From f56d0db5bd9b352bbd33aa4524d642a13905a28c Mon Sep 17 00:00:00 2001
From: yzct12345 <87620833+yzct12345@users.noreply.github.com>
Date: Mon, 2 Aug 2021 15:18:58 +0000
Subject: [PATCH] decoders: Optimize swizzle copy performance (#6790)

This makes UnswizzleTexture up to two times faster. It is the main bottleneck in NVDEC video decoding.
---
 src/video_core/textures/decoders.cpp | 52 +++++++++++++++++++++++-----
 1 file changed, 43 insertions(+), 9 deletions(-)

diff --git a/src/video_core/textures/decoders.cpp b/src/video_core/textures/decoders.cpp
index f1f523ad10..c32ae956a3 100644
--- a/src/video_core/textures/decoders.cpp
+++ b/src/video_core/textures/decoders.cpp
@@ -18,9 +18,9 @@
 
 namespace Tegra::Texture {
 namespace {
-template <bool TO_LINEAR>
-void Swizzle(std::span<u8> output, std::span<const u8> input, u32 bytes_per_pixel, u32 width,
-             u32 height, u32 depth, u32 block_height, u32 block_depth, u32 stride_alignment) {
+template <bool TO_LINEAR, u32 BYTES_PER_PIXEL>
+void SwizzleImpl(std::span<u8> output, std::span<const u8> input, u32 width, u32 height, u32 depth,
+                 u32 block_height, u32 block_depth, u32 stride_alignment) {
     // The origin of the transformation can be configured here, leave it as zero as the current API
     // doesn't expose it.
     static constexpr u32 origin_x = 0;
@@ -28,9 +28,9 @@ void Swizzle(std::span<u8> output, std::span<const u8> input, u32 bytes_per_pixe
     static constexpr u32 origin_z = 0;
 
     // We can configure here a custom pitch
-    // As it's not exposed 'width * bpp' will be the expected pitch.
-    const u32 pitch = width * bytes_per_pixel;
-    const u32 stride = Common::AlignUpLog2(width, stride_alignment) * bytes_per_pixel;
+    // As it's not exposed 'width * BYTES_PER_PIXEL' will be the expected pitch.
+    const u32 pitch = width * BYTES_PER_PIXEL;
+    const u32 stride = Common::AlignUpLog2(width, stride_alignment) * BYTES_PER_PIXEL;
 
     const u32 gobs_in_x = Common::DivCeilLog2(stride, GOB_SIZE_X_SHIFT);
     const u32 block_size = gobs_in_x << (GOB_SIZE_SHIFT + block_height + block_depth);
@@ -54,14 +54,14 @@ void Swizzle(std::span<u8> output, std::span<const u8> input, u32 bytes_per_pixe
                                  ((block_y & block_height_mask) << GOB_SIZE_SHIFT);
 
             for (u32 column = 0; column < width; ++column) {
-                const u32 x = (column + origin_x) * bytes_per_pixel;
+                const u32 x = (column + origin_x) * BYTES_PER_PIXEL;
                 const u32 offset_x = (x >> GOB_SIZE_X_SHIFT) << x_shift;
 
                 const u32 base_swizzled_offset = offset_z + offset_y + offset_x;
                 const u32 swizzled_offset = base_swizzled_offset + table[x % GOB_SIZE_X];
 
                 const u32 unswizzled_offset =
-                    slice * pitch * height + line * pitch + column * bytes_per_pixel;
+                    slice * pitch * height + line * pitch + column * BYTES_PER_PIXEL;
 
                 if (const auto offset = (TO_LINEAR ? unswizzled_offset : swizzled_offset);
                     offset >= input.size()) {
@@ -73,11 +73,45 @@ void Swizzle(std::span<u8> output, std::span<const u8> input, u32 bytes_per_pixe
 
                 u8* const dst = &output[TO_LINEAR ? swizzled_offset : unswizzled_offset];
                 const u8* const src = &input[TO_LINEAR ? unswizzled_offset : swizzled_offset];
-                std::memcpy(dst, src, bytes_per_pixel);
+
+                std::memcpy(dst, src, BYTES_PER_PIXEL);
             }
         }
     }
 }
+
+template <bool TO_LINEAR>
+void Swizzle(std::span<u8> output, std::span<const u8> input, u32 bytes_per_pixel, u32 width,
+             u32 height, u32 depth, u32 block_height, u32 block_depth, u32 stride_alignment) {
+    switch (bytes_per_pixel) {
+    case 1:
+        return SwizzleImpl<TO_LINEAR, 1>(output, input, width, height, depth, block_height,
+                                         block_depth, stride_alignment);
+    case 2:
+        return SwizzleImpl<TO_LINEAR, 2>(output, input, width, height, depth, block_height,
+                                         block_depth, stride_alignment);
+    case 3:
+        return SwizzleImpl<TO_LINEAR, 3>(output, input, width, height, depth, block_height,
+                                         block_depth, stride_alignment);
+    case 4:
+        return SwizzleImpl<TO_LINEAR, 4>(output, input, width, height, depth, block_height,
+                                         block_depth, stride_alignment);
+    case 6:
+        return SwizzleImpl<TO_LINEAR, 6>(output, input, width, height, depth, block_height,
+                                         block_depth, stride_alignment);
+    case 8:
+        return SwizzleImpl<TO_LINEAR, 8>(output, input, width, height, depth, block_height,
+                                         block_depth, stride_alignment);
+    case 12:
+        return SwizzleImpl<TO_LINEAR, 12>(output, input, width, height, depth, block_height,
+                                          block_depth, stride_alignment);
+    case 16:
+        return SwizzleImpl<TO_LINEAR, 16>(output, input, width, height, depth, block_height,
+                                          block_depth, stride_alignment);
+    default:
+        UNREACHABLE_MSG("Invalid bytes_per_pixel={}", bytes_per_pixel);
+    }
+}
 } // Anonymous namespace
 
 void UnswizzleTexture(std::span<u8> output, std::span<const u8> input, u32 bytes_per_pixel,