[PATCH] D84108: [SimplifyCFG][LoopRotate] SimplifyCFG: disable common instruction hoisting by default, enable late in pipeline

Mon Nov 30 05:09:38 PST 2020

fhahn added a comment.
Herald added a subscriber: pengfei.

Just a heads up: we are seeing a notable 3.5% regression caused by this change for ARM64 with LTO for CINT2006/473.astar.

I had a first look and it seems like there's some bad interactions with the LTO pipeline. The problem in this case is the following: we now rotate a loop just before the vectorizer which requires duplicating a function call in the preheader when compiling the individual files. But this then stops inlining during LTO. I'll look into whether we should avoid rotating such loops in the 'prepare-for-lto' stage.

Also, what is the status of the regressions reported by @echristo ? Was it possible to address them?

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  https://reviews.llvm.org/D84108/new/

https://reviews.llvm.org/D84108