[PATCH] D157581: [SelectionDAG][X86][WIP] Don't always seperate conditions in `(br (and/or cond0, cond1))` into seperate branches

Wed Aug 9 21:45:56 PDT 2023

craig.topper added a comment.

In D157581#4575458 <https://reviews.llvm.org/D157581#4575458>, @goldstein.w.n wrote:

> In D157581#4575452 <https://reviews.llvm.org/D157581#4575452>, @craig.topper wrote:
>
>> I have wondered in the past if this should be done by codegenprepare instead of SelectionDAGBuilder. I believe codegenprepare does it for fast isel.
>>
>> The current code in SelectionDAGBuilder doesn’t sink an AND so it blocks forming TEST instructions. CodegenPrepare already knows how to sink AND to be near compare.
>
> Is in break up the branches in IR instead then let selectiondagbuilder just translate 1-1?
> I see `splitBranchCondition` in CodeGenPrepare. You'd suggest there?

Yep that looks like the code. I see there is a FIXME there to remove the SelectionDAGBuilder code. If I remember right CodeGenPrepare creates the branches in a different order than SelectionDAGBuilder does. Whether that's good or bad I don't know, just that it's different.

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https://reviews.llvm.org/D157581