when get_rand_instr is called with include_category, return null if no match. Simulation should fail as it is likely due to improper configuration

Author: Bounti

src/isa/riscv_instr.sv

@@ -215,8 +215,12 @@ class riscv_instr extends uvm_object;
          idx = $urandom_range(0, allowed_instr.size()-1);
          name = allowed_instr[idx];
        end else begin
-         idx = $urandom_range(0, instr_names.size()-1);
-         name = instr_names[idx];
+         if ( include_category.size() > 0 ) begin
+           return null;
+         end else begin
+           idx = $urandom_range(0, instr_names.size()-1);
+           name = instr_names[idx];
+         end
        end
      end else begin
        if (!std::randomize(name) with {

src/riscv_directed_instr_lib.sv

@@ -336,8 +336,7 @@ class riscv_push_stack_instr extends riscv_rand_instr_stream;
       enable_branch = 0;
     end
     if(enable_branch) begin
-      //branch_instr = riscv_instr::get_rand_instr(.include_category({BRANCH}));
-      branch_instr = riscv_instr::get_rand_instr(.include_instr({BEQ, BNE, BLT, BGE, BLTU, BGEU}));
+      branch_instr = riscv_instr::get_rand_instr(.include_category({BRANCH}));
       `DV_CHECK_RANDOMIZE_FATAL(branch_instr)
       branch_instr.imm_str = push_start_label;
       branch_instr.branch_assigned = 1'b1;