<html><head></head><body style="word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space; "><br><div><div>Le 4 juil. 2012 à 15:57, Enea Zaffanella a écrit :</div><br class="Apple-interchange-newline"><blockquote type="cite"><div>On 07/04/2012 03:35 PM, Jean-Daniel Dupas wrote:<br><blockquote type="cite"><br></blockquote><blockquote type="cite">Le 4 juil. 2012 à 14:42, Abramo Bagnara a écrit :<br></blockquote><blockquote type="cite"><br></blockquote><blockquote type="cite"><blockquote type="cite">Il 04/07/2012 14:01, Jean-Daniel Dupas ha scritto:<br></blockquote></blockquote><blockquote type="cite"><blockquote type="cite"><blockquote type="cite"><br></blockquote></blockquote></blockquote><blockquote type="cite"><blockquote type="cite"><blockquote type="cite">Le 4 juil. 2012 à 12:42, Enea Zaffanella a écrit :<br></blockquote></blockquote></blockquote><blockquote type="cite"><blockquote type="cite"><blockquote type="cite"><br></blockquote></blockquote></blockquote><blockquote type="cite"><blockquote type="cite"><blockquote type="cite"><blockquote type="cite">We have noticed that, in the AST produced by clang, the expression<br></blockquote></blockquote></blockquote></blockquote><blockquote type="cite"><blockquote type="cite"><blockquote type="cite"><blockquote type="cite">argument of a CXXDeleteExpr node is implicitly converted to void*:<br></blockquote></blockquote></blockquote></blockquote><blockquote type="cite"><blockquote type="cite"><blockquote type="cite"><blockquote type="cite"><br></blockquote></blockquote></blockquote></blockquote><blockquote type="cite"><blockquote type="cite"><blockquote type="cite"><blockquote type="cite"># cat delete.cc<br></blockquote></blockquote></blockquote></blockquote><blockquote type="cite"><blockquote type="cite"><blockquote type="cite"><blockquote type="cite">struct S {};<br></blockquote></blockquote></blockquote></blockquote><blockquote type="cite"><blockquote type="cite"><blockquote type="cite"><blockquote type="cite"><br></blockquote></blockquote></blockquote></blockquote><blockquote type="cite"><blockquote type="cite"><blockquote type="cite"><blockquote type="cite">void free(S* ps) {<br></blockquote></blockquote></blockquote></blockquote><blockquote type="cite"><blockquote type="cite"><blockquote type="cite"><blockquote type="cite"> delete ps;<br></blockquote></blockquote></blockquote></blockquote><blockquote type="cite"><blockquote type="cite"><blockquote type="cite"><blockquote type="cite">}<br></blockquote></blockquote></blockquote></blockquote><blockquote type="cite"><blockquote type="cite"><blockquote type="cite"><blockquote type="cite"><br></blockquote></blockquote></blockquote></blockquote><blockquote type="cite"><blockquote type="cite"><blockquote type="cite"><blockquote type="cite"># llvm/Debug+Asserts/bin/clang -cc1 -ast-dump delete.cc<br></blockquote></blockquote></blockquote></blockquote><blockquote type="cite"><blockquote type="cite"><blockquote type="cite"><blockquote type="cite">[...]<br></blockquote></blockquote></blockquote></blockquote><blockquote type="cite"><blockquote type="cite"><blockquote type="cite"><blockquote type="cite">void free(S *ps) (CompoundStmt 0x4822650 <delete.cc:3:18, line:5:1><br></blockquote></blockquote></blockquote></blockquote><blockquote type="cite"><blockquote type="cite"><blockquote type="cite"><blockquote type="cite"> (CXXDeleteExpr 0x4822628 <line:4:3, col:10> 'void'<br></blockquote></blockquote></blockquote></blockquote><blockquote type="cite"><blockquote type="cite"><blockquote type="cite"><blockquote type="cite"> (ImplicitCastExpr 0x4821df8 <col:10> 'void *' <BitCast><br></blockquote></blockquote></blockquote></blockquote><blockquote type="cite"><blockquote type="cite"><blockquote type="cite"><blockquote type="cite"> (ImplicitCastExpr 0x4821de0 <col:10> 'struct S *' <LValueToRValue><br></blockquote></blockquote></blockquote></blockquote><blockquote type="cite"><blockquote type="cite"><blockquote type="cite"><blockquote type="cite"> (DeclRefExpr 0x4821db8 <col:10> 'struct S *' lvalue ParmVar<br></blockquote></blockquote></blockquote></blockquote><blockquote type="cite"><blockquote type="cite"><blockquote type="cite"><blockquote type="cite">0x47eeb20 'ps' 'struct S *')))))<br></blockquote></blockquote></blockquote></blockquote><blockquote type="cite"><blockquote type="cite"><blockquote type="cite"><blockquote type="cite"><br></blockquote></blockquote></blockquote></blockquote><blockquote type="cite"><blockquote type="cite"><blockquote type="cite"><blockquote type="cite"><br></blockquote></blockquote></blockquote></blockquote><blockquote type="cite"><blockquote type="cite"><blockquote type="cite"><blockquote type="cite">What are the reasons for introducing such an implicit cast?<br></blockquote></blockquote></blockquote></blockquote><blockquote type="cite"><blockquote type="cite"><blockquote type="cite"><blockquote type="cite"><br></blockquote></blockquote></blockquote></blockquote><blockquote type="cite"><blockquote type="cite"><blockquote type="cite"><blockquote type="cite">Enea.<br></blockquote></blockquote></blockquote></blockquote><blockquote type="cite"><blockquote type="cite"><blockquote type="cite"><br></blockquote></blockquote></blockquote><blockquote type="cite"><blockquote type="cite"><blockquote type="cite">Just a though, but isn't it because the signature of delete is:<br></blockquote></blockquote></blockquote><blockquote type="cite"><blockquote type="cite"><blockquote type="cite"><br></blockquote></blockquote></blockquote><blockquote type="cite"><blockquote type="cite"><blockquote type="cite">operator delete(void *);<br></blockquote></blockquote></blockquote><blockquote type="cite"><blockquote type="cite"><br></blockquote></blockquote><blockquote type="cite"><blockquote type="cite">I don't think so:<br></blockquote></blockquote><blockquote type="cite"><blockquote type="cite"><br></blockquote></blockquote><blockquote type="cite"><blockquote type="cite">delete ptr;<br></blockquote></blockquote><blockquote type="cite"><blockquote type="cite"><br></blockquote></blockquote><blockquote type="cite"><blockquote type="cite">is something very different from<br></blockquote></blockquote><blockquote type="cite"><blockquote type="cite"><br></blockquote></blockquote><blockquote type="cite"><blockquote type="cite">operator delete(ptr);<br></blockquote></blockquote><blockquote type="cite"><br></blockquote><blockquote type="cite"><br></blockquote><blockquote type="cite">I'm not sure it is quite different.<br></blockquote><blockquote type="cite"><br></blockquote><blockquote type="cite">This is the IR generated by clang++ for this code with c++filt _ZdlPv =<br></blockquote><blockquote type="cite">operator delete(void*):<br></blockquote><blockquote type="cite"><br></blockquote><blockquote type="cite">define void @_Z4freeP1S(%struct.S* %ps) nounwind uwtable ssp {<br></blockquote><blockquote type="cite">entry:<br></blockquote><blockquote type="cite"> %isnull = icmp eq %struct.S* %ps, null<br></blockquote><blockquote type="cite"> br i1 %isnull, label %delete.end, label %delete.notnull<br></blockquote><blockquote type="cite"><br></blockquote><blockquote type="cite">delete.notnull: ; preds = %entry<br></blockquote><blockquote type="cite"> %0 = getelementptr inbounds %struct.S* %ps, i64 0, i32 0<br></blockquote><blockquote type="cite"> tail call void @_ZdlPv(i8* %0) nounwind<br></blockquote><blockquote type="cite"> br label %delete.end<br></blockquote><blockquote type="cite"><br></blockquote><blockquote type="cite">delete.end: ; preds = %delete.notnull, %entry<br></blockquote><blockquote type="cite"> ret void<br></blockquote><blockquote type="cite">}<br></blockquote><blockquote type="cite"><br></blockquote><blockquote type="cite">declare void @_ZdlPv(i8*) nounwind<br></blockquote><blockquote type="cite"><br></blockquote><blockquote type="cite"><br></blockquote><blockquote type="cite"><br></blockquote><blockquote type="cite"><br></blockquote><blockquote type="cite">-- Jean-Daniel<br></blockquote><br><br>Sorry for the misunderstanding, but the original question was not really meant to be restricted to classes having a trivial destructor (if you add a non-trivial destructor to class S then "delete ps" will call it, whereas "operator delete(ps)" will not).<br><br>To rephrase my question: since in the general case "delete ps" may also call the destructor, why is its argument (always) converted to void*?<br><br>Cheers,<br>Enea.<br></div></blockquote><br></div><div><br></div><div>AFAIK, even with a non trivial destructor, the code always end up calling the operator delete(void *) to free the memory.</div><div><br></div><div>It will generate something like this:</div><div><br></div><div>call the destructor on the struct.</div><div>call operator delete((void *)ps);</div><div><br></div><div>or in LLVM IR:</div><div><div style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; font-family: Menlo; font-size: 11px; "> tail call void @_ZN1SD1Ev(%struct.S* %ps) nounwind // ps->~S()</div><div style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; font-family: Menlo; font-size: 11px; "> %<span style="color: #2f2fcf">0</span> = getelementptr inbounds %struct.S* %ps, i64 <span style="color: #2f2fcf">0</span>, i32 <span style="color: #2f2fcf">0</span></div><div style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; font-family: Menlo; font-size: 11px; "> tail call void @_ZdlPv(i8* %<span style="color: #2f2fcf">0</span>) nounwind // operator delete((void *)ps)</div><div style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; font-family: Menlo; font-size: 11px; "> br label %delete.end</div><div style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; font-family: Menlo; font-size: 11px; "><br></div></div><br><div apple-content-edited="true">
<span class="Apple-style-span" style="border-collapse: separate; -webkit-border-horizontal-spacing: 0px; -webkit-border-vertical-spacing: 0px; "><div>-- Jean-Daniel</div><div><br></div><div><br></div></span><br class="Apple-interchange-newline">
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