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// ============================================================================

//        __

//   \\__/ o\    (C) 2017-2018  Robert Finch, Waterloo

//    \  __ /    All rights reserved.

//     \/_//     robfinch<remove>@finitron.ca

//       ||

//

// CC64 - 'C' derived language compiler

//  - 64 bit CPU

//

// This source file is free software: you can redistribute it and/or modify 

// it under the terms of the GNU Lesser General Public License as published 

// by the Free Software Foundation, either version 3 of the License, or     

// (at your option) any later version.                                      

//                                                                          

// This source file is distributed in the hope that it will be useful,      

// but WITHOUT ANY WARRANTY; without even the implied warranty of           

// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the            

// GNU General Public License for more details.                             

//                                                                          

// You should have received a copy of the GNU General Public License        

// along with this program.  If not, see <http://www.gnu.org/licenses/>.    

//                                                                          

// ============================================================================

//

#include "stdafx.h"

//

// Returns the desirability of optimization for a subexpression.

//

// Immediate constants have low priority because small constants

// can be directly encoded in the instruction. There's no value to

// placing them in registers.

int CSE::OptimizationDesireability()

{

        if (exp==nullptr)

                return (0);

        if( voidf || (exp->nodetype == en_icon &&

                       exp->i < 32768 && exp->i >= -32768))

        return (0);

 /* added this line to disable register optimization of global variables.

    The compiler would assign a register to a global variable ignoring

    the fact that the value might change due to a subroutine call.

  */

        if (exp->nodetype == en_nacon)

                return (0);

        // No value to optimizing function call names, the called function

        // address will typically fit in a single 32/48 bit opcode. It's faster

        // to call a fixed label rather than an address in a register, because

        // the address is known at the fetch phase of the processor. A register

        // based address may be predicted by the processor and so is almost as

        // fast. Storing the address in a register can reduce the size of code.

        // If the function name can be optimized to a register then

        // a 16-bit compressed JAL can be used.

        if (exp->nodetype == en_cnacon && !opt_size)

                return (0);

        if (exp->isVolatile)

                return (0);

        // Prevent Inline code from being allocated a pointer in a register.

        if (exp->sym) {

                if (exp->sym->fi) {

                        if (exp->sym->fi->IsInline)

                                return (0);

                }

        }

        // Left values are worth more to optimization than right values.

    if( IsLValue(exp) )

            return (2 * uses);

    return (uses);

}