[PATCH] D15718: Recognize pattern for ctpop in instcombine

Krzysztof Parzyszek via llvm-commits llvm-commits at lists.llvm.org
Wed Feb 3 05:10:38 PST 2016

kparzysz added a comment.

To answer David's question: the main reason why it's here is that after the instruction combiner, the code is transformed in a way that makes the detection of the popcnt pattern more difficult.  At this stage, there is some regularity in the IR that can be exploited to check for popcnt patterns of varying widths.
As far as downstream optimizations are involved---this transformation will reduce code size by quite a bit, and any optimization that can be limited by code size could potentially be enabled by this change.



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