[DebugInfo] Fix potential CU mismatch for attachRangesOrLowHighPC

When a CU attaches some ranges for a subprogram or an inlined code, the CU should be that of the subprogram/inlined code that was emitted.
If not, then these emitted ranges will use the incorrect base of the CU in `emitRangeList`.

A reproducible example is:
When linking these two LLVM IRs,  dsymutil will report no mapping for range or inconsistent range data warnings.

`foo.swift`
```swift
import AppKit.NSLayoutConstraint

public class Foo {

    public var c: Int {
        get {
            Int(NSLayoutConstraint().constant)
        }
        set {
        }
    }

}
```

`main.swift`
```swift
// no mapping for range
let f: Foo! = nil
// inconsistent range data
//let l: Foo = Foo()
```

Reviewed By: dblaikie

Differential Revision: https://reviews.llvm.org/D136039

llvm/lib/CodeGen/AsmPrinter/DwarfCompileUnit.cpp

@@ -445,7 +445,12 @@ void DwarfCompileUnit::attachLowHighPC(DIE &D, const MCSymbol *Begin,
 // scope then create and insert DIEs for these variables.
 DIE &DwarfCompileUnit::updateSubprogramScopeDIE(const DISubprogram *SP) {
   DIE *SPDie = getOrCreateSubprogramDIE(SP, includeMinimalInlineScopes());
+  auto *ContextCU = static_cast<DwarfCompileUnit *>(SPDie->getUnit());
+  return ContextCU->updateSubprogramScopeDIEImpl(SP, SPDie);
+}
 
+DIE &DwarfCompileUnit::updateSubprogramScopeDIEImpl(const DISubprogram *SP,
+                                                    DIE *SPDie) {
   SmallVector<RangeSpan, 2> BB_List;
   // If basic block sections are on, ranges for each basic block section has
   // to be emitted separately.
@@ -1015,15 +1020,18 @@ sortLocalVars(SmallVectorImpl<DbgVariable *> &Input) {
 DIE &DwarfCompileUnit::constructSubprogramScopeDIE(const DISubprogram *Sub,
                                                    LexicalScope *Scope) {
   DIE &ScopeDIE = updateSubprogramScopeDIE(Sub);
+  auto *ContextCU = static_cast<DwarfCompileUnit *>(ScopeDIE.getUnit());
 
   if (Scope) {
     assert(!Scope->getInlinedAt());
     assert(!Scope->isAbstractScope());
     // Collect lexical scope children first.
     // ObjectPointer might be a local (non-argument) local variable if it's a
     // block's synthetic this pointer.
-    if (DIE *ObjectPointer = createAndAddScopeChildren(Scope, ScopeDIE))
-      addDIEEntry(ScopeDIE, dwarf::DW_AT_object_pointer, *ObjectPointer);
+    if (DIE *ObjectPointer =
+            ContextCU->createAndAddScopeChildren(Scope, ScopeDIE))
+      ContextCU->addDIEEntry(ScopeDIE, dwarf::DW_AT_object_pointer,
+                             *ObjectPointer);
   }
 
   // If this is a variadic function, add an unspecified parameter.

llvm/lib/CodeGen/AsmPrinter/DwarfCompileUnit.h

@@ -192,6 +192,7 @@ class DwarfCompileUnit final : public DwarfUnit {
   /// variables in this scope then create and insert DIEs for these
   /// variables.
   DIE &updateSubprogramScopeDIE(const DISubprogram *SP);
+  DIE &updateSubprogramScopeDIEImpl(const DISubprogram *SP, DIE *SPDie);
 
   void constructScopeDIE(LexicalScope *Scope, DIE &ParentScopeDIE);
 

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

@@ -0,0 +1,61 @@
+; RUN: %llc_dwarf %s -O0 -filetype=obj -o %t.o
+; RUN: llvm-dwarfdump %t.o --debug-info --verify
+
+; We want to check that when the CU attaches ranges use the correct ContextCU.
+; In the following example, after accessing `@foo`, `bar` an `inlined_baz` are created in `foo.swift` CU.
+; Setting ranges in `@bar` will then use `bar.swift` CU.
+; An incorrect address is eventually calculated based on Base.
+
+; The origin code is:
+; foo.swift
+; import AppKit.NSLayoutConstraint
+; public class Foo {
+;     public var c: Int {
+;         get {
+;             Int(NSLayoutConstraint().constant)
+;         }
+;         set {
+;         }
+;     }
+; }
+; main.swift
+; // no mapping for range
+; let f: Foo! = nil
+
+; After LTO, `main.swift` will create a global variable, then `Foo` (and relative DIE) created in `main.swift` CU.
+
+define void @foo() !dbg !6 {
+  ret void, !dbg !9
+}
+
+define void @bar(i32* %0) !dbg !15 {
+  store i32 1, i32* %0, align 4, !dbg !16
+  store i32 1, i32* %0, align 4, !dbg !21
+  ret void, !dbg !16
+}
+
+!llvm.dbg.cu = !{!0, !2}
+!llvm.module.flags = !{!4, !5}
+
+!0 = distinct !DICompileUnit(language: DW_LANG_Swift, file: !1, isOptimized: true, runtimeVersion: 5, emissionKind: FullDebug)
+!1 = !DIFile(filename: "foo.swift", directory: "")
+!2 = distinct !DICompileUnit(language: DW_LANG_Swift, file: !3, isOptimized: true, runtimeVersion: 5, emissionKind: FullDebug)
+!3 = !DIFile(filename: "bar.swift", directory: "")
+!4 = !{i32 7, !"Dwarf Version", i32 4}
+!5 = !{i32 2, !"Debug Info Version", i32 3}
+!6 = distinct !DISubprogram(name: "foo", scope: !0, type: !7, spFlags: DISPFlagDefinition, unit: !0)
+!7 = !DISubroutineType(types: !8)
+!8 = !{}
+!9 = !DILocation(line: 0, scope: !10, inlinedAt: !13)
+!10 = distinct !DISubprogram(name: "init", scope: !12, file: !11, type: !7, spFlags: DISPFlagDefinition, unit: !0)
+!11 = !DIFile(filename: "<compiler-generated>", directory: "")
+!12 = distinct !DICompositeType(tag: DW_TAG_structure_type, name: "Type", file: !3, runtimeLang: DW_LANG_Swift, identifier: "Type")
+!13 = !DILocation(line: 0, scope: !14)
+!14 = distinct !DILexicalBlock(scope: !6, file: !1)
+!15 = distinct !DISubprogram(name: "bar", scope: !12, type: !7, spFlags: DISPFlagDefinition, unit: !2)
+!16 = !DILocation(line: 0, scope: !17, inlinedAt: !19)
+!17 = distinct !DILexicalBlock(scope: !18, file: !3)
+!18 = distinct !DISubprogram(name: "inlined_baz", scope: !12, file: !3, type: !7, spFlags: DISPFlagDefinition, unit: !2)
+!19 = !DILocation(line: 0, scope: !20)
+!20 = distinct !DILexicalBlock(scope: !15, file: !3)
+!21 = !DILocation(line: 0, scope: !15)