[cfe-dev] operator new

[Sebastian Redl]

On 11.04.2012, at 16:32, Михаил wrote:

> Hi.
> 
> Is there a way to understand what class(struct) was created by operator new by analysing generated bytecode? 
> 
> I thought that after   %call = tail call noalias i8* @_Znwj(i32 <size>)  is goes bitcast of %call to need struct, but for next example it is wrong.
> 
> For exampe I have a function:
> 
> Query* WildcardQuery::clone() const{
> 	return _CLNEW WildcardQuery(*this);
> }
> 
> And bytecode for this:
> 
> define %"class.lucene::search::Query.1814"* @_ZNK6lucene6search13WildcardQuery5cloneEv(%"class.lucene::search::WildcardQuery.2404"* nocapture %this) align 2 {
> entry:
>  %call = tail call noalias i8* @_Znwj(i32 12)
>  %0 = bitcast i8* %call to %"class.lucene::search::MultiTermQuery.1815"*
>  %1 = getelementptr inbounds %"class.lucene::search::WildcardQuery.2404"* %this, i32 0, i32 0
>  invoke void @_ZN6lucene6search14MultiTermQueryC2ERKS1_(%"class.lucene::search::MultiTermQuery.1815"* %0, %"class.lucene::search::MultiTermQuery.1815"* %1)
>          to label %invoke.cont unwind label %lpad

That's the inlined base constructor.

> 
> invoke.cont:                                      ; preds = %entry
>  %2 = bitcast i8* %call to i32 (...)***
>  store i32 (...)** bitcast (i8** getelementptr inbounds ([13 x i8*]* @_ZTVN6lucene6search13WildcardQueryE, i32 0, i32 2) to i32 (...)**), i32 (...)*** %2, align 4

That's the inlined vtable initialization.

>  %3 = bitcast i8* %call to %"class.lucene::search::Query.1814"*
>  ret %"class.lucene::search::Query.1814"* %3

And that's the cast to the return type.

The question is, why is the constructor of WildcardQuery inlined here? Did you run any inlining pass? (It could be that Clang inlines trivial constructors itself.)

Sebastian