The bug

Bamboo is responsible for a lot of unnecessary lag caused by it running a particularly expensive calculation for every single bamboo block in a given chunk, despite said calculation always returning 1.0F. As such, the rendering of bamboo could be optimised considerably simply by providing 1.0F directly rather than requiring it to be calculated each time.

How to fix

The FastBamboo mod for 1.14 (https://www.curseforge.com/minecraft/mc-mods/fast-bamboo) contains a fix for this issue, but does not seem to have been updated for around three years. RandomPatches (https://www.curseforge.com/minecraft/mc-mods/randompatches-forge) also contains a fix for this alongside other bugs such as MC-13187, but itself does not seem to have been updated past 1.16.

Further notes

I am reporting this as a bug since several other tickets regarding unoptimised code have been made and subsequently fixed (MC-33383, MC-41407, MC-217303, MC-233950), so this probably doesn't count as a feature request.