[PATCH] D79785: [ARM] Register pressure with -mthumb forces register reload before each call

[Oliver Stannard (Linaro) via Phabricator via llvm-commits]

ostannard added a comment.

That sounds very fragile - I can easily imagine future, unrelated changes removing that COPY, or emitting one in the case which doesn't currently have one, which would completely change the effect of this patch.

I think the right way to do this is to look through the COPYs, find all the uses of the constant pool load, and do this transformation if and only if there are fewer than three uses of the load.

The alternative would be to not do the direct->indirect transformation in the first place for Thumb1-only targets, since they don't have enough registers to make it worthwhile very often. That would be trading off some generated code quality for simpler implementation.


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https://reviews.llvm.org/D79785