vp9: Mark functions with [[nodiscard]] where applicable

Prevents values from mistakenly being discarded in cases where it's a
bug to do so.

src/video_core/command_classes/codecs/vp9.cpp

@@ -200,7 +200,7 @@ constexpr std::array<s32, 254> map_lut{
 
 // 6.2.14 Tile size calculation
 
-s32 CalcMinLog2TileCols(s32 frame_width) {
+[[nodiscard]] s32 CalcMinLog2TileCols(s32 frame_width) {
     const s32 sb64_cols = (frame_width + 63) / 64;
     s32 min_log2 = 0;
 
@@ -211,7 +211,7 @@ s32 CalcMinLog2TileCols(s32 frame_width) {
     return min_log2;
 }
 
-s32 CalcMaxLog2TileCols(s32 frame_width) {
+[[nodiscard]] s32 CalcMaxLog2TileCols(s32 frame_width) {
     const s32 sb64_cols = (frame_width + 63) / 64;
     s32 max_log2 = 1;
 
@@ -223,7 +223,7 @@ s32 CalcMaxLog2TileCols(s32 frame_width) {
 }
 
 // Recenters probability. Based on section 6.3.6 of VP9 Specification
-s32 RecenterNonNeg(s32 new_prob, s32 old_prob) {
+[[nodiscard]] s32 RecenterNonNeg(s32 new_prob, s32 old_prob) {
     if (new_prob > old_prob * 2) {
         return new_prob;
     }
@@ -236,7 +236,7 @@ s32 RecenterNonNeg(s32 new_prob, s32 old_prob) {
 }
 
 // Adjusts old_prob depending on new_prob. Based on section 6.3.5 of VP9 Specification
-s32 RemapProbability(s32 new_prob, s32 old_prob) {
+[[nodiscard]] s32 RemapProbability(s32 new_prob, s32 old_prob) {
     new_prob--;
     old_prob--;
 

src/video_core/command_classes/codecs/vp9.h

@@ -37,11 +37,11 @@ public:
     /// Signal the end of the bitstream
     void End();
 
-    std::vector<u8>& GetBuffer() {
+    [[nodiscard]] std::vector<u8>& GetBuffer() {
         return base_stream.GetBuffer();
     }
 
-    const std::vector<u8>& GetBuffer() const {
+    [[nodiscard]] const std::vector<u8>& GetBuffer() const {
         return base_stream.GetBuffer();
     }
 
@@ -75,10 +75,10 @@ public:
     void Flush();
 
     /// Returns byte_array
-    std::vector<u8>& GetByteArray();
+    [[nodiscard]] std::vector<u8>& GetByteArray();
 
     /// Returns const byte_array
-    const std::vector<u8>& GetByteArray() const;
+    [[nodiscard]] const std::vector<u8>& GetByteArray() const;
 
 private:
     /// Write bit_count bits from value into buffer
@@ -104,7 +104,7 @@ public:
     std::vector<u8>& ComposeFrameHeader(NvdecCommon::NvdecRegisters& state);
 
     /// Returns true if the most recent frame was a hidden frame.
-    bool WasFrameHidden() const {
+    [[nodiscard]] bool WasFrameHidden() const {
         return hidden;
     }
 
@@ -141,17 +141,17 @@ private:
     void WriteMvProbabilityUpdate(VpxRangeEncoder& writer, u8 new_prob, u8 old_prob);
 
     /// Returns VP9 information from NVDEC provided offset and size
-    Vp9PictureInfo GetVp9PictureInfo(const NvdecCommon::NvdecRegisters& state);
+    [[nodiscard]] Vp9PictureInfo GetVp9PictureInfo(const NvdecCommon::NvdecRegisters& state);
 
     /// Read and convert NVDEC provided entropy probs to Vp9EntropyProbs struct
     void InsertEntropy(u64 offset, Vp9EntropyProbs& dst);
 
     /// Returns frame to be decoded after buffering
-    Vp9FrameContainer GetCurrentFrame(const NvdecCommon::NvdecRegisters& state);
+    [[nodiscard]] Vp9FrameContainer GetCurrentFrame(const NvdecCommon::NvdecRegisters& state);
 
     /// Use NVDEC providied information to compose the headers for the current frame
-    std::vector<u8> ComposeCompressedHeader();
-    VpxBitStreamWriter ComposeUncompressedHeader();
+    [[nodiscard]] std::vector<u8> ComposeCompressedHeader();
+    [[nodiscard]] VpxBitStreamWriter ComposeUncompressedHeader();
 
     GPU& gpu;
     std::vector<u8> frame;