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Chez Scheme: improve repair for arm32 return-address reference

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Since the offset is always a multiple of 4, expand the range of
compactly encoded offsets.
This commit is contained in:
Matthew Flatt 2020-09-03 06:42:22 -06:00
parent f5895ebc97
commit 3f0631116a
2 changed files with 20 additions and 9 deletions
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14
racket/src/ChezScheme/s/arm32.ss
View File

@ -1674,10 +1674,14 @@
(bitwise-arithmetic-shift-left (logand n #xffffff) 8)
(bitwise-arithmetic-shift-right n 24)))))))))
;; A region of funky12 where there's no number that fits when a smaller number doesn't
(define connected-funky12
;; restrict funky12 so that an code offset n will not fit
;; if a smaller offset wouldn't fit, which prevents bouncing
;; in the loop that computes label offsets
(define code-offset-funky12
(lambda (n)
(and (fixnum? n) (#%$fxu< n #x100)
(safe-assert (and (fixnum? n) (fx= 0 (fxand n 3))))
(and (fixnum? n)
(#%$fxu< n #x400)
(funky12 n))))
(define shift-count?
@ -2192,11 +2196,11 @@
(let ([incr-offset (adjust-return-point-offset incr-offset l)])
(let ([disp (fx- next-addr (fx- offset incr-offset) 4)])
(cond
[(connected-funky12 disp)
[(code-offset-funky12 disp)
(Trivit (dest)
; aka adr, encoding A1
(emit addi #f dest `(reg . ,%pc) disp '()))]
[(connected-funky12 (- disp))
[(code-offset-funky12 (- disp))
(Trivit (dest)
; aka adr, encoding A2
(emit subi #f dest `(reg . ,%pc) (- disp) '()))]

15
racket/src/ChezScheme/s/cpnanopass.ss
View File

@ -15925,10 +15925,17 @@
(dump (cdr trace-list) addr))))
(car trace-list)))))
(fprintf p "~d:~9t<end~@[ ~a~]>\n" size name))))
; munge gets the code in forward order, but really wants to process it
; backwards to find the label offsets. Maybe the size would be better
; tracked by doing it more like cp2 does right now and then patching in
; the foward jumps and tightening up the code.
;; munge gets the code in forward order, but really wants to process it
;; backwards to find the label offsets. Maybe the size would be better
;; tracked by doing it more like cp2 does right now and then patching in
;; the foward jumps and tightening up the code.
;;
;; If label addresses computed this time are not the same as last time,
;; then `munge-recur?` is set, and some loop will try `munge` again.
;; For that loop to converge, the instruction encoding for a larger label
;; offset must not get smaller; otherwise, code might get further away,
;; leading to some smaller encoding, which pulls code back closer, leading
;; to a larger encoding, and so on.
(define-who munge
(lambda (c* size)
(define (munge-pass c* iteration)