[all-commits] [llvm/llvm-project] 5fe146: [InstCombine] Simplify switch with selects (#84143)

[Yingwei Zheng via All-commits]

  Branch: refs/heads/main
  Home:   https://github.com/llvm/llvm-project
  Commit: 5fe146672d2b1c9f257a6ee045e0bc13fed1e504
      https://github.com/llvm/llvm-project/commit/5fe146672d2b1c9f257a6ee045e0bc13fed1e504
  Author: Yingwei Zheng <dtcxzyw2333 at gmail.com>
  Date:   2024-04-15 (Mon, 15 Apr 2024)

  Changed paths:
    M llvm/lib/Transforms/InstCombine/InstructionCombining.cpp
    A llvm/test/Transforms/InstCombine/switch-select.ll

  Log Message:
  -----------
  [InstCombine] Simplify switch with selects (#84143)

An example from https://github.com/image-rs/image:
```
define void @test_ult_rhsc(i8 %x) {
  %val = add nsw i8 %x, -2
  %cmp = icmp ult i8 %val, 11
  %cond = select i1 %cmp, i8 %val, i8 6
  switch i8 %cond, label %bb1 [
  i8 0, label %bb2
  i8 10, label %bb3
  ]

bb1:
  call void @func1()
  unreachable
bb2:
  call void @func2()
  unreachable
bb3:
  call void @func3()
  unreachable
}
```

When `%cmp` evaluates to false, we can prove that the range of `%val` is
[11, umax]. Thus we can safely replace `%cond` with `%val` since both
`switch 6` and `switch %val` go to the default dest `%bb1`.

Alive2: https://alive2.llvm.org/ce/z/uSTj6w
Godbolt: https://godbolt.org/z/MGrG84bzr

This patch will benefit many rust applications and some C/C++
applications (e.g., cvc5).



To unsubscribe from these emails, change your notification settings at https://github.com/llvm/llvm-project/settings/notifications