https://d.puremagic.com/issues/show_bug.cgi?id=12153

           Summary: Ternary operator on static array lvalues creates copy
           Product: D
           Version: D2
          Platform: All
        OS/Version: All
            Status: NEW
          Keywords: wrong-code
          Severity: normal
          Priority: P2
         Component: DMD
        AssignedTo: nobody@puremagic.com
        ReportedBy: thecybershadow@gmail.com


--- Comment #0 from Vladimir Panteleev <thecybershadow@gmail.com> 2014-02-13 21:39:54 EET ---
void main()
{
    int[1] i, j;
    bool b = true;
    (b ? i : j) = [4];
    assert(i == [4]);
}

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yebblies <yebblies@gmail.com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |yebblies@gmail.com


--- Comment #1 from yebblies <yebblies@gmail.com> 2014-02-16 02:21:21 EST ---
Sigh, the backend sees

int[1] i = 0;
int[1] j = 0;
bool b = true;
(b ? i : j)[] = [4];
assert(i == [4]);
return 0;

Another bug caused by lowering static array ops to slice ops.

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Kenji Hara <k.hara.pg@gmail.com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Keywords|                            |pull
           Severity|normal                      |major


--- Comment #2 from Kenji Hara <k.hara.pg@gmail.com> 2014-02-19 01:47:31 PST ---
(In reply to comment #1)
> Sigh, the backend sees
> 
> int[1] i = 0;
> int[1] j = 0;
> bool b = true;
> (b ? i : j)[] = [4];
> assert(i == [4]);
> return 0;
> 
> Another bug caused by lowering static array ops to slice ops.

Translating to the slice ops is not a problem. This is a glue-layer bug for cond expression.

https://github.com/D-Programming-Language/dmd/pull/3285

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--- Comment #3 from yebblies <yebblies@gmail.com> 2014-02-19 21:07:20 EST ---
(In reply to comment #2)
> (In reply to comment #1)
> > Sigh, the backend sees
> > 
> > int[1] i = 0;
> > int[1] j = 0;
> > bool b = true;
> > (b ? i : j)[] = [4];
> > assert(i == [4]);
> > return 0;
> > 
> > Another bug caused by lowering static array ops to slice ops.
> 
> Translating to the slice ops is not a problem. This is a glue-layer bug for cond expression.
> 

Sure it is.  If instead of converting `a = b` (where lhs is a static array) into `a[] = b[]` the compiler left the lhs intact as a static array, then converting the condexp to an lvalue would have resulted in `*(b ? &i : &j) = [4]` and this bug would not have occurred.

> https://github.com/D-Programming-Language/dmd/pull/3285

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--- Comment #4 from Kenji Hara <k.hara.pg@gmail.com> 2014-02-19 02:31:26 PST ---
(In reply to comment #3)
> Sure it is.  If instead of converting `a = b` (where lhs is a static array) into `a[] = b[]` the compiler left the lhs intact as a static array, then converting the condexp to an lvalue would have resulted in `*(b ? &i : &j) = [4]` and this bug would not have occurred.

But in the cond exp, both i and j are already lvalue. So translating lvalue (b
? i : j) to lvalue *(b ? &i : &j) is redundant in front-end layer and will
never occur.

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--- Comment #5 from yebblies <yebblies@gmail.com> 2014-02-19 21:38:16 EST ---
(In reply to comment #4)
> (In reply to comment #3)
> > Sure it is.  If instead of converting `a = b` (where lhs is a static array) into `a[] = b[]` the compiler left the lhs intact as a static array, then converting the condexp to an lvalue would have resulted in `*(b ? &i : &j) = [4]` and this bug would not have occurred.
> 
> But in the cond exp, both i and j are already lvalue. So translating lvalue (b
> ? i : j) to lvalue *(b ? &i : &j) is redundant in front-end layer and will
> never occur.

Sure it will.
This:

int a, b, c;

void main()
{
    c ? a : b = c;
}

results in this getting sent to codegen:

*(c ? & a : & b) = c;

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--- Comment #6 from github-bugzilla@puremagic.com 2014-02-23 14:19:12 PST ---
Commits pushed to master at https://github.com/D-Programming-Language/dmd

https://github.com/D-Programming-Language/dmd/commit/7438d1227a17436077e3df68ba40ef1ff8e0788c fix Issue 12153 - Ternary operator on static array lvalues creates copy

https://github.com/D-Programming-Language/dmd/commit/ec7cf0a99f791495d142ed8a8799a022c0be84ef Merge pull request #3285 from 9rnsr/fix12153

Issue 12153 - Ternary operator on static array lvalues creates copy

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Kenji Hara <k.hara.pg@gmail.com> changed:

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


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