[Dwarf] Reference the correct CU when inlining

[ellis]

Summary

Sometimes when a function is inlined into a different CU, llvm-dwarfdump --verify would find an inlined subroutine with an invalid abstract origin. This is because DwarfUnit::addDIEEntry() will incorrectly assume the inlined subroutine and the abstract origin are from the same CU if it can't find the CU for the inlined subroutine.

In the added test, the inlined subroutine for bar() is created before the CU for B.swift is created, so it tries to point to goo() in the wrong CU. Interestingly, if we swap the order of the two functions then we don't see a crash since the module for goo() is created first.

The fix is to give a parent DIE to ScopeDIE before calling addDIEEntry() so that its CU can be found. Luckily, constructInlinedScopeDIE() is only called once so we can pass it the DIE of the scope's parent and give it a child just after it's created.

constructInlinedScopeDIE() should always return a DIE, so assert that it is not null.

[aprantl]

llvm/test/DebugInfo/dwarfdump-inlined.ll

2

Can you add CHECKs that actually verify that the dwarfdump output is as expected? RIght now this test will also succeed if llc decides to strip out the debug info entirely ;-)

[dblaikie]

(this is fine by me - I will say this code is all pretty subtle, but the fix is good - the sooner we can add a DIE to its parent, the better for precisely these sort of reasons)
I'll leave the final approval for @aprantl once he's good with it. (& yeah, I agree - the test should verify that the DIE ended up in the right unit, etc)

[ellis]

Move test to DebugInfo/Generic and add checks to verify dwarfdump output.

[aprantl]

llvm/test/DebugInfo/Generic/cross-cu-inlining-2.ll

61 ↗

(On Diff #465146)

I'm not sure if the FORMs will be identical on all targets, so you may need to move this back into a subdirectory where you can restrict this to one specific target and object file format. But the bots will let you know if that's the case.

[kyulee]

Thanks for quickly fixing and approving this!

[ellis]

llvm/test/DebugInfo/Generic/cross-cu-inlining-2.ll

61 ↗

(On Diff #465146)

Thanks for the heads up. I'll land in the morning and make fixes as necessary.

[ellis]

fix whitespace

llvm/lib/CodeGen/AsmPrinter/DwarfCompileUnit.h

public:
   /// lexical scope.
   void addScopeRangeList(DIE &ScopeDIE, SmallVector<RangeSpan, 2> Range);
 
   void attachRangesOrLowHighPC(DIE &D, SmallVector<RangeSpan, 2> Ranges);
 
   void attachRangesOrLowHighPC(DIE &D,
                                const SmallVectorImpl<InsnRange> &Ranges);
 
-  /// This scope represents inlined body of a function. Construct
+  /// This scope represents an inlined body of a function. Construct a
   /// DIE to represent this concrete inlined copy of the function.
-  DIE *constructInlinedScopeDIE(LexicalScope *Scope);
+  DIE *constructInlinedScopeDIE(LexicalScope *Scope, DIE &ParentScopeDIE);
 
   /// Construct new DW_TAG_lexical_block for this scope and
   /// attach DW_AT_low_pc/DW_AT_high_pc labels.
   DIE *constructLexicalScopeDIE(LexicalScope *Scope);
 
   /// constructVariableDIE - Construct a DIE for the given DbgVariable.
   DIE *constructVariableDIE(DbgVariable &DV, bool Abstract = false);
 

llvm/lib/CodeGen/AsmPrinter/DwarfCompileUnit.cpp

void DwarfCompileUnit::constructScopeDIE(LexicalScope *Scope,
 
   assert((Scope->getInlinedAt() || !isa<DISubprogram>(DS)) &&
          "Only handle inlined subprograms here, use "
          "constructSubprogramScopeDIE for non-inlined "
          "subprograms");
 
   // Emit inlined subprograms.
   if (Scope->getParent() && isa<DISubprogram>(DS)) {
-    DIE *ScopeDIE = constructInlinedScopeDIE(Scope);
-    if (!ScopeDIE)
-      return;
-
-    ParentScopeDIE.addChild(ScopeDIE);
+    DIE *ScopeDIE = constructInlinedScopeDIE(Scope, ParentScopeDIE);
+    assert(ScopeDIE && "Scope DIE should not be null.");
     createAndAddScopeChildren(Scope, *ScopeDIE);
     return;
   }
 
   // Early exit when we know the scope DIE is going to be null.
   if (DD->isLexicalScopeDIENull(Scope))
     return;
 
do {
       if (MBB->sameSection(EndMBB))
         break;
       MBB = MBB->getNextNode();
     } while (true);
   }
   attachRangesOrLowHighPC(Die, std::move(List));
 }
 
-// This scope represents inlined body of a function. Construct DIE to
-// represent this concrete inlined copy of the function.
-DIE *DwarfCompileUnit::constructInlinedScopeDIE(LexicalScope *Scope) {
+DIE *DwarfCompileUnit::constructInlinedScopeDIE(LexicalScope *Scope,
+                                                DIE &ParentScopeDIE) {
   assert(Scope->getScopeNode());
   auto *DS = Scope->getScopeNode();
   auto *InlinedSP = getDISubprogram(DS);
   // Find the subprogram's DwarfCompileUnit in the SPMap in case the subprogram
   // was inlined from another compile unit.
   DIE *OriginDIE = getAbstractSPDies()[InlinedSP];
   assert(OriginDIE && "Unable to find original DIE for an inlined subprogram.");
 
   auto ScopeDIE = DIE::get(DIEValueAllocator, dwarf::DW_TAG_inlined_subroutine);
+  ParentScopeDIE.addChild(ScopeDIE);
   addDIEEntry(*ScopeDIE, dwarf::DW_AT_abstract_origin, *OriginDIE);
 
   attachRangesOrLowHighPC(*ScopeDIE, Scope->getRanges());
 
   // Add the call site information to the DIE.
   const DILocation *IA = Scope->getInlinedAt();
   addUInt(*ScopeDIE, dwarf::DW_AT_call_file, None,
           getOrCreateSourceID(IA->getFile()));

llvm/test/DebugInfo/dwarfdump-inlined.ll

+; REQUIRES: object-emission
+; RUN: %llc_dwarf %s -filetype=obj -o - | llvm-dwarfdump - --verify
+
+; Test that we can inline from a different CU.
+
+define void @foo() !dbg !24 {
+  ret void, !dbg !28
+}
+
+define void @bar() !dbg !34 {
+  ret void, !dbg !35
+}
+
+!llvm.dbg.cu = !{!0, !3}
+!llvm.module.flags = !{!5, !6, !7, !8, !9, !10, !11, !12, !13, !14, !15, !16, !17, !18, !19, !20, !21, !22, !23}
+
+!0 = distinct !DICompileUnit(language: DW_LANG_Swift, file: !1, isOptimized: true, runtimeVersion: 5, emissionKind: FullDebug, globals: !2, imports: !2)
+!1 = !DIFile(filename: "A.swift", directory: "")
+!2 = !{}
+!3 = distinct !DICompileUnit(language: DW_LANG_Swift, file: !4, isOptimized: true, runtimeVersion: 5, emissionKind: FullDebug, imports: !2)
+!4 = !DIFile(filename: "B.swift", directory: "")
+!5 = !{i32 2, !"SDK Version", [2 x i32] [i32 16, i32 0]}
+!6 = !{i32 1, !"Objective-C Version", i32 2}
+!7 = !{i32 1, !"Objective-C Image Info Version", i32 0}
+!8 = !{i32 1, !"Objective-C Garbage Collection", i8 0}
+!9 = !{i32 1, !"Objective-C Class Properties", i32 64}
+!10 = !{i32 7, !"Dwarf Version", i32 4}
+!11 = !{i32 2, !"Debug Info Version", i32 3}
+!12 = !{i32 1, !"wchar_size", i32 4}
+!13 = !{i32 8, !"branch-target-enforcement", i32 0}
+!14 = !{i32 8, !"sign-return-address", i32 0}
+!15 = !{i32 8, !"sign-return-address-all", i32 0}
+!16 = !{i32 8, !"sign-return-address-with-bkey", i32 0}
+!17 = !{i32 8, !"PIC Level", i32 2}
+!18 = !{i32 7, !"uwtable", i32 1}
+!19 = !{i32 7, !"frame-pointer", i32 1}
+!20 = !{i32 1, !"Swift Version", i32 7}
+!21 = !{i32 1, !"Swift ABI Version", i32 7}
+!22 = !{i32 1, !"Swift Major Version", i8 5}
+!23 = !{i32 1, !"Swift Minor Version", i8 7}
+!24 = distinct !DISubprogram(name: "foo", scope: !25, file: !1, line: 116, type: !27, scopeLine: 116, spFlags: DISPFlagDefinition, unit: !0, retainedNodes: !2)
+!25 = distinct !DICompositeType(tag: DW_TAG_structure_type, name: "FooTy", scope: !26, file: !1, size: 64, elements: !2)
+!26 = !DIModule(scope: null, name: "Mod")
+!27 = !DISubroutineType(types: !2)
+!28 = !DILocation(line: 0, scope: !29, inlinedAt: !32)
+!29 = distinct !DISubprogram(name: "init", scope: !31, file: !30, type: !27, spFlags: DISPFlagDefinition, unit: !0, retainedNodes: !2)
+!30 = !DIFile(filename: "<compiler-generated>", directory: "")
+!31 = distinct !DICompositeType(tag: DW_TAG_structure_type, name: "ModController", scope: !26, file: !4, size: 64, elements: !2, runtimeLang: DW_LANG_Swift)
+!32 = !DILocation(line: 117, column: 29, scope: !33)
+!33 = distinct !DILexicalBlock(scope: !24, file: !1, line: 116, column: 68)
+!34 = distinct !DISubprogram(name: "bar", scope: !31, file: !4, line: 21, type: !27, scopeLine: 21, unit: !3, retainedNodes: !2)
+!35 = !DILocation(line: 0, scope: !36, inlinedAt: !37)
+!36 = distinct !DISubprogram(name: "goo", scope: !26, file: !30, type: !27, unit: !3, retainedNodes: !2)
+!37 = !DILocation(line: 21, column: 26, scope: !34)