[llvm] [SimplifyLibCalls] fdim constant fold (PR #109235)

[Matt Arsenault via llvm-commits]

================
@@ -3109,6 +3109,50 @@ Value *LibCallSimplifier::optimizeRemquo(CallInst *CI, IRBuilderBase &B) {
   return ConstantFP::get(CI->getType(), Rem);
 }
 
+/// Constant folds fdim
+Value *LibCallSimplifier::optimizeFdim(CallInst *CI, IRBuilderBase &B) {
+  // Cannot perform the fold unless the call has attribute memory(none)
+  if (!CI->doesNotAccessMemory())
+    return nullptr;
+
+  // TODO : Handle undef values
+  // propagate poison if any
----------------
arsenm wrote:

```suggestion
  // Propagate poison if any
```

https://github.com/llvm/llvm-project/pull/109235