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cleaned up engine.c a bit (fewer ifdefs)
added direct threading for the Alpha architecture
timings.sc contains some timings (not well organized)

/* preliminary machine file for DEC Alpha

  Copyright (C) 1995 Free Software Foundation, Inc.

  This file is part of Gforth.

  Gforth is free software; you can redistribute it and/or
  modify it under the terms of the GNU General Public License
  as published by the Free Software Foundation; either version 2
  of the License, or (at your option) any later version.

  This program 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, write to the Free Software
  Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
*/

/* Be careful: long long on Alpha are 64 bit :-(( */
#define LONG_LATENCY

#if !defined(USE_TOS) && !defined(USE_NO_TOS)
#define USE_TOS
#endif

#ifndef INDIRECT_THREADED
#ifndef DIRECT_THREADED
/* #define DIRECT_THREADED */
#endif
#endif

#define FLUSH_ICACHE(addr,size)		asm("call_pal 0x86") /* imb (instruction-memory barrier) */

#include "32bit.h"

#ifdef DIRECT_THREADED
#ifdef WORDS_BIGENDIAN
#error Direct threading only supported for little-endian Alphas.
/* big-endian Alphas still store instructions in little-endian format,
   so you would have to reverse the instruction accesses in the following
*/
#endif
#if SIZEOF_CHAR_P != 8
#error Direct threading only supported for Alphas with 64-bit Cells.
/* some of the stuff below assumes that the first cell in a code field
   can contain 2 instructions

   A simple way around this problem would be to have _alpha_docol
   contain &&dodoes. This would slow down colon defs, however.

   Another way is to use a special DOES_HANDLER, like most other CPUs */
#endif

#warning Direct threading for Alpha may not work with all compiler versions

typedef int Int32;
typedef short Int16;

/* PFA gives the parameter field address corresponding to a cfa */
#define PFA(cfa)	(((Cell *)cfa)+2)
/* PFA1 is a special version for use just after a NEXT1 */
/* the improvement here is that we may destroy cfa before using PFA1 */
#define PFA1(cfa)       PFA(cfa)

/*
   On the Alpha, code (in the text segment) typically cannot be
   reached from the dictionary (in the data segment) with a normal
   branch. It also usually takes too long (and too much space on
   32-bit systems) to load the address as literal and jump indirectly.
   
   So, what we do is this: a pointer into our code (at docol, to be
   exact) is kept in a register: _alpha_docol. When the innner
   interpreter jumps to the word address of a variable etc., the
   destination address is computed from that with a lda instruction
   and stored in another register: _alpha_ca. Then an indirect jump
   through _alpha_ca is performed. For docol, we need not compute
   _alpha_ca first.

   How do we tell gcc all this? We declare the registers as variables:
   _alpha_docol as explicit variable, to avoid spilling; _alpha_ca is
   so short-lived, so it hopefully won't be spilled. A
   pseudo-primitive cpu_dep is created with code that let's gcc's data
   flow analysis know that _alpha_docol is used and that _alpha_ca may
   be defined and used after any NEXT and before any primitive.  We
   let gcc choose the register for _alpha_ca and simply change the
   code gcc produces for the cpu_dep routine.
*/

#define CPU_DEP2	register Label _alpha_docol asm("$9")=&&docol; \
			register Label _alpha_ca;

#define CPU_DEP3	cpu_dep: asm("lda %0, 500(%1)":"=r"(_alpha_ca):"r"(_alpha_docol)); goto *_alpha_ca;

#define CPU_DEP1	(&&cpu_dep)


/* CODE_ADDRESS is the address of the code jumped to through the code field */
#define CODE_ADDRESS(wa)	({Int32 *_wa=(Int32 *)(wa); \
				    (_wa[0]&0xfc000000)==0x68000000 ? /*JMP?*/\
				    &&docol : \
				    &&docol+((Int16 *)_wa)[0]; })

#define _CPU_DEP_LABEL	(symbols[DOESJUMP])
#define _DOCOL_LABEL	(symbols[DOCOL])

/* MAKE_CF creates an appropriate code field at the wa; ca is the
   code address. For the Alpha, this is a lda followed by a jmp */
#define MAKE_CF(wa,ca)	({ \
			     Int32 *_wa=(Int32 *)(wa); \
			     Int32 *_ca=(Int32 *)(ca); \
			     _wa[0]=((((Int32 *)_CPU_DEP_LABEL)[0] & 0xffff0000)| \
				      ((((Cell)_ca)-((Cell)_DOCOL_LABEL)) & 0xffff)); \
			     _wa[1]=((((Int32 *)_CPU_DEP_LABEL)[1] & 0xffffc000)| \
				      (((((Cell)_ca)-((Cell)_wa)-8) & 0xffff)>>2)); \
			 })

/* this is the point where the does code for the word with the xt cfa
   starts. Because the jump to the code field takes only one cell on
   64-bit systems we can use the second cell of the cfa for storing
   the does address */
#define DOES_CODE(cfa)	((Xt *)(((Cell *)(cfa))[1]))
/* this is a special version of DOES_CODE for use in dodoes */
#define DOES_CODE1(label)	DOES_CODE(label)

/* the does handler resides between DOES> and the following Forth
   code. Since the code-field jumps directly to dodoes, the
   does-handler is not needed for the Alpha architecture */
#define DOES_HANDLER_SIZE       (2*sizeof(Cell))
#define MAKE_DOES_HANDLER(addr)   0

/* This makes a code field for a does-defined word. doesp is the
   address of the does-code. On the Alpha, the code field consists of
   a jump to dodoes and the address of the does code */
#define MAKE_DOES_CF(cfa,doesp) ({Xt *_cfa = (Xt *)(cfa); \
				    MAKE_CF(_cfa, symbols[DODOES]); \
				    _cfa[1] = (doesp); })
#endif