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Fix 64->32 bit cross-compilation of large-ish fixnums

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* module/system/vm/assembler.scm (immediate-bits): Fix a bug whereby
  compiling to a 32-bit target from a 64-bit host would treat all
  integers whose representation fit into 32 bits as immediates.  This
  would result in integer constants between #x20000000 and 0x3fffffff
  being residualized in such a way that they would be loaded as negative
  numbers.
This commit is contained in:
Andy Wingo 2016-06-17 15:05:39 +02:00
commit 8b87567085
1 changed files with 23 additions and 23 deletions
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46
module/system/vm/assembler.scm
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@ -939,32 +939,32 @@ lists. This procedure can be called many times before calling
;;; to the table.
;;;
(define tc2-int 2)
(define (immediate-bits asm x)
"Return the bit pattern to write into the buffer if @var{x} is
immediate, and @code{#f} otherwise."
(let* ((bits (object-address x))
(mask (case (asm-word-size asm)
((4) #xffffffff)
((8) #xffffffffFFFFFFFF)
(else (error "unexpected word size"))))
(fixnum-min (1- (ash mask -3)))
(fixnum-max (ash mask -3)))
(cond
((not (zero? (logand bits 6)))
;; Object is an immediate on the host. It's immediate if it can
;; fit into a word on the target.
(and (= bits (logand bits mask))
bits))
((and (exact-integer? x) (<= fixnum-min x fixnum-max))
;; Object is a bignum that would be an immediate on the target.
(let ((fixnum-bits (if (negative? x)
(+ fixnum-max 1 (logand x fixnum-max))
x)))
(logior (ash x 2) tc2-int)))
(else
;; Otherwise not an immediate.
#f))))
(define tc2-int 2)
(if (exact-integer? x)
;; Object is an immediate if it is a fixnum on the target.
(call-with-values (lambda ()
(case (asm-word-size asm)
((4) (values #x1fffffff
(- #x20000000)))
((8) (values #x1fffffffFFFFFFFF
(- #x2000000000000000)))
(else (error "unexpected word size"))))
(lambda (fixnum-min fixnum-max)
(and (<= fixnum-min x fixnum-max)
(let ((fixnum-bits (if (negative? x)
(+ fixnum-max 1 (logand x fixnum-max))
x)))
(logior (ash fixnum-bits 2) tc2-int)))))
;; Otherwise, the object will be immediate on the target if and
;; only if it is immediate on the host. Except for integers,
;; which we handle specially above, any immediate value is an
;; immediate on both 32-bit and 64-bit targets.
(let ((bits (object-address x)))
(and (not (zero? (logand bits 6)))
bits))))
(define-record-type <stringbuf>
(make-stringbuf string)