The software renderer enables RLE encoding for textures created with SDL_TEXTUREACCESS_STATIC. RLE encoding is somewhat expensive, and it doesn't support all of the texture features. When a texture feature unsupported by RLE is used, the texture gets RLE-decoded. Then it may get RLE-encoded again, and RLE-decoded again, and encoded again and decoded again, perhaps many times per frame.

An example is color mod. I draw a texture to the screen about 4000 times per frame (it contains all of the tiles drawn on screen), and each time set a different color mod. Often the color mod is white. Often it is not. Each time it transitions to/from white, the texture gets be RLE encoded/decoded. This is very undesirable.

Possible fixes:
1. Don't use RLE encoding in the software renderer.
2. Make the software renderer remember incompatible features have been used and permanently disable RLE for that texture. This way you get RLE for plain textures but don't have to worry about frequent encoding and decoding.
3. Make the RLE blitter support color mod, etc.

#2 seems like the best balance of work vs. payoff.