/**
 * Break down a D type into basic (register) types for the 32-bit x86 ABI.
 *
 * Copyright:   Copyright (C) 1999-2020 by The D Language Foundation, All Rights Reserved
 * Authors:     $(LINK2 http://www.digitalmars.com, Walter Bright)
 * License:     $(LINK2 http://www.boost.org/LICENSE_1_0.txt, Boost License 1.0)
 * Source:      $(LINK2 https://github.com/dlang/dmd/blob/master/src/dmd/argtypes_x86.d, _argtypes_x86.d)
 * Documentation:  https://dlang.org/phobos/dmd_argtypes_x86.html
 * Coverage:    https://codecov.io/gh/dlang/dmd/src/master/src/dmd/argtypes_x86.d
 */

module dmd.argtypes_x86;

import core.stdc.stdio;
import core.checkedint;

import dmd.declaration;
import dmd.globals;
import dmd.mtype;
import dmd.visitor;

/****************************************************
 * This breaks a type down into 'simpler' types that can be passed to a function
 * in registers, and returned in registers.
 * This is the implementation for the 32-bit x86 ABI.
 * Params:
 *      t = type to break down
 * Returns:
 *      tuple of types, each element can be passed in a register.
 *      A tuple of zero length means the type cannot be passed/returned in registers.
 *      null indicates a `void`.
 */
extern (C++) TypeTuple toArgTypes_x86(Type t)
{
    extern (C++) final class ToArgTypes : Visitor
    {
        alias visit = Visitor.visit;
    public:
        TypeTuple result;

        /*****
         * Pass type in memory (i.e. on the stack), a tuple of one type, or a tuple of 2 types
         */
        void memory()
        {
            //printf("\ttoArgTypes() %s => [ ]\n", t.toChars());
            result = TypeTuple.empty; // pass on the stack
        }

        ///
        void oneType(Type t)
        {
            result = new TypeTuple(t);
        }

        ///
        void twoTypes(Type t1, Type t2)
        {
            result = new TypeTuple(t1, t2);
        }


        override void visit(Type)
        {
            // not valid for a parameter
        }

        override void visit(TypeError)
        {
            result = new TypeTuple(Type.terror);
        }

        override void visit(TypeBasic t)
        {
            Type t1 = null;
            Type t2 = null;
            switch (t.ty)
            {
            case Tvoid:
                return;
            case Tbool:
            case Tint8:
            case Tuns8:
            case Tint16:
            case Tuns16:
            case Tint32:
            case Tuns32:
            case Tfloat32:
            case Tint64:
            case Tuns64:
            case Tint128:
            case Tuns128:
            case Tfloat64:
            case Tfloat80:
                t1 = t;
                break;
            case Timaginary32:
                t1 = Type.tfloat32;
                break;
            case Timaginary64:
                t1 = Type.tfloat64;
                break;
            case Timaginary80:
                t1 = Type.tfloat80;
                break;
            case Tcomplex32:
                t1 = Type.tfloat64;
                t2 = Type.tfloat64;
                break;
            case Tcomplex64:
                t1 = Type.tfloat64;
                t2 = Type.tfloat64;
                break;
            case Tcomplex80:
                t1 = Type.tfloat80;
                t2 = Type.tfloat80;
                break;
            case Tchar:
                t1 = Type.tuns8;
                break;
            case Twchar:
                t1 = Type.tuns16;
                break;
            case Tdchar:
                t1 = Type.tuns32;
                break;
            default:
                assert(0);
            }
            if (t1)
            {
                if (t2)
                    return twoTypes(t1, t2);
                else
                    return oneType(t1);
            }
            else
                return memory();
        }

        override void visit(TypeVector t)
        {
            return oneType(t);
        }

        override void visit(TypeAArray)
        {
            return oneType(Type.tvoidptr);
        }

        override void visit(TypePointer)
        {
            return oneType(Type.tvoidptr);
        }

        /*************************************
         * Convert a floating point type into the equivalent integral type.
         */
        static Type mergeFloatToInt(Type t)
        {
            switch (t.ty)
            {
            case Tfloat32:
            case Timaginary32:
                t = Type.tint32;
                break;
            case Tfloat64:
            case Timaginary64:
            case Tcomplex32:
                t = Type.tint64;
                break;
            default:
                debug
                {
                    printf("mergeFloatToInt() %s\n", t.toChars());
                }
                assert(0);
            }
            return t;
        }

        /*************************************
         * This merges two types into an 8byte type.
         * Params:
         *      t1 = first type (can be null)
         *      t2 = second type (can be null)
         *      offset2 = offset of t2 from start of t1
         * Returns:
         *      type that encompasses both t1 and t2, null if cannot be done
         */
        static Type argtypemerge(Type t1, Type t2, uint offset2)
        {
            //printf("argtypemerge(%s, %s, %d)\n", t1 ? t1.toChars() : "", t2 ? t2.toChars() : "", offset2);
            if (!t1)
            {
                assert(!t2 || offset2 == 0);
                return t2;
            }
            if (!t2)
                return t1;
            const sz1 = t1.size(Loc.initial);
            const sz2 = t2.size(Loc.initial);
            assert(sz1 != SIZE_INVALID && sz2 != SIZE_INVALID);
            if (t1.ty != t2.ty && (t1.ty == Tfloat80 || t2.ty == Tfloat80))
                return null;
            // [float,float] => [cfloat]
            if (t1.ty == Tfloat32 && t2.ty == Tfloat32 && offset2 == 4)
                return Type.tfloat64;
            // Merging floating and non-floating types produces the non-floating type
            if (t1.isfloating())
            {
                if (!t2.isfloating())
                    t1 = mergeFloatToInt(t1);
            }
            else if (t2.isfloating())
                t2 = mergeFloatToInt(t2);
            Type t;
            // Pick type with larger size
            if (sz1 < sz2)
                t = t2;
            else
                t = t1;
            // If t2 does not lie within t1, need to increase the size of t to enclose both
            bool overflow;
            const offset3 = addu(offset2, sz2, overflow);
            assert(!overflow);
            if (offset2 && sz1 < offset3)
            {
                switch (offset3)
                {
                case 2:
                    t = Type.tint16;
                    break;
                case 3:
                case 4:
                    t = Type.tint32;
                    break;
                default:
                    t = Type.tint64;
                    break;
                }
            }
            return t;
        }

        override void visit(TypeDArray)
        {
            /* Should be done as if it were:
             * struct S { size_t length; void* ptr; }
             */
            return twoTypes(Type.tsize_t, Type.tvoidptr);
        }

        override void visit(TypeDelegate)
        {
            /* Should be done as if it were:
             * struct S { void* funcptr; void* ptr; }
             */
            return twoTypes(Type.tvoidptr, Type.tvoidptr);
        }

        override void visit(TypeSArray t)
        {
            const sz = t.size(Loc.initial);
            if (sz > 16)
                return memory();

            const dim = t.dim.toInteger();
            Type tn = t.next;
            const tnsize = tn.size();
            const tnalignsize = tn.alignsize();

            /*****
             * Get the nth element of this array.
             * Params:
             *   n = element number, from 0..dim
             *   offset = set to offset of the element from the start of the array
             *   alignsize = set to the aligned size of the element
             * Returns:
             *   type of the element
             */
            extern (D) Type getNthElement(size_t n, out uint offset, out uint alignsize)
            {
                offset = cast(uint)(n * tnsize);
                alignsize = tnalignsize;
                return tn;
            }

            aggregate(sz, cast(size_t)dim, &getNthElement);
        }

        override void visit(TypeStruct t)
        {
            //printf("TypeStruct.toArgTypes() %s\n", t.toChars());

            if (!t.sym.isPOD())
                return memory();

            /*****
             * Get the nth field of this struct.
             * Params:
             *   n = field number, from 0..nfields
             *   offset = set to offset of the field from the start of the type
             *   alignsize = set to the aligned size of the field
             * Returns:
             *   type of the field
             */
            extern (D) Type getNthField(size_t n, out uint offset, out uint alignsize)
            {
                auto field = t.sym.fields[n];
                offset = field.offset;
                alignsize = field.type.alignsize();
                return field.type;
            }

            aggregate(t.size(Loc.initial), t.sym.fields.dim, &getNthField);
        }

        /*******************
         * Handle aggregates (struct, union, and static array) and set `result`
         * Params:
         *      sz = total size of aggregate
         *      nfields = number of fields in the aggregate (dimension for static arrays)
         *      getFieldInfo = get information about the nth field in the aggregate
         */
        extern (D) void aggregate(d_uns64 sz, size_t nfields, Type delegate(size_t, out uint, out uint) getFieldInfo)
        {
            if (nfields == 0)
                return memory();

            Type t1 = null;
            switch (cast(uint)sz)
            {
            case 1:
                t1 = Type.tint8;
                break;
            case 2:
                t1 = Type.tint16;
                break;
            case 4:
                t1 = Type.tint32;
                break;
            case 8:
                t1 = Type.tint64;
                break;
            case 16:
                t1 = null; // could be a TypeVector
                break;
            default:
                return memory();
            }
            if (global.params.targetOS == TargetOS.FreeBSD && nfields == 1 &&
                (sz == 4 || sz == 8))
            {
                /* FreeBSD changed their 32 bit ABI at some point before 10.3 for the following:
                 *  struct { float f;  } => arg1type is float
                 *  struct { double d; } => arg1type is double
                 * Cannot find any documentation on it.
                 */

                uint foffset;
                uint falignsize;
                Type ftype = getFieldInfo(0, foffset, falignsize);
                TypeTuple tup = toArgTypes_x86(ftype);
                if (tup && tup.arguments.dim == 1)
                {
                    Type ft1 = (*tup.arguments)[0].type;
                    if (ft1.ty == Tfloat32 || ft1.ty == Tfloat64)
                        return oneType(ft1);
                }
            }

            if (t1)
                return oneType(t1);
            else
                return memory();
        }

        override void visit(TypeEnum t)
        {
            t.toBasetype().accept(this);
        }

        override void visit(TypeClass)
        {
            result = new TypeTuple(Type.tvoidptr);
        }
    }

    scope ToArgTypes v = new ToArgTypes();
    t.accept(v);
    return v.result;
}
