Merge pull request #3518 from wwylele/hashable-struct

Common/Hash: abstract HashableStruct from GLShader::PicaShaderConfig

src/common/hash.h

@@ -5,6 +5,7 @@
 #pragma once
 
 #include <cstddef>
+#include <cstring>
 #include "common/cityhash.h"
 #include "common/common_types.h"
 
@@ -21,16 +22,50 @@ static inline u64 ComputeHash64(const void* data, size_t len) {
 }
 
 /**
- * Computes a 64-bit hash of a struct. In addition to being POD (trivially copyable and having
- * standard layout), it is also critical that either the struct includes no padding, or that any
- * padding is initialized to a known value by memsetting the struct to 0 before filling it in.
+ * Computes a 64-bit hash of a struct. In addition to being trivially copyable, it is also critical
+ * that either the struct includes no padding, or that any padding is initialized to a known value
+ * by memsetting the struct to 0 before filling it in.
  */
 template <typename T>
 static inline u64 ComputeStructHash64(const T& data) {
-    static_assert(
-        std::is_trivially_copyable<T>::value && std::is_standard_layout<T>::value,
-        "Type passed to ComputeStructHash64 must be trivially copyable and standard layout");
+    static_assert(std::is_trivially_copyable<T>(),
+                  "Type passed to ComputeStructHash64 must be trivially copyable");
     return ComputeHash64(&data, sizeof(data));
 }
 
+/// A helper template that ensures the padding in a struct is initialized by memsetting to 0.
+template <typename T>
+struct HashableStruct {
+    // In addition to being trivially copyable, T must also have a trivial default constructor,
+    // because any member initialization would be overridden by memset
+    static_assert(std::is_trivial<T>(), "Type passed to HashableStruct must be trivial");
+    /*
+     * We use a union because "implicitly-defined copy/move constructor for a union X copies the
+     * object representation of X." and "implicitly-defined copy assignment operator for a union X
+     * copies the object representation (3.9) of X." = Bytewise copy instead of memberwise copy.
+     * This is important because the padding bytes are included in the hash and comparison between
+     * objects.
+     */
+    union {
+        T state;
+    };
+
+    HashableStruct() {
+        // Memset structure to zero padding bits, so that they will be deterministic when hashing
+        std::memset(&state, 0, sizeof(T));
+    }
+
+    bool operator==(const HashableStruct<T>& o) const {
+        return std::memcmp(&state, &o.state, sizeof(T)) == 0;
+    };
+
+    bool operator!=(const HashableStruct<T>& o) const {
+        return !(*this == o);
+    };
+
+    size_t Hash() const {
+        return Common::ComputeStructHash64(state);
+    }
+};
+
 } // namespace Common

src/video_core/renderer_opengl/gl_shader_gen.cpp

@@ -65,8 +65,6 @@ PicaShaderConfig PicaShaderConfig::BuildFromRegs(const Pica::Regs& regs) {
     PicaShaderConfig res;
 
     auto& state = res.state;
-    // Memset structure to zero padding bits, so that they will be deterministic when hashing
-    std::memset(&state, 0, sizeof(PicaShaderConfig::State));
 
     state.scissor_test_mode = regs.rasterizer.scissor_test.mode;
 

src/video_core/renderer_opengl/gl_shader_gen.h

@@ -24,36 +24,6 @@ enum Attributes {
     ATTRIBUTE_VIEW,
 };
 
-/**
- * This struct contains all state used to generate the GLSL shader program that emulates the current
- * Pica register configuration. This struct is used as a cache key for generated GLSL shader
- * programs. The functions in gl_shader_gen.cpp should retrieve state from this struct only, not by
- * directly accessing Pica registers. This should reduce the risk of bugs in shader generation where
- * Pica state is not being captured in the shader cache key, thereby resulting in (what should be)
- * two separate shaders sharing the same key.
- *
- * We use a union because "implicitly-defined copy/move constructor for a union X copies the object
- * representation of X." and "implicitly-defined copy assignment operator for a union X copies the
- * object representation (3.9) of X." = Bytewise copy instead of memberwise copy. This is important
- * because the padding bytes are included in the hash and comparison between objects.
- */
-union PicaShaderConfig {
-
-    /// Construct a PicaShaderConfig with the given Pica register configuration.
-    static PicaShaderConfig BuildFromRegs(const Pica::Regs& regs);
-
-    bool TevStageUpdatesCombinerBufferColor(unsigned stage_index) const {
-        return (stage_index < 4) && (state.combiner_buffer_input & (1 << stage_index));
-    }
-
-    bool TevStageUpdatesCombinerBufferAlpha(unsigned stage_index) const {
-        return (stage_index < 4) && ((state.combiner_buffer_input >> 4) & (1 << stage_index));
-    }
-
-    bool operator==(const PicaShaderConfig& o) const {
-        return std::memcmp(&state, &o.state, sizeof(PicaShaderConfig::State)) == 0;
-    };
-
 // NOTE: MSVC15 (Update 2) doesn't think `delete`'d constructors and operators are TC.
 //       This makes BitField not TC when used in a union or struct so we have to resort
 //       to this ugly hack.
@@ -75,7 +45,7 @@ union PicaShaderConfig {
     }
 };
 
-    struct State {
+struct PicaShaderConfigState {
     Pica::FramebufferRegs::CompareFunc alpha_test_func;
     Pica::RasterizerRegs::ScissorMode scissor_test_mode;
     Pica::TexturingRegs::TextureConfig::TextureType texture0_type;
@@ -128,8 +98,28 @@ union PicaShaderConfig {
         u32 lut_offset;
         Pica::TexturingRegs::ProcTexFilter lut_filter;
     } proctex;
+};
 
-    } state;
+/**
+ * This struct contains all state used to generate the GLSL shader program that emulates the current
+ * Pica register configuration. This struct is used as a cache key for generated GLSL shader
+ * programs. The functions in gl_shader_gen.cpp should retrieve state from this struct only, not by
+ * directly accessing Pica registers. This should reduce the risk of bugs in shader generation where
+ * Pica state is not being captured in the shader cache key, thereby resulting in (what should be)
+ * two separate shaders sharing the same key.
+ */
+struct PicaShaderConfig : Common::HashableStruct<PicaShaderConfigState> {
+
+    /// Construct a PicaShaderConfig with the given Pica register configuration.
+    static PicaShaderConfig BuildFromRegs(const Pica::Regs& regs);
+
+    bool TevStageUpdatesCombinerBufferColor(unsigned stage_index) const {
+        return (stage_index < 4) && (state.combiner_buffer_input & (1 << stage_index));
+    }
+
+    bool TevStageUpdatesCombinerBufferAlpha(unsigned stage_index) const {
+        return (stage_index < 4) && ((state.combiner_buffer_input >> 4) & (1 << stage_index));
+    }
 };
 
 /**
@@ -152,7 +142,7 @@ namespace std {
 template <>
 struct hash<GLShader::PicaShaderConfig> {
     size_t operator()(const GLShader::PicaShaderConfig& k) const {
-        return Common::ComputeStructHash64(k.state);
+        return k.Hash();
     }
 };
 } // namespace std