http://d.puremagic.com/issues/show_bug.cgi?id=9844

           Summary: DMD (-m64) int->long conversion bug
           Product: D
           Version: D2
          Platform: x86_64
        OS/Version: Linux
            Status: NEW
          Severity: blocker
          Priority: P5
         Component: DMD
        AssignedTo: nobody@puremagic.com
        ReportedBy: safety0ff.bugz@gmail.com


--- Comment #0 from safety0ff.bugz@gmail.com 2013-03-30 20:01:23 PDT ---
This program:
import std.stdio;
void main() {
    int a = -1;
    long b = a;
    long c = -1;
    writeln("a = ",a);
    writeln("b = ",b);
    writeln("c = ",c);
    assert(a==b&&b==c&&a==c);
}
Gives the following erroneous output:
a = -1
b = -1
c = 4294967295
core.exception.AssertError@buggy(9): Assertion failure

Using 64bit output from DMD 2.062 (also DMD git 6202b02f0e from DPaste.)

The following compilers/options give the expected output:
DMD 2.062 -m32
LDC 2.060 (64 bit on DPaste)
GDC 2.060 (64 bit on DPaste)

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--- Comment #1 from safety0ff.bugz@gmail.com 2013-03-31 01:58:24 PDT ---
Also, adding the explicit "L" integer suffix does not help.

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--- Comment #2 from safety0ff.bugz@gmail.com 2013-03-31 02:30:52 PDT ---
When passing the -O (optimize) flag, the issue does not manifest itself.

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safety0ff.bugz@gmail.com changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Priority|P5                          |P1


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John Colvin <john.loughran.colvin@gmail.com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |john.loughran.colvin@gmail.
                   |                            |com


--- Comment #3 from John Colvin <john.loughran.colvin@gmail.com> 2013-04-03 20:05:58 BST ---
A simplified test:

import std.stdio;
void foo() {
    int a = -1;
    long b = -1;
    writeln(a); // -1
    writeln(b); // (2^32)-1
}

The mistake only happens when a and b are initialised to the same negative value.

In light of that and after some perusing of the asm generated, it appears that dmd goes "-1 == -1" and uses the same value for a as for b, except of course that doesn't work because of the different sign bit positions for int and long.

e.g.

mov    eax,0xffffffff              //rax is now 0x00000000ffffffff
mov    DWORD PTR [rbp-0x10],eax
mov    QWORD PTR [rbp-0x8],rax


I don't get any bug with ldc, so it's probably either a recent regression or a backend problem.

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--- Comment #4 from safety0ff.bugz@gmail.com 2013-04-03 22:10:50 PDT ---
(In reply to comment #3)
> The mistake only happens when a and b are initialised to the same negative value.
> 
> In light of that and after some perusing of the asm generated, it appears that dmd goes "-1 == -1" and uses the same value for a as for b, except of course that doesn't work because of the different sign bit positions for int and long.

Yes, you're right, as demonstrated in this program:
import std.stdio;
void main() {
    int a = -2;
    long b = -1;
    long c = -2;
    writeln(a); // -2
    writeln(b); // -1
    writeln(c); // 2^32-2
}

I suppose I should now find a better title for this issue.

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--- Comment #5 from safety0ff.bugz@gmail.com 2013-04-04 13:54:00 PDT ---
Created an attachment (id=1206)
this kludge makes things work for me

This kludge makes things work for me.

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Index Int <vlad.z.4096@gmail.com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |vlad.z.4096@gmail.com


--- Comment #6 from Index Int <vlad.z.4096@gmail.com> 2013-04-04 20:34:29 PDT ---
The recent version of LDC (based on DMD v2.062 and LLVM 3.3svn) does not suffer
from this issue.

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Walter Bright <bugzilla@digitalmars.com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |bugzilla@digitalmars.com
            Version|D2                          |D1 & D2
         OS/Version|Linux                       |All


--- Comment #7 from Walter Bright <bugzilla@digitalmars.com> 2013-04-05 01:15:49 PDT ---
https://github.com/D-Programming-Language/dmd/pull/1846

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--- Comment #8 from github-bugzilla@puremagic.com 2013-04-07 07:30:02 PDT ---
Commits pushed to master at https://github.com/D-Programming-Language/dmd

https://github.com/D-Programming-Language/dmd/commit/34706176b888442c11d426fa98852a13c3a6b342 fix Issue 9844 - DMD (-m64) int long initialisation bug

https://github.com/D-Programming-Language/dmd/commit/2e1547d1bcea7cfae6f9489343bc15e6a193cba6 Merge pull request #1846 from WalterBright/fix9844

fix Issue 9844 - DMD (-m64) int long initialisation bug

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