0002719: Proble in the Mac OS X compiler [PPC code generator]

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0002719

OCaml

OCaml general

public

2004-06-14 20:09

2012-09-11 09:24

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administrator

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Priority

normal

Severity

minor

Reproducibility

always

Status

acknowledged

Resolution

open

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Product Version

Target Version

4.00.2+dev

Fixed in Version

Summary

0002719: Proble in the Mac OS X compiler [PPC code generator]

Description

Full_Name: Sylvain Chevillard
Version: 3.07+17
OS: Mac OS X v10.3
Submission from: 132.176.250.100 (132.176.250.100)

I have noticed a bug which should be in the Mac OS X compiler of ocaml, I
think.
Here is a minimal buggy code :

open Printf

let bug () =
  let mat = [| [|false|] |]
  and test = ref false in
    printf "Value of test at the beginning : %b\n" !test; flush stdout;
    (try let _ = mat.(0).(-1) in
       (test := true;
        printf "Am I going through this block of instructions ?\n";
        flush stdout)
     with Invalid_argument _ -> printf "Value of test now : %b\n" !test
    );
    (try if mat.(0).(-1) then ()
     with Invalid_argument _ -> ()
    )

let () = bug ()

We are waiting that the program (when run) should write :
Value of test at the beginning : false
Value of test now : false

and actually, that is what you could see when you run the bytecode generated by
ocamlc or if you compile the code on an x86 architecture with native compiler.

But, with the native compiler on Mac OS X, the program writes :
Value of test at the beginning : false
Value of test now : true

Notice that this part of the code seems to be useless but is actually essential
to the bug :
    (try if mat.(0).(-1) then ()
     with Invalid_argument _ -> ()
    )

I think that it is a problem of pipeline in the processor. The instruction
test := true;
is probably pipelined in the processor and is run even when the exception is
raised.

Happy coding!

Sylvain Chevillard

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0004892

resolved

'index out of bound' check too early?

Notes
(0003002) administrator (administrator) 2004-07-01 13:25	Bug in scheduling of Icheckbound. The obvious fix diminishes the usefulness of the scheduler quite a bit. Will not fix in 3.08.

Issue History
Date Modified	Username	Field	Change
2005-11-18 10:14	administrator	New Issue
2007-12-12 16:22	doligez	Summary	Proble in the Mac OS X compiler => Proble in the Mac OS X compiler [PPC code generator]
2007-12-12 16:22	doligez	Description Updated
2009-10-15 17:38	doligez	Relationship added	related to 0004892
2012-07-11 17:36	doligez	Target Version	=> 4.01.0+dev
2012-07-31 13:37	doligez	Target Version	4.01.0+dev => 4.00.1+dev
2012-09-11 09:24	doligez	Target Version	4.00.1+dev => 4.00.2+dev