[cfe-dev] Why the argument of `delete' is converted to void* ?

[Jean-Daniel Dupas]

Le 4 juil. 2012 à 14:42, Abramo Bagnara a écrit :

> Il 04/07/2012 14:01, Jean-Daniel Dupas ha scritto:
>> 
>> Le 4 juil. 2012 à 12:42, Enea Zaffanella a écrit :
>> 
>>> We have noticed that, in the AST produced by clang, the expression 
>>> argument of a CXXDeleteExpr node is implicitly converted to void*:
>>> 
>>> # cat delete.cc
>>> struct S {};
>>> 
>>> void free(S* ps) {
>>>  delete ps;
>>> }
>>> 
>>> # llvm/Debug+Asserts/bin/clang -cc1 -ast-dump delete.cc
>>> [...]
>>> void free(S *ps) (CompoundStmt 0x4822650 <delete.cc:3:18, line:5:1>
>>>  (CXXDeleteExpr 0x4822628 <line:4:3, col:10> 'void'
>>>    (ImplicitCastExpr 0x4821df8 <col:10> 'void *' <BitCast>
>>>      (ImplicitCastExpr 0x4821de0 <col:10> 'struct S *' <LValueToRValue>
>>>        (DeclRefExpr 0x4821db8 <col:10> 'struct S *' lvalue ParmVar 
>>> 0x47eeb20 'ps' 'struct S *')))))
>>> 
>>> 
>>> What are the reasons for introducing such an implicit cast?
>>> 
>>> Enea.
>> 
>> Just a though, but isn't it because the signature of delete is:
>> 
>> operator delete(void *);
> 
> I don't think so:
> 
> delete ptr;
> 
> is something very different from
> 
> operator delete(ptr);


I'm not sure it is quite different.

This is the IR generated by clang++ for this code with c++filt _ZdlPv = operator delete(void*):

define void @_Z4freeP1S(%struct.S* %ps) nounwind uwtable ssp {
entry:
  %isnull = icmp eq %struct.S* %ps, null
  br i1 %isnull, label %delete.end, label %delete.notnull

delete.notnull:                                   ; preds = %entry
  %0 = getelementptr inbounds %struct.S* %ps, i64 0, i32 0
  tail call void @_ZdlPv(i8* %0) nounwind
  br label %delete.end

delete.end:                                       ; preds = %delete.notnull, %entry
  ret void
}

declare void @_ZdlPv(i8*) nounwind




-- Jean-Daniel




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