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

[via llvm-commits]

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@@ -8037,6 +8037,46 @@ Instruction *InstCombinerImpl::visitFCmpInst(FCmpInst &I) {
       if (Instruction *NV = FoldOpIntoSelect(I, cast<SelectInst>(LHSI)))
         return NV;
       break;
+    case Instruction::FSub:
+      switch (Pred) {
+      default:
+        break;
+      case FCmpInst::FCMP_UGT:
+      case FCmpInst::FCMP_ULT:
+      case FCmpInst::FCMP_UNE:
+      case FCmpInst::FCMP_OEQ:
+      case FCmpInst::FCMP_OGE:
+      case FCmpInst::FCMP_OLE:
+        // Skip optimization: fsub x, y unless guaranteed !isinf(x) ||
+        // !isinf(y).
+        if (!LHSI->hasOneUse() ||
----------------
SahilPatidar wrote:

Can we do it this way:
```cpp
      if (LHSI->hasOneUse())
        if (Instruction *NV = foldFCmpFSubIntoFCmp(I, LHSI, RHSC, *this))
          return NV;
```

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