X-Git-Url: http://repo.macrolet.net/gitweb/?a=blobdiff_plain;f=src%2Fcompiler%2Fbackend.lisp;h=04c4e3510c1af48df08629ace4a33229dd4d1998;hb=90ca09b75fbc3b63b2f7d09c67b04b866dd783f6;hp=6c0c529214907da4ecfd807e7297f1ca58551c06;hpb=aa2dc9529460ea0d9c99998dc87283fc1a43e808;p=sbcl.git

diff --git a/src/compiler/backend.lisp b/src/compiler/backend.lisp
index 6c0c529..04c4e35 100644
--- a/src/compiler/backend.lisp
+++ b/src/compiler/backend.lisp
@@ -30,10 +30,7 @@
 
 ;;; the byte order of the target machine. :BIG-ENDIAN has the MSB first (e.g.
 ;;; IBM RT), :LITTLE-ENDIAN has the MSB last (e.g. DEC VAX).
-;;;
-;;; KLUDGE: In a sort of pun, this is also used as the value of 
-;;; BACKEND-BYTE-FASL-FILE-IMPLEMENTATION. -- WHN 20000302
-(defvar *backend-byte-order* nil)
+(defvar *backend-byte-order*)
 (declaim (type (member nil :little-endian :big-endian) *backend-byte-order*))
 
 ;;; translation from SC numbers to SC info structures. SC numbers are always
@@ -115,10 +112,6 @@
 (defvar *backend-parsed-vops* (make-hash-table :test 'eq))
 (declaim (type hash-table *backend-parsed-vops*))
 
-;;; the backend-specific aspects of the info environment
-(defvar *backend-info-environment* nil)
-(declaim (type list *backend-info-environment*))
-
 ;;; support for the assembler
 (defvar *backend-instruction-formats* (make-hash-table :test 'eq))
 (defvar *backend-instruction-flavors* (make-hash-table :test 'equal))
@@ -231,3 +224,51 @@
 ;;; the VM support routines
 (defvar *backend-support-routines* (make-vm-support-routines))
 (declaim (type vm-support-routines *backend-support-routines*))
+
+;;;; This is a prototype interface to support Christophe Rhodes' new
+;;;; (sbcl-0.pre7.57) VOP :GUARD clauses for implementations which
+;;;; depend on CPU variants, e.g. the differences between I486,
+;;;; Pentium, and Pentium Pro, or the differences between different
+;;;; SPARC versions.
+
+;;;; Christophe Rhodes' longer explanation (cut and pasted
+;;;; from CLiki SBCL internals site 2001-10-12):
+#|
+In CMUCL, the :guard argument to VOPs provided a way of disallowing
+the use of a particular VOP in compiled code. As an example, from the
+SPARC code in CMUCL,
+
+(DEFINE-VOP? (FAST-V8-TRUNCATE/SIGNED=>SIGNED? FAST-SAFE-ARITH-OP?)
+  (:TRANSLATE TRUNCATE?)
+  ...
+  (:GUARD (OR (BACKEND-FEATUREP :SPARC-V8)
+              (AND (BACKEND-FEATUREP :SPARC-V9)
+                   (NOT (BACKEND-FEATUREP :SPARC-64)))))
+  ...)
+
+and at the IR2 translation stage, the function #'`(LAMBDA () ,GUARD) would be called. 
+
+Until SBCL-0.7pre57, this is translated as 
+  (:GUARD #!+(OR :SPARC-V8 (AND :SPARC-V9 (NOT :SPARC-64))) T
+          #!-(OR :SPARC-V8 (AND :SPARC-V9 (NOT :SPARC-64))) NIL)
+which means that whether this VOP will ever be used is determined at
+compiler compile-time depending on the contents of
+*SHEBANG-FEATURES*?.
+
+As of SBCL-0.7pre57, a new special variable,
+SB-C:*BACKEND-SUBFEATURES*?, is introduced. As of that version, only
+VOPs translating %log1p? query it, and :PENTIUM-STYLE-FYL2XP1 is the
+only useful value to be pushed onto that list, for x86. This is not
+yet an ideal interface, but it does allow for compile-time
+conditionalization.
+|#
+
+;;; The default value of NIL means use only unguarded VOPs.
+(defvar *backend-subfeatures* nil)
+
+;;; possible *BACKEND-SUBFEATURES* values:
+;;;
+;;; :PENTIUM-STYLE-FYL2XP1 is a useful value for x86 SBCLs to have on
+;;; SB-C:*BACKEND-SUBFEATURES*?; it enables the use of the
+;;; %flog1p-pentium? VOP rather than the %flog1p? VOP, which is a few
+;;; instructions longer.