http://d.puremagic.com/issues/show_bug.cgi?id=3914

           Summary: Struct as argument that fits in register has member
                    accessed wrong
           Product: D
           Version: 2.041
          Platform: x86
        OS/Version: Windows
            Status: NEW
          Severity: normal
          Priority: P2
         Component: DMD
        AssignedTo: nobody@puremagic.com
        ReportedBy: crimson.magus@gmail.com


--- Comment #0 from Aldo Nunez <crimson.magus@gmail.com> 2010-03-09 10:54:31 PST ---
Depending on the build options and where in a function the struct parameter is used, referencing one member will actually reference another one.

Given the following program:

import std.stdio;

struct SS
{
    char a;
    char b;
    char c;
    char d;
//    char e;
}

void A( SS ss1 )
{
C:    //writeln( ss1.a, ss1.b, ss1.c, ss1.d );

    char temp;

    temp = ss1.a;
    ss1.a = ss1.d;
    ss1.d = temp;

    temp = ss1.b;
    ss1.b = ss1.c;
    ss1.c = temp;

B:    //writeln( ss1.a, ss1.b, ss1.c, ss1.d );

    temp = ss1.a;
    ss1.a = ss1.d;
    ss1.d = temp;

    temp = ss1.b;
    ss1.b = ss1.c;
    ss1.c = temp;

A:    writeln( ss1.a, ss1.b, ss1.c, ss1.d );
}

void main()
{
    SS ss3;

    ss3.a = 'A';
    ss3.b = 'L';
    ss3.c = 'D';
    ss3.d = 'O';

    A( ss3 );
}

If lines A, B, and C are enabled in the following pattern along with the given build options, you get these results:

    (none)    -g    -rel    -rel-O    -O    -g -O
A    ALDO    ALDO    ALDO    ALDA    ALDA    ALDA

B, A    ODLA    ODLA    ODLA    ADLA    ADLA    ADLA
    ALDO    ALDO    ALDO    ALDA    ALDA    ALDA

C, B, A    ALDA    ALDO    ALDA    ALDA    ALDA    ALDA
    ODLA    ODLA    ODLA    ODLA    ODLA    ODLA
    ALDO    ALDO    ALDO    ALDO    ALDO    ALDO

In particular, notice that field 'd' starts off wrong.
If I uncomment field 'e', or change one of them to an int, the problem goes
away.

At C, "ALDO" should be printed.
At B, "ODLA" should be printed.
At A, "ALDO" should be printed.

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |clugdbug@yahoo.com.au
           Severity|normal                      |critical


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--- Comment #1 from Don <clugdbug@yahoo.com.au> 2010-03-11 12:51:37 PST ---
Here's a slightly reduced test case which doesn't require any compiler flags.
Not a regression, fails even on DMD0.165.
It's a problem with variadic function parameters and fastpar arguments.
------------
struct SS {
    char a, b, c, d;
}

void show(char[] args...) {
    assert(args[0]=='A');
    assert(args[1]=='L');
    assert(args[2]=='D');
    assert(args[3]=='O');
}

void A( SS ss ) {
    show( ss.a, ss.b, ss.c, ss.d );
}

void main(){
    SS ss3;
    ss3.a = 'A';
    ss3.b = 'L';
    ss3.c = 'D';
    ss3.d = 'O';
    A( ss3 );
}

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

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


--- Comment #2 from Don <clugdbug@yahoo.com.au> 2010-03-12 05:51:40 PST ---
PATCH: The struct ss is passed in EAX. The backend wants ss.b. It sees that
ss.b is already in EAX, so it doesn't reload it into AX. But AX actually
contains ss.a.
Solution: Disable the optimisation in cod1.loaddata() if it's a subsequent
member of the struct.

Index: cod1.c ===================================================================
--- cod1.c    (revision 413)
+++ cod1.c    (working copy)
@@ -3453,6 +3453,7 @@
     // See if we can use register that parameter was passed in
     if (regcon.params && e->EV.sp.Vsym->Sclass == SCfastpar &&
     regcon.params & mask[e->EV.sp.Vsym->Spreg] &&
+    !(e->Eoper == OPvar && e->EV.sp.Voffset > 0) && // Must be at the base of
that variable
     sz <= REGSIZE)            // make sure no 'paint' to a larger size
happened
     {
     reg = e->EV.sp.Vsym->Spreg;

=========================
Reduced test case:
=========================
struct Snake {
    short a, b;
}

void venom(short dd)
{
  assert(dd == 'B');
}

void serpent( Snake ss ) {
  venom(ss.b);
}

void main(){
    Snake s;
    s.a = 'A';
    s.b = 'B';
    serpent( s );
}

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Walter Bright <bugzilla@digitalmars.com> changed:

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


--- Comment #3 from Walter Bright <bugzilla@digitalmars.com> 2010-03-12 21:59:21 PST ---
changeset 416

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

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


--- Comment #4 from Don <clugdbug@yahoo.com.au> 2010-04-09 19:15:20 PDT ---
Fixed DMD1.058 and DMD2.042.

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