http://d.puremagic.com/issues/show_bug.cgi?id=7595

           Summary: Data being overwritten.
           Product: D
           Version: D2
          Platform: All
        OS/Version: All
            Status: NEW
          Severity: regression
          Priority: P2
         Component: DMD
        AssignedTo: nobody@puremagic.com
        ReportedBy: iteronvexor@gmail.com


--- Comment #0 from iteronvexor@gmail.com 2012-02-26 12:46:33 PST ---
As discussed here: http://www.digitalmars.com/pnews/read.php?server=news.digitalmars.com&group=digitalmars.D.learn&artnum=33006


bug.d
---------------->8---------------->8----------------
@trusted:

import std.datetime : benchmark;
import std.stdio    : writefln, writeln;

alias double Real;

void ben(alias fun)(string msg, uint n = 1_000_000) {
 auto b = benchmark!fun(n);
 writefln(" %s %s ms", msg, b[0].to!("msecs", int));
}

struct Matrix(int row, int col) {

private:
 alias row Row;
 alias col Col;
 alias Real[Row * Col] Data;

public:
 Data _data = void;
 alias _data this;
 this(const Real[Row*Col] data) pure nothrow { _data = data; }
}

M inverse(M)(const auto ref M m)  {
 writeln(m[]);
 M minv = m;
 return minv;
}

unittest {
 alias Matrix!(4, 4) Matrix4x4;
 auto m9 = Matrix4x4([4, 0, 0, 0, 0, 0, 2, 0, 0, 1, 2, 0, 1, 0, 0, 1]);
 ben!( {auto r = inverse(m9);} )("4x4 inverse:");
}
----------------8<----------------8<----------------

t1.d
---------------->8---------------->8----------------
import std.stdio;

void main(){ }
----------------8<----------------8<----------------

Once you have those two files, compile with this:

dmd -unittest t1.d bug.d

and then run t1:

./t1

The output you get should look like this:

...
[0, 4, 0, 0, 0, 0, 0, 2, 0, 0, 1, 2, 0, 1, 0, 0]


Obviously the output is wrong.  'm9' for some reason is getting overwritten.  In my project this caused big problems because there are other m# with different values, and their values would literally get copied to m9.  Calling inverse() on m9 then would fail because the other matrices are not invertible.  Placing a writeln() in inverse() helped me realize that what was being passed to inverse() was being modified somewhere.  I'm still now sure how m9 is being modified.

Another point, compiling with this:

dmd -unittest bug.d t1.d

and then running bug:

./bug

doesn't trigger the bug.

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Lukasz Wrzosek <luk.wrzosek@gmail.com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |luk.wrzosek@gmail.com


--- Comment #1 from Lukasz Wrzosek <luk.wrzosek@gmail.com> 2012-02-26 13:20:48 PST ---
I can confirm this bug with dmd 2.058 32bit:

output with dmd -unittest bug.d t1.d:
[4, 0, 0, 0, 0, 0, 2, 0, 0, 1, 2, 0, 1, 0, 0, 1]

output with dmd -unittest t1.d bug.d:
[0, 5.31017e-315, 0, 0, 0, 0, 0, 5.30499e-315, 0, 0, 5.29981e-315,
5.30499e-315, 0, 5.29981e-315, 0, 0]


ldc and gdc, both work

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Walter Bright <bugzilla@digitalmars.com> changed:

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


--- Comment #2 from Walter Bright <bugzilla@digitalmars.com> 2012-03-04 12:59:52 PST ---
bug.d reduces to:
-----------------
@trusted:

import core.stdc.stdio;
import std.datetime : benchmark;

struct Matrix {
    int[4] _data;
}

void inverse(const ref Matrix m)  {
    for (size_t i = 0; i < 4; i++)
        printf("m._data[%d] = %d\n", i, m._data[i]);
}

unittest {
    Matrix m9;
    m9._data[0] = 1;
    m9._data[1] = 2;
    m9._data[2] = 3;
    m9._data[3] = 4;
    for (size_t i = 0; i < 4; i++)
        printf("m9._data[%d] = %d\n", i, m9._data[i]);

    benchmark!( { inverse(m9);} )(1);
}

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--- Comment #3 from github-bugzilla@puremagic.com 2012-03-04 18:07:03 PST ---
Commit pushed to master at https://github.com/D-Programming-Language/dmd

https://github.com/D-Programming-Language/dmd/commit/d531901667997c260bfaa2d8776f27c1acc716cf fix Issue 7595 - Data being overwritten.

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Walter Bright <bugzilla@digitalmars.com> changed:

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


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