http://d.puremagic.com/issues/show_bug.cgi?id=3736

           Summary: corrupted struct returned by function with
                    optimizations (-O)
           Product: D
           Version: 2.030
          Platform: Other
        OS/Version: Windows
            Status: NEW
          Keywords: wrong-code
          Severity: regression
          Priority: P2
         Component: DMD
        AssignedTo: nobody@puremagic.com
        ReportedBy: spam@extrawurst.org


--- Comment #0 from Stephan Dilly <spam@extrawurst.org> 2010-01-23 10:02:04 PST ---
building the following code with -O corrupts the return value of getFoo. sorry could not reduce it more:

import std.stdio;

struct Foo
{
    float x=0;
}

struct Bar
{
    Foo p0;
    Foo p1;
}

Bar a = {Foo(0),Foo(400)};

Foo getFoo(Foo _pos)
{
    Bar stillok = a;

    float d0 = (a.p0.x - _pos.x);
    float d1 = (a.p0.x - _pos.x);

    if( d0 > d1 )
    {
        return stillok.p0;
    }
    else
    {
        return stillok.p1;
    }
}

void main()
{
    writefln("%s", getFoo( Foo(100) ).x );
}

// prints 6.91062e-39 under dmd2039
// prints 3.2372e-39 under dmd2030

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |clugdbug@yahoo.com.au
            Version|2.030                       |1.020
           Severity|regression                  |critical


--- Comment #1 from Don <clugdbug@yahoo.com.au> 2010-01-24 23:53:23 PST ---
This isn't actually a regression. It fails on D2.00, and D1.020, 1.041, 1.055 as well.

Reduced test case:
---------------
struct Foo
{
    int x;
}

Foo getFoo(Foo irrelevant)
{
    Foo p = Foo(400);
    if ( p.x > p.x )
        return irrelevant;
    else
        return p;
}

void main()
{
   assert(getFoo( Foo(0) ).x == 400);
}

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--- Comment #2 from Don <clugdbug@yahoo.com.au> 2010-02-07 13:47:44 PST ---
The problem has something to do with the transformation from if(cond) return xxx; else return yyy;  into return cond ? xxx : yyy;

If I comment out blockopt.c brcombine() lines 734-764, the test case doesn't fail. That doesn't necessarily mean that the problem lies there, though.

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Keywords|                            |patch


--- Comment #3 from Don <clugdbug@yahoo.com.au> 2010-02-08 21:02:14 PST ---
This seems to be a problem with transformations which copy the type 'Ety'
without
also copying the size 'Enumbytes', but you need the struct size to be retained.
when the struct size is zero, blocks get dropped and bad codegen results.
This particular bug is fixed by adding:
in optelem(), cgelem.c line 4376 (this is called with op==OPcond).

  if (!OTrtol(op) && op != OPparam && op != OPcolon && op != OPcolon2 &&
          e1->Eoper == OPcomma)
      {    // Convert ((a,b) op c) to (a,(b op c))
        e1->Ety = e->Ety;
+        e1->Enumbytes = e->Enumbytes;
        e->E1 = e1->E2;
        e1->E2 = e;
        e = e1;
        goto beg;
      }

blockopt.c, brcombine() line 755:

            if (EOP(b3->Belem))
                continue;
            ty = (bc2 == BCretexp) ? b2->Belem->Ety : TYvoid;
            e = el_bin(OPcolon2,ty,b2->Belem,b3->Belem);
            b->Belem = el_bin(OPcond,ty,b->Belem,e);
            }
+            b->Belem->Enumbytes = b2->Belem->Enumbytes;
            b->BC = bc2;


A dozen lines further down the same function are two other calls to el_bin(OPcond,...) or el_bin(OPcolon2,...) in brcombine in blockopt.c.

So I suspect line 797 should also be added:

                e = el_bin(OPcolon2,b2->Belem->Ety,
                    b2->Belem,b3->Belem);
                e = el_bin(OPcond,e->Ety,b->Belem,e);
+                e->Enumbytes=b2->Belem->Enumbytes;
                }

But this is just speculation, I don't have a test case which fails there.
There are no other instances of el_bin(OPcond,...) or el_bin(OPcolon2,...)
anywhere else in the backend.
I suspect there are other cases in the backend where types are transferred
but Enumbytes is lost. (there are several in el_comma in cgelem.c).
But mostly this probably just results in lost optimisation opportunities.

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--- Comment #4 from Don <clugdbug@yahoo.com.au> 2010-02-10 00:58:30 PST ---
Here is a test case which fails in DMC 8.42n. It hits the breakpoint when compiled with -O.
----------
struct Foo {
    int x;
};

Foo getFoo(Foo irrelevant) {
    Foo p;
    p.x=400;
    if ( p.x > p.x )
        return irrelevant;
    else
        return p;
}

void main() {
   Foo z;
   z.x=0;
   int y = getFoo( z ).x;
   if (y!=400) _asm int 3;
}
----------

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Walter Bright <bugzilla@digitalmars.com> changed:

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


--- Comment #5 from Walter Bright <bugzilla@digitalmars.com> 2010-02-12 01:36:21 PST ---
Changeset 380

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Kosmonaut <Kosmonaut@tempinbox.com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |Kosmonaut@tempinbox.com


--- Comment #6 from Kosmonaut <Kosmonaut@tempinbox.com> 2010-02-12 11:48:07 PST ---
(In reply to comment #5)
> Changeset 380

http://www.dsource.org/projects/dmd/changeset/380

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Walter Bright <bugzilla@digitalmars.com> changed:

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


--- Comment #7 from Walter Bright <bugzilla@digitalmars.com> 2010-03-08 22:22:18 PST ---
Fixed dmd 1.057 and 2.041

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