[PATCH] D89976: [ValueTracking] add range limits for ctpop

Thu Oct 22 11:23:02 PDT 2020

spatel added a comment.

In D89976#2348050 <https://reviews.llvm.org/D89976#2348050>, @davezarzycki wrote:

> FYI -- I'm not sure if it'll change the test impact of this patch, but I did commit a bunch of x86 vector popcnt tests to the repository this morning.

IIUC those were codegen tests -- 8556f38 <https://reviews.llvm.org/rG8556f38b0d6268103a6da08dc01c360f8e20fc32> -- so there won't be any overlap with the change here. I think some targets do run -instsimplify as a pre-codegen IR pass, but x86 is not one of them.
In general, we want to have this kind of analysis in IR to efficiently reduce code as quickly as possible. If there's evidence that these patterns are created later in the pipeline, then we could repeat them in codegen. But we don't want to have that redundancy blindly because everything has a compile-time cost.

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  https://reviews.llvm.org/D89976/new/

https://reviews.llvm.org/D89976