VHDL, process not updating variable's value, implementing a Merge Sort

Question

I am trying to implement an example of Merge Sort algorithm on VHDL in order to sort 4 128bit numbers.
I am using sequential code. I have a process on which I make comparisons. The process consists of 3 phases which implement the logic behind Merge Sort.
The problem is that I am using a variable count : integer which counts clock cycles. I want the phases to follow clock cycles.
It seems like the simulation enters the first IF statement (of Phase 1) but does not enter the others so I guess count variable does not update its value.
I have tried several changes but seems like I am missing something here. I know the post is a little big, I would appreciate any help! Thanks!

entity Merge_Sort is
    Port ( clk : in STD_LOGIC;
           reset : in STD_LOGIC;
           en : in STD_LOGIC;
           In_a : in STD_LOGIC_VECTOR(15 downto 0 ) ;
           In_b : in STD_LOGIC_VECTOR(15 downto 0 ) ;
           In_c : in STD_LOGIC_VECTOR(15 downto 0 ) ;
           In_d : in STD_LOGIC_VECTOR(15 downto 0 ) ;
           Sorted_a : out STD_LOGIC_VECTOR(15 downto 0 ) ;
           Sorted_b : out STD_LOGIC_VECTOR(15 downto 0 ) ;
           Sorted_c : out STD_LOGIC_VECTOR(15 downto 0 ) ;
           Sorted_d : out STD_LOGIC_VECTOR(15 downto 0 )  );
end Merge_Sort;

architecture Behavioral of Merge_Sort is

signal temp1a,temp1b,temp1c,temp1d  : STD_LOGIC_VECTOR(15 downto 0 ) ;
TYPE arr2 IS ARRAY  (0 to 1 ) of STD_LOGIC_VECTOR(15 downto 0) ;
TYPE arr4 IS ARRAY  (0 to 3 ) of STD_LOGIC_VECTOR(15 downto 0) ;
signal Array1 , Array2 : arr2  ;
signal  mergedArr : arr4  ;
signal temp : std_logic_vector(15 downto 0 )  ; 

begin
   temp1a <= (others =>'0' ) WHEN reset ='1' else                  -- Asychronous Resetting 
         In_a ; 
   temp1b <= (others =>'0' ) WHEN reset ='1' else
                In_b ; 
   temp1c <= (others =>'0' ) WHEN reset ='1' else                     -- Asychronous Resetting 
                        In_c ; 
   temp1d <= (others =>'0' ) WHEN reset ='1' else
                         In_d ; 


Sorted_a <= MergedArr(0) ;
Sorted_b <= MergedArr(1) ;
Sorted_c <= MergedArr(2) ;
Sorted_d <= MergedArr(3) ;



   Sort: PROCESS(clk)

   variable count : integer range 0 to 3   ;   


BEGIN 
     if(reset ='1' ) then count := 0 ;
     end if ;

       IF ( clk'EVENT AND clk='1' ) then                 -- Conditions for process to run 
         IF (en ='1') then 

          IF(count =0) THEN      -- Phase 1 of sort
            if (temp1a<temp1b ) then  Array1(0)<=temp1a  ; Array1(1) <= temp1b ; 
            else                      Array1(1)<=temp1a ;  Array1(0) <= temp1b   ;
            end if ;

            if (temp1c<temp1d ) then  Array2(0)<=temp1c  ;Array2(1) <= temp1d ; 
            else                      Array2(1)<=temp1c ;  Array2(0) <= temp1d   ;
            end if ;

            count := count +1 ;
          END IF ; 

           IF( count = 1) THEN    -- Phase 2 of sort , computing min and max of array 
                  if ( Array1(1) < Array2(1) ) then   MergedArr(1) <= Array1(1) ;  MergedArr(3) <= Array2(1) ;
                  else                               MergedArr(3) <= Array1(1) ;  MergedArr(1) <= Array2(1) ;
                  end if ; 

                  if ( Array1(0) < Array2(0) ) then   MergedArr(0) <= Array1(0) ;  MergedArr(2) <= Array2(0) ;
                   else                               MergedArr(2) <= Array1(0) ;  MergedArr(0) <= Array2(0) ;
                  end if ;            
               count:= count +1 ;
            END IF ;

            IF(count =2 ) THEN       -- Phase 3 of sort  ,  FINAL 
                if ( MergedArr(1) > MergedArr(2) ) then    
                     temp<= MergedArr(2 ) ;
                     MergedArr(2) <= MergedArr(1) ;
                     MergedArr(1) <= temp ; 
                 end if ;
            END IF ;


           END IF;
         END IF ;
END PROCESS ; 

end Behavioral;

Answer 1

The variable count is updated immediately inside each IF condition. So, for example, inside the IF(count=0) , it is incremented to 1. Then it reaches the IF(count=1) statement, which will of course already be true.

I think really all you need to do is change it to IF ... ELSIF statements:

  IF(count =0) THEN      -- Phase 1 of sort
      ...
  ELSIF( count = 1) THEN    -- Phase 2 of sort , computing min and max of array 
      ...
  ELSIF(count =2 ) THEN       -- Phase 3 of sort  ,  FINAL 

and I think it will work exactly as you expect.