segmentation fault when using tuple over member variable in more than one method

[ghost]

test.d:

template Tuple(Stuff ...) {
    alias Stuff Tuple;
}
struct S {
    int i;
    alias Tuple!i t;
    void a() {
        auto x = t;
    }
    void b() {
        auto x = t;
    }
}

ldc2 -c test.d:

0  ldc2            0x00000000011953ef
1  ldc2            0x0000000001195859
2  libpthread.so.0 0x00007f914eba5cb0
3  ldc2            0x00000000006cc443 DtoNestedVariable(Loc, Type*, VarDeclaration*, bool) + 147
4  ldc2            0x000000000069f43a ThisExp::toElem(IRState*) + 202
5  ldc2            0x000000000069f0e0 DotVarExp::toElem(IRState*) + 224
6  ldc2            0x000000000069cf6d AssignExp::toElem(IRState*) + 173
7  ldc2            0x00000000006c567f DtoVarDeclaration(VarDeclaration*) + 111
8  ldc2            0x00000000006c5b68 DtoDeclarationExp(Dsymbol*) + 312
9  ldc2            0x00000000006c5d57 DtoDeclarationExp(Dsymbol*) + 807
10 ldc2            0x00000000006c5a95 DtoDeclarationExp(Dsymbol*) + 101
11 ldc2            0x000000000069bd21 DeclarationExp::toElem(IRState*) + 65
12 ldc2            0x000000000069bc4d Expression::toElemDtor(IRState*) + 77
13 ldc2            0x000000000067c6aa ExpStatement::toIR(IRState*) + 74
14 ldc2            0x000000000067bfab CompoundStatement::toIR(IRState*) + 91
15 ldc2            0x0000000000664ad5 DtoDefineFunction(FuncDeclaration*) + 1797
16 ldc2            0x00000000006cd1e9 Ir::emitFunctionBodies() + 41
17 ldc2            0x0000000000668d1d Module::genLLVMModule(llvm::LLVMContext&, Ir*) + 669
18 ldc2            0x000000000059a577 main + 7623
19 libc.so.6       0x00007f914dddf76d __libc_start_main + 237
20 ldc2            0x00000000005ad0e9
Segmentation fault (core dumped)

[dnadlinger]

Thanks for the solid bug report. Unfortunately, I won't be able to work on LDC during the next two weeks, but I'll try to have a look at it as soon as possible in February.

[smunix]

Here is the whole stacktrace:

0 in getParentFunc of /home/smunix/programming/d-projects/ldc/gen/nested.cpp:30
1 in DtoNestedVariable of /home/smunix/programming/d-projects/ldc/gen/nested.cpp:86
2 in ThisExp::toElem of /home/smunix/programming/d-projects/ldc/gen/toir.cpp:1542
3 in DotVarExp::toElem of /home/smunix/programming/d-projects/ldc/gen/toir.cpp:1425
4 in AssignExp::toElem of /home/smunix/programming/d-projects/ldc/gen/toir.cpp:612
5 in DtoInitializer of /home/smunix/programming/d-projects/ldc/gen/llvmhelpers.cpp:1445
6 in DtoVarDeclaration of /home/smunix/programming/d-projects/ldc/gen/llvmhelpers.cpp:1146
7 in DtoDeclarationExp of /home/smunix/programming/d-projects/ldc/gen/llvmhelpers.cpp:1183
8 in DtoDeclarationExp of /home/smunix/programming/d-projects/ldc/gen/llvmhelpers.cpp:1258
9 in DtoDeclarationExp of /home/smunix/programming/d-projects/ldc/gen/llvmhelpers.cpp:1174
10 in DeclarationExp::toElem of /home/smunix/programming/d-projects/ldc/gen/toir.cpp:95
11 in Expression::toElemDtor of /home/smunix/programming/d-projects/ldc/gen/toir.cpp:72
12 in ExpStatement::toIR of /home/smunix/programming/d-projects/ldc/gen/statements.cpp:208
13 in CompoundStatement::toIR of /home/smunix/programming/d-projects/ldc/gen/statements.cpp:55
14 in DtoDefineFunction of /home/smunix/programming/d-projects/ldc/gen/functions.cpp:1079
15 in Ir::emitFunctionBodies of /home/smunix/programming/d-projects/ldc/ir/ir.cpp:62
16 in Module::genLLVMModule of /home/smunix/programming/d-projects/ldc/gen/module.cpp:301
17 in main of /home/smunix/programming/d-projects/ldc/driver/main.cpp:1100

[smunix]

As we can see, in frame 1 the ThisExp ("this.i") is being evaluated from function is "void b()". "getParentFunc" tries its best to put a hand on "this" parent while checking that it's function "void b()", but this never happens. At some point before, in function "void a()", I suspect that the ThisExp was given "void a()" as its parent symbol, and that never changed since then.

(gdb) fr 12
#12 0x00000000008de3d0 in ExpStatement::toIR (this=0x1e185d0, p=0x7fffffffd240) at /home/smunix/programming/d-projects/ldc/gen/statements.cpp:208
208 e = exp->toElemDtor(p);
(gdb) p p->func()->decl->toChars()
$105 = 0x1e17e74 "b"

(gdb) fr 1
#1 0x00000000008be040 in DtoNestedVariable (loc=..., astype=0x1e16d80, vd=0x1eb61d0, byref=true) at /home/smunix/programming/d-projects/ldc/gen/nested.cpp:86
86 fd = getParentFunc(fd, false);
(gdb) p fd->toChars()
$102 = 0x1e17e74 "b"
(gdb) p vd->toParent2()->toChars()
$103 = 0x1e17584 "a"
(gdb) p vd->toChars()

As the following excerpt (func=DtoNestedVariable, file nested.cpp) from the code shows it, we are in function b and we check whether we can assess the needed frame or not. "assert(fd)". Since this->parent is "a" and not "b", we'll never reach "b"'s frame from the this pointer. At one point, fd turns out to be null and the assertion fails.

// Check whether we can access the needed frame
FuncDeclaration *fd = irfunc->decl;
while (fd != vdparent) {
    if (fd->isStatic()) {
        error(loc, "function %s cannot access frame of function %s", irfunc->decl->toPrettyChars(), vdparent->toPrettyChars());
        return new DVarValue(astype, vd, llvm::UndefValue::get(getPtrToType(DtoType(astype))));
    }
    fd = getParentFunc(fd, false);
    assert(fd);
}

[smunix]

I still need to figure out why "this" keeps saying that its parent function is "void a() {}" while being accessed from function "void b() {}".

[John-Colvin]

Gdc also ICEs on this: http://bugzilla.gdcproject.org/show_bug.cgi?id=49

[John-Colvin]

relevant: dlang/dmd#1880 and dlang/dmd#1881

[dnadlinger]

@John-Colvin: Thanks a lot for revisiting the open issues! Wish I could spend more time actually hacking on LDC right now…

[redstar]

Upstream is fixed and merged.