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order of evaluation vs the ! operator #7346

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vicuna opened this Issue Sep 8, 2016 · 1 comment

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vicuna commented Sep 8, 2016

Original bug ID: 7346
Reporter: @damiendoligez
Assigned to: @mshinwell
Status: closed (set by @mshinwell on 2016-12-13T10:22:18Z)
Resolution: duplicate
Priority: normal
Severity: major
Version: 4.04.0 +dev / +beta1 / +beta2
Target version: 4.05.0 +dev/beta1/beta2/beta3/rc1
Category: middle end (typedtree to clambda)
Related to: #4072 #6136
Monitored by: @gasche @yallop @hcarty

Bug description

With ocamlopt, the order of evaluation of function arguments depends on the code generated for the argument after inlining.

With ocamlc and ocamlopt+flambda, the order is always the same.

Steps to reproduce

Try this with ocamlc and ocamlopt:

let get r = !r [@@inline never]

let i = ref 0
let incr_i () = incr i; !i

let f (x, y) = Printf.printf "%d %d\n" x y [@@inline never]
let _ = f (incr_i (), get i)

let g x y = Printf.printf "%d %d\n" x y [@@inline never]
let () = g (incr_i ()) (get i)

They give the same result, all is well.
Remove the [@@inline never] annotation on the first line and they give different results.
Now make the function more complex (let get r = !r + (let rec f x = if x < 1 then 0 else 1 + f (x-1) in f 0)) and the result changes again.

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vicuna commented Dec 13, 2016

Comment author: @mshinwell

Superceded by #966

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