[all-commits] [llvm/llvm-project] 0d95b2: [LICM] Reassociate & hoist add expressions

[Max Kazantsev via All-commits]

  Branch: refs/heads/main
  Home:   https://github.com/llvm/llvm-project
  Commit: 0d95b20b63d7acc459dc0b2a7b2e4f9924c0adce
      https://github.com/llvm/llvm-project/commit/0d95b20b63d7acc459dc0b2a7b2e4f9924c0adce
  Author: Max Kazantsev <mkazantsev at azul.com>
  Date:   2023-05-22 (Mon, 22 May 2023)

  Changed paths:
    M llvm/lib/Transforms/Scalar/LICM.cpp
    M llvm/test/Transforms/LICM/hoist-add-sub.ll

  Log Message:
  -----------
  [LICM] Reassociate & hoist add expressions

This patch allows LICM to reassociate and hoist following expressions:
```
loop:
  %sum = add nsw %iv, %C1
  %cmp = icmp <signed pred> %sum, C2
```
where `C1` and `C2` are loop invariants. The reassociated version looks like
```
preheader:
  %inv_sum = C2 - C1
...
loop:
  %cmp = icmp <signed pred> %iv, %inv_sum
```
In order to prove legality, we need both initial addition and the newly created subtraction
to happen without overflow.

Differential Revision: https://reviews.llvm.org/D149132
Reviewed By: skatkov