Render: Implemented simple render target pool

This avoids creating and destroying render targets every frame,
which is a significant CPU overhead.

Old render targets are destroyed after 3 frames.

Source/Core/VideoCommon/TextureCacheBase.cpp

@@ -22,6 +22,7 @@
 enum
 {
 	TEXTURE_KILL_THRESHOLD = 200,
+	RENDER_TARGET_KILL_THRESHOLD = 3,
 };
 
 TextureCache *g_texture_cache;
@@ -30,6 +31,7 @@ GC_ALIGNED16(u8 *TextureCache::temp) = nullptr;
 unsigned int TextureCache::temp_size;
 
 TextureCache::TexCache TextureCache::textures;
+TextureCache::RenderTargetPool TextureCache::render_target_pool;
 
 TextureCache::BackupConfig TextureCache::backup_config;
 
@@ -67,6 +69,12 @@ void TextureCache::Invalidate()
 		delete tex.second;
 	}
 	textures.clear();
+
+	for (auto& rt : render_target_pool)
+	{
+		delete rt;
+	}
+	render_target_pool.clear();
 }
 
 TextureCache::~TextureCache()
@@ -138,6 +146,22 @@ void TextureCache::Cleanup()
 			++iter;
 		}
 	}
+
+	for (size_t i = 0; i < render_target_pool.size();)
+	{
+		auto rt = render_target_pool[i];
+
+		if (frameCount > RENDER_TARGET_KILL_THRESHOLD + rt->frameCount)
+		{
+			delete rt;
+			render_target_pool[i] = render_target_pool.back();
+			render_target_pool.pop_back();
+		}
+		else
+		{
+			++i;
+		}
+	}
 }
 
 void TextureCache::InvalidateRange(u32 start_address, u32 size)
@@ -868,8 +892,17 @@ void TextureCache::CopyRenderTargetToTexture(u32 dstAddr, unsigned int dstFormat
 		}
 		else if (!(entry->type == TCET_EC_VRAM && entry->virtual_width == scaled_tex_w && entry->virtual_height == scaled_tex_h))
 		{
-			// remove it and recreate it as a render target
+			if (entry->type == TCET_EC_VRAM)
-			delete entry;
+			{
+				// try to re-use this render target later
+				FreeRenderTarget(entry);
+			}
+			else
+			{
+				// remove it and recreate it as a render target
+				delete entry;
+			}
+
 			entry = nullptr;
 		}
 	}
@@ -877,7 +910,7 @@ void TextureCache::CopyRenderTargetToTexture(u32 dstAddr, unsigned int dstFormat
 	if (nullptr == entry)
 	{
 		// create the texture
-		textures[dstAddr] = entry = g_texture_cache->CreateRenderTargetTexture(scaled_tex_w, scaled_tex_h);
+		textures[dstAddr] = entry = AllocateRenderTarget(scaled_tex_w, scaled_tex_h);
 
 		// TODO: Using the wrong dstFormat, dumb...
 		entry->SetGeneralParameters(dstAddr, 0, dstFormat, 1);
@@ -890,3 +923,26 @@ void TextureCache::CopyRenderTargetToTexture(u32 dstAddr, unsigned int dstFormat
 
 	entry->FromRenderTarget(dstAddr, dstFormat, srcFormat, srcRect, isIntensity, scaleByHalf, cbufid, colmat);
 }
+
+TextureCache::TCacheEntryBase* TextureCache::AllocateRenderTarget(unsigned int width, unsigned int height)
+{
+	for (size_t i = 0; i < render_target_pool.size(); ++i)
+	{
+		auto rt = render_target_pool[i];
+
+		if (rt->virtual_width != width || rt->virtual_height != height)
+			continue;
+
+		render_target_pool[i] = render_target_pool.back();
+		render_target_pool.pop_back();
+
+		return rt;
+	}
+
+	return g_texture_cache->CreateRenderTargetTexture(width, height);
+}
+
+void TextureCache::FreeRenderTarget(TCacheEntryBase* entry)
+{
+	render_target_pool.push_back(entry);
+}

Source/Core/VideoCommon/TextureCacheBase.h

@@ -119,9 +119,14 @@ private:
 	static PC_TexFormat LoadCustomTexture(u64 tex_hash, int texformat, unsigned int level, unsigned int& width, unsigned int& height);
 	static void DumpTexture(TCacheEntryBase* entry, unsigned int level);
 
+	static TCacheEntryBase* AllocateRenderTarget(unsigned int width, unsigned int height);
+	static void FreeRenderTarget(TCacheEntryBase* entry);
+
 	typedef std::map<u32, TCacheEntryBase*> TexCache;
+	typedef std::vector<TCacheEntryBase*> RenderTargetPool;
 
 	static TexCache textures;
+	static RenderTargetPool render_target_pool;
 
 	// Backup configuration values
 	static struct BackupConfig