->branch_false = AddLabel(block, block->stack, pc + 1, function_id);
+    } else {
+        block->cond = IR::Condition{true};
+    }
+    return true;
+}
+
+void CFG::AnalyzeBRA(Block* block, FunctionId function_id, Location pc, Instruction inst,
+                     bool is_absolute) {
+    const Location bra_pc{is_absolute ? inst.branch.Absolute() : BranchOffset(pc, inst)};
+    block->branch_true = AddLabel(block, block->stack, bra_pc, function_id);
+}
+
+CFG::AnalysisState CFG::AnalyzeBRX(Block* block, Location pc, Instruction inst, bool is_absolute,
+                                   FunctionId function_id) {
+    const std::optional brx_table{TrackIndirectBranchTable(env, pc, program_start)};
+    if (!brx_table) {
+        TrackIndirectBranchTable(env, pc, program_start);
+        throw NotImplementedException("Failed to track indirect branch");
+    }
+    const IR::FlowTest flow_test{inst.branch.flow_test};
+    const Predicate pred{inst.Pred()};
+    if (flow_test != IR::FlowTest::T || pred != Predicate{true}) {
+        throw NotImplementedException("Conditional indirect branch");
+    }
+    std::vector<u32> targets;
+    targets.reserve(brx_table->num_entries);
+    for (u32 i = 0; i < brx_table->num_entries; ++i) {
+        u32 target{env.ReadCbufValue(brx_table->cbuf_index, brx_table->cbuf_offset + i * 4)};
+        if (!is_absolute) {
+            target += pc.Offset();
+        }
+        target += static_cast<u32>(brx_table->branch_offset);
+        target += 8;
+        targets.push_back(target);
+    }
+    std::ranges::sort(targets);
+    targets.erase(std::unique(targets.begin(), targets.end()), targets.end());
+
+    block->indirect_branches.reserve(targets.size());
+    for (const u32 target : targets) {
+        Block* const branch{AddLabel(block, block->stack, target, function_id)};
+        block->indirect_branches.push_back({
+            .block = branch,
+            .address = target,
+        });
+    }
+    block->cond = IR::Condition{true};
+    block->end = pc + 1;
+    block->end_class = EndClass::IndirectBranch;
+    block->branch_reg = brx_table->branch_reg;
+    block->branch_offset = brx_table->branch_offset + 8;
+    if (!is_absolute) {
+        block->branch_offset += pc.Offset();
+    }
+    return AnalysisState::Branch;
+}
+
+CFG::AnalysisState CFG::AnalyzeEXIT(Block* block, FunctionId function_id, Location pc,
+                                    Instruction inst) {
+    const IR::FlowTest flow_test{inst.branch.flow_test};
+    const Predicate pred{inst.Pred()};
+    if (pred == Predicate{false} || flow_test == IR::FlowTest::F) {
+        // EXIT will never be taken
+        return AnalysisState::Continue;
+    }
+    if (exits_to_dispatcher && function_id != 0) {
+        throw NotImplementedException("Dispatch EXIT on external function");
+    }
+    if (pred != Predicate{true} || flow_test != IR::FlowTest::T) {
+        if (block->stack.Peek(Token::PEXIT).has_value()) {
+            throw NotImplementedException("Conditional EXIT with PEXIT token");
+        }
+        const IR::Condition cond{flow_test, static_cast<IR::Pred>(pred.index), pred.negated};
+        if (exits_to_dispatcher) {
+            block->end = pc;
+            block->end_class = EndClass::Branch;
+            block->cond = cond;
+            block->branch_true = dispatch_block;
+            block->branch_false = AddLabel(block, block->stack, pc + 1, function_id);
+            return AnalysisState::Branch;
+        }
+        AnalyzeCondInst(block, function_id, pc, EndClass::Exit, cond);
+        return AnalysisState::Branch;
+    }
+    if (const std::optional<Location> exit_pc{block->stack.Peek(Token::PEXIT)}) {
+        const Stack popped_stack{block->stack.Remove(Token::PEXIT)};
+        block->cond = IR::Condition{true};
+        block->branch_true = AddLabel(block, popped_stack, *exit_pc, function_id);
+        block->branch_false = nullptr;
+        return AnalysisState::Branch;
+    }
+    if (exits_to_dispatcher) {
+        block->cond = IR::Condition{true};
+        block->end = pc;
+        block->end_class = EndClass::Branch;
+        block->branch_true = dispatch_block;
+        block->branch_false = nullptr;
+        return AnalysisState::Branch;
+    }
+    block->end = pc + 1;
+    block->end_class = EndClass::Exit;
+    return AnalysisState::Branch;
+}
+
+Block* CFG::AddLabel(Block* block, Stack stack, Location pc, FunctionId function_id) {
+    Function& function{functions[function_id]};
+    if (block->begin == pc) {
+        // Jumps to itself
+        return block;
+    }
+    if (const auto it{function.blocks.find(pc, Compare{})}; it != function.blocks.end()) {
+        // Block already exists and it has been visited
+        if (function.blocks.begin() != it) {
+            // Check if the previous node is the virtual variant of the label
+            // This won't exist if a virtual node is not needed or it hasn't been visited
+            // If it hasn't been visited and a virtual node is needed, this will still behave as
+            // expected because the node impersonated with its virtual node.
+            const auto prev{std::prev(it)};
+            if (it->begin.Virtual() == prev->begin) {
+                return &*prev;
+            }
+        }
+        return &*it;
+    }
+    // Make sure we don't insert the same layer twice
+    const auto label_it{std::ranges::find(function.labels, pc, &Label::address)};
+    if (label_it != function.labels.end()) {
+        return label_it->block;
+    }
+    Block* const new_block{block_pool.Create()};
+    new_block->begin = pc;
+    new_block->end = pc;
+    new_block->end_class = EndClass::Branch;
+    new_block->cond = IR::Condition(true);
+    new_block->stack = stack;
+    new_block->branch_true = nullptr;
+    new_block->branch_false = nullptr;
+    function.labels.push_back(Label{
+        .address{pc},
+        .block = new_block,
+        .stack{std::move(stack)},
+    });
+    return new_block;
+}
+
+std::string CFG::Dot() const {
+    int node_uid{0};
+
+    std::string dot{"digraph shader {\n"};
+    for (const Function& function : functions) {
+        dot += fmt::format("\tsubgraph cluster_{} {{\n", function.entrypoint);
+        dot += fmt::format("\t\tnode [style=filled];\n");
+        for (const Block& block : function.blocks) {
+            const std::string name{NameOf(block)};
+            const auto add_branch = [&](Block* branch, bool add_label) {
+                dot += fmt::format("\t\t{}->{}", name, NameOf(*branch));
+                if (add_label && block.cond != IR::Condition{true} &&
+                    block.cond != IR::Condition{false}) {
+                    dot += fmt::format(" [label=\"{}\"]", block.cond);
+                }
+                dot += '\n';
+            };
+            dot += fmt::format("\t\t{};\n", name);
+            switch (block.end_class) {
+            case EndClass::Branch:
+                if (block.cond != IR::Condition{false}) {
+                    add_branch(block.branch_true, true);
+                }
+                if (block.cond != IR::Condition{true}) {
+                    add_branch(block.branch_false, false);
+                }
+                break;
+            case EndClass::IndirectBranch:
+                for (const IndirectBranch& branch : block.indirect_branches) {
+                    add_branch(branch.block, false);
+                }
+                break;
+            case EndClass::Call:
+                dot += fmt::format("\t\t{}->N{};\n", name, node_uid);
+                dot += fmt::format("\t\tN{}->{};\n", node_uid, NameOf(*block.return_block));
+                dot += fmt::format("\t\tN{} [label=\"Call {}\"][shape=square][style=stripped];\n",
+                                   node_uid, block.function_call);
+                dot += '\n';
+                ++node_uid;
+                break;
+            case EndClass::Exit:
+                dot += fmt::format("\t\t{}->N{};\n", name, node_uid);
+                dot += fmt::format("\t\tN{} [label=\"Exit\"][shape=square][style=stripped];\n",
+                                   node_uid);
+                ++node_uid;
+                break;
+            case EndClass::Return:
+                dot += fmt::format("\t\t{}->N{};\n", name, node_uid);
+                dot += fmt::format("\t\tN{} [label=\"Return\"][shape=square][style=stripped];\n",
+                                   node_uid);
+                ++node_uid;
+                break;
+            case EndClass::Kill:
+                dot += fmt::format("\t\t{}->N{};\n", name, node_uid);
+                dot += fmt::format("\t\tN{} [label=\"Kill\"][shape=square][style=stripped];\n",
+                                   node_uid);
+                ++node_uid;
+                break;
+            }
+        }
+        if (function.entrypoint == 8) {
+            dot += fmt::format("\t\tlabel = \"main\";\n");
+        } else {
+            dot += fmt::format("\t\tlabel = \"Function {}\";\n", function.entrypoint);
+        }
+        dot += "\t}\n";
+    }
+    if (!functions.empty()) {
+        auto& function{functions.front()};
+        if (function.blocks.empty()) {
+            dot += "Start;\n";
+        } else {
+            dot += fmt::format("\tStart -> {};\n", NameOf(*function.blocks.begin()));
+        }
+        dot += fmt::format("\tStart [shape=diamond];\n");
+    }
+    dot += "}\n";
+    return dot;
+}
+
+} // namespace Shader::Maxwell::Flow