<html><head><meta http-equiv="Content-Type" content="text/html; charset=utf-8"></head><body style="word-wrap: break-word; -webkit-nbsp-mode: space; line-break: after-white-space;" class="">Hi Richard,<div class=""><br class=""></div><div class="">Thanks for your reply!<br class=""><div><br class=""><blockquote type="cite" class=""><div class="">On Mar 30, 2018, at 8:49 PM, Richard Smith <<a href="mailto:richard@metafoo.co.uk" class="">richard@metafoo.co.uk</a>> wrote:</div><br class="Apple-interchange-newline"><div class=""><div dir="auto" style="font-family: Helvetica; font-size: 12px; font-style: normal; font-variant-caps: normal; font-weight: normal; letter-spacing: normal; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; word-spacing: 0px; -webkit-text-stroke-width: 0px;" class=""><div class=""><div class="gmail_quote"><blockquote class="gmail_quote" style="margin: 0px 0px 0px 0.8ex; border-left-width: 1px; border-left-style: solid; border-left-color: rgb(204, 204, 204); padding-left: 1ex;"><div style="word-wrap: break-word; line-break: after-white-space;" class=""><div class=""><div class=""><div class=""><br class=""><br class=""></div>Right, sure, but I don’t have a convenient way to find that DecompositionDecl from a given BindingDecl,</div><div class="">and sometimes I need to act based on the BindingDecl alone.</div></div></div></blockquote></div></div><div dir="auto" class=""><br class=""></div><div dir="auto" class="">Can you give an example?</div></div></div></blockquote><div><br class=""></div><div>Let’s say a structured binding is written into, and then some function is called, and then we read from that binding again.</div><div>If it was global, we have to assume any function call can invalidate it, but if it’s local and it wasn’t passed as a parameter,</div><div>chances are it will remain the same.</div><div><br class=""></div><blockquote type="cite" class=""><div dir="auto" style="font-family: Helvetica; font-size: 12px; font-style: normal; font-variant-caps: normal; font-weight: normal; letter-spacing: normal; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; word-spacing: 0px; -webkit-text-stroke-width: 0px;" class=""><div dir="auto" class="">It was chosen because it matches the semantic model desired by the designers of the feature. For example, you can't handle bitfields if you model structured bindings as reference variables.</div><div dir="auto" class=""><br class=""></div><div dir="auto" class="">This was a somewhat controversial decision, but it doesn't look like it's going to be reversed.</div><div dir="auto" class=""><div class="gmail_quote"><blockquote class="gmail_quote" style="margin: 0px 0px 0px 0.8ex; border-left-width: 1px; border-left-style: solid; border-left-color: rgb(204, 204, 204); padding-left: 1ex;"><div style="word-wrap: break-word; line-break: after-white-space;" class=""><div class=""><div class=""><blockquote type="cite" class=""><div class=""><div dir="ltr" style="font-family: Helvetica; font-size: 12px; font-style: normal; font-variant-caps: normal; font-weight: normal; letter-spacing: normal; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; word-spacing: 0px;" class=""><div class="gmail_extra"><div class="gmail_quote"><div class="">That's what the CFG for the above function should represent.</div></div></div></div></div></blockquote><div class=""><br class=""></div><div class="">Sorry, I’m not sure what do you mean here: from my understanding, CFG does not transform AST inside statements (apart from maybe tiny syntactic things).</div></div></div></div></blockquote></div></div><div dir="auto" class=""><br class=""></div><div dir="auto" class="">IIRC, the CFG expands CXXDefaultArgExprs and CXXDefaultInitExprs; this case is analogous to those.</div></div></blockquote><div><br class=""></div><div>Yes, you are right; To be honest, I wasn’t previously familiar with that part of the codebase.</div><div>Yet still, those are very simple replacements, and IIRC those are the only two.</div><div><br class=""></div><div>Supporting structured bindings would be indeed easier if we could have a simpler AST,</div><div>could you give an advice on what would be an equivalent AST we should rewrite to?</div><div><br class=""></div><div>Would producing a MemberExpr reading from the struct at *use* time be completely semantically equivalent?</div><div>My previous impression was that for structured bindings load from the struct happens when the binding occurs,</div><div>not when the actual read is performed.</div><div>[though of course such rewrites would impede producing good diagnostic messages for the user]</div><br class=""><blockquote type="cite" class=""><div dir="auto" style="font-family: Helvetica; font-size: 12px; font-style: normal; font-variant-caps: normal; font-weight: normal; letter-spacing: normal; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; word-spacing: 0px; -webkit-text-stroke-width: 0px;" class=""><div dir="auto" class=""><div class="gmail_quote"><blockquote class="gmail_quote" style="margin: 0px 0px 0px 0.8ex; border-left-width: 1px; border-left-style: solid; border-left-color: rgb(204, 204, 204); padding-left: 1ex;"><div style="word-wrap: break-word; line-break: after-white-space;" class=""><div class=""><div class=""><blockquote type="cite" class=""><div class=""><div dir="ltr" style="font-family: Helvetica; font-size: 12px; font-style: normal; font-variant-caps: normal; font-weight: normal; letter-spacing: normal; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; word-spacing: 0px;" class=""><div class="gmail_extra"><div class="gmail_quote"><div class="">The BindingDecls should not even show up, except as sugar so that clients who care can know that the 'e.x' expression was /written as/ 'v'.</div><blockquote class="gmail_quote" style="margin: 0px 0px 0px 0.8ex; border-left-width: 1px; border-left-style: solid; border-left-color: rgb(204, 204, 204); padding-left: 1ex;"><div style="word-wrap: break-word; line-break: after-white-space;" class=""><div class=""><span class=""><blockquote type="cite" class=""><div class=""><div dir="ltr" class=""><div class="gmail_extra"><div class="gmail_quote"><div class="">I'd imagine this is best modeled by generating CFG nodes for the subexpression on each occurrence of such a DeclRefExpr, much like (IIRC) is done for CXXDefaultArgExpr and CXXDefaultInitExpr. That seems like it would not require too many special cases elsewhere.</div><div class=""><br class=""></div><div class="">(Perhaps the static analyzer needs more than that in order to produce more user-friendly diagnostics?)</div></div></div></div></div></blockquote><div class=""><br class=""></div></span>We are not even there yet for structured bindings, just trying to make the analyzer understand them.<br class=""><br class=""></div><div class=""><br class=""></div><br class=""></div><br class="">_______________________________________________<br class="">cfe-dev mailing list<br class=""><a href="mailto:cfe-dev@lists.llvm.org" target="_blank" rel="noreferrer" class="">cfe-dev@lists.llvm.org</a><br class=""><a href="http://lists.llvm.org/cgi-bin/mailman/listinfo/cfe-dev" rel="noreferrer noreferrer" target="_blank" class="">http://lists.llvm.org/cgi-bin/mailman/listinfo/cfe-dev</a></blockquote></div></div></div></div></blockquote></div><br class=""></div></div>_______________________________________________<br class="">cfe-dev mailing list<br class=""><a href="mailto:cfe-dev@lists.llvm.org" target="_blank" rel="noreferrer" class="">cfe-dev@lists.llvm.org</a><br class=""><a href="http://lists.llvm.org/cgi-bin/mailman/listinfo/cfe-dev" rel="noreferrer noreferrer" target="_blank" class="">http://lists.llvm.org/cgi-bin/mailman/listinfo/cfe-dev</a></blockquote></div></div></div></blockquote></div><br class=""></div></body></html>