<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=""><br class=""><div><br class=""><blockquote type="cite" class=""><div class="">On Sep 23, 2019, at 15:15, Shoaib Meenai via libcxx-dev <<a href="mailto:libcxx-dev@lists.llvm.org" class="">libcxx-dev@lists.llvm.org</a>> wrote:</div><br class="Apple-interchange-newline"><div class=""><div class="WordSection1" style="page: WordSection1; caret-color: rgb(0, 0, 0); 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; text-decoration: none;"><div style="margin: 0in 0in 0.0001pt; font-size: 11pt; font-family: Calibri, sans-serif;" class="">Ah, sorry – my apologies.<o:p class=""></o:p></div><div style="margin: 0in 0in 0.0001pt; font-size: 11pt; font-family: Calibri, sans-serif;" class=""><o:p class=""> </o:p></div><div style="border-style: solid none none; border-top-width: 1pt; border-top-color: rgb(181, 196, 223); padding: 3pt 0in 0in;" class=""><div style="margin: 0in 0in 0.0001pt; font-size: 11pt; font-family: Calibri, sans-serif;" class=""><b class=""><span style="font-size: 12pt;" class="">From:<span class="Apple-converted-space"> </span></span></b><span style="font-size: 12pt;" class="">Marshall Clow <<a href="mailto:mclow.lists@gmail.com" class="">mclow.lists@gmail.com</a>><br class=""><b class="">Date:<span class="Apple-converted-space"> </span></b>Monday, September 23, 2019 at 12:14 PM<br class=""><b class="">To:<span class="Apple-converted-space"> </span></b>Shoaib Meenai <<a href="mailto:smeenai@fb.com" class="">smeenai@fb.com</a>><br class=""><b class="">Cc:<span class="Apple-converted-space"> </span></b>"<a href="mailto:libcxx-dev@lists.llvm.org" class="">libcxx-dev@lists.llvm.org</a>" <<a href="mailto:libcxx-dev@lists.llvm.org" class="">libcxx-dev@lists.llvm.org</a>><br class=""><b class="">Subject:<span class="Apple-converted-space"> </span></b>Re: [libcxx-dev] Non-merged type info name comparison<o:p class=""></o:p></span></div></div><div class=""><div style="margin: 0in 0in 0.0001pt; font-size: 11pt; font-family: Calibri, sans-serif;" class=""><o:p class=""> </o:p></div></div><div class=""><div class=""><div style="margin: 0in 0in 0.0001pt; font-size: 11pt; font-family: Calibri, sans-serif;" class="">On Mon, Sep 23, 2019 at 12:02 PM Shoaib Meenai via libcxx-dev <<a href="mailto:libcxx-dev@lists.llvm.org" style="color: purple; text-decoration: underline;" class="">libcxx-dev@lists.llvm.org</a>> wrote:<o:p class=""></o:p></div></div><div class=""><blockquote style="border-style: none none none solid; border-left-width: 1pt; border-left-color: rgb(204, 204, 204); padding: 0in 0in 0in 6pt; margin-left: 4.8pt; margin-right: 0in;" class=""><div class=""><div class=""><div style="margin: 0in 0in 0.0001pt; font-size: 11pt; font-family: Calibri, sans-serif;" class="">In<span class="Apple-converted-space"> </span><a href="https://urldefense.proofpoint.com/v2/url?u=https-3A__reviews.llvm.org_rL361913&d=DwMFaQ&c=5VD0RTtNlTh3ycd41b3MUw&r=o3kDXzdBUE3ljQXKeTWOMw&m=zXNo5HfpEBs2AeK5MYbybBHSXRWS2rfFR2LYPo1zuhA&s=5In-WOhspL-mxLcgsafyIl0_G_S9IkKnfaj3lVT6y44&e=" target="_blank" style="color: purple; text-decoration: underline;" class="">https://reviews.llvm.org/rL361913</a>, libc++ gained the option to make type info comparisons use a strcmp on the type info name, which is useful for when we can’t guarantee RTTI uniqueness. I believe libstdc++ also defaults to strcmp comparisons. However, libstdc++ doesn’t perform the string comparison when the type info name begins with the * character [1], which is the case for e.g. types defined in anonymous namespaces. Should libc++’s implementation be changed to match, at least when targeting Linux?</div></div></div></blockquote></div></div></div></div></blockquote><div>Actually, in what cases can we guarantee that RTTI has been fully duplicated? For example, I don't think anything prevents users from using a shared library that redefines the RTTI for a type, no?</div><div><br class=""></div><div>I've had a couple of complaints of people saying we should do the string comparison -- I wonder whether we might have put performance above correctness in this case. My reasoning is that if we don't have a valid use case under which RTTI is guaranteed to be unique, we should do the string comparison. And if we do have such a use case, we should evaluate how prominent it is to determine whether we do the slow-but-correct approach by default, or the fast-but-sometimes-incorrect approach by default.</div><div><br class=""></div><div>Louis</div><br class=""><blockquote type="cite" class=""><div class=""><div class="WordSection1" style="page: WordSection1; caret-color: rgb(0, 0, 0); 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; text-decoration: none;"><div class=""><div class=""><blockquote style="border-style: none none none solid; border-left-width: 1pt; border-left-color: rgb(204, 204, 204); padding: 0in 0in 0in 6pt; margin-left: 4.8pt; margin-right: 0in;" class=""><div class=""><div class=""><div style="margin: 0in 0in 0.0001pt; font-size: 11pt; font-family: Calibri, sans-serif;" class=""><o:p class=""></o:p></div><div style="margin: 0in 0in 0.0001pt; font-size: 11pt; font-family: Calibri, sans-serif;" class=""> <o:p class=""></o:p></div><div style="margin: 0in 0in 0.0001pt; font-size: 11pt; font-family: Calibri, sans-serif;" class="">[1]<span class="Apple-converted-space"> </span><a href="https://github.com/gcc-mirror/gcc/blo" target="_blank" style="color: purple; text-decoration: underline;" class="">https://github.com/gcc-mirror/gcc/blo</a> (rest of link elided)<o:p class=""></o:p></div></div></div><div style="margin: 0in 0in 0.0001pt; font-size: 11pt; font-family: Calibri, sans-serif;" class=""><o:p class=""> </o:p></div></blockquote><div class=""><div style="margin: 0in 0in 0.0001pt; font-size: 11pt; font-family: Calibri, sans-serif;" class=""><o:p class=""> </o:p></div></div><div class=""><div style="margin: 0in 0in 0.0001pt; font-size: 11pt; font-family: Calibri, sans-serif;" class="">Please don't post links/snippets of GPL code here; we can't look at them for licensing reasons.<o:p class=""></o:p></div></div><div class=""><div style="margin: 0in 0in 0.0001pt; font-size: 11pt; font-family: Calibri, sans-serif;" class=""><o:p class=""> </o:p></div></div><div class=""><div style="margin: 0in 0in 0.0001pt; font-size: 11pt; font-family: Calibri, sans-serif;" class="">-- Marshall<o:p class=""></o:p></div></div><div class=""><div style="margin: 0in 0in 0.0001pt; font-size: 11pt; font-family: Calibri, sans-serif;" class=""> <o:p class=""></o:p></div></div></div></div></div><span style="caret-color: rgb(0, 0, 0); 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; text-decoration: none; float: none; display: inline !important;" class="">_______________________________________________</span><br style="caret-color: rgb(0, 0, 0); font-family: Helvetica; font-size: 12px; font-style: normal; font-variant-caps: normal; font-weight: normal; letter-spacing: normal; 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