Merge pull request #6585 from ameerj/hades

Shader Decompiler Rewrite

1 files changed, 383 insertions, 0 deletions

diff --git a/src/shader_recompiler/ir_opt/ssa_rewrite_pass.cpp b/src/shader_recompiler/ir_opt/ssa_rewrite_pass.cpp
new file mode 100644
index 000000000..53145fb5e
--- /dev/null
+++ b/src/shader_recompiler/ir_opt/ssa_rewrite_pass.cpp
@@ -0,0 +1,383 @@
+// Copyright 2021 yuzu Emulator Project
+// Licensed under GPLv2 or any later version
+// Refer to the license.txt file included.
+
+// This file implements the SSA rewriting algorithm proposed in
+//
+//      Simple and Efficient Construction of Static Single Assignment Form.
+//      Braun M., Buchwald S., Hack S., Leiba R., Mallon C., Zwinkau A. (2013)
+//      In: Jhala R., De Bosschere K. (eds)
+//      Compiler Construction. CC 2013.
+//      Lecture Notes in Computer Science, vol 7791.
+//      Springer, Berlin, Heidelberg
+//
+//      https://link.springer.com/chapter/10.1007/978-3-642-37051-9_6
+//
+
+#include <span>
+#include <variant>
+#include <vector>
+
+#include <boost/container/flat_map.hpp>
+#include <boost/container/flat_set.hpp>
+
+#include "shader_recompiler/frontend/ir/basic_block.h"
+#include "shader_recompiler/frontend/ir/opcodes.h"
+#include "shader_recompiler/frontend/ir/pred.h"
+#include "shader_recompiler/frontend/ir/reg.h"
+#include "shader_recompiler/frontend/ir/value.h"
+#include "shader_recompiler/ir_opt/passes.h"
+
+namespace Shader::Optimization {
+namespace {
+struct FlagTag {
+    auto operator<=>(const FlagTag&) const noexcept = default;
+};
+struct ZeroFlagTag : FlagTag {};
+struct SignFlagTag : FlagTag {};
+struct CarryFlagTag : FlagTag {};
+struct OverflowFlagTag : FlagTag {};
+
+struct GotoVariable : FlagTag {
+    GotoVariable() = default;
+    explicit GotoVariable(u32 index_) : index{index_} {}
+
+    auto operator<=>(const GotoVariable&) const noexcept = default;
+
+    u32 index;
+};
+
+struct IndirectBranchVariable {
+    auto operator<=>(const IndirectBranchVariable&) const noexcept = default;
+};
+
+using Variant = std::variant<IR::Reg, IR::Pred, ZeroFlagTag, SignFlagTag, CarryFlagTag,
+                             OverflowFlagTag, GotoVariable, IndirectBranchVariable>;
+using ValueMap = boost::container::flat_map<IR::Block*, IR::Value>;
+
+struct DefTable {
+    const IR::Value& Def(IR::Block* block, IR::Reg variable) {
+        return block->SsaRegValue(variable);
+    }
+    void SetDef(IR::Block* block, IR::Reg variable, const IR::Value& value) {
+        block->SetSsaRegValue(variable, value);
+    }
+
+    const IR::Value& Def(IR::Block* block, IR::Pred variable) {
+        return preds[IR::PredIndex(variable)][block];
+    }
+    void SetDef(IR::Block* block, IR::Pred variable, const IR::Value& value) {
+        preds[IR::PredIndex(variable)].insert_or_assign(block, value);
+    }
+
+    const IR::Value& Def(IR::Block* block, GotoVariable variable) {
+        return goto_vars[variable.index][block];
+    }
+    void SetDef(IR::Block* block, GotoVariable variable, const IR::Value& value) {
+        goto_vars[variable.index].insert_or_assign(block, value);
+    }
+
+    const IR::Value& Def(IR::Block* block, IndirectBranchVariable) {
+        return indirect_branch_var[block];
+    }
+    void SetDef(IR::Block* block, IndirectBranchVariable, const IR::Value& value) {
+        indirect_branch_var.insert_or_assign(block, value);
+    }
+
+    const IR::Value& Def(IR::Block* block, ZeroFlagTag) {
+        return zero_flag[block];
+    }
+    void SetDef(IR::Block* block, ZeroFlagTag, const IR::Value& value) {
+        zero_flag.insert_or_assign(block, value);
+    }
+
+    const IR::Value& Def(IR::Block* block, SignFlagTag) {
+        return sign_flag[block];
+    }
+    void SetDef(IR::Block* block, SignFlagTag, const IR::Value& value) {
+        sign_flag.insert_or_assign(block, value);
+    }
+
+    const IR::Value& Def(IR::Block* block, CarryFlagTag) {
+        return carry_flag[block];
+    }
+    void SetDef(IR::Block* block, CarryFlagTag, const IR::Value& value) {
+        carry_flag.insert_or_assign(block, value);
+    }
+
+    const IR::Value& Def(IR::Block* block, OverflowFlagTag) {
+        return overflow_flag[block];
+    }
+    void SetDef(IR::Block* block, OverflowFlagTag, const IR::Value& value) {
+        overflow_flag.insert_or_assign(block, value);
+    }
+
+    std::array<ValueMap, IR::NUM_USER_PREDS> preds;
+    boost::container::flat_map<u32, ValueMap> goto_vars;
+    ValueMap indirect_branch_var;
+    ValueMap zero_flag;
+    ValueMap sign_flag;
+    ValueMap carry_flag;
+    ValueMap overflow_flag;
+};
+
+IR::Opcode UndefOpcode(IR::Reg) noexcept {
+    return IR::Opcode::UndefU32;
+}
+
+IR::Opcode UndefOpcode(IR::Pred) noexcept {
+    return IR::Opcode::UndefU1;
+}
+
+IR::Opcode UndefOpcode(const FlagTag&) noexcept {
+    return IR::Opcode::UndefU1;
+}
+
+IR::Opcode UndefOpcode(IndirectBranchVariable) noexcept {
+    return IR::Opcode::UndefU32;
+}
+
+enum class Status {
+    Start,
+    SetValue,
+    PreparePhiArgument,
+    PushPhiArgument,
+};
+
+template <typename Type>
+struct ReadState {
+    ReadState(IR::Block* block_) : block{block_} {}
+    ReadState() = default;
+
+    IR::Block* block{};
+    IR::Value result{};
+    IR::Inst* phi{};
+    IR::Block* const* pred_it{};
+    IR::Block* const* pred_end{};
+    Status pc{Status::Start};
+};
+
+class Pass {
+public:
+    template <typename Type>
+    void WriteVariable(Type variable, IR::Block* block, const IR::Value& value) {
+        current_def.SetDef(block, variable, value);
+    }
+
+    template <typename Type>
+    IR::Value ReadVariable(Type variable, IR::Block* root_block) {
+        boost::container::small_vector<ReadState<Type>, 64> stack{
+            ReadState<Type>(nullptr),
+            ReadState<Type>(root_block),
+        };
+        const auto prepare_phi_operand{[&] {
+            if (stack.back().pred_it == stack.back().pred_end) {
+                IR::Inst* const phi{stack.back().phi};
+                IR::Block* const block{stack.back().block};
+                const IR::Value result{TryRemoveTrivialPhi(*phi, block, UndefOpcode(variable))};
+                stack.pop_back();
+                stack.back().result = result;
+                WriteVariable(variable, block, result);
+            } else {
+                IR::Block* const imm_pred{*stack.back().pred_it};
+                stack.back().pc = Status::PushPhiArgument;
+                stack.emplace_back(imm_pred);
+            }
+        }};
+        do {
+            IR::Block* const block{stack.back().block};
+            switch (stack.back().pc) {
+            case Status::Start: {
+                if (const IR::Value& def = current_def.Def(block, variable); !def.IsEmpty()) {
+                    stack.back().result = def;
+                } else if (!block->IsSsaSealed()) {
+                    // Incomplete CFG
+                    IR::Inst* phi{&*block->PrependNewInst(block->begin(), IR::Opcode::Phi)};
+                    phi->SetFlags(IR::TypeOf(UndefOpcode(variable)));
+
+                    incomplete_phis[block].insert_or_assign(variable, phi);
+                    stack.back().result = IR::Value{&*phi};
+                } else if (const std::span imm_preds = block->ImmPredecessors();
+                           imm_preds.size() == 1) {
+                    // Optimize the common case of one predecessor: no phi needed
+                    stack.back().pc = Status::SetValue;
+                    stack.emplace_back(imm_preds.front());
+                    break;
+                } else {
+                    // Break potential cycles with operandless phi
+                    IR::Inst* const phi{&*block->PrependNewInst(block->begin(), IR::Opcode::Phi)};
+                    phi->SetFlags(IR::TypeOf(UndefOpcode(variable)));
+
+                    WriteVariable(variable, block, IR::Value{phi});
+
+                    stack.back().phi = phi;
+                    stack.back().pred_it = imm_preds.data();
+                    stack.back().pred_end = imm_preds.data() + imm_preds.size();
+                    prepare_phi_operand();
+                    break;
+                }
+            }
+                [[fallthrough]];
+            case Status::SetValue: {
+                const IR::Value result{stack.back().result};
+                WriteVariable(variable, block, result);
+                stack.pop_back();
+                stack.back().result = result;
+                break;
+            }
+            case Status::PushPhiArgument: {
+                IR::Inst* const phi{stack.back().phi};
+                phi->AddPhiOperand(*stack.back().pred_it, stack.back().result);
+                ++stack.back().pred_it;
+            }
+                [[fallthrough]];
+            case Status::PreparePhiArgument:
+                prepare_phi_operand();
+                break;
+            }
+        } while (stack.size() > 1);
+        return stack.back().result;
+    }
+
+    void SealBlock(IR::Block* block) {
+        const auto it{incomplete_phis.find(block)};
+        if (it != incomplete_phis.end()) {
+            for (auto& pair : it->second) {
+                auto& variant{pair.first};
+                auto& phi{pair.second};
+                std::visit([&](auto& variable) { AddPhiOperands(variable, *phi, block); }, variant);
+            }
+        }
+        block->SsaSeal();
+    }
+
+private:
+    template <typename Type>
+    IR::Value AddPhiOperands(Type variable, IR::Inst& phi, IR::Block* block) {
+        for (IR::Block* const imm_pred : block->ImmPredecessors()) {
+            phi.AddPhiOperand(imm_pred, ReadVariable(variable, imm_pred));
+        }
+        return TryRemoveTrivialPhi(phi, block, UndefOpcode(variable));
+    }
+
+    IR::Value TryRemoveTrivialPhi(IR::Inst& phi, IR::Block* block, IR::Opcode undef_opcode) {
+        IR::Value same;
+        const size_t num_args{phi.NumArgs()};
+        for (size_t arg_index = 0; arg_index < num_args; ++arg_index) {
+            const IR::Value& op{phi.Arg(arg_index)};
+            if (op.Resolve() == same.Resolve() || op == IR::Value{&phi}) {
+                // Unique value or self-reference
+                continue;
+            }
+            if (!same.IsEmpty()) {
+                // The phi merges at least two values: not trivial
+                return IR::Value{&phi};
+            }
+            same = op;
+        }
+        // Remove the phi node from the block, it will be reinserted
+        IR::Block::InstructionList& list{block->Instructions()};
+        list.erase(IR::Block::InstructionList::s_iterator_to(phi));
+
+        // Find the first non-phi instruction and use it as an insertion point
+        IR::Block::iterator reinsert_point{std::ranges::find_if_not(list, IR::IsPhi)};
+        if (same.IsEmpty()) {
+            // The phi is unreachable or in the start block
+            // Insert an undefined instruction and make it the phi node replacement
+            // The "phi" node reinsertion point is specified after this instruction
+            reinsert_point = block->PrependNewInst(reinsert_point, undef_opcode);
+            same = IR::Value{&*reinsert_point};
+            ++reinsert_point;
+        }
+        // Reinsert the phi node and reroute all its uses to the "same" value
+        list.insert(reinsert_point, phi);
+        phi.ReplaceUsesWith(same);
+        // TODO: Try to recursively remove all phi users, which might have become trivial
+        return same;
+    }
+
+    boost::container::flat_map<IR::Block*, boost::container::flat_map<Variant, IR::Inst*>>
+        incomplete_phis;
+    DefTable current_def;
+};
+
+void VisitInst(Pass& pass, IR::Block* block, IR::Inst& inst) {
+    switch (inst.GetOpcode()) {
+    case IR::Opcode::SetRegister:
+        if (const IR::Reg reg{inst.Arg(0).Reg()}; reg != IR::Reg::RZ) {
+            pass.WriteVariable(reg, block, inst.Arg(1));
+        }
+        break;
+    case IR::Opcode::SetPred:
+        if (const IR::Pred pred{inst.Arg(0).Pred()}; pred != IR::Pred::PT) {
+            pass.WriteVariable(pred, block, inst.Arg(1));
+        }
+        break;
+    case IR::Opcode::SetGotoVariable:
+        pass.WriteVariable(GotoVariable{inst.Arg(0).U32()}, block, inst.Arg(1));
+        break;
+    case IR::Opcode::SetIndirectBranchVariable:
+        pass.WriteVariable(IndirectBranchVariable{}, block, inst.Arg(0));
+        break;
+    case IR::Opcode::SetZFlag:
+        pass.WriteVariable(ZeroFlagTag{}, block, inst.Arg(0));
+        break;
+    case IR::Opcode::SetSFlag:
+        pass.WriteVariable(SignFlagTag{}, block, inst.Arg(0));
+        break;
+    case IR::Opcode::SetCFlag:
+        pass.WriteVariable(CarryFlagTag{}, block, inst.Arg(0));
+        break;
+    case IR::Opcode::SetOFlag:
+        pass.WriteVariable(OverflowFlagTag{}, block, inst.Arg(0));
+        break;
+    case IR::Opcode::GetRegister:
+        if (const IR::Reg reg{inst.Arg(0).Reg()}; reg != IR::Reg::RZ) {
+            inst.ReplaceUsesWith(pass.ReadVariable(reg, block));
+        }
+        break;
+    case IR::Opcode::GetPred:
+        if (const IR::Pred pred{inst.Arg(0).Pred()}; pred != IR::Pred::PT) {
+            inst.ReplaceUsesWith(pass.ReadVariable(pred, block));
+        }
+        break;
+    case IR::Opcode::GetGotoVariable:
+        inst.ReplaceUsesWith(pass.ReadVariable(GotoVariable{inst.Arg(0).U32()}, block));
+        break;
+    case IR::Opcode::GetIndirectBranchVariable:
+        inst.ReplaceUsesWith(pass.ReadVariable(IndirectBranchVariable{}, block));
+        break;
+    case IR::Opcode::GetZFlag:
+        inst.ReplaceUsesWith(pass.ReadVariable(ZeroFlagTag{}, block));
+        break;
+    case IR::Opcode::GetSFlag:
+        inst.ReplaceUsesWith(pass.ReadVariable(SignFlagTag{}, block));
+        break;
+    case IR::Opcode::GetCFlag:
+        inst.ReplaceUsesWith(pass.ReadVariable(CarryFlagTag{}, block));
+        break;
+    case IR::Opcode::GetOFlag:
+        inst.ReplaceUsesWith(pass.ReadVariable(OverflowFlagTag{}, block));
+        break;
+    default:
+        break;
+    }
+}
+
+void VisitBlock(Pass& pass, IR::Block* block) {
+    for (IR::Inst& inst : block->Instructions()) {
+        VisitInst(pass, block, inst);
+    }
+    pass.SealBlock(block);
+}
+} // Anonymous namespace
+
+void SsaRewritePass(IR::Program& program) {
+    Pass pass;
+    const auto end{program.post_order_blocks.rend()};
+    for (auto block = program.post_order_blocks.rbegin(); block != end; ++block) {
+        VisitBlock(pass, *block);
+    }
+}
+
+} // namespace Shader::Optimization