[NFC] MemoryBuiltins: tease out a getFreeFunctionDataForFunction helper

[durin42]

Summary

I'll need this in my next change.

[reames]

LGTM

[reames]

Landed as b2d091aa, I forgot to include the review link.

llvm/lib/Analysis/MemoryBuiltins.cpp

 #include "llvm/IR/Value.h"
 #include "llvm/Support/Casting.h"
 #include "llvm/Support/Debug.h"
 #include "llvm/Support/MathExtras.h"
 #include "llvm/Support/raw_ostream.h"
 #include <cassert>
 #include <cstdint>
 #include <iterator>
+#include <type_traits>
 #include <utility>
 
 using namespace llvm;
 
 #define DEBUG_TYPE "memory-builtins"
 
 enum AllocType : uint8_t {
   OpNewLike          = 1<<0, // allocates; never returns null
static const std::pair<LibFunc, FreeFnsTy> FreeFnData[] = {
     {LibFunc_ZdaPvSt11align_val_tRKSt9nothrow_t, {3}}, // delete[](void*, align_val_t, nothrow)
     {LibFunc_ZdlPvjSt11align_val_t,              {3}}, // delete(void*, unsigned int, align_val_t)
     {LibFunc_ZdlPvmSt11align_val_t,              {3}}, // delete(void*, unsigned long, align_val_t)
     {LibFunc_ZdaPvjSt11align_val_t,              {3}}, // delete[](void*, unsigned int, align_val_t)
     {LibFunc_ZdaPvmSt11align_val_t,              {3}}, // delete[](void*, unsigned long, align_val_t)
 };
 // clang-format on
 
-/// isLibFreeFunction - Returns true if the function is a builtin free()
-bool llvm::isLibFreeFunction(const Function *F, const LibFunc TLIFn) {
+Optional<FreeFnsTy> getFreeFunctionDataForFunction(const Function *Callee,
+                                                   const LibFunc TLIFn) {
   const auto *Iter =
       find_if(FreeFnData, [TLIFn](const std::pair<LibFunc, FreeFnsTy> &P) {
         return P.first == TLIFn;
       });
-  if (Iter == std::end(FreeFnData)) {
-    return false;
-  }
-  const FreeFnsTy *FnData = &Iter->second;
+  if (Iter == std::end(FreeFnData))
+    return None;
+  return Iter->second;
+
+/// isLibFreeFunction - Returns true if the function is a builtin free()
+bool llvm::isLibFreeFunction(const Function *F, const LibFunc TLIFn) {
+  Optional<FreeFnsTy> FnData = getFreeFunctionDataForFunction(F, TLIFn);
+  if (!FnData.hasValue())
+    return false;
 
   // Check free prototype.
   // FIXME: workaround for PR5130, this will be obsolete when a nobuiltin
   // attribute will exist.
   FunctionType *FTy = F->getFunctionType();
   if (!FTy->getReturnType()->isVoidTy())
     return false;
   if (FTy->getNumParams() != FnData->NumParams)