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digitalmars.D.bugs - [Issue 11510] New: Relax restriction for overlapped pointer field access in safe code/during CTFE

reply d-bugmail puremagic.com writes:
https://d.puremagic.com/issues/show_bug.cgi?id=11510

           Summary: Relax restriction for overlapped pointer field access
                    in safe code/during CTFE
           Product: D
           Version: D2
          Platform: All
        OS/Version: All
            Status: NEW
          Keywords: CTFE, spec
          Severity: enhancement
          Priority: P2
         Component: DMD
        AssignedTo: nobody puremagic.com
        ReportedBy: k.hara.pg gmail.com



Currently in  safe code, declaring struct variable which contains any
overlapped pointer(==reference) fields is entirely disallowed.

struct S {
    union {
        size_t x;
        int* y; // pointer field
    }
    int[] arr;
}

// This is necessary to avoid related compiler bug
S _dummy = S();

void test()  safe {
    S s;
    // Error: variable s unions containing pointers are not allowed
    // in  safe functions
}

However I think this is too limited behavior. Even if S.y is an overlapped
pointer field,

1. Declaring a variable typed S
2. Both reading and writing unoverlapped field S.arr
3. Both reading and writing overlapped field S.x
4. Writing overlapped pointer field S.y

should be allowed.


the  safe code. But it is nothing wrong, as same as
declaring size_t variable with void initializer.

void test()  safe {
    size_t num = void;
}

Even the value of 'num' is garbage, using it won't cause any memory corruption
in  safe. So currently it is properly accepted by compiler.

---

And the semantics should also work during CTFE. For CTFE, one following
restriction is necessary.

- Any field value reinterpretation by using two overlapped fields is
disallowed.
If it's detected in CTFE, should raise compile-time error.

Therefore, following code should work as expected.

bool test() {
    S s;    // declaration is OK

    s.y = [1,2,3].ptr;            // writing overlapped pointer field is OK
    assert(s.y[0..3] == [1,2,3]); // reading valid field is OK

    s.x = 10;
    assert(s.x == 10);

    // There's no reinterpretation between S.x and S.y
    return true;
}
static assert(test());  // run CTFE

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next sibling parent d-bugmail puremagic.com writes:
https://d.puremagic.com/issues/show_bug.cgi?id=11510






 // This is necessary to avoid related compiler bug
 S _dummy = S();


The "related bug" is bug 11427.

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prev sibling next sibling parent d-bugmail puremagic.com writes:
https://d.puremagic.com/issues/show_bug.cgi?id=11510


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

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Keywords|                            |pull



https://github.com/D-Programming-Language/dmd/pull/2757

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prev sibling next sibling parent d-bugmail puremagic.com writes:
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Commits pushed to master at https://github.com/D-Programming-Language/dmd

https://github.com/D-Programming-Language/dmd/commit/a2932981ee03abe13e9fdacf07ad29d162fc4b16
fix Issue 11510 - Relax restriction for overlapped pointer field access in safe
code/during CTFE

Check overlapped field default initializations immediately after the struct
size is determined.

https://github.com/D-Programming-Language/dmd/commit/475c5437525d759891be381961c076d2e1dc3e2b


Issue 11510 - Relax restriction for overlapped pointer field access in safe
code/during CTFE

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Dec 16 2013
prev sibling parent d-bugmail puremagic.com writes:
https://d.puremagic.com/issues/show_bug.cgi?id=11510


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

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |jmdavisProg gmx.com



*** Issue 10035 has been marked as a duplicate of this issue. ***

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Jan 14 2014