[all-commits] [llvm/llvm-project] b33a13: [mlir][arith] Add support for expanding arith.maxn...

[Han-Chung Wang via All-commits]

  Branch: refs/heads/main
  Home:   https://github.com/llvm/llvm-project
  Commit: b33a131c828437efff36179458562e62774da881
      https://github.com/llvm/llvm-project/commit/b33a131c828437efff36179458562e62774da881
  Author: Han-Chung Wang <hanhan0912 at gmail.com>
  Date:   2023-12-20 (Wed, 20 Dec 2023)

  Changed paths:
    M mlir/lib/Dialect/Arith/Transforms/ExpandOps.cpp
    M mlir/test/Dialect/Arith/expand-ops.mlir

  Log Message:
  -----------
  [mlir][arith] Add support for expanding arith.maxnumf/minnumf ops. (#75989)

The maxnum/minnum semantics can be found at
https://llvm.org/docs/LangRef.html#llvm-minnum-intrinsic.

The revision also updates function names in lit tests to match op name.

Take arith.maxnumf as example:

```
func.func @maxnumf(%lhs: f32, %rhs: f32) -> f32 {
  %result = arith.maxnumf %lhs, %rhs : f32
  return %result : f32
}
```

will be expanded to

```
func.func @maxnumf(%lhs: f32, %rhs: f32) -> f32 {
  %0 = arith.cmpf ugt, %lhs, %rhs : f32
  %1 = arith.select %0, %lhs, %rhs : f32
  %2 = arith.cmpf uno, %lhs, %lhs : f32
  %3 = arith.select %2, %rhs, %1 : f32
  return %3 : f32
}
```

Case 1: Both LHS and RHS are not NaN; LHS > RHS

In this case, `%1` is LHS. `%3` and `%1` have the same value, so `%3` is
LHS.

Case 2: LHS is NaN and RHS is not NaN

In this case, `%2` is true, so `%3` is always RHS.

Case 3: LHS is not NaN and RHS is NaN

In this case, `%0` is true and `%1` is LHS. `%2` is false, so `%3` and
`%1` have the same value, which is LHS.

Case 4: Both LHS and RHS are NaN:

`%1` and RHS are all NaN, so the result is still NaN.