[Guile-commits] 10/11: Port effects analysis to CPS2

[Andy Wingo]

wingo pushed a commit to branch master
in repository guile.

commit 80c162b67cdc546ad9908a6023c3331a934ab7a7
Author: Andy Wingo <address@hidden>
Date:   Thu May 14 16:35:26 2015 +0200

    Port effects analysis to CPS2
    
    * module/Makefile.am (CPS2_LANG_SOURCES): Add effects-analysis.scm.
    * module/language/cps2/effects-analysis.scm: New file, based on
      cps/effects-analysis.scm.
    * module/language/cps2/utils.scm (intmap-map):
      (compute-defining-expressions, compute-constant-values): New helpers.
---
 module/Makefile.am                        |    1 +
 module/language/cps2/effects-analysis.scm |  484 +++++++++++++++++++++++++++++
 module/language/cps2/utils.scm            |   39 +++-
 3 files changed, 523 insertions(+), 1 deletions(-)

diff --git a/module/Makefile.am b/module/Makefile.am
index 145b04f..6c6830f 100644
--- a/module/Makefile.am
+++ b/module/Makefile.am
@@ -149,6 +149,7 @@ CPS_LANG_SOURCES =                                          
\
 CPS2_LANG_SOURCES =                                            \
   language/cps2.scm                                            \
   language/cps2/compile-cps.scm                                        \
+  language/cps2/effects-analysis.scm                           \
   language/cps2/renumber.scm                                   \
   language/cps2/optimize.scm                                   \
   language/cps2/simplify.scm                                   \
diff --git a/module/language/cps2/effects-analysis.scm 
b/module/language/cps2/effects-analysis.scm
new file mode 100644
index 0000000..a41c5f2
--- /dev/null
+++ b/module/language/cps2/effects-analysis.scm
@@ -0,0 +1,484 @@
+;;; Effects analysis on CPS
+
+;; Copyright (C) 2011, 2012, 2013, 2014, 2015 Free Software Foundation, Inc.
+
+;;;; This library is free software; you can redistribute it and/or
+;;;; modify it under the terms of the GNU Lesser General Public
+;;;; License as published by the Free Software Foundation; either
+;;;; version 3 of the License, or (at your option) any later version.
+;;;; 
+;;;; This library is distributed in the hope that it will be useful,
+;;;; but WITHOUT ANY WARRANTY; without even the implied warranty of
+;;;; MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+;;;; Lesser General Public License for more details.
+;;;; 
+;;;; You should have received a copy of the GNU Lesser General Public
+;;;; License along with this library; if not, write to the Free Software
+;;;; Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 
USA
+
+;;; Commentary:
+;;;
+;;; A helper module to compute the set of effects caused by an
+;;; expression.  This information is useful when writing algorithms that
+;;; move code around, while preserving the semantics of an input
+;;; program.
+;;;
+;;; The effects set is represented as an integer with three parts.  The
+;;; low 4 bits indicate effects caused by an expression, as a bitfield.
+;;; The next 4 bits indicate the kind of memory accessed by the
+;;; expression, if it accesses mutable memory.  Finally the rest of the
+;;; bits indicate the field in the object being accessed, if known, or
+;;; -1 for unknown.
+;;;
+;;; In this way we embed a coarse type-based alias analysis in the
+;;; effects analysis.  For example, a "car" call is modelled as causing
+;;; a read to field 0 on a &pair, and causing a &type-check effect.  If
+;;; any intervening code sets the car of any pair, that will block
+;;; motion of the "car" call, because any write to field 0 of a pair is
+;;; seen by effects analysis as being a write to field 0 of all pairs.
+;;;
+;;; Code:
+
+(define-module (language cps2 effects-analysis)
+  #:use-module (language cps2)
+  #:use-module (language cps2 utils)
+  #:use-module (language cps intmap)
+  #:use-module (ice-9 match)
+  #:export (expression-effects
+            compute-effects
+            synthesize-definition-effects
+
+            &allocation
+            &type-check
+            &read
+            &write
+
+            &fluid
+            &prompt
+            &car
+            &cdr
+            &vector
+            &box
+            &module
+            &struct
+            &string
+            &bytevector
+
+            &object
+            &field
+
+            &allocate
+            &read-object
+            &read-field
+            &write-object
+            &write-field
+
+            &no-effects
+            &all-effects
+
+            exclude-effects
+            effect-free?
+            constant?
+            causes-effect?
+            causes-all-effects?
+            effect-clobbers?))
+
+(define-syntax define-flags
+  (lambda (x)
+    (syntax-case x ()
+      ((_ all shift name ...)
+       (let ((count (length #'(name ...))))
+         (with-syntax (((n ...) (iota count))
+                       (count count))
+           #'(begin
+               (define-syntax name (identifier-syntax (ash 1 n)))
+               ...
+               (define-syntax all (identifier-syntax (1- (ash 1 count))))
+               (define-syntax shift (identifier-syntax count)))))))))
+
+(define-syntax define-enumeration
+  (lambda (x)
+    (define (count-bits n)
+      (let lp ((out 1))
+        (if (< n (ash 1 (1- out)))
+            out
+            (lp (1+ out)))))
+    (syntax-case x ()
+      ((_ mask shift name ...)
+       (let* ((len (length #'(name ...)))
+              (bits (count-bits len)))
+         (with-syntax (((n ...) (iota len))
+                       (bits bits))
+           #'(begin
+               (define-syntax name (identifier-syntax n))
+               ...
+               (define-syntax mask (identifier-syntax (1- (ash 1 bits))))
+               (define-syntax shift (identifier-syntax bits)))))))))
+
+(define-flags &all-effect-kinds &effect-kind-bits
+  ;; Indicates that an expression may cause a type check.  A type check,
+  ;; for the purposes of this analysis, is the possibility of throwing
+  ;; an exception the first time an expression is evaluated.  If the
+  ;; expression did not cause an exception to be thrown, users can
+  ;; assume that evaluating the expression again will not cause an
+  ;; exception to be thrown.
+  ;;
+  ;; For example, (+ x y) might throw if X or Y are not numbers.  But if
+  ;; it doesn't throw, it should be safe to elide a dominated, common
+  ;; subexpression (+ x y).
+  &type-check
+
+  ;; Indicates that an expression may return a fresh object.  The kind
+  ;; of object is indicated in the object kind field.
+  &allocation
+
+  ;; Indicates that an expression may cause a read from memory.  The
+  ;; kind of memory is given in the object kind field.  Some object
+  ;; kinds have finer-grained fields; those are expressed in the "field"
+  ;; part of the effects value.  -1 indicates "the whole object".
+  &read
+
+  ;; Indicates that an expression may cause a write to memory.
+  &write)
+
+(define-enumeration &memory-kind-mask &memory-kind-bits
+  ;; Indicates than an expression may access unknown kinds of memory.
+  &unknown-memory-kinds
+
+  ;; Indicates that an expression depends on the value of a fluid
+  ;; variable, or on the current fluid environment.
+  &fluid
+
+  ;; Indicates that an expression depends on the current prompt
+  ;; stack.
+  &prompt
+
+  ;; Indicates that an expression depends on the value of the car or cdr
+  ;; of a pair.
+  &pair
+
+  ;; Indicates that an expression depends on the value of a vector
+  ;; field.  The effect field indicates the specific field, or zero for
+  ;; an unknown field.
+  &vector
+
+  ;; Indicates that an expression depends on the value of a variable
+  ;; cell.
+  &box
+
+  ;; Indicates that an expression depends on the current module.
+  &module
+
+  ;; Indicates that an expression depends on the value of a struct
+  ;; field.  The effect field indicates the specific field, or zero for
+  ;; an unknown field.
+  &struct
+
+  ;; Indicates that an expression depends on the contents of a string.
+  &string
+
+  ;; Indicates that an expression depends on the contents of a
+  ;; bytevector.  We cannot be more precise, as bytevectors may alias
+  ;; other bytevectors.
+  &bytevector)
+
+(define-inlinable (&field kind field)
+  (ash (logior (ash field &memory-kind-bits) kind) &effect-kind-bits))
+(define-inlinable (&object kind)
+  (&field kind -1))
+
+(define-inlinable (&allocate kind)
+  (logior &allocation (&object kind)))
+(define-inlinable (&read-field kind field)
+  (logior &read (&field kind field)))
+(define-inlinable (&read-object kind)
+  (logior &read (&object kind)))
+(define-inlinable (&write-field kind field)
+  (logior &write (&field kind field)))
+(define-inlinable (&write-object kind)
+  (logior &write (&object kind)))
+
+(define-syntax &no-effects (identifier-syntax 0))
+(define-syntax &all-effects
+  (identifier-syntax
+   (logior &all-effect-kinds (&object &unknown-memory-kinds))))
+
+(define-inlinable (constant? effects)
+  (zero? effects))
+
+(define-inlinable (causes-effect? x effects)
+  (not (zero? (logand x effects))))
+
+(define-inlinable (causes-all-effects? x)
+  (eqv? x &all-effects))
+
+(define (effect-clobbers? a b)
+  "Return true if A clobbers B.  This is the case if A is a write, and B
+is or might be a read or a write to the same location as A."
+  (define (locations-same?)
+    (let ((a (ash a (- &effect-kind-bits)))
+          (b (ash b (- &effect-kind-bits))))
+      (or (eqv? &unknown-memory-kinds (logand a &memory-kind-mask))
+          (eqv? &unknown-memory-kinds (logand b &memory-kind-mask))
+          (and (eqv? (logand a &memory-kind-mask) (logand b &memory-kind-mask))
+               ;; A negative field indicates "the whole object".
+               ;; Non-negative fields indicate only part of the object.
+               (or (< a 0) (< b 0) (= a b))))))
+  (and (not (zero? (logand a &write)))
+       (not (zero? (logand b (logior &read &write))))
+       (locations-same?)))
+
+(define-inlinable (indexed-field kind var constants)
+  (let ((val (intmap-ref constants var (lambda (_) #f))))
+    (if (and (exact-integer? val) (<= 0 val))
+        (&field kind val)
+        (&object kind))))
+
+(define *primitive-effects* (make-hash-table))
+
+(define-syntax-rule (define-primitive-effects* constants
+                      ((name . args) effects ...)
+                      ...)
+  (begin
+    (hashq-set! *primitive-effects* 'name
+                (case-lambda*
+                 ((constants . args) (logior effects ...))
+                 (_ &all-effects)))
+    ...))
+
+(define-syntax-rule (define-primitive-effects ((name . args) effects ...) ...)
+  (define-primitive-effects* constants ((name . args) effects ...) ...))
+
+;; Miscellaneous.
+(define-primitive-effects
+  ((values . _)))
+
+;; Generic effect-free predicates.
+(define-primitive-effects
+  ((eq? . _))
+  ((eqv? . _))
+  ((equal? . _))
+  ((pair? arg))
+  ((null? arg))
+  ((nil? arg ))
+  ((symbol? arg))
+  ((variable? arg))
+  ((vector? arg))
+  ((struct? arg))
+  ((string? arg))
+  ((number? arg))
+  ((char? arg))
+  ((bytevector? arg))
+  ((keyword? arg))
+  ((bitvector? arg))
+  ((procedure? arg))
+  ((thunk? arg)))
+
+;; Fluids.
+(define-primitive-effects
+  ((fluid-ref f)                   (&read-object &fluid)       &type-check)
+  ((fluid-set! f v)                (&write-object &fluid)      &type-check)
+  ((push-fluid f v)                (&write-object &fluid)      &type-check)
+  ((pop-fluid)                     (&write-object &fluid)      &type-check))
+
+;; Prompts.
+(define-primitive-effects
+  ((make-prompt-tag #:optional arg) (&allocate &unknown-memory-kinds)))
+
+;; Pairs.
+(define-primitive-effects
+  ((cons a b)                      (&allocate &pair))
+  ((list . _)                      (&allocate &pair))
+  ((car x)                         (&read-field &pair 0)       &type-check)
+  ((set-car! x y)                  (&write-field &pair 0)      &type-check)
+  ((cdr x)                         (&read-field &pair 1)       &type-check)
+  ((set-cdr! x y)                  (&write-field &pair 1)      &type-check)
+  ((memq x y)                      (&read-object &pair)        &type-check)
+  ((memv x y)                      (&read-object &pair)        &type-check)
+  ((list? arg)                     (&read-field &pair 1))
+  ((length l)                      (&read-field &pair 1)       &type-check))
+
+;; Variables.
+(define-primitive-effects
+  ((box v)                         (&allocate &box))
+  ((box-ref v)                     (&read-object &box)         &type-check)
+  ((box-set! v x)                  (&write-object &box)        &type-check))
+
+;; Vectors.
+(define (vector-field n constants)
+  (indexed-field &vector n constants))
+(define (read-vector-field n constants)
+  (logior &read (vector-field n constants)))
+(define (write-vector-field n constants)
+  (logior &write (vector-field n constants)))
+(define-primitive-effects* constants
+  ((vector . _)                    (&allocate &vector))
+  ((make-vector n init)            (&allocate &vector)         &type-check)
+  ((make-vector/immediate n init)  (&allocate &vector))
+  ((vector-ref v n)                (read-vector-field n constants) &type-check)
+  ((vector-ref/immediate v n)      (read-vector-field n constants) &type-check)
+  ((vector-set! v n x)             (write-vector-field n constants) 
&type-check)
+  ((vector-set!/immediate v n x)   (write-vector-field n constants) 
&type-check)
+  ((vector-length v)                                           &type-check))
+
+;; Structs.
+(define (struct-field n constants)
+  (indexed-field &struct n constants))
+(define (read-struct-field n constants)
+  (logior &read (struct-field n constants)))
+(define (write-struct-field n constants)
+  (logior &write (struct-field n constants)))
+(define-primitive-effects* constants
+  ((allocate-struct vt n)          (&allocate &struct)         &type-check)
+  ((allocate-struct/immediate v n) (&allocate &struct)         &type-check)
+  ((make-struct vt ntail . _)      (&allocate &struct)         &type-check)
+  ((make-struct/no-tail vt . _)    (&allocate &struct)         &type-check)
+  ((struct-ref s n)                (read-struct-field n constants) &type-check)
+  ((struct-ref/immediate s n)      (read-struct-field n constants) &type-check)
+  ((struct-set! s n x)             (write-struct-field n constants) 
&type-check)
+  ((struct-set!/immediate s n x)   (write-struct-field n constants) 
&type-check)
+  ((struct-vtable s)                                           &type-check))
+
+;; Strings.
+(define-primitive-effects
+  ((string-ref s n)                (&read-object &string)      &type-check)
+  ((string-set! s n c)             (&write-object &string)     &type-check)
+  ((number->string _)              (&allocate &string)         &type-check)
+  ((string->number _)              (&read-object &string)      &type-check)
+  ((string-length s)                                           &type-check))
+
+;; Bytevectors.
+(define-primitive-effects
+  ((bytevector-length _)                                       &type-check)
+
+  ((bv-u8-ref bv n)                (&read-object &bytevector)  &type-check)
+  ((bv-s8-ref bv n)                (&read-object &bytevector)  &type-check)
+  ((bv-u16-ref bv n)               (&read-object &bytevector)  &type-check)
+  ((bv-s16-ref bv n)               (&read-object &bytevector)  &type-check)
+  ((bv-u32-ref bv n)               (&read-object &bytevector)  &type-check)
+  ((bv-s32-ref bv n)               (&read-object &bytevector)  &type-check)
+  ((bv-u64-ref bv n)               (&read-object &bytevector)  &type-check)
+  ((bv-s64-ref bv n)               (&read-object &bytevector)  &type-check)
+  ((bv-f32-ref bv n)               (&read-object &bytevector)  &type-check)
+  ((bv-f64-ref bv n)               (&read-object &bytevector)  &type-check)
+
+  ((bv-u8-set! bv n x)             (&write-object &bytevector) &type-check)
+  ((bv-s8-set! bv n x)             (&write-object &bytevector) &type-check)
+  ((bv-u16-set! bv n x)            (&write-object &bytevector) &type-check)
+  ((bv-s16-set! bv n x)            (&write-object &bytevector) &type-check)
+  ((bv-u32-set! bv n x)            (&write-object &bytevector) &type-check)
+  ((bv-s32-set! bv n x)            (&write-object &bytevector) &type-check)
+  ((bv-u64-set! bv n x)            (&write-object &bytevector) &type-check)
+  ((bv-s64-set! bv n x)            (&write-object &bytevector) &type-check)
+  ((bv-f32-set! bv n x)            (&write-object &bytevector) &type-check)
+  ((bv-f64-set! bv n x)            (&write-object &bytevector) &type-check))
+
+;; Modules.
+(define-primitive-effects
+  ((current-module)                (&read-object &module))
+  ((cache-current-module! m scope) (&write-object &box))
+  ((resolve name bound?)           (&read-object &module)      &type-check)
+  ((cached-toplevel-box scope name bound?)                     &type-check)
+  ((cached-module-box mod name public? bound?)                 &type-check)
+  ((define! name val)              (&read-object &module) (&write-object 
&box)))
+
+;; Numbers.
+(define-primitive-effects
+  ((= . _)                         &type-check)
+  ((< . _)                         &type-check)
+  ((> . _)                         &type-check)
+  ((<= . _)                        &type-check)
+  ((>= . _)                        &type-check)
+  ((zero? . _)                     &type-check)
+  ((add . _)                       &type-check)
+  ((mul . _)                       &type-check)
+  ((sub . _)                       &type-check)
+  ((div . _)                       &type-check)
+  ((sub1 . _)                      &type-check)
+  ((add1 . _)                      &type-check)
+  ((quo . _)                       &type-check)
+  ((rem . _)                       &type-check)
+  ((mod . _)                       &type-check)
+  ((complex? _)                    &type-check)
+  ((real? _)                       &type-check)
+  ((rational? _)                   &type-check)
+  ((inf? _)                        &type-check)
+  ((nan? _)                        &type-check)
+  ((integer? _)                    &type-check)
+  ((exact? _)                      &type-check)
+  ((inexact? _)                    &type-check)
+  ((even? _)                       &type-check)
+  ((odd? _)                        &type-check)
+  ((ash n m)                       &type-check)
+  ((logand . _)                    &type-check)
+  ((logior . _)                    &type-check)
+  ((logxor . _)                    &type-check)
+  ((lognot . _)                    &type-check)
+  ((logtest a b)                   &type-check)
+  ((logbit? a b)                   &type-check)
+  ((sqrt _)                        &type-check)
+  ((abs _)                         &type-check))
+
+;; Characters.
+(define-primitive-effects
+  ((char<? . _)                    &type-check)
+  ((char<=? . _)                   &type-check)
+  ((char>=? . _)                   &type-check)
+  ((char>? . _)                    &type-check)
+  ((integer->char _)               &type-check)
+  ((char->integer _)               &type-check))
+
+(define (primitive-effects constants name args)
+  (let ((proc (hashq-ref *primitive-effects* name)))
+    (if proc
+        (apply proc constants args)
+        &all-effects)))
+
+(define (expression-effects exp constants)
+  (match exp
+    ((or ($ $const) ($ $prim) ($ $values))
+     &no-effects)
+    ((or ($ $fun) ($ $rec))
+     (&allocate &unknown-memory-kinds))
+    (($ $prompt)
+     (&write-object &prompt))
+    ((or ($ $call) ($ $callk))
+     &all-effects)
+    (($ $branch k exp)
+     (expression-effects exp constants))
+    (($ $primcall name args)
+     (primitive-effects constants name args))))
+
+(define (compute-effects conts)
+  (let ((constants (compute-constant-values conts)))
+    (intmap-map
+     (lambda (label cont)
+       (match cont
+         (($ $kargs names syms ($ $continue k src exp))
+          (expression-effects exp constants))
+         (($ $kreceive arity kargs)
+          (match arity
+            (($ $arity _ () #f () #f) &type-check)
+            (($ $arity () () _ () #f) (&allocate &pair))
+            (($ $arity _ () _ () #f) (logior (&allocate &pair) &type-check))))
+         (($ $kfun) &type-check)
+         (($ $kclause) &type-check)
+         (($ $ktail) &no-effects)))
+     conts)))
+
+;; There is a way to abuse effects analysis in CSE to also do scalar
+;; replacement, effectively adding `car' and `cdr' expressions to `cons'
+;; expressions, and likewise with other constructors and setters.  This
+;; routine adds appropriate effects to `cons' and `set-car!' and the
+;; like.
+;;
+;; This doesn't affect CSE's ability to eliminate expressions, given
+;; that allocations aren't eliminated anyway, and the new effects will
+;; just cause the allocations not to commute with e.g. set-car!  which
+;; is what we want anyway.
+(define (synthesize-definition-effects effects)
+  (intmap-map (lambda (label fx)
+                (if (logtest (logior &write &allocation) fx)
+                    (logior fx &read)
+                    fx))
+              effects))
diff --git a/module/language/cps2/utils.scm b/module/language/cps2/utils.scm
index c1fcd39..bf20c95 100644
--- a/module/language/cps2/utils.scm
+++ b/module/language/cps2/utils.scm
@@ -37,13 +37,15 @@
 
             ;; Various utilities.
             fold1 fold2
+            intmap-map
             intset->intmap
             worklist-fold
             fixpoint
 
             ;; Flow analysis.
-            compute-predecessors
+            compute-constant-values
             compute-function-body
+            compute-predecessors
             compute-idoms
             compute-dom-edges
             ))
@@ -102,6 +104,14 @@
          (lambda (s0 s1)
            (lp l s0 s1)))))))
 
+(define (intmap-map proc map)
+  (persistent-intmap
+   (intmap-fold (lambda (k v out)
+                  (intmap-add! out k (proc k v)
+                               (lambda (old new) new)))
+                map
+                map)))
+
 (define (intset->intmap f set)
   (persistent-intmap
    (intset-fold (lambda (label preds)
@@ -135,6 +145,33 @@
                (values x0* x1*)
                (lp x0* x1*))))))))
 
+(define (compute-defining-expressions conts)
+  (define (meet-defining-expressions old new)
+    ;; If there are multiple definitions, punt and
+    ;; record #f.
+    #f)
+  (persistent-intmap
+   (intmap-fold (lambda (label cont defs)
+                  (match cont
+                    (($ $kargs _ _ ($continue k exp))
+                     (match (intmap-ref conts k)
+                       (($ $kargs (_) (var))
+                        (intmap-add! defs var exp meet-defining-expressions))
+                       (_ defs)))
+                    (_ defs)))
+                conts
+                empty-intmap)))
+
+(define (compute-constant-values conts)
+  (persistent-intmap
+   (intmap-fold (lambda (var exp out)
+                  (match exp
+                    (($ $const val)
+                     (intmap-add! out var val))
+                    (_ out)))
+                (compute-defining-expressions conts)
+                empty-intmap)))
+
 (define (compute-function-body conts kfun)
   (persistent-intset
    (let visit-cont ((label kfun) (labels empty-intset))