[PATCH] D77058: [Clang] Add llvm.loop.unroll.disable to loops with -fno-unroll-loops.

[Florian Hahn via Phabricator via cfe-commits]

fhahn added a comment.

In D77058#1964427 <https://reviews.llvm.org/D77058#1964427>, @Meinersbur wrote:

> Note that loop-metadata is best-effort only and may be forgotten in the optimization pipeline.


Agreed, that can be a potential issue (I tried to note that in the description), but I think that's pretty much the same issue we have with the loop related pragmas. Ideally there would be even more incentive now to fix the offending transforms.

> Do we also need an equivalent to `-Xclang -disable-O0-optnone`?
> 
> Personally, I don't like to the `optnone` approach: There have been many post on llvm-dev using `clang -emit-llvm` and being surprised that `opt` has no effect.

Ah yes, optnone is a common pitfall :(

IIUC we don't need a patch similar like this one for optnone, as it already gets added to the function attributes (for -O0) and has an option to disable adding it (-Xclang -disable-O0-optnone) on a per-TU basis.


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https://reviews.llvm.org/D77058