[Guile-commits] 26/41: Slower range saturation in type inference

[Andy Wingo]

wingo pushed a commit to branch master
in repository guile.

commit 672853657c3775bb822a53d65785c69c545201ab
Author: Andy Wingo <address@hidden>
Date:   Fri Nov 20 13:23:32 2015 +0100

    Slower range saturation in type inference
    
    * module/language/cps/types.scm (*max-size-t*): New definition.
      (type-entry-saturating-union): Saturate more slowly, first stopping at
      [0,*max-size-t*] then at [&range-min, &range-max] before saturating to
      [-inf.0, +inf.0].  This allows most offset phi variables to have their
      range inferred within the u64 range.
---
 module/language/cps/types.scm |   21 +++++++++++++++++++--
 1 files changed, 19 insertions(+), 2 deletions(-)

diff --git a/module/language/cps/types.scm b/module/language/cps/types.scm
index 41d4f56..543f550 100644
--- a/module/language/cps/types.scm
+++ b/module/language/cps/types.scm
@@ -206,6 +206,15 @@
 (define-compile-time-value &range-min (- #x8000000000000000))
 (define-compile-time-value &range-max    #xffffFFFFffffFFFF)
 
+;; This is a hack that takes advantage of knowing that
+;; most-positive-fixnum is the size of a word, but with two tag bits and
+;; one sign bit.  We also assume that the current common architectural
+;; restriction of a maximum 48-bit address space means that we won't see
+;; a size_t value above 2^48.
+(define *max-size-t*
+  (min (+ (ash most-positive-fixnum 3) #b111)
+       (1- (ash 1 48))))
+
 (define-inlinable (make-unclamped-type-entry type min max)
   (vector type min max))
 (define-inlinable (type-entry-type tentry)
@@ -271,10 +280,18 @@
      (logior (type-entry-type a) (type-entry-type b))
      (let ((a-min (type-entry-min a))
            (b-min (type-entry-min b)))
-       (if (< b-min a-min) -inf.0 a-min))
+       (cond
+        ((not (< b-min a-min)) a-min)
+        ((> 0 b-min) 0)
+        ((> &range-min b-min) &range-min)
+        (else -inf.0)))
      (let ((a-max (type-entry-max a))
            (b-max (type-entry-max b)))
-       (if (> b-max a-max) +inf.0 a-max))))))
+       (cond
+        ((not (> b-max a-max)) a-max)
+        ((> *max-size-t* b-max) *max-size-t*)
+        ((> &range-max b-max) &range-max)
+        (else +inf.0)))))))
 
 (define (type-entry-intersection a b)
   (cond