Fix make-array transforms.

[sbcl.git] / OPTIMIZATIONS

diff --git a/OPTIMIZATIONS b/OPTIMIZATIONS
index 0308f85..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)
@@ -173,18 +168,13 @@ NULL-TN directly.
       (declare (dynamic-extent l))
       (mapc #'print l))))
 
-Result of MAKE is not stack allocated, which means that
-stack-allocation of structures is impossible.
+Result of MAKE is not stack allocated.
 --------------------------------------------------------------------------------
 #22
 IR2 does not perform unused code flushing.
 --------------------------------------------------------------------------------
-#23
-Python does not know that &REST lists are LISTs (and cannot derive it).
---------------------------------------------------------------------------------
 #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
@@ -213,6 +203,10 @@ enough to eliminate something like ':initial-element 0'.  Such an optimization
 is valid if the vector is being allocated in the heap, but not if it is being
 allocated on the stack.  You could remove this optimization, but that makes
 the heap-allocated case somewhat slower...)
+
+To do this, extend ALLOCATE-VECTOR with ALLOW-JUNK argument, and when
+stack allocating don't zero if it is true -- and probably ALLOW-JUNK iff
+the vector is a specialized one (cannot have pointers.)
 --------------------------------------------------------------------------------
 #28
 a. Accessing raw slots in structure instances is more inefficient than
@@ -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:
@@ -311,32 +290,6 @@ using the x86 FP stack.  It would be nice if SBCL included an SSE2-based
 floating point backend with a compile-time option to switch between the
 two.
 --------------------------------------------------------------------------------
-#34
-Compiling
-
-(defun foo (x y)
-  (declare (type (integer 0 45) x y))
-  (+ x y))
-
-results in the following error trapping code for type-checking the
-arguments:
-
-;      424: L0:   8B058CE31812     MOV EAX, [#x1218E38C]      ; '(MOD 46)
-;      42A:       0F0B0A           BREAK 10                   ; error trap
-;      42D:       05               BYTE #X05
-;      42E:       1F               BYTE #X1F                  ; OBJECT-NOT-TYPE-ERROR
-;      42F:       FECE01           BYTE #XFE, #XCE, #X01      ; EDI
-;      432:       0E               BYTE #X0E                  ; EAX
-;      433: L1:   8B0590E31812     MOV EAX, [#x1218E390]      ; '(MOD 46)
-;      439:       0F0B0A           BREAK 10                   ; error trap
-;      43C:       03               BYTE #X03
-;      43D:       1F               BYTE #X1F                  ; OBJECT-NOT-TYPE-ERROR
-;      43E:       8E               BYTE #X8E                  ; EDX
-;      43F:       0E               BYTE #X0E                  ; EAX
-
-Notice that '(MOD 46) has two entries in the constant vector.  Having
-one would be preferable.
---------------------------------------------------------------------------------
 #35
 Compiling
 
@@ -416,3 +369,38 @@ currently compiles to code that ensures the TLS index at runtime, which
 is both a decently large chunk of code and unnecessary, as we could ensure
 the TLS index at load-time as well.
 
+--------------------------------------------------------------------------------
+#40
+
+When FTYPE is declared -- to say (function (t t t t t) t), and
+function has a compiler-macro,
+
+  (apply #'foo 'x1 x2 'x3 more)
+
+can be transformed into
+
+  (apply (lambda (x2 x4 x5) (foo 'x1 x2 'x3 x4 x5)) x2 more)
+
+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.