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</o:shapelayout></xml><![endif]--></head><body lang=EN-GB link=blue vlink=purple><div class=WordSection1><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D'>Thank you very much Richard!<o:p></o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D'><o:p> </o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D'>Attaching the updated patch for your review<o:p></o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D'><o:p> </o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D'><o:p> </o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D'><o:p> </o:p></span></p><div style='border:none;border-top:solid #B5C4DF 1.0pt;padding:3.0pt 0cm 0cm 0cm'><p class=MsoNormal><b><span lang=EN-US style='font-size:10.0pt;font-family:"Tahoma","sans-serif"'>From:</span></b><span lang=EN-US style='font-size:10.0pt;font-family:"Tahoma","sans-serif"'> metafoo@gmail.com [mailto:metafoo@gmail.com] <b>On Behalf Of </b>Richard Smith<br><b>Sent:</b> 10 January 2014 23:25<br><b>To:</b> Artyom Skrobov<br><b>Cc:</b> cfe commits<br><b>Subject:</b> Re: [PATCH] Warn when NULL is returned from 'operator new' without 'throw()'<o:p></o:p></span></p></div><p class=MsoNormal><o:p> </o:p></p><div><div><div><p class=MsoNormal>On Fri, Jan 10, 2014 at 5:07 AM, Artyom Skrobov <<a href="mailto:Artyom.Skrobov@arm.com" target="_blank">Artyom.Skrobov@arm.com</a>> wrote:<o:p></o:p></p><div><p class=MsoNormal style='margin-bottom:12.0pt'>Thank you for your suggestions Richard!<br>One point though:<o:p></o:p></p></div><div><p class=MsoNormal style='margin-bottom:12.0pt'>> Please use RetValExp->isNullPointerConstant instead.<br>> Please also add testcases for operator new returning nullptr, and<br>returning expressions such as 1 - 1, and for operator new marked as<br>'noexcept'.<o:p></o:p></p></div><div><p class=MsoNormal>I want to note that expressions such as 1-1 are invalid as return values<br>from operator new, and produce "error: cannot initialize return object of<br>type 'void *' with an rvalue of type 'int'"<o:p></o:p></p></div><div><p class=MsoNormal><o:p> </o:p></p></div><div><p class=MsoNormal>Expressions such as 1 - 1 are valid null pointer constants in C++98 but not in C++11.<o:p></o:p></p></div><div><p class=MsoNormal> <o:p></o:p></p></div><blockquote style='border:none;border-left:solid #CCCCCC 1.0pt;padding:0cm 0cm 0cm 6.0pt;margin-left:4.8pt;margin-right:0cm'><div><p class=MsoNormal>At the same time, expressions such as (void*)(1-1) are not recognized either<br>by isNullPointerConstant or by EvaluateAsInt as integer zeroes, namely<br>because they are not integers.<o:p></o:p></p></div></blockquote><div><p class=MsoNormal><o:p> </o:p></p></div><div><p class=MsoNormal>In C++11, (void*)(1 - 1) is a reinterpret_cast of 0 to void*, and isn't (necessarily) a null pointer. In C++98, it's a static_cast, and is a null pointer.<o:p></o:p></p></div><div><p class=MsoNormal> <o:p></o:p></p></div><blockquote style='border:none;border-left:solid #CCCCCC 1.0pt;padding:0cm 0cm 0cm 6.0pt;margin-left:4.8pt;margin-right:0cm'><div><p class=MsoNormal>For a reference, GCC doesn't warn on<br><br> void *operator new(size_t n) {<br> return (void*)(1-1);<br> }<br><br>which isn't too bad; but neither does it warn on<br><br> void *operator new(size_t n) {<br> void* blah = 0;<br> return blah;<br> }<o:p></o:p></p></div></blockquote><div><p class=MsoNormal><o:p> </o:p></p></div><div><p class=MsoNormal>OK, I would not expect a warning here.<o:p></o:p></p></div><div><p class=MsoNormal> <o:p></o:p></p></div><blockquote style='border:none;border-left:solid #CCCCCC 1.0pt;padding:0cm 0cm 0cm 6.0pt;margin-left:4.8pt;margin-right:0cm'><div><p class=MsoNormal>nor even on<br><br> void *operator new(size_t n) {<br> return (void*)0;<br> }<o:p></o:p></p></div></blockquote><div><p class=MsoNormal><o:p> </o:p></p></div><div><p class=MsoNormal>I *would* expect a warning here.<o:p></o:p></p></div><div><p class=MsoNormal> <o:p></o:p></p></div><blockquote style='border:none;border-left:solid #CCCCCC 1.0pt;padding:0cm 0cm 0cm 6.0pt;margin-left:4.8pt;margin-right:0cm'><div><p class=MsoNormal>which seems quite valuable to be able to detect.<br><br>isNullPointerConstant doesn't recognize the two latter cases as null pointer<br>constants, either.<o:p></o:p></p></div></blockquote><div><p class=MsoNormal><o:p> </o:p></p></div><div><p class=MsoNormal>Sorry for sending you in the wrong direction!<o:p></o:p></p></div><div><p class=MsoNormal> <o:p></o:p></p></div><blockquote style='border:none;border-left:solid #CCCCCC 1.0pt;padding:0cm 0cm 0cm 6.0pt;margin-left:4.8pt;margin-right:0cm'><div><p class=MsoNormal>Do you think Clang should be able to detect such null-pointer-expressions?<br>If so, could you advise how it could be implemented, seeing that<br>isNullPointerConstant and EvaluateAsInt prove ineffective?<o:p></o:p></p></div></blockquote><div><p class=MsoNormal><o:p> </o:p></p></div><div><p class=MsoNormal>It looks like the best way to achieve this is to use Expr::EvaluateAsBooleanCondition on the (converted) return expression. That matches what we do for __attribute__((nonnull)).<o:p></o:p></p></div></div></div></div></div></body></html>