[DebugInfo] Consider debug label scope has an extra lexical block file

[twoh]

Summary

There are places where a case that debug label scope has an extra lexical block file is not considered properly. The modified test won't pass without this patch.

[dblaikie]

Might be helpful to have (at least for the review, doesn't necessarily need to be formalized into a lit test and checked in) a minimal source reproduction so we can more readily see what's happening here?

[twoh]

@dblaikie Thank you for the comment. I encountered this problem while manipulating LLVM IR, and not sure how realistic the code can be if I synthesize one to reproduce this problem. Still, I think this is worth fixing unless we can guarantee that debug label scope won't have a DILexicalBlockFile.

[aprantl]

Seems reasonable to me.

[aprantl]

(I'm approaching this from the point of "if the verifier accepts the IR, the backend has to deal with it", but David is right in pointing out that there may be a bug further up the pipeline and that perhaps it should be fixed and made illegal in IR.)

llvm/lib/CodeGen/AsmPrinter/AsmPrinter.cpp

static bool emitDebugLabelComment(const MachineInstr *MI, AsmPrinter &AP) {
   if (MI->getNumOperands() != 1)
     return false;
 
   SmallString<128> Str;
   raw_svector_ostream OS(Str);
   OS << "DEBUG_LABEL: ";
 
   const DILabel *V = MI->getDebugLabel();
-  if (auto *SP = dyn_cast<DISubprogram>(V->getScope())) {
+  if (auto *SP = dyn_cast<DISubprogram>(
+          V->getScope()->getNonLexicalBlockFileScope())) {
     StringRef Name = SP->getName();
     if (!Name.empty())
       OS << Name << ":";
   }
   OS << V->getName();
 
   // NOTE: Want this comment at start of line, don't emit with AddComment.
   AP.OutStreamer->emitRawComment(OS.str());

llvm/lib/CodeGen/AsmPrinter/DwarfDebug.cpp

void DwarfDebug::collectEntityInfo(DwarfCompileUnit &TheCU,
   for (const auto &I : DbgLabels) {
     InlinedEntity IL = I.first;
     const MachineInstr *MI = I.second;
     if (MI == nullptr)
       continue;
 
     LexicalScope *Scope = nullptr;
     const DILabel *Label = cast<DILabel>(IL.first);
+    // The scope could have an extra lexical block file.
+    const DILocalScope *LocalScope =
+        Label->getScope()->getNonLexicalBlockFileScope();
     // Get inlined DILocation if it is inlined label.
     if (const DILocation *IA = IL.second)
-      Scope = LScopes.findInlinedScope(Label->getScope(), IA);
+      Scope = LScopes.findInlinedScope(LocalScope, IA);
     else
-      Scope = LScopes.findLexicalScope(Label->getScope());
+      Scope = LScopes.findLexicalScope(LocalScope);
     // If label scope is not found then skip this label.
     if (!Scope)
       continue;
 
     Processed.insert(IL);
     /// At this point, the temporary label is created.
     /// Save the temporary label to DbgLabel entity to get the
     /// actually address when generating Dwarf DIE.

llvm/test/DebugInfo/Generic/debug-label.ll

 !3 = !{!10}
 !4 = !{i32 2, !"Debug Info Version", i32 3}
 !6 = distinct !DISubprogram(name: "foo", scope: !1, file: !1, line: 1, type: !7, isLocal: false, isDefinition: true, scopeLine: 2, isOptimized: false, unit: !0, retainedNodes: !3)
 !7 = !DISubroutineType(types: !8)
 !8 = !{!9, !9, !9}
 !9 = !DIBasicType(name: "int", size: 32, encoding: DW_ATE_signed)
 !10 = !DILabel(scope: !6, name: "top", file: !1, line: 4)
 !11 = !DILocation(line: 4, column: 1, scope: !6)
-!12 = !DILabel(scope: !6, name: "done", file: !1, line: 7)
+!12 = !DILabel(scope: !15, name: "done", file: !1, line: 7)
 !13 = !DILocation(line: 7, column: 1, scope: !6)
 !14 = !DILocation(line: 8, column: 3, scope: !6)
+!15 = !DILexicalBlockFile(discriminator: 2, file: !1, scope: !6)