1 files changed, 108 insertions, 0 deletions
diff --git a/src/shader_recompiler/frontend/maxwell/indirect_branch_table_track.cpp b/src/shader_recompiler/frontend/maxwell/indirect_branch_table_track.cpp
new file mode 100644
index 000000000..96453509d
--- /dev/null
+++ b/src/shader_recompiler/frontend/maxwell/indirect_branch_table_track.cpp
@@ -0,0 +1,108 @@
+// Copyright 2021 yuzu Emulator Project
+// Licensed under GPLv2 or any later version
+// Refer to the license.txt file included.
+
+#include <optional>
+
+#include "common/common_types.h"
+#include "shader_recompiler/exception.h"
+#include "shader_recompiler/frontend/maxwell/decode.h"
+#include "shader_recompiler/frontend/maxwell/indirect_branch_table_track.h"
+#include "shader_recompiler/frontend/maxwell/opcodes.h"
+#include "shader_recompiler/frontend/maxwell/translate/impl/load_constant.h"
+
+namespace Shader::Maxwell {
+namespace {
+union Encoding {
+    u64 raw;
+    BitField<0, 8, IR::Reg> dest_reg;
+    BitField<8, 8, IR::Reg> src_reg;
+    BitField<20, 19, u64> immediate;
+    BitField<56, 1, u64> is_negative;
+    BitField<20, 24, s64> brx_offset;
+};
+
+template <typename Callable>
+std::optional<u64> Track(Environment& env, Location block_begin, Location& pos, Callable&& func) {
+    while (pos >= block_begin) {
+        const u64 insn{env.ReadInstruction(pos.Offset())};
+        --pos;
+        if (func(insn, Decode(insn))) {
+            return insn;
+        }
+    }
+    return std::nullopt;
+}
+
+std::optional<u64> TrackLDC(Environment& env, Location block_begin, Location& pos,
+                            IR::Reg brx_reg) {
+    return Track(env, block_begin, pos, [brx_reg](u64 insn, Opcode opcode) {
+        const LDC::Encoding ldc{insn};
+        return opcode == Opcode::LDC && ldc.dest_reg == brx_reg && ldc.size == LDC::Size::B32 &&
+               ldc.mode == LDC::Mode::Default;
+    });
+}
+
+std::optional<u64> TrackSHL(Environment& env, Location block_begin, Location& pos,
+                            IR::Reg ldc_reg) {
+    return Track(env, block_begin, pos, [ldc_reg](u64 insn, Opcode opcode) {
+        const Encoding shl{insn};
+        return opcode == Opcode::SHL_imm && shl.dest_reg == ldc_reg;
+    });
+}
+
+std::optional<u64> TrackIMNMX(Environment& env, Location block_begin, Location& pos,
+                              IR::Reg shl_reg) {
+    return Track(env, block_begin, pos, [shl_reg](u64 insn, Opcode opcode) {
+        const Encoding imnmx{insn};
+        return opcode == Opcode::IMNMX_imm && imnmx.dest_reg == shl_reg;
+    });
+}
+} // Anonymous namespace
+
+std::optional<IndirectBranchTableInfo> TrackIndirectBranchTable(Environment& env, Location brx_pos,
+                                                                Location block_begin) {
+    const u64 brx_insn{env.ReadInstruction(brx_pos.Offset())};
+    const Opcode brx_opcode{Decode(brx_insn)};
+    if (brx_opcode != Opcode::BRX && brx_opcode != Opcode::JMX) {
+        throw LogicError("Tracked instruction is not BRX or JMX");
+    }
+    const IR::Reg brx_reg{Encoding{brx_insn}.src_reg};
+    const s32 brx_offset{static_cast<s32>(Encoding{brx_insn}.brx_offset)};
+
+    Location pos{brx_pos};
+    const std::optional<u64> ldc_insn{TrackLDC(env, block_begin, pos, brx_reg)};
+    if (!ldc_insn) {
+        return std::nullopt;
+    }
+    const LDC::Encoding ldc{*ldc_insn};
+    const u32 cbuf_index{static_cast<u32>(ldc.index)};
+    const u32 cbuf_offset{static_cast<u32>(static_cast<s32>(ldc.offset.Value()))};
+    const IR::Reg ldc_reg{ldc.src_reg};
+
+    const std::optional<u64> shl_insn{TrackSHL(env, block_begin, pos, ldc_reg)};
+    if (!shl_insn) {
+        return std::nullopt;
+    }
+    const Encoding shl{*shl_insn};
+    const IR::Reg shl_reg{shl.src_reg};
+
+    const std::optional<u64> imnmx_insn{TrackIMNMX(env, block_begin, pos, shl_reg)};
+    if (!imnmx_insn) {
+        return std::nullopt;
+    }
+    const Encoding imnmx{*imnmx_insn};
+    if (imnmx.is_negative != 0) {
+        return std::nullopt;
+    }
+    const u32 imnmx_immediate{static_cast<u32>(imnmx.immediate.Value())};
+    return IndirectBranchTableInfo{
+        .cbuf_index{cbuf_index},
+        .cbuf_offset{cbuf_offset},
+        .num_entries{imnmx_immediate + 1},
+        .branch_offset{brx_offset},
+        .branch_reg{brx_reg},
+    };
+}
+
+} // namespace Shader::Maxwell