[llvm] [TLI] Add getLibFunc in TLI API that accepts an Instruction. (PR #75919)

[Paul Walker via llvm-commits]

================
@@ -621,3 +622,62 @@ TEST_F(TargetLibraryInfoTest, ValidProto) {
     EXPECT_TRUE(isLibFunc(F, LF));
   }
 }
+
+namespace {
+
+// Creates TLI for AArch64 and VecLibrary ARmPL, and uses it to get the TLI
+// names for different FRem Instructions.
+class TLITestAarch64ArmPl : public ::testing::Test {
+private:
+  SMDiagnostic Err;
+  const Triple TargetTriple;
+  const TargetLibraryInfoImpl::VectorLibrary VecLib;
+
+protected:
+  LLVMContext Ctx;
+  std::unique_ptr<Module> M;
+  std::unique_ptr<TargetLibraryInfoImpl> TLII;
+  std::unique_ptr<TargetLibraryInfo> TLI;
+
+  /// Create TLI for AArch64 with VecLib ArmPL.
+  TLITestAarch64ArmPl()
+      : TargetTriple(Triple("aarch64-unknown-linux-gnu")),
+        VecLib(TargetLibraryInfoImpl::ArmPL) {
+    TLII = std::make_unique<TargetLibraryInfoImpl>(
+        TargetLibraryInfoImpl(TargetTriple));
+    TLII->addVectorizableFunctionsFromVecLib(VecLib, TargetTriple);
+    TLI = std::make_unique<TargetLibraryInfo>(TargetLibraryInfo(*TLII));
+    // Create a dummy module needed for tests.
+    M = parseAssemblyString("declare void @dummy()", Err, Ctx);
+    EXPECT_NE(M.get(), nullptr)
+        << "Loading an invalid module.\n " << Err.getMessage() << "\n";
+  }
+
+  /// Creates an FRem Instruction of Type \p Ty, and uses it to get the TLI
+  /// function name.
+  StringRef getFremScalarName(Type *Ty) {
+    // Use a dummy function and a BB to create an FRem Instruction.
+    FunctionType *FTy = FunctionType::get(Ty, {Ty, Ty}, false);
+    Function *F = Function::Create(FTy, Function::ExternalLinkage, "foo", *M);
+    BasicBlock *BB = BasicBlock::Create(Ctx, "entry", F);
+    IRBuilder<> Builder(BB);
+    Builder.SetInsertPoint(BB);
+    auto *FRem =
+        dyn_cast<Instruction>(Builder.CreateFRem(F->getArg(0), F->getArg(1)));
+
----------------
paulwalker-arm wrote:

Is this necessary.  Does creating the instruction directly (e.g. `BinaryOperator::Create()`) not work?

https://github.com/llvm/llvm-project/pull/75919