http://d.puremagic.com/issues/show_bug.cgi?id=4210

           Summary: Random crashes / heisenbugs caused by dmd commit 478
           Product: D
           Version: unspecified
          Platform: Other
        OS/Version: Linux
            Status: NEW
          Keywords: patch, wrong-code
          Severity: regression
          Priority: P2
         Component: DMD
        AssignedTo: nobody@puremagic.com
        ReportedBy: nfxjfg@gmail.com


--- Comment #0 from nfxjfg@gmail.com 2010-05-19 15:46:03 PDT ---
This bug report is for dmd 1.061. (Bugzilla doesn't list the newer dmd
versions.)
Older versions are not affected.

Compiling and running a mid-sized project with dmd 1.061, I experience random segfaults and memory corruption. I have no clue what it causes, I have no test case, and I don't know how to progress further.

One symptom was that looking up an associative array string key crashed in Tango's murmur hash routine. Outputting the string showed it was corrupted (even though I don't know why the string could be successfully printed, but the hash routine failed.) Another symptom was that taking the address of a virtual function from a valid, non-null object references yielded a corrupted delegate: the .funcptr contained something like 0x6xxxxxxx, which is way off the normal function addresses around 0x8xxxxxx. Which crash exactly happened first changed as I inserted print calls for debugging.

However, I could track down what change exactly caused this: it's dmd commit 478 (http://dsource.org/projects/dmd/changeset/478). Revision 477 still worked fine.

Undoing that commit makes it work with dmd 1.061, and I suggest the inverse patch as the solution.

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Walter Bright <bugzilla@digitalmars.com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |bugzilla@digitalmars.com


--- Comment #1 from Walter Bright <bugzilla@digitalmars.com> 2010-05-19 17:44:34 PDT ---
changeset 477 fixes other bugs, so rolling it back isn't much of a solution. Better would be to find what the problem is.

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nfxjfg@gmail.com changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Keywords|patch                       |
            Summary|Random crashes / heisenbugs |Random crashes / heisenbugs
                   |caused by dmd commit 478    |caused by dmd commit 478:
                   |                            |compiler fucks up vtables


--- Comment #2 from nfxjfg@gmail.com 2010-05-19 19:32:43 PDT ---
The offending commit is 478, not 477.

After some hours of messing around, I've actually managed to create a testcase:

template X(alias fn) {
    alias typeof(fn) X;
}

void a()(T1 x) {
    alias X!(T1.foo) P; //line 7

    x.foo();
}

class T1 {
    void foo() {
    }
}

class T2 : T1 {
    void bla() {
        assert(false); //line 19
    }
}

void main() {
    a!()(new T2());
}

The code never calls T2.bla(), only T1.foo(). But the assertion on line 19 is triggered. The problem is that the compiler generates two vtable entries for T1.foo, and the second entry is "overwritten" by T2.bla. Thus, when it tries to call T1.foo by using the second vtable entry, it actually calls T2.bla.

Commenting line 7 makes the problem go away, which hints that the forward referencing handling is broken. Which doesn't make commit 478 so utterly unrelated anymore.

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--- Comment #3 from Walter Bright <bugzilla@digitalmars.com> 2010-05-20 11:33:14 PDT ---
Thanks for producing this test case, it is most helpful.

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--- Comment #4 from Walter Bright <bugzilla@digitalmars.com> 2010-05-23 16:46:08 PDT ---
I cannot reproduce the failure, either with the last release (2.046) or the
current version.

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--- Comment #5 from Walter Bright <bugzilla@digitalmars.com> 2010-05-23 16:46:50 PDT ---
Uh, I take that back. It works fine with D2, fails on D1.

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--- Comment #6 from Walter Bright <bugzilla@digitalmars.com> 2010-05-23 17:52:06 PDT ---
changeset 498

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Walter Bright <bugzilla@digitalmars.com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|NEW                         |RESOLVED
         Resolution|                            |FIXED


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Don <clugdbug@yahoo.com.au> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |aziz.koeksal@gmail.com


--- Comment #7 from Don <clugdbug@yahoo.com.au> 2010-06-07 04:42:01 PDT ---
*** Issue 4192 has been marked as a duplicate of this issue. ***

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