Fix make-array transforms.

[sbcl.git] / OPTIMIZATIONS

diff --git a/OPTIMIZATIONS b/OPTIMIZATIONS
index 581291c..42119ac 100644 (file)
--- a/OPTIMIZATIONS
+++ b/OPTIMIZATIONS
@@ -157,11 +157,6 @@ sbcl-0.8.12.30, this affects at least DUMP-OBJECT through
 COMPOUND-OBJECT-P, and (LABELS MAYBE-EMIT-MAKE-LOAD-FORMS GROVEL)
 through TYPEP UNBOXED-ARRAY, within the compiler itself.
 --------------------------------------------------------------------------------
-#18
-(lambda (x) (declare (null x)) (sxhash x)) goes through SYMBOL-HASH
-rather than either constant-folding or manipulating NIL-VALUE or
-NULL-TN directly.
---------------------------------------------------------------------------------
 #20
 (defun-with-dx foo (x)
   (flet ((make (x)
@@ -179,8 +174,7 @@ Result of MAKE is not stack allocated.
 IR2 does not perform unused code flushing.
 --------------------------------------------------------------------------------
 #24
-a. Iterations on &REST lists, returning them as VALUES could be
-   rewritten with &MORE vectors.
+a. Iterations on &REST lists could be rewritten with &MORE vectors.
 b. Implement local unknown-values mv-call (useful for fast type checking).
 --------------------------------------------------------------------------------
 #26
@@ -247,21 +241,6 @@ vm-support-routine COMBINATION-IMPLEMENTATION-STYLE and its use in
 src/compiler/ir1opt.lisp, IR1-OPTIMIZE-COMBINATION.  The above
 optimizations are left as an exercise for the reader.)
 --------------------------------------------------------------------------------
-#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.
---------------------------------------------------------------------------------
 #31
 The typecheck generated for a declaration like (integer 0 45) on x86 looks
 like:
@@ -405,3 +384,23 @@ can be transformed into
 which allows compiler-macro-expansion for FOO. (Only constant
 arguments can be moved inside the new lambda -- otherwise evaluation
 order is altered.)
+
+--------------------------------------------------------------------------------
+#41
+
+The unibyte external formats are written in a very generic way.  Three
+optimizations immediately applicable that could be automatically
+generated:
+
+(a) if the external format merely permutes the first 256 characters, a
+    constant-time lookup (rather than a binary search) could be
+    performed on output.  This applies at least to EBCDIC, which
+    currently has a hand-rolled mapper instead.
+
+(b) if there are no undefined characters corresponding to the 256
+    codes, then no error checking need be done on input.
+
+(c) if there is a way to use particular bits of the exceptional
+    characters, constant-time output (rather than binary search) can
+    still be achieved as used to be done by the latin-9 external
+    format before 1.0.31.