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<p class="msipheader87abd423" style="margin:0in"><span style="font-size:10.0pt;font-family:"Arial",sans-serif;color:#317100">[AMD Public Use]</span><o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal" style="margin-bottom:12.0pt">Hi Paul,<o:p></o:p></p>
<p class="MsoNormal">Thanks for the hints for a possible implementation by mimicking something close to Enumerations. I noticed 2 problems doing so:<o:p></o:p></p>
<ol style="margin-top:0in" start="1" type="1">
<li class="MsoListParagraph" style="margin-left:0in;mso-list:l3 level1 lfo3">Enumerators are integers, while a constant can be of any type(at least basic types provided by the base language).<o:p></o:p></li><li class="MsoListParagraph" style="margin-left:0in;mso-list:l3 level1 lfo3">Restricting Scope of a Constant, Scoping concerns with Enumerator as depicted in
<a href="https://bugs.llvm.org/show_bug.cgi?id=49153">https://bugs.llvm.org/show_bug.cgi?id=49153</a><o:p></o:p></li></ol>
<p class="MsoNormal" style="margin-left:.25in"><o:p> </o:p></p>
<p class="MsoNormal">We did some digging in LLVM history, seems like there were some attempts for bringing DW_TAG_constant back in 2010;<br>
However things are not clear with respect to overall support, as a result it was dropped.<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">Second last commit cites some GDB related concerns(back in 2010) for removal of DW_TAG_constant from LLVM.<o:p></o:p></p>
<p class="MsoNormal">[…]<o:p></o:p></p>
<p class="MsoNormal">commit b407bb2789e0c1daea1b7d7e896e6a600e408cf0<o:p></o:p></p>
<p class="MsoNormal">Author: Duncan P. N. Exon Smith <<a href="mailto:dexonsmith@apple.com">dexonsmith@apple.com</a>><o:p></o:p></p>
<p class="MsoNormal">Date: Mon Feb 9 22:48:04 2015 +0000<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal"> DebugInfo: Remove DW_TAG_constant<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal"> Remove handling for DW_TAG_constant. We started producing it in<o:p></o:p></p>
<p class="MsoNormal"> r110656, but reverted that in r110876 without dropping the support.<o:p></o:p></p>
<p class="MsoNormal"> Finish the job.<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal"> llvm-svn: 228623<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">commit 4d597e82684d462bc98f2ff934e37d3c5e38a0c9<o:p></o:p></p>
<p class="MsoNormal">Author: Devang Patel <<a href="mailto:dpatel@apple.com">dpatel@apple.com</a>><o:p></o:p></p>
<p class="MsoNormal">Date: Wed Aug 11 23:17:54 2010 +0000<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal"> Even if a variable has constant value all the time, it is still a variable in gdb's eyes.<o:p></o:p></p>
<p class="MsoNormal"> Tested by scope.exp in gdb testsuite.<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal"> llvm-svn: 110876<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">commit b219746c80be195e914d6f620427217818476ba8<o:p></o:p></p>
<p class="MsoNormal">Author: Devang Patel <<a href="mailto:dpatel@apple.com">dpatel@apple.com</a>><o:p></o:p></p>
<p class="MsoNormal">Date: Tue Aug 10 07:11:13 2010 +0000<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal"> Handle TAG_constant for integers.<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal"> llvm-svn: 110656<o:p></o:p></p>
<p class="MsoNormal">[…]<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">Now, that GDB has support for DW_TAG_constant is pretty decent. So I wanted to take this opportunity to define a new DIConstant metadata which will eventually materialize as DW_TAG_constant in DWARF.<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">Supporting arguments with respect to this:<o:p></o:p></p>
<ol style="margin-top:0in" start="1" type="1">
<li class="MsoListParagraph" style="margin-left:0in;mso-list:l1 level1 lfo6">Languages such as Fortran and the new Frontend Flang(now part of LLVM) can utilize this for producing debug-info.<o:p></o:p></li><li class="MsoListParagraph" style="margin-left:0in;mso-list:l1 level1 lfo6">Other languages that have named constant and there potential front-ends(living down-stream or not part of LLVM) should be able utilize this too.<o:p></o:p></li></ol>
<p class="MsoNormal"><br>
Thanks ..much!<o:p></o:p></p>
<p class="MsoNormal">Sourabh.<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
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<div style="border:none;border-top:solid #E1E1E1 1.0pt;padding:3.0pt 0in 0in 0in">
<p class="MsoNormal"><b>From:</b> paul.robinson@sony.com <paul.robinson@sony.com>
<br>
<b>Sent:</b> Wednesday, February 10, 2021 7:23 PM<br>
<b>To:</b> Tomar, Sourabh Singh <SourabhSingh.Tomar@amd.com>; llvm-dev@lists.llvm.org<br>
<b>Cc:</b> George, Jini Susan <JiniSusan.George@amd.com>; chih-ping.chen@intel.com; Sharma, Alok Kumar <AlokKumar.Sharma@amd.com><br>
<b>Subject:</b> RE: [DebugInfo]: Representing constants in debug-info<o:p></o:p></p>
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</div>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">[CAUTION: External Email] <o:p></o:p></p>
<div>
<p class="MsoNormal">I don’t see any use of DW_TAG_constant in the LLVM tree, except in the DWARFLinker, which isn’t what you need.<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">Most things not needed by C-family languages aren’t supported, because to date nobody has needed them (or if they did, they implemented the support downstream). The closest similar thing would be enumerator constants; you could probably
imitate what’s done for those fairly easily.<o:p></o:p></p>
<p class="MsoNormal">--paulr<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
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<div style="border:none;border-top:solid #E1E1E1 1.0pt;padding:3.0pt 0in 0in 0in">
<p class="MsoNormal"><b>From:</b> llvm-dev <<a href="mailto:llvm-dev-bounces@lists.llvm.org">llvm-dev-bounces@lists.llvm.org</a>>
<b>On Behalf Of </b>Tomar, Sourabh Singh via llvm-dev<br>
<b>Sent:</b> Wednesday, February 10, 2021 12:54 AM<br>
<b>To:</b> llvm-dev <<a href="mailto:llvm-dev@lists.llvm.org">llvm-dev@lists.llvm.org</a>><br>
<b>Cc:</b> George, Jini Susan <<a href="mailto:JiniSusan.George@amd.com">JiniSusan.George@amd.com</a>>; Chen, Chih-Ping <<a href="mailto:chih-ping.chen@intel.com">chih-ping.chen@intel.com</a>>; Sharma, Alok Kumar <<a href="mailto:AlokKumar.Sharma@amd.com">AlokKumar.Sharma@amd.com</a>><br>
<b>Subject:</b> [llvm-dev] [DebugInfo]: Representing constants in debug-info<o:p></o:p></p>
</div>
</div>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="msipheader87abd423" style="margin:0in"><span style="font-size:10.0pt;font-family:"Arial",sans-serif;color:#317100">[AMD Public Use]</span><o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">Hi Everyone,<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">Is there a way of representing **constants** in LLVM debug-info ? Languages such as FORTRAN has constants<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">i.e, consider the following Fortran snippet<o:p></o:p></p>
<p class="MsoNormal">[…]<o:p></o:p></p>
<p class="MsoNormal">Module foo<o:p></o:p></p>
<p class="MsoNormal">Integer, parameter :: bar = 200 ! Constant<o:p></o:p></p>
<p class="MsoNormal">End module foo<o:p></o:p></p>
<p class="MsoNormal">[…]<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">A front-end may choose to emit as Global Constant in LLVM IR as:<o:p></o:p></p>
<p class="MsoNormal">[…]<o:p></o:p></p>
<p class="MsoNormal">@bar.. = internal constant i32 200<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">A naïve attempt to represent it as GlobalVariable(or constant) as<o:p></o:p></p>
<p class="MsoNormal">[…]<o:p></o:p></p>
<p class="MsoNormal">!7 = !DIGlobalVariableExpression(var: !8, expr: !DIExpression(DW_OP_consts, 200))<o:p></o:p></p>
<p class="MsoNormal">!8 = distinct !DIGlobalVariable(name: "bar", scope: !2, file: !3, line: 3, type: !9, isLocal: false, isDefinition: true)<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">This will materialize in DWARF as:<o:p></o:p></p>
<p class="MsoNormal">0x0000004a: DW_TAG_variable<o:p></o:p></p>
<p class="MsoNormal"> DW_AT_name ("bar")<o:p></o:p></p>
<p class="MsoNormal"> …<o:p></o:p></p>
<p class="MsoNormal"> DW_AT_location (DW_OP_addr 0x2007d4, DW_OP_consts +200) // This is incorrect, pointing to data section<o:p></o:p></p>
<p class="MsoNormal">[…]<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">Gfortran is representing this as: **DW_TAG_constant**<br>
0x00000055: **<b>DW_TAG_constant</b>**<o:p></o:p></p>
<p class="MsoNormal"> DW_AT_name ("bar")<o:p></o:p></p>
<p class="MsoNormal"> …<o:p></o:p></p>
<p class="MsoNormal"> DW_AT_type (0x0000006a "const integer(kind=4)")<o:p></o:p></p>
<p class="MsoNormal"> DW_AT_external (true)<o:p></o:p></p>
<p class="MsoNormal"> DW_AT_const_value (0xc8)<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">Do we have Metadata analog of (DW_TAG_constant) ? I think the primary question here is to how represent this ?<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">Any inputs appreciated!<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">Thanks.. much!<br>
Sourabh.<o:p></o:p></p>
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