This code makes the DMD compiler segfault
struct LeafType {
string Compile_not_ovloaded() {
return "expression";
}
};
struct MatrixASTNode {
LeafType Right;
string Compile() {
return Right.Compile_not_ovloaded();
}
};
void main() {
enum AST = MatrixASTNode();
enum s=AST.Compile();
}
I'm not sure if it's valid D, but MatrixASTNode.Compile seems like it
should be evaluable at compile time. segfaults are bad anyway. A search
with the keyword "segfault" didn't seem to turn up any existing bugs
with promising titles, so I assume this is a new bug (I'll put it in
bugzilla if nobody can think of an existing bug).
I've tried compiling a debug version of svn dmd and I traced the bug
down to what appears to be a stack overflow. These two functions in
interpret.c seem to call each other repeatedly.
Expression *ThisExp::interpret(InterState *istate)
{
if (istate && istate->localThis)
return istate->localThis->interpret(istate);
error("value of 'this' is not known at compile time");
return EXP_CANT_INTERPRET;
}
Expression *DotVarExp::interpret(InterState *istate)
{ Expression *e = EXP_CANT_INTERPRET;
#if LOG
printf("DotVarExp::interpret() %s\n", toChars());
#endif
Expression *ex = e1->interpret(istate); // <- we never get past here
if (ex != EXP_CANT_INTERPRET)
{
if (ex->op == TOKstructliteral)
{ StructLiteralExp *se = (StructLiteralExp *)ex;
VarDeclaration *v = var->isVarDeclaration();
if (v)
{ e = se->getField(type, v->offset);
if (!e)
{
error("couldn't find field %s in %s", v->toChars(),
type->toChars());
e = EXP_CANT_INTERPRET;
}
return e;
}
}
else
error("%s.%s is not yet implemented at compile time",
e1->toChars(), var->toChars());
}
If you turn logging on for the file you get this:
CallExp::interpret() MatrixASTNode(LeafType()).Compile()
********
FuncDeclaration::interpret(istate = (nil)) Compile
cantInterpret = 0, semanticRun = 5
StructLiteralExp::interpret() MatrixASTNode(LeafType())
StructLiteralExp::interpret() LeafType()
CompoundStatement::interpret()
ExpStatement::interpret(assert(&this,"null this"))
AssertExp::interpret() assert(&this,"null this")
StructLiteralExp::interpret() MatrixASTNode(LeafType())
StructLiteralExp::interpret() LeafType()
ReturnStatement::interpret(this.Right.Compile_not_ovloaded())
CallExp::interpret() this.Right.Compile_not_ovloaded()
********
FuncDeclaration::interpret(istate = 0xbfe685a0) Compile_not_ovloaded
cantInterpret = 0, semanticRun = 5
DotVarExp::interpret() this.Right
StructLiteralExp::interpret() MatrixASTNode(LeafType())
StructLiteralExp::interpret() LeafType()
CompoundStatement::interpret()
ExpStatement::interpret(assert(&this,"null this"))
AssertExp::interpret() assert(&this,"null this")
DotVarExp::interpret() this.Right
DotVarExp::interpret() this.Right
DotVarExp::interpret() this.Right
DotVarExp::interpret() this.Right
...an so on until stack overflow
The reason for the recursion happens is that in the contect of
DotVarExp::interpret istate->localThis == this so in ThisExp::interpret
the statement
istate->localThis->interpret(istate);
goes right back to DotVarExp::interpret again.
Unfortunately I don't really know enough about the internals of dmd so
say what the fix is, but I hope this information is helpful.
