AttributorAttributes: guard against TLI being nullptr

[durin42]

Summary

I didn't dig into this very much because it appears to be totally valid
(especially once these properties can come from attributes instead
of only from hard-coded library functions) for TLI to not be defined,
and nothing broke when I added this check, including with all my other
patches applied.

[jdoerfert]

LG

llvm/lib/Transforms/IPO/AttributorAttributes.cpp

auto AllocationIdentifierCB = [&](Instruction &I) {
       // To do heap to stack, we need to know that the allocation itself is
       // removable once uses are rewritten, and that we can initialize the
       // alloca to the same pattern as the original allocation result.
       if (isAllocationFn(CB, TLI) && isAllocRemovable(CB, TLI)) {
         auto *I8Ty = Type::getInt8Ty(CB->getParent()->getContext());
         if (nullptr != getInitialValueOfAllocation(CB, TLI, I8Ty)) {
           AllocationInfo *AI = new (A.Allocator) AllocationInfo{CB};
           AllocationInfos[CB] = AI;
+          if (TLI)
             TLI->getLibFunc(*CB, AI->LibraryFunctionId);
         }
       }
       return true;
     };
 
     bool UsedAssumedInformation = false;
     bool Success = A.checkForAllCallLikeInstructions(
         AllocationIdentifierCB, *this, UsedAssumedInformation,