src/compiler/early-assem.lisp

   1 ;;;; constants and types for assembly
   2
   3 ;;;; This software is part of the SBCL system. See the README file for
   4 ;;;; more information.
   5 ;;;;
   6 ;;;; This software is derived from the CMU CL system, which was
   7 ;;;; written at Carnegie Mellon University and released into the
   8 ;;;; public domain. The software is in the public domain and is
   9 ;;;; provided with absolutely no warranty. See the COPYING and CREDITS
  10 ;;;; files for more information.
  11
  12 (in-package "SB!ASSEM")
  13
  14 ;;; FIXME: It might make sense to use SB!VM:BYTE-FOO values here
  15 ;;; instead of the various ASSEMBLY-UNIT-FOO things, and then define a
  16 ;;; BYTE type. One problem: BYTE is exported from the CL package, so
  17 ;;; ANSI says that we're not supposed to be attaching any new meanings
  18 ;;; to it. Perhaps rename SB!VM:BYTE-FOO to SB!VM:VMBYTE-FOO or
  19 ;;; SB!VM:VM-BYTE-FOO, and then define the SB!VM:VMBYTE or
  20 ;;; SB!VM:VM-BYTE types?
  21 ;;;
  22 ;;; If this was done, some of this file could go away, and the rest
  23 ;;; could probably be merged back into assem.lisp. (This file was
  24 ;;; created simply in order to move the ASSEMBLY-UNIT-related
  25 ;;; definitions before compiler/generic/core.lisp in the build
  26 ;;; sequence.)
  27
  28 ;;; ASSEMBLY-UNIT-BITS -- the number of bits in the minimum assembly
  29 ;;; unit, (also referred to as a ``byte''). Hopefully, different
  30 ;;; instruction sets won't require changing this.
  31 (def!constant assembly-unit-bits 8)
  32 (def!constant assembly-unit-mask (1- (ash 1 assembly-unit-bits)))
  33
  34 (def!type assembly-unit ()
  35   `(unsigned-byte ,assembly-unit-bits))
  36
  37 ;;; Some functions which accept assembly units can meaningfully accept
  38 ;;; signed values with the same number of bits and silently munge them
  39 ;;; into appropriate unsigned values. (This is handy behavior e.g.
  40 ;;; when assembling branch instructions on the X86.)
  41 (def!type possibly-signed-assembly-unit ()
  42   `(or assembly-unit
  43        (signed-byte ,assembly-unit-bits)))
  44
  45 ;;; the maximum alignment we can guarantee given the object format. If
  46 ;;; the loader only loads objects 8-byte aligned, we can't do any
  47 ;;; better then that ourselves.
  48 (def!constant max-alignment sb!vm:n-lowtag-bits)
  49
  50 (def!type alignment ()
  51   `(integer 0 ,max-alignment))