[PATCH] D76057: [Reassociate] recognize more than one pairs for later CSE - NFC

[ChenZheng via Phabricator via llvm-commits]

shchenz created this revision.
shchenz added reviewers: spatel, lebedev.ri, efriedma, qcolombet, mcrosier, davide, dsanders.
Herald added subscribers: llvm-commits, wuzish, kosarev, hiraditya.
Herald added a project: LLVM.

Motivated case:

  void foo(int a, int b, int c, int d, int* res1, int* res2, int* res3)
  {
    *res1 = a + b + c + d;
    *res2 = b + c;
    *res3 = a + d;
  }

There are two common expressions `a+d` & `c+d`, currently `Reassociate` can recognize one of them.

It gets:

  %add = add i32 %b, %c
  %add.1 = add i32 %add, %a
  %add.2 = add i32 %add.1, %d
  store i32 %add, i32*res2, align 4, !tbaa !2
  store i32 %add.2, i32* %res1, align 4, !tbaa !2
  %add.3 = add nsw i32 %a, %d
  store i32 %add.3, i32* %res3, align 4, !tbaa !2
  ret void

But we expect:

  %add1 = add i32 %d, %a
  %add = add i32 %c, %b
  %add2 = add i32 %add, %add1
  store i32 %add2, i32* %res1, align 4, !tbaa !2
  store i32 %add, i32* %res2, align 4, !tbaa !2
  store i32 %add1, i32* %res3, align 4, !tbaa !2
  ret void

This is first part to recognize more than one pattern. This is NFC.
Changes about rewriting these common expressions will be posted in following patches.


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D76057

Files:
  llvm/include/llvm/Transforms/Scalar/Reassociate.h
  llvm/lib/Transforms/Scalar/Reassociate.cpp

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