[llvm-dev] StripDeadDebugInfo for static inline functions.
Jonas Devlieghere via llvm-dev
llvm-dev at lists.llvm.org
Mon Jan 15 04:04:30 PST 2018
+ Adrian
+ David
Hi Arsen,
This sounds like a bug to me. Have you tried reproducing it on trunk? For instance, I see that the relation between DICompileUnit and DISubprogram was changed in the meantime (https://reviews.llvm.org/D19034 <https://reviews.llvm.org/D19034>).
If this no longer occurs on master you could bisect the compiler to find the commit(s) that fix this and consider backporting them locally. If not, you should file a bug on bugs.llvm.org <http://bugs.llvm.org/> and attach the source and commands you’re running. I’d be happy to take a look at it.
Jonas
> On 14 Jan 2018, at 16:33, Arsen Hakobyan via llvm-dev <llvm-dev at lists.llvm.org> wrote:
>
> Thanks Paul,
> Hi Adrian and David I would really appreciate any comments, thoughts assumptions.
>
> If additional information is needed please let me know.
>
> Regards,
> Arsen
>
> On Sat, Jan 13, 2018 at 2:54 AM, Robinson, Paul <paul.robinson at sony.com <mailto:paul.robinson at sony.com>> wrote:
> Hi Arsen, we are beyond what I understand about how metadata operates. Maybe Adrian or David knows.
>
> --paulr
>
> <>
> From: Arsen Hakobyan [mailto:hakobyan.ars at gmail.com <mailto:hakobyan.ars at gmail.com>]
> Sent: Friday, January 12, 2018 12:16 PM
> To: Robinson, Paul
> Cc: llvm-dev at lists.llvm.org <mailto:llvm-dev at lists.llvm.org>; David Blaikie
> Subject: Re: [llvm-dev] StripDeadDebugInfo for static inline functions.
>
>
>
> Just one update:
>
>
>
> the function causing the segmentation fault is the following:
>
>
>
> 359 void DwarfDebug::constructAbstractSubprogramScopeDIE(LexicalScope *Scope) {
> 360 assert(Scope && Scope->getScopeNode());
> 361 assert(Scope->isAbstractScope());
> 362 assert(!Scope->getInlinedAt());
> 363
> 364 const MDNode *SP = Scope->getScopeNode();
> 365
> 366 ProcessedSPNodes.insert(SP);
> 367
> 368 // Find the subprogram's DwarfCompileUnit in the SPMap in case the subprogram
> 369 // was inlined from another compile unit.
> 370 auto &CU = SPMap[SP];
> 371 forBothCUs(*CU, [&](DwarfCompileUnit &CU) {
> 372 CU.constructAbstractSubprogramScopeDIE(Scope);
> 373 });
> 374 }
>
>
>
>
> Here I checked that "SPMap.lookup(Scope->getScopeNode());" returns null. If the transformation does right things then probably there is other issue and SPMap[SP] for inlined function should find the main CompileUnit anyway. What do you think about this?
>
>
>
> Regards,
>
> Arsen
>
>
>
> On Sat, Jan 13, 2018 at 12:11 AM, Arsen Hakobyan <hakobyan.ars at gmail.com <mailto:hakobyan.ars at gmail.com>> wrote:
>
> Hi Paul,
>
>
>
> Thanks for your response.
>
> Let me actually post more details visualizing my case. Assuming that can help.
>
>
>
> so the IR before the opt tool is running is:
>
>
>
> ; Function Attrs: nounwind
> define i16 @main() #0 !dbg !13 {
> entry:
> %retval = alloca i16, align 1
> ...
> }
>
> ; Function Attrs: inlinehint nounwind
> define internal void @delay(i16 %d) #4 !dbg !69 {
> entry:
> %d.addr = alloca i16, align 1
> %i = alloca i16, align 1
> ...
> }
>
> !llvm.dbg.cu <http://llvm.dbg.cu/> = !{!0}
> !llvm.module.flags = !{!84, !85}
> !llvm.ident = !{!86}
>
> !0 = distinct !DICompileUnit(language: DW_LANG_C99, file: !1, producer: "clang version 3.8.0 Revision 72230", isOptimized: true, runtimeVersion: 0, emissionKind: 1, enums: !2, retainedTypes: !3, subprograms: !12, globals: !73)
> ...
> !12 = !{!13, !54, !57, !60, !61, !62, !65, !66, !67, !68, !69}
> !13 = distinct !DISubprogram(name: "main", scope: !14, file: !14, line: 15, type: !15, isLocal: false, isDefinition: true, scopeLine: 15, isOptimized: true, variables: !17)
> ...
> !54 = distinct !DISubprogram(name: ...
> !57 = distinct !DISubprogram(name: ...
> !60 = distinct !DISubprogram(name: ...
> !61 = distinct !DISubprogram(name: ...
> !62 = distinct !DISubprogram(name: ...
> !65 = distinct !DISubprogram(name: ...
> !66 = distinct !DISubprogram(name: ...
> !67 = distinct !DISubprogram(name: ...
> !68 = distinct !DISubprogram(name: ...
> !69 = distinct !DISubprogram(name: "delay", scope: !14, file: !14, line: 9, type: !55, isLocal: true, isDefinition: true, scopeLine: 9, flags: DIFlagPrototyped, isOptimized: true, variables: !70)
> !70 = !{!71, !72}
> !71 = !DILocalVariable(name: "d", arg: 1, scope: !69, file: !14, line: 9, type: !11)
> !72 = !DILocalVariable(name: "i", scope: !69, file: !14, line: 9, type: !11)
> ...
>
>
>
>
>
>
>
>
> The IR after opt is:
>
>
>
> ; Function Attrs: nounwind
> define i16 @main() #0 !dbg !13 {
> entry:
> ...
> }
>
> !llvm.dbg.cu <http://llvm.dbg.cu/> = !{!0}
> !llvm.module.flags = !{!64, !65}
> !llvm.ident = !{!66}
>
> !0 = distinct !DICompileUnit(language: DW_LANG_C99, file: !1, producer: "clang version 3.8.0 Revision 72230", isOptimized: true, runtimeVersion: 0, emissionKind: 1, enums: !2, retainedTypes: !3, subprograms: !12, globals: !54)
> ...
> !12 = !{!13}
> !13 = distinct !DISubprogram(name: "main", scope: !14, file: !14, line: 15, type: !15, isLocal: false, isDefinition: true, scopeLine: 15, isOptimized: true, variables: !17)
> !14 = !DIFile(filename: "main.c", directory: "path_to_directory")
> ...
> !68 = !DILocalVariable(name: "d", arg: 1, scope: !69, file: !14, line: 9, type: !11)
> !69 = distinct !DISubprogram(name: "delay", scope: !14, file: !14, line: 9, type: !70, isLocal: true, isDefinition: true, scopeLine: 9, flags: DIFlagPrototyped, isOptimized: true, variables: !72)
> ...
> !73 = !DILocalVariable(name: "i", scope: !69, file: !14, line: 9, type: !11)
> ...
>
>
>
>
> I checked the StripSymbol.cpp file and there is no difference between version I am using (from clang 3.8) and current (6.0.0) version.
>
>
>
> As you can see the !12 node does not contain reference to !69 after optimizations which I think is incorrect. I assume that !69 has not been removed because there are two nodes (!68 and !73) referenced to it as the scope. But that should force the transformations to not remove the link from !12. Is it right?
>
>
>
> Thank you very much.
>
> Arsen
>
>
>
>
>
> On Fri, Jan 12, 2018 at 10:21 PM, Robinson, Paul <paul.robinson at sony.com <mailto:paul.robinson at sony.com>> wrote:
>
> I'm not as familiar with all the ins and outs of metadata as maybe I should be, but ultimately the inlined function should have a DWARF description contained within the description of the caller (which is why you're seeing the call to constructAbstractSubprogramScopeDIE). That suggests that the DISubprogram for the inlined function ought to remain, and its scope should be the DICompileUnit.
>
> --paulr
>
> <>
> From: llvm-dev [mailto:llvm-dev-bounces at lists.llvm.org <mailto:llvm-dev-bounces at lists.llvm.org>] On Behalf Of Arsen Hakobyan via llvm-dev
> Sent: Friday, January 12, 2018 1:57 AM
> To: llvm-dev at lists.llvm.org <mailto:llvm-dev at lists.llvm.org>
> Subject: [llvm-dev] StripDeadDebugInfo for static inline functions.
>
>
>
> Hi all,
>
>
>
> I would like to understand the strip-dead-debug-info transformation.
>
> In my test case there is a static inline function with two local variables.
>
> It appears that the function is already inlined before strip-dead-debug-info starts its work. As a result the DICompileUnit is cleaned and its subprograms list has no reference to the DISubprogram for the inlined function, but as there is reference from the DILocalVariables to the DISubprogram it remains (IMHO).
>
> This caused to a segmentation fault while running llc on the optimized IR file at function "constructAbstractSubprogramScopeDIE" in file DwarfDebug.cpp because the scope of the DISubprogram is null (I assume it should be the DICompileUnit).
>
>
>
> So I would like to know what would be the correct solution for this issue: Update optimization to not remove reference from the subprograms list, or to skip finding scope in llc.
>
>
>
> Any help is highly appreciated.
>
>
>
> Thanks,
>
> Arsen
>
>
>
>
>
> --
>
>
>
> If it's not fun you're not doing it right -- Fran Tarkenton
>
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> --
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>
> If it's not fun you're not doing it right -- Fran Tarkenton
>
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> --
>
>
>
> If it's not fun you're not doing it right -- Fran Tarkenton
>
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> --
>
> If it's not fun you're not doing it right -- Fran Tarkenton
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