3 files changed, 471 insertions, 16 deletions

diff --git a/src/video_core/shader/control_flow.cpp b/src/video_core/shader/control_flow.cpp
new file mode 100644
index 000000000..fcf22c7f2
--- /dev/null
+++ b/src/video_core/shader/control_flow.cpp
@@ -0,0 +1,393 @@
+
+#include <list>
+#include <map>
+#include <unordered_set>
+#include <vector>
+
+#include "common/assert.h"
+#include "common/common_types.h"
+#include "video_core/shader/control_flow.h"
+#include "video_core/shader/shader_ir.h"
+
+namespace VideoCommon::Shader {
+
+using Tegra::Shader::Instruction;
+using Tegra::Shader::OpCode;
+
+constexpr s32 unassigned_branch = -2;
+
+struct BlockBranchInfo {
+    Condition condition{};
+    s32 address{exit_branch};
+    bool kill{};
+    bool is_sync{};
+    bool is_brk{};
+};
+
+struct BlockInfo {
+    BlockInfo() {}
+    u32 start{};
+    u32 end{};
+    bool visited{};
+    BlockBranchInfo branch{};
+
+    bool IsInside(const u32 address) const {
+        return start <= address && address <= end;
+    }
+};
+
+struct Stamp {
+    Stamp() = default;
+    Stamp(u32 address, u32 target) : address{address}, target{target} {}
+    u32 address{};
+    u32 target{};
+    bool operator==(const Stamp& sb) const {
+        return std::tie(address, target) == std::tie(sb.address, sb.target);
+    }
+    bool operator<(const Stamp& sb) const {
+        return address < sb.address;
+    }
+    bool operator>(const Stamp& sb) const {
+        return address > sb.address;
+    }
+    bool operator<=(const Stamp& sb) const {
+        return address <= sb.address;
+    }
+    bool operator>=(const Stamp& sb) const {
+        return address >= sb.address;
+    }
+};
+
+struct CFGRebuildState {
+    explicit CFGRebuildState(const ProgramCode& program_code, const std::size_t program_size)
+        : program_code{program_code}, program_size{program_size} {
+        // queries.clear();
+        block_info.clear();
+        labels.clear();
+        visited_address.clear();
+        ssy_labels.clear();
+        pbk_labels.clear();
+        inspect_queries.clear();
+    }
+
+    std::vector<BlockInfo> block_info{};
+    std::list<u32> inspect_queries{};
+    // std::list<Query> queries{};
+    std::unordered_set<u32> visited_address{};
+    std::unordered_set<u32> labels{};
+    std::set<Stamp> ssy_labels;
+    std::set<Stamp> pbk_labels;
+    const ProgramCode& program_code;
+    const std::size_t program_size;
+};
+
+enum class BlockCollision : u32 { None = 0, Found = 1, Inside = 2 };
+
+std::pair<BlockCollision, std::vector<BlockInfo>::iterator> TryGetBlock(CFGRebuildState& state,
+                                                                        u32 address) {
+    auto it = state.block_info.begin();
+    while (it != state.block_info.end()) {
+        if (it->start == address) {
+            return {BlockCollision::Found, it};
+        }
+        if (it->IsInside(address)) {
+            return {BlockCollision::Inside, it};
+        }
+        it++;
+    }
+    return {BlockCollision::None, it};
+}
+
+struct ParseInfo {
+    BlockBranchInfo branch_info{};
+    u32 end_address{};
+};
+
+BlockInfo* CreateBlockInfo(CFGRebuildState& state, u32 start, u32 end) {
+    auto& it = state.block_info.emplace_back();
+    it.start = start;
+    it.end = end;
+    state.visited_address.insert(start);
+    return &it;
+}
+
+Pred GetPredicate(u32 index, bool negated) {
+    return static_cast<Pred>(index + (negated ? 8 : 0));
+}
+
+enum class ParseResult : u32 {
+    ControlCaught = 0,
+    BlockEnd = 1,
+    AbnormalFlow = 2,
+};
+
+ParseResult ParseCode(CFGRebuildState& state, u32 address, ParseInfo& parse_info) {
+
+    u32 offset = static_cast<u32>(address);
+    u32 end_address = static_cast<u32>(state.program_size - 10U) * 8U;
+
+    auto insert_label = ([](CFGRebuildState& state, u32 address) {
+        auto pair = state.labels.emplace(address);
+        if (pair.second) {
+            state.inspect_queries.push_back(address);
+        }
+    });
+
+    while (true) {
+        if (offset >= end_address) {
+            parse_info.branch_info.address = exit_branch;
+            break;
+        }
+        if (state.visited_address.count(offset) != 0) {
+            parse_info.branch_info.address = offset;
+            break;
+        }
+        const Instruction instr = {state.program_code[offset]};
+        const auto opcode = OpCode::Decode(instr);
+        if (!opcode || opcode->get().GetType() != OpCode::Type::Flow) {
+            offset++;
+            continue;
+        }
+
+        switch (opcode->get().GetId()) {
+        case OpCode::Id::EXIT: {
+            const auto pred_index = static_cast<u32>(instr.pred.pred_index);
+            parse_info.branch_info.condition.predicate =
+                GetPredicate(pred_index, instr.negate_pred != 0);
+            if (parse_info.branch_info.condition.predicate == Pred::NeverExecute) {
+                offset++;
+                continue;
+            }
+            const ConditionCode cc = instr.flow_condition_code;
+            parse_info.branch_info.condition.cc = cc;
+            if (cc == ConditionCode::F) {
+                offset++;
+                continue;
+            }
+            parse_info.branch_info.address = exit_branch;
+            parse_info.branch_info.kill = false;
+            parse_info.branch_info.is_sync = false;
+            parse_info.branch_info.is_brk = false;
+            parse_info.end_address = offset;
+
+            return ParseResult::ControlCaught;
+        }
+        case OpCode::Id::BRA: {
+            if (instr.bra.constant_buffer != 0) {
+                return ParseResult::AbnormalFlow;
+            }
+            const auto pred_index = static_cast<u32>(instr.pred.pred_index);
+            parse_info.branch_info.condition.predicate =
+                GetPredicate(pred_index, instr.negate_pred != 0);
+            if (parse_info.branch_info.condition.predicate == Pred::NeverExecute) {
+                offset++;
+                continue;
+            }
+            const ConditionCode cc = instr.flow_condition_code;
+            parse_info.branch_info.condition.cc = cc;
+            if (cc == ConditionCode::F) {
+                offset++;
+                continue;
+            }
+            u32 branch_offset = offset + instr.bra.GetBranchTarget();
+            if (branch_offset == 0) {
+                parse_info.branch_info.address = exit_branch;
+            } else {
+                parse_info.branch_info.address = branch_offset;
+            }
+            insert_label(state, branch_offset);
+            parse_info.branch_info.kill = false;
+            parse_info.branch_info.is_sync = false;
+            parse_info.branch_info.is_brk = false;
+            parse_info.end_address = offset;
+
+            return ParseResult::ControlCaught;
+        }
+        case OpCode::Id::SYNC: {
+            parse_info.branch_info.condition;
+            const auto pred_index = static_cast<u32>(instr.pred.pred_index);
+            parse_info.branch_info.condition.predicate =
+                GetPredicate(pred_index, instr.negate_pred != 0);
+            if (parse_info.branch_info.condition.predicate == Pred::NeverExecute) {
+                offset++;
+                continue;
+            }
+            const ConditionCode cc = instr.flow_condition_code;
+            parse_info.branch_info.condition.cc = cc;
+            if (cc == ConditionCode::F) {
+                offset++;
+                continue;
+            }
+            parse_info.branch_info.address = unassigned_branch;
+            parse_info.branch_info.kill = false;
+            parse_info.branch_info.is_sync = true;
+            parse_info.branch_info.is_brk = false;
+            parse_info.end_address = offset;
+
+            return ParseResult::ControlCaught;
+        }
+        case OpCode::Id::BRK: {
+            parse_info.branch_info.condition;
+            const auto pred_index = static_cast<u32>(instr.pred.pred_index);
+            parse_info.branch_info.condition.predicate =
+                GetPredicate(pred_index, instr.negate_pred != 0);
+            if (parse_info.branch_info.condition.predicate == Pred::NeverExecute) {
+                offset++;
+                continue;
+            }
+            const ConditionCode cc = instr.flow_condition_code;
+            parse_info.branch_info.condition.cc = cc;
+            if (cc == ConditionCode::F) {
+                offset++;
+                continue;
+            }
+            parse_info.branch_info.address = unassigned_branch;
+            parse_info.branch_info.kill = false;
+            parse_info.branch_info.is_sync = false;
+            parse_info.branch_info.is_brk = true;
+            parse_info.end_address = offset;
+
+            return ParseResult::ControlCaught;
+        }
+        case OpCode::Id::KIL: {
+            parse_info.branch_info.condition;
+            const auto pred_index = static_cast<u32>(instr.pred.pred_index);
+            parse_info.branch_info.condition.predicate =
+                GetPredicate(pred_index, instr.negate_pred != 0);
+            if (parse_info.branch_info.condition.predicate == Pred::NeverExecute) {
+                offset++;
+                continue;
+            }
+            const ConditionCode cc = instr.flow_condition_code;
+            parse_info.branch_info.condition.cc = cc;
+            if (cc == ConditionCode::F) {
+                offset++;
+                continue;
+            }
+            parse_info.branch_info.address = exit_branch;
+            parse_info.branch_info.kill = true;
+            parse_info.branch_info.is_sync = false;
+            parse_info.branch_info.is_brk = false;
+            parse_info.end_address = offset;
+
+            return ParseResult::ControlCaught;
+        }
+        case OpCode::Id::SSY: {
+            const u32 target = offset + instr.bra.GetBranchTarget();
+            insert_label(state, target);
+            state.ssy_labels.emplace(offset, target);
+            break;
+        }
+        case OpCode::Id::PBK: {
+            const u32 target = offset + instr.bra.GetBranchTarget();
+            insert_label(state, target);
+            state.pbk_labels.emplace(offset, target);
+            break;
+        }
+        default:
+            break;
+        }
+
+        offset++;
+    }
+    parse_info.branch_info.kill = false;
+    parse_info.branch_info.is_sync = false;
+    parse_info.branch_info.is_brk = false;
+    parse_info.end_address = offset - 1;
+    return ParseResult::BlockEnd;
+}
+
+bool TryInspectAddress(CFGRebuildState& state) {
+    if (state.inspect_queries.empty()) {
+        return false;
+    }
+    u32 address = state.inspect_queries.front();
+    state.inspect_queries.pop_front();
+    auto search_result = TryGetBlock(state, address);
+    BlockInfo* block_info;
+    switch (search_result.first) {
+    case BlockCollision::Found: {
+        return true;
+        break;
+    }
+    case BlockCollision::Inside: {
+        // This case is the tricky one:
+        // We need to Split the block in 2 sepprate blocks
+        auto it = search_result.second;
+        block_info = CreateBlockInfo(state, address, it->end);
+        it->end = address - 1;
+        block_info->branch = it->branch;
+        BlockBranchInfo forward_branch{};
+        forward_branch.address = address;
+        it->branch = forward_branch;
+        return true;
+        break;
+    }
+    default:
+        break;
+    }
+    ParseInfo parse_info;
+    ParseResult parse_result = ParseCode(state, address, parse_info);
+    if (parse_result == ParseResult::AbnormalFlow) {
+        // if it's the end of the program, end it safely
+        // if it's AbnormalFlow, we end it as false, ending the CFG reconstruction
+        return false;
+    }
+
+    block_info = CreateBlockInfo(state, address, parse_info.end_address);
+    block_info->branch = parse_info.branch_info;
+    if (parse_info.branch_info.condition.IsUnconditional()) {
+        return true;
+    }
+
+    u32 fallthrough_address = parse_info.end_address + 1;
+    state.inspect_queries.push_front(fallthrough_address);
+    return true;
+}
+
+bool ScanFlow(const ProgramCode& program_code, u32 program_size, u32 start_address,
+              ShaderCharacteristics& result_out) {
+    CFGRebuildState state{program_code, program_size};
+    // Inspect Code and generate blocks
+    state.labels.clear();
+    state.labels.emplace(start_address);
+    state.inspect_queries.push_back(start_address);
+    while (!state.inspect_queries.empty()) {
+        if (!TryInspectAddress(state)) {
+            return false;
+        }
+    }
+    std::sort(state.block_info.begin(), state.block_info.end(),
+              [](const BlockInfo& a, const BlockInfo& b) -> bool { return a.start < b.start; });
+    // Remove unvisited blocks
+    result_out.blocks.clear();
+    result_out.decompilable = false;
+    result_out.start = start_address;
+    result_out.end = start_address;
+    for (auto& block : state.block_info) {
+        ShaderBlock new_block{};
+        new_block.start = block.start;
+        new_block.end = block.end;
+        new_block.branch.cond = block.branch.condition;
+        new_block.branch.kills = block.branch.kill;
+        new_block.branch.address = block.branch.address;
+        result_out.end = std::max(result_out.end, block.end);
+        result_out.blocks.push_back(new_block);
+    }
+    if (result_out.decompilable) {
+        return true;
+    }
+    auto back = result_out.blocks.begin();
+    auto next = std::next(back);
+    while (next != result_out.blocks.end()) {
+        if (state.labels.count(next->start) == 0 && next->start == back->end + 1) {
+            back->end = next->end;
+            next = result_out.blocks.erase(next);
+            continue;
+        }
+        back = next;
+        next++;
+    }
+    return true;
+}
+} // namespace VideoCommon::Shader
diff --git a/src/video_core/shader/control_flow.h b/src/video_core/shader/control_flow.h
new file mode 100644
index 000000000..16736d57a
--- /dev/null
+++ b/src/video_core/shader/control_flow.h
@@ -0,0 +1,55 @@
+#pragma once
+
+#include <cstring>
+#include <list>
+#include <optional>
+#include <vector>
+
+#include "video_core/engines/shader_bytecode.h"
+#include "video_core/shader/shader_ir.h"
+
+namespace VideoCommon::Shader {
+
+using Tegra::Shader::ConditionCode;
+using Tegra::Shader::Pred;
+
+constexpr s32 exit_branch = -1;
+
+struct Condition {
+    Pred predicate{Pred::UnusedIndex};
+    ConditionCode cc{ConditionCode::T};
+
+    bool IsUnconditional() const {
+        return (predicate == Pred::UnusedIndex) && (cc == ConditionCode::T);
+    }
+};
+
+struct ShaderBlock {
+    ShaderBlock() {}
+    ShaderBlock(const ShaderBlock& sb) = default;
+    u32 start{};
+    u32 end{};
+    struct Branch {
+        Condition cond{};
+        bool kills{};
+        s32 address{};
+        bool operator==(const Branch& b) const {
+            return std::memcmp(this, &b, sizeof(Branch)) == 0;
+        }
+    } branch;
+    bool operator==(const ShaderBlock& sb) const {
+        return std::memcmp(this, &sb, sizeof(ShaderBlock)) == 0;
+    }
+};
+
+struct ShaderCharacteristics {
+    std::list<ShaderBlock> blocks;
+    bool decompilable{};
+    u32 start;
+    u32 end;
+};
+
+bool ScanFlow(const ProgramCode& program_code, u32 program_size, u32 start_address,
+              ShaderCharacteristics& result_out);
+
+} // namespace VideoCommon::Shader
diff --git a/src/video_core/shader/decode.cpp b/src/video_core/shader/decode.cpp
index 2c9ff28f2..7f433c56b 100644
--- a/src/video_core/shader/decode.cpp
+++ b/src/video_core/shader/decode.cpp
@@ -11,6 +11,7 @@
 #include "common/common_types.h"
 #include "video_core/engines/shader_bytecode.h"
 #include "video_core/engines/shader_header.h"
+#include "video_core/shader/control_flow.h"
 #include "video_core/shader/node_helper.h"
 #include "video_core/shader/shader_ir.h"
 
@@ -51,25 +52,31 @@ constexpr bool IsSchedInstruction(u32 offset, u32 main_offset) {
 void ShaderIR::Decode() {
     std::memcpy(&header, program_code.data(), sizeof(Tegra::Shader::Header));
 
-    std::set<u32> labels;
-    const ExitMethod exit_method = Scan(main_offset, MAX_PROGRAM_LENGTH, labels);
-    if (exit_method != ExitMethod::AlwaysEnd) {
-        UNREACHABLE_MSG("Program does not always end");
-    }
-
-    if (labels.empty()) {
-        basic_blocks.insert({main_offset, DecodeRange(main_offset, MAX_PROGRAM_LENGTH)});
+    ShaderCharacteristics shader_info{};
+    bool can_proceed = ScanFlow(program_code, MAX_PROGRAM_LENGTH, main_offset, shader_info);
+    if (can_proceed) {
+        coverage_begin = shader_info.start;
+        coverage_end = shader_info.end;
+        if (shader_info.decompilable) {
+            return;
+        }
+        // we can't decompile it, fallback to standard method
+        for (const auto& block : shader_info.blocks) {
+            basic_blocks.insert({block.start, DecodeRange(block.start, block.end + 1)});
+        }
         return;
     }
-
-    labels.insert(main_offset);
-
-    for (const u32 label : labels) {
-        const auto next_it = labels.lower_bound(label + 1);
-        const u32 next_label = next_it == labels.end() ? MAX_PROGRAM_LENGTH : *next_it;
-
-        basic_blocks.insert({label, DecodeRange(label, next_label)});
+    LOG_CRITICAL(HW_GPU, "Flow Analysis failed, falling back to brute force compiling");
+
+    // Now we need to deal with an undecompilable shader. We need to brute force
+    // a shader that captures every position.
+    coverage_begin = shader_info.start;
+    const u32 shader_end = static_cast<u32>(MAX_PROGRAM_LENGTH);
+    coverage_end = shader_end;
+    for (u32 label = main_offset; label < shader_end; label++) {
+        basic_blocks.insert({label, DecodeRange(label, label + 1)});
     }
+    return;
 }
 
 ExitMethod ShaderIR::Scan(u32 begin, u32 end, std::set<u32>& labels) {