glsl: Rework variable allocator to allow for variable reuse

src/shader_recompiler/backend/glsl/var_alloc.h

@@ -0,0 +1,100 @@
+// Copyright 2021 yuzu Emulator Project
+// Licensed under GPLv2 or any later version
+// Refer to the license.txt file included.
+
+#pragma once
+
+#include <bitset>
+#include <string>
+#include <vector>
+
+#include "common/bit_field.h"
+#include "common/common_types.h"
+
+namespace Shader::IR {
+class Inst;
+class Value;
+enum class Type;
+} // namespace Shader::IR
+
+namespace Shader::Backend::GLSL {
+enum class GlslVarType : u32 {
+    U1,
+    F16x2,
+    S32,
+    U32,
+    F32,
+    S64,
+    U64,
+    F64,
+    U32x2,
+    F32x2,
+    U32x3,
+    F32x3,
+    U32x4,
+    F32x4,
+    Void,
+};
+
+struct Id {
+    union {
+        u32 raw;
+        BitField<0, 1, u32> is_valid;
+        BitField<1, 4, GlslVarType> type;
+        BitField<5, 27, u32> index;
+    };
+
+    bool operator==(Id rhs) const noexcept {
+        return raw == rhs.raw;
+    }
+    bool operator!=(Id rhs) const noexcept {
+        return !operator==(rhs);
+    }
+};
+static_assert(sizeof(Id) == sizeof(u32));
+
+class VarAlloc {
+public:
+    static constexpr size_t NUM_VARS = 511;
+    struct UseTracker {
+        size_t num_used{};
+        std::bitset<NUM_VARS> var_use{};
+        bool uses_temp{};
+    };
+
+    std::string Define(IR::Inst& inst, GlslVarType type);
+    std::string Define(IR::Inst& inst, IR::Type type);
+
+    std::string Consume(const IR::Value& value);
+    std::string ConsumeInst(IR::Inst& inst);
+
+    std::string GetGlslType(GlslVarType type) const;
+    std::string GetGlslType(IR::Type type) const;
+
+    const UseTracker& GetUseTracker(GlslVarType type) const;
+    std::string Representation(u32 index, GlslVarType type) const;
+
+private:
+    GlslVarType RegType(IR::Type type) const;
+    Id Alloc(GlslVarType type);
+    void Free(Id id);
+    UseTracker& GetUseTracker(GlslVarType type);
+    std::string Representation(Id id) const;
+
+    UseTracker var_bool{};
+    UseTracker var_f16x2{};
+    UseTracker var_s32{};
+    UseTracker var_u32{};
+    UseTracker var_u32x2{};
+    UseTracker var_u32x3{};
+    UseTracker var_u32x4{};
+    UseTracker var_f32{};
+    UseTracker var_f32x2{};
+    UseTracker var_f32x3{};
+    UseTracker var_f32x4{};
+    UseTracker var_u64{};
+    UseTracker var_s64{};
+    UseTracker var_f64{};
+};
+
+} // namespace Shader::Backend::GLSL