X-Git-Url: http://repo.macrolet.net/gitweb/?a=blobdiff_plain;f=src%2Fcompiler%2Fgeneric%2Fearly-objdef.lisp;h=ef6563c42057e7d11a7660a38833c5e560d8243a;hb=5dcf5905dc38232b3cc5ec6b309ea5c6424db957;hp=be69981154de5a24f86d9fa8214f8933539ef784;hpb=6fb6e66f531dfb6140ec3e0cc8f84f6ecd1927ca;p=sbcl.git

diff --git a/src/compiler/generic/early-objdef.lisp b/src/compiler/generic/early-objdef.lisp
index be69981..ef6563c 100644
--- a/src/compiler/generic/early-objdef.lisp
+++ b/src/compiler/generic/early-objdef.lisp
@@ -15,11 +15,27 @@
 ;;; a pain for people just learning to find their way around the code
 ;;; who want to use lexical search to figure out where things like
 ;;; EVEN-FIXNUM-LOWTAG are defined. Remove the :SUFFIXes and just expand
-;;; out the full names. Or even define them in DEF-FROB EVEN-FIXNUM-LOWTAG
+;;; out the full names. Or even define them in DEF EVEN-FIXNUM-LOWTAG
 ;;; style so searches like 'def.*even-fixnum-lowtag' can find them.
 
-;;; tags for the main low-level types, to be stored in the low three
-;;; bits to identify the type of a machine word 
+;;; Tags for the main low-level types are stored in the low three
+;;; bits to identify the type of a machine word.  Certain constraints 
+;;; apply:
+;;;   * EVEN-FIXNUM-LOWTAG and ODD-FIXNUM-LOWTAG must be 0 and 4: code
+;;;     which shifts left two places to convert raw integers to tagged
+;;;     fixnums is ubiquitous.
+;;;   * LIST-POINTER-LOWTAG + 4 = OTHER-POINTER-LOWTAG: NIL is both a
+;;;     cons and a symbol (at the same address) and depends on this.
+;;;     See the definition of SYMBOL in objdef.lisp
+;;;   * OTHER-POINTER-LOWTAG > 4: Some code in the SPARC backend,
+;;;     which uses bit 2 of the ALLOC register to indicate that
+;;;     PSEUDO-ATOMIC is on, doesn't strip the low bits of reg_ALLOC
+;;;     before ORing in OTHER-POINTER-LOWTAG within a PSEUDO-ATOMIC
+;;;     section.
+;;; (These are just the ones we know about as of sbcl-0.7.1.22. There
+;;; might easily be more, since these values have stayed highly
+;;; constrained for more than a decade, an inviting target for
+;;; inventive abstraction-phobic maintainers.:-)
 (eval-when (:compile-toplevel :load-toplevel :execute)
   ;; The EVAL-WHEN is necessary (at least for Lispworks), because the
   ;; second DEFENUM uses the value of OTHER-IMMEDIATE-0-LOWTAG, which is
@@ -42,9 +58,44 @@
 ;;; the heap types, stored in 8 bits of the header of an object on the
 ;;; heap, to identify the type of the heap object (which'll be at
 ;;; least two machine words, often more)
-(defenum (:suffix -type
-	  :start (+ (ash 1 lowtag-bits) other-immediate-0-lowtag)
-	  :step (ash 1 (1- lowtag-bits)))
+;;;
+;;; Note: the order specified here is not critical for correctness,
+;;; but (FIXME) with %TEST-HEADERS as currently defined, BIGNUM must
+;;; be first, and COMPLEX-ARRAY must be last.
+;;;
+;;; However, for efficiency, we prefer contiguous sets of widetags for
+;;; "similar" objects, so that type checking can be done with a range
+;;; check, rather than several individual checks.
+;;;
+;;; * BIGNUM + RATIO (+ FIXNUM) = RATIONAL
+;;;
+;;; * SINGLE-FLOAT + DOUBLE-FLOAT + LONG-FLOAT = FLOAT
+;;;
+;;; * RATIONAL + FLOAT = REAL
+;;;
+;;; * (FIXME: COMPLEX example, which needs fixing anyway -- see
+;;;   UPGRADED-COMPLEX-PART-TYPE)
+;;;
+;;; * SIMPLE-ARRAY-* = (SIMPLE-ARRAY * (*))
+;;;
+;;; * SIMPLE-ARRAY-NIL + SIMPLE-BASE-STRING = SIMPLE-STRING
+;;;
+;;; * SIMPLE-ARRAY + COMPLEX-ARRAYOID = (SATISFIES ARRAY-HEADER-P)
+;;;
+;;; In addition, with
+;;; sufficient care we can cause extra combinations to appear with
+;;; differences in only one bit, permitting a more efficient type
+;;; test.  As an example, if SIMPLE-BASE-STRING = 0xA6 and
+;;; COMPLEX-BASE-STRING = 0xE6, then the type test for BASE-STRING is
+;;;
+;;;   AND   tag, ~0x40, tag
+;;;   ANDcc tag,  0xA6, tag
+;;;   JNE   tag, label
+;;;
+;;; rather than two separate tests and jumps 
+(defenum (:suffix -widetag
+	  :start (+ (ash 1 n-lowtag-bits) other-immediate-0-lowtag)
+	  :step (ash 1 (1- n-lowtag-bits)))
   bignum
   ratio
   single-float
@@ -55,14 +106,49 @@
   complex-double-float
   #!+long-float complex-long-float
 
-  simple-array
-  simple-string
-  simple-bit-vector
-  simple-vector
+  code-header
+  simple-fun-header
+  closure-header
+  funcallable-instance-header
+
+  return-pc-header
+  value-cell-header
+  symbol-header
+  base-char
+  sap
+  unbound-marker
+  weak-pointer
+  instance-header
+  fdefn
+
+  unused00
+  unused01
+  unused02
+  unused03
+  unused04
+  unused05
+  unused06
+  unused07
+  #!-long-float unused08
+  #!-long-float unused09
+  
+  #!+long-float simple-array-long-float
+  #!+long-float simple-array-complex-long-float
+  #!-long-float unused10
+  #!-long-float unused11
+
   simple-array-unsigned-byte-2
   simple-array-unsigned-byte-4
+  simple-array-unsigned-byte-7
   simple-array-unsigned-byte-8
+  simple-array-unsigned-byte-15
   simple-array-unsigned-byte-16
+  simple-array-nil
+  simple-base-string
+  simple-bit-vector
+  simple-vector
+  simple-array-unsigned-byte-29
+  simple-array-unsigned-byte-31
   simple-array-unsigned-byte-32
   simple-array-signed-byte-8
   simple-array-signed-byte-16
@@ -70,30 +156,15 @@
   simple-array-signed-byte-32
   simple-array-single-float
   simple-array-double-float
-  #!+long-float simple-array-long-float
   simple-array-complex-single-float
   simple-array-complex-double-float
-  #!+long-float simple-array-complex-long-float
-  complex-string
+  simple-array
+  complex-vector-nil
+  complex-base-string
   complex-bit-vector
   complex-vector
   complex-array
-
-  code-header
-  simple-fun-header
-  closure-header
-  funcallable-instance-header
-  closure-fun-header
-
-  return-pc-header
-  value-cell-header
-  symbol-header
-  base-char
-  sap
-  unbound-marker
-  weak-pointer
-  instance-header
-  fdefn)
+)
 
 ;;; the different vector subtypes
 (defenum (:prefix vector- :suffix -subtype)