Generate block inside case statement system verilog

Question

I want to selectively compile below code in system verilog:

always_comb begin
out = 0;
case(exp)
state_1: out = a*b;
state_2: out = b|c;
state_3: out = c^d;
endcase
end

Is this the right way of doing it? Will the state_3 code be removed in synthesis?

parameter PARAM_1 = 1'b1;  
parameter PARAM_2 = 1'b1;
parameter PARAM_3 = 1'b0;

always_comb begin
out = 0;
case(exp)
state_1: if (PARAM_1 == 1'b1) out = a*b;
state_2: if (PARAM_2 == 1'b1) out = b|c;
state_3: if (PARAM_3 == 1'b1) out = c^d;
endcase
end

I want the output of the above code be like below after synthesis.

always_comb begin
out = 0;
case(exp)
state_1: out = a*b;
state_2: out = b|c;
endcase
end

Is there a way of doing the same using generate block? The below code won't work since there are multiple driver for out varaible in different block.

parameter PARAM_1 = 1'b1;  
parameter PARAM_2 = 1'b1;
parameter PARAM_3 = 1'b0;

generate 
if (PARAM_1 ==1'b1) begin
    always_comb begin
    case(exp)
    state_1: out = a*b;
    default : out = 0;
    endcase
 end
 endgenerate


generate 
if (PARAM_2 ==1'b1) begin
    always_comb begin
    case(exp)
    state_1: out = b|c;
    default : out = 0;
    endcase
 end
 endgenerate


generate 
if (PARAM_3 ==1'b1) begin
    always_comb begin
    case(exp)
    state_1: out = c^d;
    default : out = 0
    endcase
 end
 endgenerate

Answer 1

There is no use of using a generate block for what you are trying to synthesize. Generate blocks are used best when you want to instantiate multiple modules.

Here is a good reference for understanding how you can use generate with case statements, but you can do this with simple for loop too.

https://www.verilogpro.com/verilog-generate-configurable-rtl/