[Issue 7595] New: Data being overwritten.

[d-bugmail at puremagic.com]

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 at puremagic.com
        ReportedBy: iteronvexor at gmail.com


--- Comment #0 from iteronvexor at 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.

-- 
Configure issuemail: http://d.puremagic.com/issues/userprefs.cgi?tab=email
------- You are receiving this mail because: -------