__fastcall for overlapped virtual destructor of Delphi base class in CLANG compiler

[AlexBelo 12]

HI all.

 

RAD 11.1.5

 

Consider the following code:

class dExc : public TObject
{
 public:
  static int Counter;
  dExc() { Counter++; printf(" dExc\n"); }
  /* __fastcall */ ~dExc() { Counter--; printf("~dExc\n"); }
};

int dExc::Counter=0;

If I compile this in "classic" mode without __fastcall I get:

[bcc32 Error] Main.cpp(19): E2113 Virtual function '~dExc::dExc()' conflicts with base class 'TObject'

 

CLANG-32 compiler shows "Success", but program crashes in destructor of ~dExc.

 

Adding __fastcall produces workable exe in both cases.

(CLANG-64 version works with and without __fastcall because 64-bit uses its own call convention AFAIK)

 

Is this a bug in CLANG-32 compiler?

 

Edited August 2, 2022 by AlexBelo

[Der schöne Günther 338]

Yes, __fastcall has zero effect on x64 and ARM, compilers will usually just ignore it.

 

It seems ctors/dtors are a special case when it comes to calling conventions.

 

See

• [RSP-30762] [bcc32c]: fastcall calling convention ignored on constructor/destructor - Embarcadero Technologies
• [RSP-23671] Unexpected compiler error - Embarcadero Technologies
• [RSP-33071] [bcc32c error] virtual function '~XXX' has different calling convention attributes ('void ()') than the function it overrides (which has calling convention 'void () __attribute__((fastcall))') : overridden virtual function is here - Embarcadero Technologies

 

From what I gathered, Embarcadero maintained their own patch queue of modifications for clang so that calling conventions were handled also for constructors/destructors but appearantly, they are struggling to keep up with clang development.

[AlexBelo 12]

Thank you for additional information.

 

__fastcall for overlapped virtual destructor of Delphi-based class in CLANG32 compiler

https://quality.embarcadero.com/browse/RSP-38783