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<p class="MsoNormal">I don’t think this has anything to do with optimization. If the type of the member expression base is completely known, it isn’t a dynamic call.
<br>
<br>
It seems that function (clang_Cursor_isDynamicCall is the one I found?) ends up calling MemberExpr->performsVirtualDispatch, which only considers AppleKext and full qualification.<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">I also note that the uses of performsVirtualDispatch calls getDevirutalizedMethod (<a href="https://clang.llvm.org/doxygen/DeclCXX_8cpp_source.html#l02107">https://clang.llvm.org/doxygen/DeclCXX_8cpp_source.html#l02107</a>).<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">I presume “isDynamicCall” (or some similar function) should be checking whether it can be devirtualized like this before deciding it is a dynamic call.<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal"><b>From:</b> cfe-dev <cfe-dev-bounces@lists.llvm.org> <b>On Behalf Of
</b>Jonathan Coe via cfe-dev<br>
<b>Sent:</b> Friday, May 15, 2020 6:37 AM<br>
<b>To:</b> Borges, Matt <matt.borges@sap.com><br>
<b>Cc:</b> cfe-dev@lists.llvm.org<br>
<b>Subject:</b> Re: [cfe-dev] clang_isDynamicCall always returns true for CallExpr which call virtual methods<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal">I guess that <span style="font-family:"Courier New"">clang_isDynamicCall</span> is not concerned with function calls that can be de-virtualised through optimisation (albeit fairly trivial optimisation).<br>
<br>
I'm interested to know how you could, in general, find out when a method will be called polymorphically but would guess that it's very hard as cross-translation unit optimisation (WPO) would have an effect. Clang's AST won't have access ot the info needed to
determine this (as far as I know).<br>
<br>
Please keep me posted on progress!<br>
<br>
Jon<o:p></o:p></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal">On Fri, 15 May 2020 at 14:28, Borges, Matt via cfe-dev <<a href="mailto:cfe-dev@lists.llvm.org">cfe-dev@lists.llvm.org</a>> wrote:<o:p></o:p></p>
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<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"><span lang="EN-CA">Hi,<o:p></o:p></span></p>
<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"><span lang="EN-CA"> <o:p></o:p></span></p>
<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"><span lang="EN-CA">Just resending. If I am asking this question on the wrong mailing list, please le me know.<o:p></o:p></span></p>
<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"><span lang="EN-CA"> <o:p></o:p></span></p>
<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"><span lang="EN-CA">Thanks,<o:p></o:p></span></p>
<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"><span lang="EN-CA">Matt<o:p></o:p></span></p>
<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"><span lang="EN-CA"> <o:p></o:p></span></p>
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<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"><b><span lang="EN-CA" style="color:black">From:
</span></b><span lang="EN-CA" style="color:black">Matt Borges <<a href="mailto:matt.borges@sap.com" target="_blank">matt.borges@sap.com</a>><br>
<b>Date: </b>Friday, May 8, 2020 at 11:36 AM<br>
<b>To: </b>"<a href="mailto:cfe-dev@lists.llvm.org" target="_blank">cfe-dev@lists.llvm.org</a>" <<a href="mailto:cfe-dev@lists.llvm.org" target="_blank">cfe-dev@lists.llvm.org</a>><br>
<b>Subject: </b>clang_isDynamicCall always returns true for CallExpr which call virtual methods</span><span lang="EN-CA"><o:p></o:p></span></p>
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<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"><span lang="EN-CA"> <o:p></o:p></span></p>
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<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"><span lang="EN-CA">Hi,<o:p></o:p></span></p>
<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"><span lang="EN-CA"> <o:p></o:p></span></p>
<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"><span lang="EN-CA">I’m visiting the AST of this simple code with libclang:<br>
<br>
</span><span lang="EN-CA" style="font-size:10.0pt;font-family:"Courier New"">class Base</span><span lang="EN-CA"><o:p></o:p></span></p>
<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"><span lang="EN-CA" style="font-size:10.0pt;font-family:"Courier New"">{</span><span lang="EN-CA"><o:p></o:p></span></p>
<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"><span lang="EN-CA" style="font-size:10.0pt;font-family:"Courier New""> public:</span><span lang="EN-CA"><o:p></o:p></span></p>
<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"><span lang="EN-CA" style="font-size:10.0pt;font-family:"Courier New""> virtual void Print() {}</span><span lang="EN-CA"><o:p></o:p></span></p>
<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"><span lang="EN-CA" style="font-size:10.0pt;font-family:"Courier New"">};</span><span lang="EN-CA"><o:p></o:p></span></p>
<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"><span lang="EN-CA" style="font-size:10.0pt;font-family:"Courier New""> </span><span lang="EN-CA"><o:p></o:p></span></p>
<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"><span lang="EN-CA" style="font-size:10.0pt;font-family:"Courier New"">class Derived : public Base</span><span lang="EN-CA"><o:p></o:p></span></p>
<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"><span lang="EN-CA" style="font-size:10.0pt;font-family:"Courier New"">{</span><span lang="EN-CA"><o:p></o:p></span></p>
<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"><span lang="EN-CA" style="font-size:10.0pt;font-family:"Courier New""> public:</span><span lang="EN-CA"><o:p></o:p></span></p>
<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"><span lang="EN-CA" style="font-size:10.0pt;font-family:"Courier New""> virtual void Print() {}</span><span lang="EN-CA"><o:p></o:p></span></p>
<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"><span lang="EN-CA" style="font-size:10.0pt;font-family:"Courier New"">};</span><span lang="EN-CA"><o:p></o:p></span></p>
<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"><span lang="EN-CA" style="font-size:10.0pt;font-family:"Courier New""> </span><span lang="EN-CA"><o:p></o:p></span></p>
<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"><span lang="EN-CA" style="font-size:10.0pt;font-family:"Courier New"">void func1( Base * b )</span><span lang="EN-CA"><o:p></o:p></span></p>
<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"><span lang="EN-CA" style="font-size:10.0pt;font-family:"Courier New"">{</span><span lang="EN-CA"><o:p></o:p></span></p>
<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"><span lang="EN-CA" style="font-size:10.0pt;font-family:"Courier New""> b->Print();</span><span lang="EN-CA"><o:p></o:p></span></p>
<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"><span lang="EN-CA" style="font-size:10.0pt;font-family:"Courier New"">}</span><span lang="EN-CA"><o:p></o:p></span></p>
<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"><span lang="EN-CA" style="font-size:10.0pt;font-family:"Courier New""> </span><span lang="EN-CA"><o:p></o:p></span></p>
<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"><span lang="EN-CA" style="font-size:10.0pt;font-family:"Courier New"">void func2( Base b )</span><span lang="EN-CA"><o:p></o:p></span></p>
<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"><span lang="EN-CA" style="font-size:10.0pt;font-family:"Courier New"">{</span><span lang="EN-CA"><o:p></o:p></span></p>
<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"><span lang="EN-CA" style="font-size:10.0pt;font-family:"Courier New""> b.Print();</span><span lang="EN-CA"><o:p></o:p></span></p>
<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"><span lang="EN-CA" style="font-size:10.0pt;font-family:"Courier New"">}</span><span lang="EN-CA"><o:p></o:p></span></p>
<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"><span lang="EN-CA" style="font-size:10.0pt;font-family:"Courier New""> </span><span lang="EN-CA"><o:p></o:p></span></p>
<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"><span lang="EN-CA" style="font-size:10.0pt;font-family:"Courier New"">void func3( Base & b )</span><span lang="EN-CA"><o:p></o:p></span></p>
<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"><span lang="EN-CA" style="font-size:10.0pt;font-family:"Courier New"">{</span><span lang="EN-CA"><o:p></o:p></span></p>
<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"><span lang="EN-CA" style="font-size:10.0pt;font-family:"Courier New""> b.Print();</span><span lang="EN-CA"><o:p></o:p></span></p>
<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"><span lang="EN-CA" style="font-size:10.0pt;font-family:"Courier New"">}</span><span lang="EN-CA"><o:p></o:p></span></p>
<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"><span lang="EN-CA" style="font-size:10.0pt;font-family:"Courier New""> </span><span lang="EN-CA"><o:p></o:p></span></p>
<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"><span lang="EN-CA">clang_isDynamicCall returns true for all three CallExpr cursors in the code. I would have expected clang_isDynamicCall to return false for the call in func2
because the call is definitely to the Print method of Base. Is this intended behaviour? If yes, is there another way to determine whether the function call is going to be made polymorphically?<o:p></o:p></span></p>
<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"><span lang="EN-CA"> <o:p></o:p></span></p>
<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"><span lang="EN-CA">Thanks in advance,<o:p></o:p></span></p>
<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"><span lang="EN-CA">Matt<o:p></o:p></span></p>
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<p class="MsoNormal">_______________________________________________<br>
cfe-dev mailing list<br>
<a href="mailto:cfe-dev@lists.llvm.org" target="_blank">cfe-dev@lists.llvm.org</a><br>
<a href="https://lists.llvm.org/cgi-bin/mailman/listinfo/cfe-dev" target="_blank">https://lists.llvm.org/cgi-bin/mailman/listinfo/cfe-dev</a><o:p></o:p></p>
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