[Run]
Filename: "{app}\vc_redist.x64.exe"; StatusMsg: "{#VCmsg}"; Check: IsWin64 and not VCinstalled

[Code]
function VCinstalled: Boolean;
 // By Michael Weiner <mailto:spam@cogit.net>
 // Function for Inno Setup Compiler
 // 13 November 2015
 // Returns True if Microsoft Visual C++ Redistributable is installed, otherwise False.
 // The programmer may set the year of redistributable to find; see below.
 var
  names: TArrayOfString;
  i: Integer;
  dName, key, year: String;
 begin
  // Year of redistributable to find; leave null to find installation for any year.
  year := '2015';
  Result := False;
  key := 'Software\Microsoft\Windows\CurrentVersion\Uninstall';
  // Get an array of all of the uninstall subkey names.
  if RegGetSubkeyNames(HKEY_LOCAL_MACHINE, key, names) then
   // Uninstall subkey names were found.
   begin
    i := 0
    while ((i < GetArrayLength(names)) and (Result = False)) do
     // The loop will end as soon as one instance of a Visual C++ redistributable is found.
     begin
      // For each uninstall subkey, look for a DisplayName value.
      // If not found, then the subkey name will be used instead.
      if not RegQueryStringValue(HKEY_LOCAL_MACHINE, key + '\' + names[i], 'DisplayName', dName) then
       dName := names[i];
      // See if the value contains both of the strings below.
      Result := (Pos(Trim('Visual C++ ' + year),dName) * Pos('Redistributable',dName) <> 0)
      i := i + 1;
     end;
   end;
 end;