http://d.puremagic.com/issues/show_bug.cgi?id=6510

           Summary: [CTFE] internal error: illegal stack value stack
           Product: D
           Version: D2
          Platform: Other
        OS/Version: All
            Status: NEW
          Severity: normal
          Priority: P2
         Component: DMD
        AssignedTo: nobody@puremagic.com
        ReportedBy: dmitry.olsh@gmail.com


--- Comment #0 from Dmitry Olshansky <dmitry.olsh@gmail.com> 2011-08-16 13:39:07 PDT ---
Recently found this one in my GSOC project. As this involves compilation of regex at CTFE, I'm not yet able to produce small test case.

dmd spits this:
..\..\fred.d(2020): Error: CTFE internal error: illegal stack value stack

Assertion failure: 'isStackValueValid(newval)' on line 5452 in file
'interpret.c'

abnormal program termination

But anyway, what kind of situation is supposed to trigger that assert?

My dmd is 2.055 compiled form github with last commit being:
 Merge pull request #293 from 9rnsr/fix2246
 4a1c9e7646ed9152f9644cd29d07968583888cb2

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

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


--- Comment #1 from Don <clugdbug@yahoo.com.au> 2011-08-16 19:32:55 PDT ---
(In reply to comment #0)
> Recently found this one in my GSOC project. As this involves compilation of regex at CTFE, I'm not yet able to produce small test case.
> 
> dmd spits this:
> ..\..\fred.d(2020): Error: CTFE internal error: illegal stack value stack
> 
> Assertion failure: 'isStackValueValid(newval)' on line 5452 in file
> 'interpret.c'
> 
> abnormal program termination
> 
> But anyway, what kind of situation is supposed to trigger that assert?

Any kind of CTFE assignment involving a non-reference type, that wasn't tested. The few lines involving the variable 'stack' around line 2020 will be the only ones involved in the bug.

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--- Comment #2 from Dmitry Olshansky <dmitry.olsh@gmail.com> 2011-08-17 02:52:42 PDT ---
Created an attachment (id=1018)
test case, stripped down parser

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--- Comment #3 from Dmitry Olshansky <dmitry.olsh@gmail.com> 2011-08-17 02:55:11 PDT ---
I've managed to get a resonably sized test case.
Apparently it has soemthing to do with -inline:

dmd fred.d  // Ok
dmd -inline fred.d //same error as before

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Dmitry Olshansky <dmitry.olsh@gmail.com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
            Summary|[CTFE] internal error:      |[CTFE] "internal error:
                   |illegal stack value stack   |illegal stack value" when
                   |                            |compiled with -inline


--- Comment #4 from Dmitry Olshansky <dmitry.olsh@gmail.com> 2011-08-17 02:57:06 PDT ---
I haven't made this point clear enough I think: the full source also fails only with -inline.

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--- Comment #5 from Don <clugdbug@yahoo.com.au> 2011-08-17 06:52:06 PDT ---
Partially reduced test case. The UNUSED static function seems to be necessary.

struct Stack(U) {
    struct Proxy {
        int[] data;
        void shrink(){   data = data[0..0]; }
    }
    Proxy stack;
    void pop() {
        stack.shrink();
    }
}

int bug6510() {
    static void UNUSED() {
        Stack!(int) junk;
        junk.pop();
    }
    Stack!(int) opstk;
    opstk.pop();
    return 3;
}

 static assert(bug6510());

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Keywords|                            |ice-on-valid-code


--- Comment #6 from Don <clugdbug@yahoo.com.au> 2011-08-17 08:34:41 PDT ---
Reduced slightly further. If you uncomment the alias, everything works. So this
is a bug which only happens when the semantic pass, and the inlining, is run on
Stack!int *during* CTFE.
The stack.shrink() call gets translated into:
ref Proxy ths = this.stack;
which CTFE chokes on. Note that this is a local reference variable, which isn't
legal D (it can only happen in compiler-generated code).

When the alias is present, the inline scan of bug6510() doesn't happen until
after CTFE has finished. But interestingly an inline scan of UNUSED() still
happens during CTFE.

---

struct Stack(U) {
    struct Proxy {
        void shrink() {}
    }
    Proxy stack;
    void pop() {
        stack.shrink();
    }
}

alias Stack!int Stuck;

int bug6510() {
    static void UNUSED() {
        Stack!(int) junk;
        junk.pop();
    }
    Stack!(int) opstk;
    opstk.pop();
    return 3;
}

static assert(bug6510());

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--- Comment #7 from Dmitry Olshansky <dmitry.olsh@gmail.com> 2011-08-17 08:52:15 PDT ---
Thanks for getting a workaround so fast, it's just awesome.
I confirm that the full source works after I added aliases to Stack!(x).

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--- Comment #9 from Don <clugdbug@yahoo.com.au> 2011-08-19 05:53:36 PDT ---
Further reduced, showing that templates are not required. Seems to require an inlined member function call to a member of a nested struct, called from a nested function. No alias trick works in this case.

struct Stack6510 {
    struct Proxy {
        void shrink() {}
    }
    Proxy stack;
    void pop() {
        stack.shrink();
    }
}

int bug6510() {
    static int used() {
        Stack6510 junk;
        junk.pop();
        return 3;
    }
    return used();
}

void main() {
    static assert(bug6510()==3);
}

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Walter Bright <bugzilla@digitalmars.com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|NEW                         |RESOLVED
                 CC|                            |bugzilla@digitalmars.com
         Resolution|                            |FIXED


--- Comment #10 from Walter Bright <bugzilla@digitalmars.com> 2011-08-22 22:47:32 PDT ---
https://github.com/D-Programming-Language/dmd/commit/563a291a5c7757fca87685909afa37100e3b44f6

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