[Float2Int] Avoid repeated hash lookups (NFC) (#107795)

Author: kazutakahirata

llvm/lib/Transforms/Scalar/Float2Int.cpp

@@ -115,11 +115,7 @@ void Float2IntPass::findRoots(Function &F, const DominatorTree &DT) {
 // Helper - mark I as having been traversed, having range R.
 void Float2IntPass::seen(Instruction *I, ConstantRange R) {
   LLVM_DEBUG(dbgs() << "F2I: " << *I << ":" << R << "\n");
-  auto IT = SeenInsts.find(I);
-  if (IT != SeenInsts.end())
-    IT->second = std::move(R);
-  else
-    SeenInsts.insert(std::make_pair(I, std::move(R)));
+  SeenInsts.insert_or_assign(I, std::move(R));
 }
 
 // Helper - get a range representing a poison value.