[PATCH] D149323: [SCEV] Don't invalidate past dependency-breaking instructions

[Nikita Popov via Phabricator via llvm-commits]

nikic added a comment.

In D149323#4304636 <https://reviews.llvm.org/D149323#4304636>, @mkazantsev wrote:

> Consider example:
>
>   %sum = add i32 %x, %y
>   %load_p= gep ptr %p, i32 %sum
>   %load1 = load %i32 load_p
>   
>   if (%load_1 == %sum) {
>     %load_2 = load %i32 load_p
>     %sum_2 = add i32 %load_2, 2
>   }
>
>
> Here we can theoretically prove that SCEV for `%load_2` is `%x + %y` (same as `%sum`) and `%sum2 = %x + %y + 1`.
>
> Now, imagine that we invalidate `%x`. With your patch, if I understand it correctly, `%sum_2` won't be invalidated.

Not sure I get the example. `%load1` and `%load_2` will both always be SCEVUnknown (loads always are, if they are SCEVable at all). The `%x + %y` is part of the load address, but it doesn't impact the SCEV of the load itself. It's part of `%load_p`, but that one will continue to be invalidated normally.


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https://reviews.llvm.org/D149323