X-Git-Url: http://repo.macrolet.net/gitweb/?a=blobdiff_plain;f=OPTIMIZATIONS;h=0c8e790a86ae463ece5795b9fcaac1d1312cf8b3;hb=2e86a718672b73c942e51dfbda7eb9db8746b6f4;hp=53438ab4a996f18951a81d5f7b69e453200b522a;hpb=f846a7a310d630cf538811959916492a28a75fb1;p=sbcl.git

diff --git a/OPTIMIZATIONS b/OPTIMIZATIONS
index 53438ab..0c8e790 100644
--- a/OPTIMIZATIONS
+++ b/OPTIMIZATIONS
@@ -187,9 +187,9 @@ stack-allocation of structures is impossible.
 --------------------------------------------------------------------------------
 #21
 (defun-with-dx foo ()
-  (let ((dx (list (list 1 2) (list 3 4)
+  (let ((dx (list (list 1 2) (list 3 4))))
     (declare (dynamic-extent dx))
-    ...)))))
+    ...))
 
 External list in DX is allocated on stack, but internal are not.
 --------------------------------------------------------------------------------
@@ -204,20 +204,6 @@ a. Iterations on &REST lists, returning them as VALUES could be
    rewritten with &MORE vectors.
 b. Implement local unknown-values mv-call (useful for fast type checking).
 --------------------------------------------------------------------------------
-#25
-EQL is implemented generically in situations where this isn't necessary.
-
-(defun f (x y)
-  (declare (type (or symbol fixnum) x)
-	   (optimize speed (safety 0) (debug 0)))
-  (eql x y))
-
-SUBTYPEP is smart enough to determine that this type is a subtype
-of (and (or (not number) fixnum) (not character))
-
-This sitation where the type is (OR NULL FIXNUM) comes up
-in cl-bench, for example in the value returned by POSITION.
---------------------------------------------------------------------------------
 #26
 SBCL cannot derive upper bound for I and uses generic arithmetic here:
 
@@ -232,3 +218,65 @@ SBCL cannot derive upper bound for I and uses generic arithmetic here:
 
 (So the constraint propagator or a possible future SSA-convertor
 should know the connection between an NLE and its CLEANUP.)
+--------------------------------------------------------------------------------
+#27
+Initialization of stack-allocated arrays is inefficient: we always
+fill the vector with zeroes, even when it is not needed (as for
+platforms with conservative GC or for arrays of unboxed objectes) and
+is performed later explicitely.
+--------------------------------------------------------------------------------
+#28
+a. Accessing raw slots in structure instances is more inefficient than
+it could be; if we placed raw slots before the header word, we would
+not need to do arithmetic at runtime to access them.  (But beware:
+this would complicate handling of the interior pointer).
+
+b. (Also note that raw slots are currently disabled on HPPA)
+--------------------------------------------------------------------------------
+#29
+Python is overly zealous when converting high-level CL functions, such
+as MIN/MAX, LOGBITP, and LOGTEST, to low-level CL functions.  Reducing
+Python's aggressiveness would make it easier to effect changes such as
+
+x86-64:
+* direct MIN/MAX on {SINGLE,DOUBLE}-FLOATs ({MIN,MAX}S{S,D})
+
+x86{,-64}:
+* direct LOGBITP on word-sized integers and fixnums (BT + JC)
+
+x86{,-64}/PPC:
+* branch-free MIN/MAX on word-sized integers and fixnums
+* efficient LOGTESTs on word-sized integers and fixnums (TEST / AND.)
+
+PPC:
+* efficient LDB on word-sized integers and fixnums (RLWINM)
+
+etc., etc.
+
+The "easier" part claimed above would come about because the functions
+would be available for :TRANSLATE through a VOP or similar, whereas with
+the current architecture, one would have to pattern-match IR1.  While
+IR1 pattern-matching would be useful in other contexts, it seems better
+here to attempt the direct :TRANSLATE route.
+
+I (NJF) don't know how to implement such architecture-specific
+optimizations whilst keeping the high->low transformations for other
+architectures.  Certainly adding #!+/- magic in compiler/*.lisp could be
+done, but such a solution is somewhat inelegant.  Moving the relevant
+DEFTRANSFORMs to the architecture-specific compiler/* areas is also
+possible, but that would duplicate quite a bit of code.
+--------------------------------------------------------------------------------
+#30
+(defun foo (x y)
+  (< x y))
+
+FOO's IR1 representation is roughly:
+
+(defun foo (x y)
+  (if (< x y)
+      T
+      NIL))
+
+However, if a full call is generated for < (and similarly for other
+predicate functions), then the IF is unnecessary, since the return value
+of (< x y) is already T or NIL.