Implement minimal emulation of TMEM caching

This is a remake of https://github.com/dolphin-emu/dolphin/pull/3749

Full credit goes to phire.

Old message:
"If none of the texture registers have changed and TMEM hasn't been invalidated or changed in other ways, we can blindly reuse the old texture cache entries without rehashing.

Not only does this fix the bloom effect in Spyro: A Hero's Tail (The game abused texture cache) but it will also provide speedups for other games which use the same texture over multiple draw calls, especially when safe texture cache is in use."

Changed the pr per phire's instructions to only return the current texture(s) if none of the texture registers were changed. If any texture register was changed, fall back to the default hashing and rebuilding textures from memory.

Source/Core/VideoCommon/TextureCacheBase.cpp

@@ -42,6 +42,8 @@ static const int TEXTURE_POOL_KILL_THRESHOLD = 3;
 
 std::unique_ptr<TextureCacheBase> g_texture_cache;
 
+std::bitset<8> TextureCacheBase::valid_bind_points;
+
 TextureCacheBase::TCacheEntry::TCacheEntry(std::unique_ptr<AbstractTexture> tex)
     : texture(std::move(tex))
 {
@@ -76,11 +78,17 @@ TextureCacheBase::TextureCacheBase()
   HiresTexture::Init();
 
   SetHash64Function();
+
+  InvalidateAllBindPoints();
 }
 
 void TextureCacheBase::Invalidate()
 {
-  UnbindTextures();
+  InvalidateAllBindPoints();
+  for (size_t i = 0; i < bound_textures.size(); ++i)
+  {
+    bound_textures[i] = nullptr;
+  }
 
   for (auto& tex : textures_by_address)
   {
@@ -138,7 +146,11 @@ void TextureCacheBase::Cleanup(int _frameCount)
   TexAddrCache::iterator tcend = textures_by_address.end();
   while (iter != tcend)
   {
-    if (iter->second->frameCount == FRAMECOUNT_INVALID)
+    if (iter->second->tmem_only)
+    {
+      iter = InvalidateTexture(iter);
+    }
+    else if (iter->second->frameCount == FRAMECOUNT_INVALID)
     {
       iter->second->frameCount = _frameCount;
       ++iter;
@@ -307,7 +319,7 @@ TextureCacheBase::DoPartialTextureUpdates(TCacheEntry* entry_to_update, u8* pale
   while (iter.first != iter.second)
   {
     TCacheEntry* entry = iter.first->second;
-    if (entry != entry_to_update && entry->IsEfbCopy() &&
+    if (entry != entry_to_update && entry->IsEfbCopy() && !entry->tmem_only &&
         entry->references.count(entry_to_update) == 0 &&
         entry->OverlapsMemoryRange(entry_to_update->addr, entry_to_update->size_in_bytes) &&
         entry->memory_stride == numBlocksX * block_size)
@@ -450,6 +462,9 @@ TextureCacheBase::TCacheEntry* TextureCacheBase::ReturnEntry(unsigned int stage,
 
   GFX_DEBUGGER_PAUSE_AT(NEXT_TEXTURE_CHANGE, true);
 
+  // We need to keep track of invalided textures until they have actually been replaced or re-loaded
+  valid_bind_points.set(stage);
+
   return entry;
 }
 
@@ -457,18 +472,19 @@ void TextureCacheBase::BindTextures()
 {
   for (size_t i = 0; i < bound_textures.size(); ++i)
   {
-    if (bound_textures[i])
+    if (IsValidBindPoint(static_cast<u32>(i)) && bound_textures[i])
       bound_textures[i]->texture->Bind(static_cast<u32>(i));
   }
 }
 
-void TextureCacheBase::UnbindTextures()
-{
-  bound_textures.fill(nullptr);
-}
-
 TextureCacheBase::TCacheEntry* TextureCacheBase::Load(const u32 stage)
 {
+  // if this stage was not invalidated by changes to texture registers, keep the current texture
+  if (IsValidBindPoint(stage) && bound_textures[stage])
+  {
+    return ReturnEntry(stage, bound_textures[stage]);
+  }
+
   const FourTexUnits& tex = bpmem.tex[stage >> 2];
   const u32 id = stage & 3;
   const u32 address = (tex.texImage3[id].image_base /* & 0x1FFFFF*/) << 5;
@@ -610,6 +626,14 @@ TextureCacheBase::TCacheEntry* TextureCacheBase::Load(const u32 stage)
   while (iter != iter_range.second)
   {
     TCacheEntry* entry = iter->second;
+
+    // Skip entries that are only left in our texture cache for the tmem cache emulation
+    if (entry->tmem_only)
+    {
+      ++iter;
+      continue;
+    }
+
     // Do not load strided EFB copies, they are not meant to be used directly
     if (entry->IsEfbCopy() && entry->native_width == nativeW && entry->native_height == nativeH &&
         entry->memory_stride == entry->BytesPerRow())
@@ -1466,6 +1490,18 @@ TextureCacheBase::InvalidateTexture(TexAddrCache::iterator iter)
     entry->textures_by_hash_iter = textures_by_hash.end();
   }
 
+  for (size_t i = 0; i < bound_textures.size(); ++i)
+  {
+    // If the entry is currently bound and not invalidated, keep it, but mark it as invalidated.
+    // This way it can still be used via tmem cache emulation, but nothing else.
+    // Spyro: A Hero's Tail is known for using such overwritten textures.
+    if (bound_textures[i] == entry && IsValidBindPoint(static_cast<u32>(i)))
+    {
+      bound_textures[i]->tmem_only = true;
+      return ++iter;
+    }
+  }
+
   auto config = entry->texture->GetConfig();
   texture_pool.emplace(config, TexPoolEntry(std::move(entry->texture)));