[PATCH] D136754: [MachineCombiner] Extend reassociation logic to handle inverse instructions

[Anton Sidorenko via Phabricator via llvm-commits]

asi-sc added reviewers: Carrot, dmgreen, craig.topper, spatel, shchenz.
asi-sc added a comment.
Herald added a subscriber: StephenFan.

Some support of add-sub reassociation was added to AArch64 in D124564 <https://reviews.llvm.org/D124564>. This patch generalizes this idea and makes implementation target-independent.

It also introduces one more invariant to machine combiner that is REASSOC_AX/XA_BY/YB patterns must be gathered only with standard mechanism (`isAssociativeAndCommutative` function, etc. ) if reassociation is performed by default implementation. This sounds reasonable for me: if we have custom pattern matcher, we must be ready to write custom reassociation. All targets except RISCV that use machine-combine do not contradict the new invariant. If this patch gets positive feedback, I'll change RISCV implementation accordingly. It will require a few changes.

There is a big diff for tests, but it is just a change in the order of operands in commutative instructions. This is required to generalize the transformation rules.


Repository:
  rG LLVM Github Monorepo

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  https://reviews.llvm.org/D136754/new/

https://reviews.llvm.org/D136754