<div dir="ltr">Under what conditions do we produce a subprogram with no attributes? At first glance that certainly seems not useful, but perhaps there's a reason for it.</div><div class="gmail_extra"><br><div class="gmail_quote">On Sat, May 7, 2016 at 3:02 AM, Aboud, Amjad <span dir="ltr"><<a href="mailto:amjad.aboud@intel.com" target="_blank">amjad.aboud@intel.com</a>></span> wrote:<br><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">
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<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1f497d">Hi David,<u></u><u></u></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1f497d">OK, I got that DIE in Compile Unit scope may point to a DIE in subprogram scope.<u></u><u></u></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1f497d">But how about that we are emitting a subprogram entry that has no attributes?<u></u><u></u></span></p><span class="">
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1f497d"><u></u> <u></u></span></p>
<p class="MsoNormal">0x0000002b: DW_TAG_subprogram [3] *<u></u><u></u></p>
<p class="MsoNormal"> <u></u><u></u></p>
<p class="MsoNormal">0x0000002c: DW_TAG_typedef [4]<u></u><u></u></p>
<p class="MsoNormal"> DW_AT_type [DW_FORM_ref4] (cu + 0x0040 => {0x00000040})<u></u><u></u></p>
<p class="MsoNormal"> DW_AT_name [DW_FORM_strp] ( .debug_str[0x00000060] = "T")<u></u><u></u></p>
<p class="MsoNormal"> DW_AT_decl_file [DW_FORM_data1] ("c:\temp\ICL\LB\retain.cpp")<u></u><u></u></p>
<p class="MsoNormal"> DW_AT_decl_line [DW_FORM_data1] (16)<u></u><u></u></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1f497d"><u></u> <u></u></span></p>
<p class="MsoNormal"><a name="m_-8895677126796975561__MailEndCompose"><span style="font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1f497d"><u></u> <u></u></span></a></p>
</span><p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1f497d">Regards,<u></u><u></u></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1f497d">Amjad<u></u><u></u></span></p>
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<p class="MsoNormal"><a name="m_-8895677126796975561______replyseparator"></a><b><span style="font-size:11.0pt;font-family:"Calibri",sans-serif">From:</span></b><span style="font-size:11.0pt;font-family:"Calibri",sans-serif"> David Blaikie [mailto:<a href="mailto:dblaikie@gmail.com" target="_blank">dblaikie@gmail.com</a>]
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<b>Sent:</b> Saturday, April 30, 2016 17:59<br>
<b>To:</b> Aboud, Amjad <<a href="mailto:amjad.aboud@intel.com" target="_blank">amjad.aboud@intel.com</a>><br>
<b>Cc:</b> Adrian Prantl <<a href="mailto:aprantl@apple.com" target="_blank">aprantl@apple.com</a>>; llvm-dev <<a href="mailto:llvm-dev@lists.llvm.org" target="_blank">llvm-dev@lists.llvm.org</a>>; Clang Dev <<a href="mailto:cfe-dev@lists.llvm.org" target="_blank">cfe-dev@lists.llvm.org</a>><br>
<b>Subject:</b> Re: Debug info scope of explicit casting type does not seem correct<u></u><u></u></span></p>
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<p class="MsoNormal"><u></u> <u></u></p>
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<p class="MsoNormal" style="margin-bottom:12.0pt">Yep, seems fine/reasonable to me. The pointer type has no logical scope so it doesn't really matter where its DIE goes.<br>
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GCC does put the pointer type in the function scope in basic cases, but it can also end up in other places. For example:<u></u><u></u></p>
<pre><span style="color:black">blaikie@blaikie-linux:~/dev$ cat func.cpp<u></u><u></u></span></pre>
<pre><span style="color:black">void sink(void*);<u></u><u></u></span></pre>
<pre><span style="color:black">template<typename T><u></u><u></u></span></pre>
<pre><span style="color:black">void f1() {<u></u><u></u></span></pre>
<pre><span style="color:black"> T *t;<u></u><u></u></span></pre>
<pre><span style="color:black"> sink(&t);<u></u><u></u></span></pre>
<pre><span style="color:black">}<u></u><u></u></span></pre>
<pre><span style="color:black">void f2() {<u></u><u></u></span></pre>
<pre><span style="color:black"> struct foo { };<u></u><u></u></span></pre>
<pre><span style="color:black"> f1<foo>();<u></u><u></u></span></pre>
<pre><span style="color:black">}<u></u><u></u></span></pre>
<pre><span style="color:black">blaikie@blaikie-linux:~/dev$ g++-4.7 -std=c++11 func.cpp -g -c && llvm-dwarfdump-tot -debug-dump=info func.o | grep DW_TAG<u></u><u></u></span></pre>
<pre><span style="color:black">0x0000000b: DW_TAG_compile_unit [1] *<u></u><u></u></span></pre>
<pre><span style="color:black">0x0000002d: DW_TAG_subprogram [2] * // f2<u></u><u></u></span></pre>
<pre><span style="color:black">0x00000051: DW_TAG_lexical_block [3] <u></u><u></u></span></pre>
<pre><span style="color:black">0x00000062: DW_TAG_structure_type [4] <u></u><u></u></span></pre>
<pre><span style="color:black">0x0000006b: DW_TAG_subprogram [5] * // f1<u></u><u></u></span></pre>
<pre><span style="color:black">0x00000087: DW_TAG_template_type_parameter [6] <u></u><u></u></span></pre>
<pre><span style="color:black">0x0000008e: DW_TAG_lexical_block [7] *<u></u><u></u></span></pre>
<pre><span style="color:black">0x0000009f: DW_TAG_variable [8] <u></u><u></u></span></pre>
<pre><span style="color:black">0x000000ab: DW_TAG_pointer_type [9] // foo*<u></u><u></u></span></pre>
<pre><span style="color:black"><u></u> <u></u></span></pre>
<pre><span style="color:black">& in fact, if you introduce another template that's similar to f1, its variable's type is 0x00ab - so it points into f1's children. Seems GCC puts it in whatever scope first references the pointer type.<u></u><u></u></span></pre>
<pre><span style="color:black"><u></u> <u></u></span></pre>
<pre><span style="color:black">I think it's probably as sensible, and a bit simpler, to put any such basic types in the CU scope.<u></u><u></u></span></pre>
<pre><span style="color:black"><u></u> <u></u></span></pre>
<pre><span style="color:black">(granted, if GCC and Clang were really smart, the pointer type in f1 could be pointer to 0x0087 - but that would really bloat the debug info (now every different way of writing foo* in every different template would be a separate type description... - that would probably be not good))<u></u><u></u></span></pre>
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<p class="MsoNormal"><u></u> <u></u></p>
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<p class="MsoNormal">On Sat, Apr 30, 2016 at 3:32 AM, Aboud, Amjad <<a href="mailto:amjad.aboud@intel.com" target="_blank">amjad.aboud@intel.com</a>> wrote:<u></u><u></u></p>
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<p class="MsoNormal">Hi,<u></u><u></u></p>
<p class="MsoNormal">I am wondering if this behavior of creating debug info is correct.<u></u><u></u></p>
<p class="MsoNormal">A type in compile unit entry is pointing to a type under subprogram entry?!<u></u><u></u></p>
<p class="MsoNormal"> <u></u><u></u></p>
<p class="MsoNormal">This is the root cause of
<a href="https://llvm.org/bugs/show_bug.cgi?id=27579" target="_blank">https://llvm.org/bugs/show_bug.cgi?id=27579</a><u></u><u></u></p>
<p class="MsoNormal"> <u></u><u></u></p>
<p class="MsoNormal">0x0000000b: DW_TAG_compile_unit [1] *<u></u><u></u></p>
<p class="MsoNormal"> <u></u><u></u></p>
<p class="MsoNormal">0x00000026: DW_TAG_pointer_type [2]<u></u><u></u></p>
<p class="MsoNormal"> DW_AT_type [DW_FORM_ref4] (cu + 0x002c => {<span style="background:yellow">0x0000002c</span>})<u></u><u></u></p>
<p class="MsoNormal"> <u></u><u></u></p>
<p class="MsoNormal">0x0000002b: DW_TAG_subprogram [3] *<u></u><u></u></p>
<p class="MsoNormal"> <u></u><u></u></p>
<p class="MsoNormal"><span style="background:yellow">0x0000002c</span>: DW_TAG_typedef [4]<u></u><u></u></p>
<p class="MsoNormal"> DW_AT_type [DW_FORM_ref4] (cu + 0x0040 => {0x00000040})<u></u><u></u></p>
<p class="MsoNormal"> DW_AT_name [DW_FORM_strp] ( .debug_str[0x00000060] = "T")<u></u><u></u></p>
<p class="MsoNormal"> DW_AT_decl_file [DW_FORM_data1] ("c:\temp\ICL\LB\retain.cpp")<u></u><u></u></p>
<p class="MsoNormal"> DW_AT_decl_line [DW_FORM_data1] (16)<u></u><u></u></p>
<p class="MsoNormal"> <u></u><u></u></p>
<p class="MsoNormal">0x00000037: NULL<u></u><u></u></p>
<p class="MsoNormal"> <u></u><u></u></p>
<p class="MsoNormal"> <u></u><u></u></p>
<p class="MsoNormal">command line:<u></u><u></u></p>
<p class="MsoNormal">clang -cc1 -triple i386-apple-ios9.0.0 -emit-obj -debug-info-kind=limited -O2 test.cpp –o - | llvm-dwarfdump -debug-dump=info -<u></u><u></u></p>
<p class="MsoNormal"> <u></u><u></u></p>
<p class="MsoNormal">> cat test.cpp<u></u><u></u></p>
<p class="MsoNormal">class A {<u></u><u></u></p>
<p class="MsoNormal">public:<u></u><u></u></p>
<p class="MsoNormal"> int x;<u></u><u></u></p>
<p class="MsoNormal">};<u></u><u></u></p>
<p class="MsoNormal"> <u></u><u></u></p>
<p class="MsoNormal"> <u></u><u></u></p>
<p class="MsoNormal">class B {<u></u><u></u></p>
<p class="MsoNormal">public:<u></u><u></u></p>
<p class="MsoNormal"> typedef A type;<u></u><u></u></p>
<p class="MsoNormal">};<u></u><u></u></p>
<p class="MsoNormal"> <u></u><u></u></p>
<p class="MsoNormal">template<typename X><u></u><u></u></p>
<p class="MsoNormal">int foo(void* in) {<u></u><u></u></p>
<p class="MsoNormal"> typedef typename X::type T;<u></u><u></u></p>
<p class="MsoNormal"> const T* p = (T*) in;<u></u><u></u></p>
<p class="MsoNormal"> return p->x;
<u></u><u></u></p>
<p class="MsoNormal">}<u></u><u></u></p>
<p class="MsoNormal"> <u></u><u></u></p>
<p class="MsoNormal">int bar() {<u></u><u></u></p>
<p class="MsoNormal">A a;<u></u><u></u></p>
<p class="MsoNormal"> return foo<B>(&a);<u></u><u></u></p>
<p class="MsoNormal">}<u></u><u></u></p>
<p class="MsoNormal"> <u></u><u></u></p>
<p class="MsoNormal">Reason for this behavior is the explicit cast “(T*)“, which leads into the following IR:<u></u><u></u></p>
<p class="MsoNormal"> <u></u><u></u></p>
<p class="MsoNormal">!0 = distinct !DICompileUnit(language: DW_LANG_C_plus_plus, file: !1, producer: "clang version 3.9.0 (trunk 267335)", isOptimized: true, runtimeVersion: 0, emissionKind: FullDebug,
enums: !2, retainedTypes: <span style="background:yellow">!3</span>)<u></u><u></u></p>
<p class="MsoNormal"><span style="background:yellow">!3</span> = !{<span style="background:yellow">!4</span>}<u></u><u></u></p>
<p class="MsoNormal"><span style="background:yellow">!4</span> = !DIDerivedType(tag: DW_TAG_pointer_type, baseType:
<span style="background:yellow">!5</span>, size: 32, align: 32) <----------------- No Scope, leads to compile unit scope!!<u></u><u></u></p>
<p class="MsoNormal"><span style="background:yellow">!5</span> = !DIDerivedType(tag: DW_TAG_typedef, name: "T", scope:
<span style="background:yellow">!7</span>, file: !6, line: 16, baseType: !20)<u></u><u></u></p>
<p class="MsoNormal"><span style="background:yellow">!7</span> = distinct !<span style="background:yellow">DISubprogram</span>(name: "foo<B>", linkageName: "_Z3fooI1BEiPv", scope: !6, file: !6, line:
15, type: !8, isLocal: false, isDefinition: true, scopeLine: 15, flags: DIFlagPrototyped, isOptimized: true, unit: !0, templateParams: !12, variables: !15)<u></u><u></u></p>
<p class="MsoNormal"> <u></u><u></u></p>
<p class="MsoNormal"> <u></u><u></u></p>
<p class="MsoNormal">Thanks,<u></u><u></u></p>
<p class="MsoNormal">Amjad<u></u><u></u></p>
<p class="MsoNormal"> <u></u><u></u></p>
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<p class="MsoNormal"><u></u> <u></u></p>
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