[PATCH] D49382: [InstrSimplify] fold sdiv if two operands are negatived and non-overflow

[Roman Lebedev via Phabricator via llvm-commits]

lebedev.ri added a comment.

In general looks sane, but a few notes.

This fold does require `nsw` on `sub`, but i'm not seeing tests for that.

  define i32 @negated_operand_bad(i32 %x) {
    %negx = sub i32 0, %x ; not nsw
    %div = sdiv i32 %negx, %x
    ret i32 %div
  }
  define i32 @knownnegation_bad(i32 %x, i32 %y) {
    %xy = sub nsw i32 %x, %y
    %yx = sub i32 %y, %x ; not nsw
    %div = sdiv i32 %xy, %yx
    ret i32 %div
  }
  define i32 @knownnegation_bad(i32 %x, i32 %y) {
    %xy = sub i32 %x, %y ; not nsw
    %yx = sub nsw i32 %y, %x
    %div = sdiv i32 %xy, %yx
    ret i32 %div
  }
  define i32 @knownnegation_bad(i32 %x, i32 %y) {
    %xy = sub i32 %x, %y ; not nsw
    %yx = sub i32 %y, %x ; not nsw
    %div = sdiv i32 %xy, %yx
    ret i32 %div
  }



================
Comment at: llvm/test/Transforms/InstSimplify/sdiv.ll:40
 }
+
+define i32 @knownnegation_2(i32 %t) {
----------------
Same as with D49423, i'd like to see a bit more tests:
```
define <3 x i32> @negated_operand_vec_undef(<3 x i32> %x) {
  %negx = sub nsw <3 x i32> <i32 0, i32 undef, i32 0>, %x
  %rem = sdiv <3 x i32> %negx, %x
  ret <3 x i32> %rem
}
define <2 x i32> @negated_operand_vec_nonsplat(<2 x i32> %x) {
  %negx = sub nsw <2 x i32> <i32 0, 1>, %x ; not 0, don't fold
  %rem = sdiv <2 x i32> %negx, %x
  ret <2 x i32> %rem
}
```


https://reviews.llvm.org/D49382