[PATCH] D88492: [InstCombine] visitTrunc - remove dead trunc(lshr (zext A), C) combine

Wed Sep 30 00:01:57 PDT 2020

lebedev.ri added a comment.

Clearly, as per tests, the motivational patterns are handled elsewhere.

In D88492#2302475 <https://reviews.llvm.org/D88492#2302475>, @xbolva00 wrote:

> Binary changes
>
> https://llvm-compile-time-tracker.com/compare.php?from=ccbb9827db4c30c93b92a204aeb2b98f9f3a723a&to=b610d73b3fe67fe6b693740dfac5fd21a60b1e44&stat=size-text

Much like with all of instcombine, i believe this heavily depends on the visitation order.
Which i guess means, this (used to) catch some unusual patterns, that didn't go through the usual def-simplification yet.
Probably lack of this fold causes some other followup folds to fire, or in different order, thus causing different final IR.

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  https://reviews.llvm.org/D88492/new/

https://reviews.llvm.org/D88492