Thank you very much Richard!
Attaching the updated patch for your review From: [email protected] [mailto:[email protected]] On Behalf Of Richard Smith Sent: 10 January 2014 23:25 To: Artyom Skrobov Cc: cfe commits Subject: Re: [PATCH] Warn when NULL is returned from 'operator new' without 'throw()' On Fri, Jan 10, 2014 at 5:07 AM, Artyom Skrobov <[email protected]> wrote: Thank you for your suggestions Richard! One point though: > Please use RetValExp->isNullPointerConstant instead. > Please also add testcases for operator new returning nullptr, and returning expressions such as 1 - 1, and for operator new marked as 'noexcept'. I want to note that expressions such as 1-1 are invalid as return values from operator new, and produce "error: cannot initialize return object of type 'void *' with an rvalue of type 'int'" Expressions such as 1 - 1 are valid null pointer constants in C++98 but not in C++11. At the same time, expressions such as (void*)(1-1) are not recognized either by isNullPointerConstant or by EvaluateAsInt as integer zeroes, namely because they are not integers. 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. For a reference, GCC doesn't warn on void *operator new(size_t n) { return (void*)(1-1); } which isn't too bad; but neither does it warn on void *operator new(size_t n) { void* blah = 0; return blah; } OK, I would not expect a warning here. nor even on void *operator new(size_t n) { return (void*)0; } I *would* expect a warning here. which seems quite valuable to be able to detect. isNullPointerConstant doesn't recognize the two latter cases as null pointer constants, either. Sorry for sending you in the wrong direction! Do you think Clang should be able to detect such null-pointer-expressions? If so, could you advise how it could be implemented, seeing that isNullPointerConstant and EvaluateAsInt prove ineffective? 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)).
operator-new-NULL.updated.patch
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