[llvm] [InstCombine] Fold fcmp ogt (x - y), 0 into fcmp ogt x, y #85245 (PR #85506)

[Matt Arsenault via llvm-commits]

================
@@ -8047,7 +8047,7 @@ Instruction *InstCombinerImpl::visitFCmpInst(FCmpInst &I) {
       case FCmpInst::FCMP_OEQ:
       case FCmpInst::FCMP_OGE:
       case FCmpInst::FCMP_OLE:
-        // fsub x, y --> isnnan(x, y) && isninf(x, y)
+        // Skip optimization: fsub x, y guaranteed isInf(x, y).
----------------
arsenm wrote:

```suggestion
        // Skip optimization: fsub x, y unless guaranteed !isinf(x) && !isinf(y).
```

https://github.com/llvm/llvm-project/pull/85506