[PATCH] D77523: Add CanonicalizeFreezeInLoops pass

[Juneyoung Lee via Phabricator via llvm-commits]

aqjune added a comment.

Hi,

In D77523#2012741 <https://reviews.llvm.org/D77523#2012741>, @jdoerfert wrote:

> I'm asking myself if it wouldn't be better to start with the freeze instructions and work our way up through the operands. At the end of the day we do a lot of work just to figure out there is no freeze or the instruction chains we build do not end in one. Am I missing something?


It's true, but we should iterate over instructions inside the loop to find freeze instructions.
Indexing freezes that are uses of induction variables will be helpful for exiting early; right now, DivRemPair is the place where it introduces freezes, but it does not do relevant conversion in x86-64, so the code will have almost zero freeze instructions.
Would it make sense if IVUsers maintains the info (existence of freeze)? I'm not familiar with the class, but may have a look.

> Also, could this drop flags of instructions not on the path between a phi and a freeze? So do we keep the `nsw` on the sub and mul in the following example:
> 
>   %iv = phi [0, ...] [%step, ...]
>   %step = add nsw %iv, 1
>   %f = freeze %step
>   %not_step1 = sub nsw %iv, 1
>   %not_step2 = mul nsw %step, 2

The nsw flags of sub and mul will be preserved. I'll add this as a test.


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https://reviews.llvm.org/D77523