[Sharkû]

Whatever origin the orcs have, Trolls are likely to share it with them. This is material I compiled long ago, but never wrote an article or post from:

_{Treebeard does not say that the Dark Lord 'created' Trolls and Ores. He says he 'made' them in counterfeit of certain creatures pre-existing. There is, to me, a wide gulf between the two statements, so wide that Treebeard's statement could (in my world) have possibly been true. [...] Treebeard is a character in my story, not me; and though he has a great memory and some earthy wisdom, he is not one of the Wise, and there is quite a lot he does not know or understand. [...] I might not (if The Hobbit had been more carefully written, and my world so much thought about 20 years ago) have used the expression 'poor little blighter', just as I should not have called the troll William. [...] There might be other 'makings' [sc. orcs]all the same which were more like puppets filled (only at a distance) with their maker's mind and will, or ant-like operating under direction of a queen-centre."}(Letter 153)

This means that trolls are only 'made out of' Ents in a way at best.

The Myths Transformed essays give various, largely inconclusive but nevertheless important ideas on orcs. One of those is also explicitly applied to trolls:

_{"Since Melkor could not 'create' an independent species, but had immense powers of corruption and distortion of those that came into his power, it is probable that these Orks had a mixed origin. Most of them plainly (and biologically) were corruptions of Elves (and probably later also of Men). But always among them (as special servants and spies of Melkor, and as leaders) there must have been numerous corrupted minor spirits who assumed similar bodily shapes. (These would exhibit terrifying and demonic characters.)
The Elves would have classed the creatures called 'trolls' (in The Hobbit and The Lord of the Rings) as Orcs - in character and origin - but they were larger and slower. It would seem evident that they were corruptions of primitive human types.}" (HoME X,5,ix)

From this we know that not only the differentiation between orcs and trolls didn't seem important to the Quendi, but also that trolls are actually just a larger type of orc, in this theory of úmaiarin origin and based on corrupted humans.

A note on the language of trolls, not found in the Appendices as it was intented, further adds to this:

_{"$17. Trolls, in their beginning creatures of lumpish and brutal nature, had nothing that could be called true language of their own; but the evil Power had at various times made use of them, teaching them what little they could learn, and even crossing their breed with that of the larger Orcs. Trolls thus took such language as they could from the Orcs, and in the west-lands the Trolls of the hills and mountains spoke a debased form of the Common Westron speech."}(HoME XII,1,ii)

This quote beautifully shows the differences between orcs and trolls, that they are dumber and larger, and generally slower; but also gives the important fact that orcs and trolls could mate. They would have to be biologically 'compatible' and therefore need to have much the same origins. This rules out Ents.