How do I check if registry key exists and exit setup - inno-setup

Question

I try to making setup file to patch previous program. The setup must be able to check if previous program is installed or not.
This is my unusable code
[Code]
function GetHKLM() : Integer;
begin
if IsWin64 then
begin
Result := HKLM64;
end
else
begin
Result := HKEY_LOCAL_MACHINE;
end;
end;
function InitializeSetup(): Boolean;
var
V: string;
begin
if RegKeyExists(GetHKLM(), 'SOFTWARE\ABC\Option\Settings')
then
MsgBox('please install ABC first!!',mbError,MB_OK);
end;
My condition is
must check windows 32- or 64-bits in for RegKeyExists
if previous program is not installed, show error message and exit setup program, else continue process.
How to modify the code?
Thank you in advance.
**Update for fix Wow6432Node problem. I try to modify my code
[Code]
function InitializeSetup: Boolean;
begin
// allow the setup to continue initially
Result := True;
// if the registry key based on current OS bitness doesn't exist, then...
if IsWin64 then
begin
if not RegKeyExists(HKLM, 'SOFTWARE\Wow6432Node\ABC\Option\Settings') then
begin
// return False to prevent installation to continue
Result := False;
// and display a message box
MsgBox('please install ABC first!!', mbError, MB_OK);
end
else
if not RegKeyExists(HKLM, 'SOFTWARE\ABC\Option\Settings' then
begin
// return False to prevent installation to continue
Result := False;
// and display a message box
MsgBox('please install ABC first!!', mbError, MB_OK);
end
end;
end;

Answer 1

The updated code in the question is incorrect -- you should never ever use Wow6432Node anywhere other than when looking at paths in RegEdit.
From the behaviour you have described, you are actually looking for a 32-bit application. In this case you can use the same code regardless of whether Windows is 32-bit or 64-bit; you were overthinking your original question.
Here is the corrected code from your updated question:
[Code]
function InitializeSetup: Boolean;
begin
// allow the setup to continue initially
Result := True;
if not RegKeyExists(HKLM, 'SOFTWARE\ABC\Option\Settings') then
begin
// return False to prevent installation to continue
Result := False;
// and display a message box
MsgBox('please install ABC first!!', mbError, MB_OK);
end;
end;