A CTFE Segfault (with explanation, but I'm not sure what the fix is).

[Gareth Charnock]

Done.

http://d.puremagic.com/issues/show_bug.cgi?id=5248

I'm sorry if I'm a bit over-cautious before submitting bugs.

On 21/11/10 22:18, Brad Roberts wrote:
> On 11/21/2010 2:11 PM, Gareth Charnock wrote:
>> 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.
>
> Please file a bug report:  http://d.puremagic.com/issues/
>
>