[llvm] [InstCombine] Add folds for `(fp_binop ({s|u}itofp x), ({s|u}itofp y))` (PR #82555)

[Yingwei Zheng via llvm-commits]

================
@@ -90,8 +90,8 @@ define float @test_3(i32 %a, i32 %b) {
 ; CHECK-LABEL: @test_3(
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dtcxzyw wrote:

```suggestion
; can be represented in float.
define float @test_3(i32 %a, i32 %b) {
; CHECK-LABEL: @test_3(
```

https://github.com/llvm/llvm-project/pull/82555