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<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D">Reid, thanks for the response. I think I now have a path forward for adding target-dependent attributes as string attributes instead of enum attributes.<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D">For informational purposes, after digging deeper into how the bitcode reader and writer work for enum attributes, I conclude:<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D"><o:p> </o:p></span></p>
<p class="MsoListParagraph" style="text-indent:-.25in;mso-list:l0 level1 lfo1"><![if !supportLists]><span style="font-size:11.0pt;font-family:Symbol;color:#1F497D"><span style="mso-list:Ignore">·<span style="font:7.0pt "Times New Roman"">
</span></span></span><![endif]><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D">Attributes are encoded in the bitcode file as groups<o:p></o:p></span></p>
<p class="MsoListParagraph" style="text-indent:-.25in;mso-list:l0 level1 lfo1"><![if !supportLists]><span style="font-size:11.0pt;font-family:Symbol;color:#1F497D"><span style="mso-list:Ignore">·<span style="font:7.0pt "Times New Roman"">
</span></span></span><![endif]><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D">Each enum attribute within a group is identified by its encoding value which matches the value is was given in the AttrKind enum specification (i.e.
its ATTR_KIND_xxx value)<o:p></o:p></span></p>
<p class="MsoListParagraph" style="text-indent:-.25in;mso-list:l0 level1 lfo1"><![if !supportLists]><span style="font-size:11.0pt;font-family:Symbol;color:#1F497D"><span style="mso-list:Ignore">·<span style="font:7.0pt "Times New Roman"">
</span></span></span><![endif]><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D">BitcodeWriter handling of enum attributes:<o:p></o:p></span></p>
<p class="MsoListParagraph" style="margin-left:1.0in;text-indent:-.25in;mso-list:l0 level2 lfo1">
<![if !supportLists]><span style="font-size:11.0pt;font-family:"Courier New";color:#1F497D"><span style="mso-list:Ignore">o<span style="font:7.0pt "Times New Roman"">
</span></span></span><![endif]><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D">The bitcode writer has an EnumAttributeImpl version of the attribute kind which you can get from Attr.getKindAsEnum(); I believe this is the index
into the Attribute specification table that gets generated from Attributes.td when llvm/clang is built<o:p></o:p></span></p>
<p class="MsoListParagraph" style="margin-left:1.0in;text-indent:-.25in;mso-list:l0 level2 lfo1">
<![if !supportLists]><span style="font-size:11.0pt;font-family:"Courier New";color:#1F497D"><span style="mso-list:Ignore">o<span style="font:7.0pt "Times New Roman"">
</span></span></span><![endif]><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D">Calling getAttrKindEncoding(x) where x is Attr.getKindAsEnum() will then present the encoding value that goes into the bitcode file to identify the
attribute kind<o:p></o:p></span></p>
<p class="MsoListParagraph" style="margin-left:1.0in;text-indent:-.25in;mso-list:l0 level2 lfo1">
<![if !supportLists]><span style="font-size:11.0pt;font-family:"Courier New";color:#1F497D"><span style="mso-list:Ignore">o<span style="font:7.0pt "Times New Roman"">
</span></span></span><![endif]><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D">There is not a limitation on the size of the AttrKind enum.
<span style="background:yellow;mso-highlight:yellow">However, there is a static assert (~line 820+ - AttributeListImpl()) that enforces that the number of slots occupied in the AttrKind enum is less than (sizeof(AvailableFunctionAttrs) * CHAR_BITS). Since AvailableFunctionAttrs
currently has type uint64_t, this static assert needs to be updated or removed (it is currently incorrectly limiting the enum to 64 slots – including the Attribute::none slot).</span><o:p></o:p></span></p>
<p class="MsoListParagraph" style="text-indent:-.25in;mso-list:l0 level1 lfo1"><![if !supportLists]><span style="font-size:11.0pt;font-family:Symbol;color:#1F497D"><span style="mso-list:Ignore">·<span style="font:7.0pt "Times New Roman"">
</span></span></span><![endif]><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D">BitcodeReader handling of enum attributes:<o:p></o:p></span></p>
<p class="MsoListParagraph" style="margin-left:1.0in;text-indent:-.25in;mso-list:l0 level2 lfo1">
<![if !supportLists]><span style="font-size:11.0pt;font-family:"Courier New";color:#1F497D"><span style="mso-list:Ignore">o<span style="font:7.0pt "Times New Roman"">
</span></span></span><![endif]><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D">The reader no longer uses the getRawAttributeMask() or addRawAttributeValue() functions. I had incorrectly assumed that they were still in play.<o:p></o:p></span></p>
<p class="MsoListParagraph" style="margin-left:1.0in;text-indent:-.25in;mso-list:l0 level2 lfo1">
<![if !supportLists]><span style="font-size:11.0pt;font-family:"Courier New";color:#1F497D"><span style="mso-list:Ignore">o<span style="font:7.0pt "Times New Roman"">
</span></span></span><![endif]><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D">The reader uses getAttrFromCode() to map the encoded value of the attribute to the Attribute specification index (i.e. ATTR_KIND_xxx -> Attribute::xxx)<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D">The reason I became concerned about running out of slots in the AttrKind enum is because my work group has a couple of target-independent attributes that we
will be looking to upstream in the near future. When I attempted to merge changes from the upstream repo into our local source base (that contains an implementation of those attributes), the static assert mentioned above prevented a successful build.<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D">I propose to update or remove the above static assert so that it correctly reflects the current state of the bitcode reader/writer with respect to enum attributes.<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D">Does that make sense?<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D">~ Todd Snider<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>
<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""> Reid Kleckner [mailto:rnk@google.com]
<br>
<b>Sent:</b> Friday, March 15, 2019 4:29 PM<br>
<b>To:</b> Snider, Todd<br>
<b>Cc:</b> llvm-dev<br>
<b>Subject:</b> [EXTERNAL] Re: [llvm-dev] [RFC] We are running out of slots in the Attribute::AttrKind enum<o:p></o:p></span></p>
<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal">Why aren't string attributes appropriate for your use case? Why do you need the attribute to be a recognized enum?<o:p></o:p></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal">I cannot find any references to CMSE_NS_CALL anywhere in trunk LLVM. The only result google gave for me for it was:<o:p></o:p></p>
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<p class="MsoNormal"><a href="https://www.iar.com/globalassets/about-us/events/ew2019/ew2019-working-effectively-with-trustzone-devices.pdf">https://www.iar.com/globalassets/about-us/events/ew2019/ew2019-working-effectively-with-trustzone-devices.pdf</a><o:p></o:p></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal">I looked at the latest code for writing bitcode, and I don't think it uses a bitmask to store enum attributes anymore. See this code:<o:p></o:p></p>
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<p class="MsoNormal"><a href="https://github.com/llvm-git-prototype/llvm/blob/a845b0985672ee66c1cc8e070ca5d5ac6e89c0c9/llvm/lib/Bitcode/Writer/BitcodeWriter.cpp#L728">https://github.com/llvm-git-prototype/llvm/blob/a845b0985672ee66c1cc8e070ca5d5ac6e89c0c9/llvm/lib/Bitcode/Writer/BitcodeWriter.cpp#L728</a><o:p></o:p></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal">So, I don't think there are any compatibility issues with adding more attributes.<o:p></o:p></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal">In your next message, you mention AvailableFunctionAttrs, and I think all that needs to be done is to rewrite it to use std::bitset, as is done in AttrBuilder.<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 Thu, Mar 14, 2019 at 1:20 PM Snider, Todd via llvm-dev <<a href="mailto:llvm-dev@lists.llvm.org">llvm-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">I would like to add a target-dependent attribute to the LLVM IR, and the guidance in
<a href="http://llvm.org/docs/HowToUseAttributes.html" target="_blank">http://llvm.org/docs/HowToUseAttributes.html</a> says that target-dependent attributes should not occupy a slot in the Attribute::AttrKind enum, but I have yet to find an attribute that
is represented in the IR that does not also have a slot in the AttrKind enum.<o:p></o:p></p>
<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"> <o:p></o:p></p>
<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto">We are limited to 63 slots in the AttrKind enum because it is represented in the bitcode with a 64-bit bitmask. There is only one free slot left and I don’t want to use it for a
target-dependent attribute. I had anticipated that only target-independent attributes would have analogous ATTR_KIND identifiers in the AtttrKind enum, yet the ARM-specific CMSE_NS_CALL and CMSE_NS_ENTRY occupy slots in the AttrKind enum.<o:p></o:p></p>
<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"> <o:p></o:p></p>
<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto">Can someone point me to an example of a target-dependent attribute represented in the LLVM IR that does not occupy a slot in the AttrKind enum?<o:p></o:p></p>
<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"> <o:p></o:p></p>
<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto">Thanks,<o:p></o:p></p>
<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"> <o:p></o:p></p>
<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto">Todd Snider<o:p></o:p></p>
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<p class="MsoNormal">_______________________________________________<br>
LLVM Developers mailing list<br>
<a href="mailto:llvm-dev@lists.llvm.org" target="_blank">llvm-dev@lists.llvm.org</a><br>
<a href="https://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev" target="_blank">https://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev</a><o:p></o:p></p>
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