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<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D">Seems like there ought to be some kind of "unreachable" warning on the "return 0;" statement?<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D">--paulr<o:p></o:p></span></p>
<p class="MsoNormal"><a name="_MailEndCompose"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D"><o:p> </o:p></span></a></p>
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<p class="MsoNormal"><b><span style="font-size:10.0pt;font-family:"Tahoma","sans-serif"">From:</span></b><span style="font-size:10.0pt;font-family:"Tahoma","sans-serif""> cfe-dev-bounces@cs.uiuc.edu [mailto:cfe-dev-bounces@cs.uiuc.edu]
<b>On Behalf Of </b>David Blaikie<br>
<b>Sent:</b> Friday, September 19, 2014 7:25 AM<br>
<b>To:</b> Martin Richtarsky; Nick Lewycky<br>
<b>Cc:</b> cfe-dev Developers<br>
<b>Subject:</b> Re: [cfe-dev] Addresses of referenced objects in clang 3.5<o:p></o:p></span></p>
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<p class="MsoNormal"><o:p> </o:p></p>
<p>(+Nick who had a hand in implementing this optimization)<o:p></o:p></p>
<p>I don't think there's a flag to control this, no.<o:p></o:p></p>
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<p class="MsoNormal">On Sep 19, 2014 1:47 AM, "Richtarsky, Martin" <<a href="mailto:martin.richtarsky@sap.com">martin.richtarsky@sap.com</a>> wrote:<o:p></o:p></p>
<p class="MsoNormal">Hi,<br>
<br>
since clang 3.5 code as below is optimized away with -O1, assuming that the address of the object<br>
can never be NULL:<br>
<br>
class A { };<br>
<br>
int func(A& a)<br>
{<br>
if (&a)<br>
{<br>
return 1;<br>
}<br>
return 0;<br>
}<br>
<br>
int main()<br>
{<br>
A &a = *reinterpret_cast<A *>(0);<br>
return func(a);<br>
}<br>
<br>
clang++ -Wall -O1 ptrnull.cpp -o ptrnull<br>
<br>
ptrnull.cpp:5:10: warning: reference cannot be bound to dereferenced null pointer<br>
in well-defined C++ code; pointer may be assumed to always convert to true [-Wundefined-bool-conversion]<br>
if (&a)<br>
~~ ^<br>
1 warning generated.<br>
<br>
<br>
./ptrnull<br>
Return code: 1<br>
<br>
This is as described in the release notes.<br>
<br>
When changing func() as follows the warning is not shown, but clang still performs<br>
the same optimization. Shouldn't the warning be shown here aswell?<br>
<br>
int func(A& a)<br>
{<br>
A *aptr = &a;<br>
if (aptr)<br>
{<br>
return 1;<br>
}<br>
return 0;<br>
}<br>
<br>
Is it possible to disable this optimization specifically (without resorting to -O0)<br>
to gradually fix codebases that rely on such checks? I saw that I can use<br>
-fsanitize=null, which helps, but disabling the optimization would still<br>
be the best temporary workaround.<br>
<br>
Thanks and Best regards,<br>
Martin<br>
<br>
<br>
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