[Issue 8423] New: Wrong code for lazy parameters.

[d-bugmail at puremagic.com]

http://d.puremagic.com/issues/show_bug.cgi?id=8423

           Summary: Wrong code for lazy parameters.
           Product: D
           Version: unspecified
          Platform: All
        OS/Version: All
            Status: NEW
          Keywords: wrong-code
          Severity: normal
          Priority: P2
         Component: DMD
        AssignedTo: nobody at puremagic.com
        ReportedBy: code at klickverbot.at


--- Comment #0 from klickverbot <code at klickverbot.at> 2012-07-24 02:53:06 PDT ---
With DMD Git master (04a74bdf) on Linux x86_64, the following snippet
asserts/hlts:

---
struct Duration
{
    int opCmp(Duration rhs)
    {
        return 1;
    }
}

void enforce(bool value, string a, string b)
{
    if (!value) assert(false);
}

void main()
{
    auto a = Duration();
    auto b = Duration();
    enforce(a > b, null, null);
}
---

Here is the relevant assembly:
---
  40194d:       e8 0e ff ff ff          call   401860
<_D4test8Duration5opCmpMFS4test8DurationZi>
  401952:       49 89 c0                mov    r8,rax
  401955:       f7 d8                   neg    eax
  401957:       41 c1 e8 1f             shr    r8d,0x1f
  40195b:       31 c0                   xor    eax,eax
  40195d:       31 c9                   xor    ecx,ecx
  40195f:       48 89 c2                mov    rdx,rax
  401962:       48 89 55 f0             mov    QWORD PTR [rbp-0x10],rdx
  401966:       48 89 ca                mov    rdx,rcx
  401969:       48 89 c7                mov    rdi,rax
  40196c:       48 89 d6                mov    rsi,rdx
  40196f:       48 8b 55 f0             mov    rdx,QWORD PTR [rbp-0x10]
  401973:       e8 38 ff ff ff          call   4018b0
<_D4test7enforceFbAyaAyaZv>
---

I haven't checked what causes DMD to emit the »shr« instruction, but it sure
kills the opCmp return value in the register. Removing one of the additional
parameters, which leads to value being passed in one of {rsi, rdi, rdx, rcx}
due to the reverse parameter order in the D calling convention, causes the bug
to disappear.

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