[PATCH] D65351: [ARM] Lower "(x<<c) > 0x80000000U" to "lsls" on Thumb1.

[Eli Friedman via Phabricator via llvm-commits]

efriedma added a comment.

> Would this also be profitable for Thumb2?

I think it saves only one instruction on ARM/Thumb2 ("cmp rN, #0x80000000" is legal).  Still worthwhile, I guess, assuming there isn't some sort of performance penalty for branching based on a shift. But I'd also have to figure out the right heuristics for D65175 <https://reviews.llvm.org/D65175>, since the transforms interact, and do a little more implementation work to lower ARMISD::LSLS.  I'll leave a FIXME.


Repository:
  rL LLVM

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  https://reviews.llvm.org/D65351/new/

https://reviews.llvm.org/D65351