27 lines
1.3 KiB
Plaintext
27 lines
1.3 KiB
Plaintext
;;;; A slice built backwards, for the survey rather than for a person.
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;;;;
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;;;; test/programs/bounds.flan already covers this, and cannot cover it here:
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;;;; it picks its case out of (at args 1) and survey.sh runs every program
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;;;; with no arguments at all. So the one backend comparison that would catch
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;;;; check_slice's lo <= hi being re-gated on --no-bounds-checks is a program
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;;;; that reaches the reversed slice on its own.
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;;;;
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;;;; What it pins is that both backends die here in *every* build. lo <= hi is
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;;;; not a bounds check — it is the claim that the length word of the %slice
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;;;; this expression builds is a count, and hi - lo is -1 — so
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;;;; --no-bounds-checks has nothing here to drop, and running this sweep with
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;;;; SURVEY_FLAGS=--no-bounds-checks must report the same MATCH as without it.
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;;;; A backend that quietly builds the slice exits 0 while the other exits 134
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;;;; and the survey says DIFFER.
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;;;;
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;;;; The two ends come from (length args), which is 1 for a program run with no
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;;;; arguments and is not a number either optimiser can see, so the branch
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;;;; cannot be folded away and the checker has no literal to object to.
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(defn main [args [string]] i32
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(let [s (bytes-view "hello")
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hi (i32 (length args))
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lo (+ hi 1)]
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(print (slice s lo hi))
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(println ""))
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0)
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