Add LLVM IR debug info support for Fortran COMMON blocks

COMMON blocks are a feature of Fortran that has no direct analog in C languages, but they are similar to data sections in assembly language programming. A COMMON block is a named area of memory that holds a collection of variables. Fortran subprograms may map the COMMON block memory area to their own, possibly distinct, non-empty list of variables. A Fortran COMMON block might look like the following example.

    COMMON /ALPHA/ I, J

    For this construct, the compiler generates a new scope-like DI construct (!DICommonBlock) into which variables (see I, J above) can be placed. As the common block implies a range of storage with global lifetime, the !DICommonBlock refers to a !DIGlobalVariable. The Fortran variable that comprise the COMMON block are also linked via metadata to offsets within the global variable that stands for the entire common block.

    @alpha_ = common global %alphabytes_ zeroinitializer, align 64, !dbg !27, !dbg !30, !dbg !33
    !14 = distinct !DISubprogram(…)
    !20 = distinct !DICommonBlock(scope: !14, declaration: !25, name: "alpha")
    !25 = distinct !DIGlobalVariable(scope: !20, name: "common alpha", type: !24)
    !27 = !DIGlobalVariableExpression(var: !25, expr: !DIExpression())
    !29 = distinct !DIGlobalVariable(scope: !20, name: "i", file: !3, type: !28)
    !30 = !DIGlobalVariableExpression(var: !29, expr: !DIExpression())
    !31 = distinct !DIGlobalVariable(scope: !20, name: "j", file: !3, type: !28)
    !32 = !DIExpression(DW_OP_plus_uconst, 4)
    !33 = !DIGlobalVariableExpression(var: !31, expr: !32)

    The DWARF generated for this is as follows.

    DW_TAG_common_block:
    DW_AT_name: alpha
    DW_AT_location: @alpha_+0
    DW_TAG_variable:
    DW_AT_name: common alpha
    DW_AT_type: array of 8 bytes
    DW_AT_location: @alpha_+0
    DW_TAG_variable:
    DW_AT_name: i
    DW_AT_type: integer*4
    DW_AT_location: @Alpha+0
    DW_TAG_variable:
    DW_AT_name: j
    DW_AT_type: integer*4
    DW_AT_location: @Alpha+4

Patch by Eric Schweitz!

Differential Revision: https://reviews.llvm.org/D54327

llvm-svn: 357934

llvm/include/llvm-c/DebugInfo.h

@@ -159,7 +159,8 @@ enum {
   LLVMDIObjCPropertyMetadataKind,
   LLVMDIImportedEntityMetadataKind,
   LLVMDIMacroMetadataKind,
-  LLVMDIMacroFileMetadataKind
+  LLVMDIMacroFileMetadataKind,
+  LLVMDICommonBlockMetadataKind
 };
 typedef unsigned LLVMMetadataKind;
 

llvm/include/llvm/Bitcode/LLVMBitCodes.h

@@ -310,6 +310,7 @@ enum MetadataCodes {
   METADATA_INDEX_OFFSET = 38,           // [offset]
   METADATA_INDEX = 39,                  // [bitpos]
   METADATA_LABEL = 40,                  // [distinct, scope, name, file, line]
+  METADATA_COMMON_BLOCK = 44,     // [distinct, scope, name, variable,...]
 };
 
 // The constants block (CONSTANTS_BLOCK_ID) describes emission for each

llvm/include/llvm/IR/DIBuilder.h

@@ -706,6 +706,16 @@ namespace llvm {
                  DITemplateParameterArray TParams = nullptr,
                  DITypeArray ThrownTypes = nullptr);
 
+    /// Create common block entry for a Fortran common block
+    /// \param Scope       Scope of this common block
+    /// \param Name        The name of this common block
+    /// \param File        The file this common block is defined
+    /// \param LineNo      Line number
+    /// \param VarList     List of variables that a located in common block
+    DICommonBlock *createCommonBlock(DIScope *Scope, DIGlobalVariable *decl,
+                                     StringRef Name, DIFile *File,
+                                     unsigned LineNo);
+
     /// This creates new descriptor for a namespace with the specified
     /// parent scope.
     /// \param Scope       Namespace scope

llvm/include/llvm/IR/DebugInfoMetadata.h

@@ -227,6 +227,7 @@ public:
     case DILexicalBlockKind:
     case DILexicalBlockFileKind:
     case DINamespaceKind:
+    case DICommonBlockKind:
     case DITemplateTypeParameterKind:
     case DITemplateValueParameterKind:
     case DIGlobalVariableKind:
@@ -485,6 +486,7 @@ public:
     case DILexicalBlockKind:
     case DILexicalBlockFileKind:
     case DINamespaceKind:
+    case DICommonBlockKind:
     case DIModuleKind:
       return true;
     }
@@ -2673,6 +2675,65 @@ public:
   }
 };
 
+class DICommonBlock : public DIScope {
+  unsigned LineNo;
+
+  friend class LLVMContextImpl;
+  friend class MDNode;
+
+  DICommonBlock(LLVMContext &Context, StorageType Storage, unsigned LineNo,
+                ArrayRef<Metadata *> Ops)
+      : DIScope(Context, DICommonBlockKind, Storage, dwarf::DW_TAG_common_block,
+                Ops), LineNo(LineNo) {}
+
+  static DICommonBlock *getImpl(LLVMContext &Context, DIScope *Scope,
+                                DIGlobalVariable *Decl, StringRef Name,
+                                DIFile *File, unsigned LineNo,
+                                StorageType Storage,
+                                bool ShouldCreate = true) {
+    return getImpl(Context, Scope, Decl, getCanonicalMDString(Context, Name),
+                   File, LineNo, Storage, ShouldCreate);
+  }
+  static DICommonBlock *getImpl(LLVMContext &Context, Metadata *Scope,
+                                Metadata *Decl, MDString *Name, Metadata *File,
+                                unsigned LineNo, 
+                                StorageType Storage, bool ShouldCreate = true);
+
+  TempDICommonBlock cloneImpl() const {
+    return getTemporary(getContext(), getScope(), getDecl(), getName(),
+                        getFile(), getLineNo());
+  }
+
+public:
+  DEFINE_MDNODE_GET(DICommonBlock,
+                    (DIScope *Scope, DIGlobalVariable *Decl, StringRef Name,
+                     DIFile *File, unsigned LineNo),
+                    (Scope, Decl, Name, File, LineNo))
+  DEFINE_MDNODE_GET(DICommonBlock,
+                    (Metadata *Scope, Metadata *Decl, MDString *Name,
+                     Metadata *File, unsigned LineNo),
+                    (Scope, Decl, Name, File, LineNo))
+
+  TempDICommonBlock clone() const { return cloneImpl(); }
+
+  DIScope *getScope() const { return cast_or_null<DIScope>(getRawScope()); }
+  DIGlobalVariable *getDecl() const {
+    return cast_or_null<DIGlobalVariable>(getRawDecl());
+  }
+  StringRef getName() const { return getStringOperand(2); }
+  DIFile *getFile() const { return cast_or_null<DIFile>(getRawFile()); }
+  unsigned getLineNo() const { return LineNo; }
+
+  Metadata *getRawScope() const { return getOperand(0); }
+  Metadata *getRawDecl() const { return getOperand(1); }
+  MDString *getRawName() const { return getOperandAs<MDString>(2); }
+  Metadata *getRawFile() const { return getOperand(3); }
+
+  static bool classof(const Metadata *MD) {
+    return MD->getMetadataID() == DICommonBlockKind;
+  }
+};
+
 /// Local variable.
 ///
 /// TODO: Split up flags.

llvm/include/llvm/IR/Metadata.def

@@ -113,6 +113,7 @@ HANDLE_SPECIALIZED_MDNODE_LEAF_UNIQUABLE(DIImportedEntity)
 HANDLE_SPECIALIZED_MDNODE_BRANCH(DIMacroNode)
 HANDLE_SPECIALIZED_MDNODE_LEAF_UNIQUABLE(DIMacro)
 HANDLE_SPECIALIZED_MDNODE_LEAF_UNIQUABLE(DIMacroFile)
+HANDLE_SPECIALIZED_MDNODE_LEAF_UNIQUABLE(DICommonBlock)
 
 #undef HANDLE_METADATA
 #undef HANDLE_METADATA_LEAF

llvm/lib/AsmParser/LLParser.cpp

@@ -4664,6 +4664,24 @@ bool LLParser::ParseDILexicalBlockFile(MDNode *&Result, bool IsDistinct) {
   return false;
 }
 
+/// ParseDICommonBlock:
+///   ::= !DICommonBlock(scope: !0, file: !2, name: "COMMON name", line: 9)
+bool LLParser::ParseDICommonBlock(MDNode *&Result, bool IsDistinct) {
+#define VISIT_MD_FIELDS(OPTIONAL, REQUIRED)                                    \
+  REQUIRED(scope, MDField, );                                                  \
+  OPTIONAL(declaration, MDField, );                                            \
+  OPTIONAL(name, MDStringField, );                                             \
+  OPTIONAL(file, MDField, );                                                   \
+  OPTIONAL(line, LineField, );						       
+  PARSE_MD_FIELDS();
+#undef VISIT_MD_FIELDS
+
+  Result = GET_OR_DISTINCT(DICommonBlock,
+                           (Context, scope.Val, declaration.Val, name.Val,
+                            file.Val, line.Val));
+  return false;
+}
+
 /// ParseDINamespace:
 ///   ::= !DINamespace(scope: !0, file: !2, name: "SomeNamespace", line: 9)
 bool LLParser::ParseDINamespace(MDNode *&Result, bool IsDistinct) {

llvm/lib/Bitcode/Reader/MetadataLoader.cpp

@@ -811,6 +811,7 @@ MetadataLoader::MetadataLoaderImpl::lazyLoadModuleMetadataBlock() {
       case bitc::METADATA_LEXICAL_BLOCK:
       case bitc::METADATA_LEXICAL_BLOCK_FILE:
       case bitc::METADATA_NAMESPACE:
+      case bitc::METADATA_COMMON_BLOCK:
       case bitc::METADATA_MACRO:
       case bitc::METADATA_MACRO_FILE:
       case bitc::METADATA_TEMPLATE_TYPE:
@@ -1528,6 +1529,17 @@ Error MetadataLoader::MetadataLoaderImpl::parseOneMetadata(
     NextMetadataNo++;
     break;
   }
+  case bitc::METADATA_COMMON_BLOCK: {
+    IsDistinct = Record[0] & 1;
+    MetadataList.assignValue(
+        GET_OR_DISTINCT(DICommonBlock,
+                        (Context, getMDOrNull(Record[1]),
+                         getMDOrNull(Record[2]), getMDString(Record[3]),
+                         getMDOrNull(Record[4]), Record[5])),
+        NextMetadataNo);
+    NextMetadataNo++;
+    break;
+  }
   case bitc::METADATA_NAMESPACE: {
     // Newer versions of DINamespace dropped file and line.
     MDString *Name;

llvm/lib/Bitcode/Writer/BitcodeWriter.cpp

@@ -317,6 +317,8 @@ private:
   void writeDILexicalBlockFile(const DILexicalBlockFile *N,
                                SmallVectorImpl<uint64_t> &Record,
                                unsigned Abbrev);
+  void writeDICommonBlock(const DICommonBlock *N,
+                          SmallVectorImpl<uint64_t> &Record, unsigned Abbrev);
   void writeDINamespace(const DINamespace *N, SmallVectorImpl<uint64_t> &Record,
                         unsigned Abbrev);
   void writeDIMacro(const DIMacro *N, SmallVectorImpl<uint64_t> &Record,
@@ -1686,6 +1688,20 @@ void ModuleBitcodeWriter::writeDILexicalBlockFile(
   Record.clear();
 }
 
+void ModuleBitcodeWriter::writeDICommonBlock(const DICommonBlock *N,
+                                             SmallVectorImpl<uint64_t> &Record,
+                                             unsigned Abbrev) {
+  Record.push_back(N->isDistinct());
+  Record.push_back(VE.getMetadataOrNullID(N->getScope()));
+  Record.push_back(VE.getMetadataOrNullID(N->getDecl()));
+  Record.push_back(VE.getMetadataOrNullID(N->getRawName()));
+  Record.push_back(VE.getMetadataOrNullID(N->getFile()));
+  Record.push_back(N->getLineNo());
+
+  Stream.EmitRecord(bitc::METADATA_COMMON_BLOCK, Record, Abbrev);
+  Record.clear();
+}
+
 void ModuleBitcodeWriter::writeDINamespace(const DINamespace *N,
                                            SmallVectorImpl<uint64_t> &Record,
                                            unsigned Abbrev) {

llvm/lib/CodeGen/AsmPrinter/DwarfCompileUnit.cpp

@@ -123,7 +123,9 @@ DIE *DwarfCompileUnit::getOrCreateGlobalVariableDIE(
 
   // Construct the context before querying for the existence of the DIE in
   // case such construction creates the DIE.
-  DIE *ContextDIE = getOrCreateContextDIE(GVContext);
+  auto *CB = GVContext ? dyn_cast<DICommonBlock>(GVContext) : nullptr;
+  DIE *ContextDIE = CB ? getOrCreateCommonBlock(CB, GlobalExprs)
+    : getOrCreateContextDIE(GVContext);
 
   // Add to map.
   DIE *VariableDIE = &createAndAddDIE(GV->getTag(), *ContextDIE, GV);
@@ -166,6 +168,13 @@ DIE *DwarfCompileUnit::getOrCreateGlobalVariableDIE(
     addTemplateParams(*VariableDIE, DINodeArray(TP));
 
   // Add location.
+  addLocationAttribute(VariableDIE, GV, GlobalExprs);
+
+  return VariableDIE;
+}
+
+void DwarfCompileUnit::addLocationAttribute(
+    DIE *VariableDIE, const DIGlobalVariable *GV, ArrayRef<GlobalExpr> GlobalExprs) {
   bool addToAccelTable = false;
   DIELoc *Loc = nullptr;
   Optional<unsigned> NVPTXAddressSpace;
@@ -288,8 +297,25 @@ DIE *DwarfCompileUnit::getOrCreateGlobalVariableDIE(
         DD->useAllLinkageNames())
       DD->addAccelName(*CUNode, GV->getLinkageName(), *VariableDIE);
   }
+}
 
-  return VariableDIE;
+DIE *DwarfCompileUnit::getOrCreateCommonBlock(
+    const DICommonBlock *CB, ArrayRef<GlobalExpr> GlobalExprs) {
+  // Construct the context before querying for the existence of the DIE in case
+  // such construction creates the DIE.
+  DIE *ContextDIE = getOrCreateContextDIE(CB->getScope());
+
+  if (DIE *NDie = getDIE(CB))
+    return NDie;
+  DIE &NDie = createAndAddDIE(dwarf::DW_TAG_common_block, *ContextDIE, CB);
+  StringRef Name = CB->getName().empty() ? "_BLNK_" : CB->getName();
+  addString(NDie, dwarf::DW_AT_name, Name);
+  addGlobalName(Name, NDie, CB->getScope());
+  if (CB->getFile())
+    addSourceLine(NDie, CB->getLineNo(), CB->getFile());
+  if (DIGlobalVariable *V = CB->getDecl())
+    getCU().addLocationAttribute(&NDie, V, GlobalExprs);
+  return &NDie;
 }
 
 void DwarfCompileUnit::addRange(RangeSpan Range) {

llvm/lib/CodeGen/AsmPrinter/DwarfCompileUnit.h

@@ -139,6 +139,12 @@ public:
   getOrCreateGlobalVariableDIE(const DIGlobalVariable *GV,
                                ArrayRef<GlobalExpr> GlobalExprs);
 
+  DIE *getOrCreateCommonBlock(const DICommonBlock *CB,
+                              ArrayRef<GlobalExpr> GlobalExprs);
+
+  void addLocationAttribute(DIE *ToDIE, const DIGlobalVariable *GV,
+                            ArrayRef<GlobalExpr> GlobalExprs);
+
   /// addLabelAddress - Add a dwarf label attribute data and value using
   /// either DW_FORM_addr or DW_FORM_GNU_addr_index.
   void addLabelAddress(DIE &Die, dwarf::Attribute Attribute,

llvm/lib/CodeGen/AsmPrinter/DwarfUnit.cpp

@@ -689,7 +689,7 @@ void DwarfUnit::updateAcceleratorTables(const DIScope *Context,
     DD->addAccelType(*CUNode, Ty->getName(), TyDIE, Flags);
 
     if (!Context || isa<DICompileUnit>(Context) || isa<DIFile>(Context) ||
-        isa<DINamespace>(Context))
+        isa<DINamespace>(Context) || isa<DICommonBlock>(Context))
       addGlobalType(Ty, TyDIE, Context);
   }
 }

llvm/lib/IR/AsmWriter.cpp

@@ -2001,6 +2001,19 @@ static void writeDINamespace(raw_ostream &Out, const DINamespace *N,
   Out << ")";
 }
 
+static void writeDICommonBlock(raw_ostream &Out, const DICommonBlock *N,
+                               TypePrinting *TypePrinter, SlotTracker *Machine,
+                               const Module *Context) {
+  Out << "!DICommonBlock(";
+  MDFieldPrinter Printer(Out, TypePrinter, Machine, Context);
+  Printer.printMetadata("scope", N->getRawScope(), false);
+  Printer.printMetadata("declaration", N->getRawDecl(), false);
+  Printer.printString("name", N->getName());
+  Printer.printMetadata("file", N->getRawFile());
+  Printer.printInt("line", N->getLineNo());
+  Out << ")";
+}
+
 static void writeDIMacro(raw_ostream &Out, const DIMacro *N,
                          TypePrinting *TypePrinter, SlotTracker *Machine,
                          const Module *Context) {

llvm/lib/IR/DIBuilder.cpp

@@ -805,6 +805,13 @@ DISubprogram *DIBuilder::createMethod(
   return SP;
 }
 
+DICommonBlock *DIBuilder::createCommonBlock(
+    DIScope *Scope, DIGlobalVariable *Decl, StringRef Name, DIFile *File,
+    unsigned LineNo) {
+  return DICommonBlock::get(
+      VMContext, Scope, Decl, Name, File, LineNo);
+}
+
 DINamespace *DIBuilder::createNameSpace(DIScope *Scope, StringRef Name,
                                         bool ExportSymbols) {
 

llvm/lib/IR/DebugInfoMetadata.cpp

@@ -222,6 +222,9 @@ DIScopeRef DIScope::getScope() const {
   if (auto *NS = dyn_cast<DINamespace>(this))
     return NS->getScope();
 
+  if (auto *CB = dyn_cast<DICommonBlock>(this))
+    return CB->getScope();
+
   if (auto *M = dyn_cast<DIModule>(this))
     return M->getScope();
 
@@ -237,6 +240,8 @@ StringRef DIScope::getName() const {
     return SP->getName();
   if (auto *NS = dyn_cast<DINamespace>(this))
     return NS->getName();
+  if (auto *CB = dyn_cast<DICommonBlock>(this))
+    return CB->getName();
   if (auto *M = dyn_cast<DIModule>(this))
     return M->getName();
   assert((isa<DILexicalBlockBase>(this) || isa<DIFile>(this) ||
@@ -694,6 +699,17 @@ DINamespace *DINamespace::getImpl(LLVMContext &Context, Metadata *Scope,
   DEFINE_GETIMPL_STORE(DINamespace, (ExportSymbols), Ops);
 }
 
+DICommonBlock *DICommonBlock::getImpl(LLVMContext &Context, Metadata *Scope,
+                                      Metadata *Decl, MDString *Name,
+                                      Metadata *File, unsigned LineNo,
+                                      StorageType Storage, bool ShouldCreate) {
+  assert(isCanonical(Name) && "Expected canonical MDString");
+  DEFINE_GETIMPL_LOOKUP(DICommonBlock, (Scope, Decl, Name, File, LineNo));
+  // The nullptr is for DIScope's File operand. This should be refactored.
+  Metadata *Ops[] = {Scope, Decl, Name, File};
+  DEFINE_GETIMPL_STORE(DICommonBlock, (LineNo), Ops);
+}
+
 DIModule *DIModule::getImpl(LLVMContext &Context, Metadata *Scope,
                             MDString *Name, MDString *ConfigurationMacros,
                             MDString *IncludePath, MDString *ISysRoot,

llvm/lib/IR/LLVMContextImpl.h

@@ -789,6 +789,31 @@ template <> struct MDNodeKeyImpl<DINamespace> {
   }
 };
 
+template <> struct MDNodeKeyImpl<DICommonBlock> {
+  Metadata *Scope;
+  Metadata *Decl;
+  MDString *Name;
+  Metadata *File;
+  unsigned LineNo;
+
+  MDNodeKeyImpl(Metadata *Scope, Metadata *Decl, MDString *Name,
+                Metadata *File, unsigned LineNo)
+      : Scope(Scope), Decl(Decl), Name(Name), File(File), LineNo(LineNo) {}
+  MDNodeKeyImpl(const DICommonBlock *N)
+      : Scope(N->getRawScope()), Decl(N->getRawDecl()), Name(N->getRawName()),
+        File(N->getRawFile()), LineNo(N->getLineNo()) {}
+
+  bool isKeyOf(const DICommonBlock *RHS) const {
+    return Scope == RHS->getRawScope() && Decl == RHS->getRawDecl() &&
+      Name == RHS->getRawName() && File == RHS->getRawFile() &&
+      LineNo == RHS->getLineNo();
+  }
+
+  unsigned getHashValue() const {
+    return hash_combine(Scope, Decl, Name, File, LineNo);
+  }
+};
+
 template <> struct MDNodeKeyImpl<DIModule> {
   Metadata *Scope;
   MDString *Name;

llvm/lib/IR/Verifier.cpp

@@ -1156,6 +1156,14 @@ void Verifier::visitDILexicalBlockFile(const DILexicalBlockFile &N) {
   visitDILexicalBlockBase(N);
 }
 
+void Verifier::visitDICommonBlock(const DICommonBlock &N) {
+  AssertDI(N.getTag() == dwarf::DW_TAG_common_block, "invalid tag", &N);
+  if (auto *S = N.getRawScope())
+    AssertDI(isa<DIScope>(S), "invalid scope ref", &N, S);
+  if (auto *S = N.getRawDecl())
+    AssertDI(isa<DIGlobalVariable>(S), "invalid declaration", &N, S);
+}
+
 void Verifier::visitDINamespace(const DINamespace &N) {
   AssertDI(N.getTag() == dwarf::DW_TAG_namespace, "invalid tag", &N);
   if (auto *S = N.getRawScope())
@@ -1224,7 +1232,6 @@ void Verifier::visitDIGlobalVariable(const DIGlobalVariable &N) {
   visitDIVariable(N);
 
   AssertDI(N.getTag() == dwarf::DW_TAG_variable, "invalid tag", &N);
-  AssertDI(!N.getName().empty(), "missing global variable name", &N);
   AssertDI(isType(N.getRawType()), "invalid type ref", &N, N.getRawType());
   AssertDI(N.getType(), "missing global variable type", &N);
   if (auto *Member = N.getRawStaticDataMemberDeclaration()) {

llvm/test/Assembler/DICommonBlock.ll

@@ -0,0 +1,26 @@
+; RUN: llvm-as < %s | llvm-dis | llvm-as | llvm-dis | FileCheck %s
+; CHECK-DAG: [[MD:![0-9]+]] = !DICommonBlock({{.*}}name: "a"
+; CHECK-DAG: !DIGlobalVariable({{.*}}name: "c",{{.*}}scope: [[MD]]
+
+@common_a = common global [32 x i8] zeroinitializer, align 8, !dbg !13, !dbg !15
+
+!llvm.dbg.cu = !{!0}
+!llvm.module.flags = !{!6, !7}
+!llvm.ident = !{!8}
+
+!0 = distinct !DICompileUnit(language: DW_LANG_Fortran90, file: !1, producer: "PGI Fortran", isOptimized: false, runtimeVersion: 2, emissionKind: FullDebug, retainedTypes: !14, globals: !3)
+!1 = !DIFile(filename: "none.f90", directory: "/not/here/")
+!2 = distinct !DIGlobalVariable(scope: !5, name: "c", file: !1, type: !12, isDefinition: true)
+!3 = !{!13, !15}
+!4 = distinct !DIGlobalVariable(scope: !5, name: "COMMON /foo/", file: !1, line: 4, isLocal: false, isDefinition: true, type: !12)
+!5 = !DICommonBlock(scope: !9, declaration: !4, name: "a", file: !1, line: 4)
+!6 = !{i32 2, !"Dwarf Version", i32 4}
+!7 = !{i32 2, !"Debug Info Version", i32 3}
+!8 = !{!"PGI Fortran"}
+!9 = distinct !DISubprogram(name: "subrtn", scope: !0, file: !1, line: 1, type: !10, isLocal: false, isDefinition: true, unit: !0)
+!10 = !DISubroutineType(types: !11)
+!11 = !{!12, !12}
+!12 = !DIBasicType(name: "int", size: 32)
+!13 = !DIGlobalVariableExpression(var: !4, expr: !DIExpression())
+!14 = !{!12, !10}
+!15 = !DIGlobalVariableExpression(var: !2, expr: !DIExpression(DW_OP_plus_uconst, 4))

llvm/test/DebugInfo/Generic/DICommonBlock.ll

@@ -0,0 +1,42 @@
+; REQUIRES: object-emission
+; RUN: %llc_dwarf -O0 -filetype=obj < %s > %t
+; RUN: llvm-dwarfdump -debug-info %t | FileCheck %s
+; CHECK: DW_TAG_common_block
+; CHECK-DAG: DW_AT_name{{.*}}"a"
+; CHECK-DAG: DW_AT_location
+; CHECK: DW_TAG_variable
+; CHECK-DAG: DW_AT_name{{.*}}"c"
+; CHECK-DAG: DW_AT_location{{.*}}DW_OP_plus_uconst{{.*}}4
+; CHECK: {{DW_TAG|NULL}}
+
+target datalayout = "e-m:o-i64:64-f80:128-n8:16:32:64-S128"
+
+@common_a = common global [32 x i8] zeroinitializer, align 8, !dbg !13, !dbg !15
+
+define i32 @subr() !dbg !9 {
+    %1 = getelementptr inbounds [32 x i8], [32 x i8]* @common_a, i64 0, i32 8
+    %2 = bitcast i8* %1 to i32*
+    %3 = load i32, i32* %2
+    ret i32 %3
+}
+
+!llvm.dbg.cu = !{!0}
+!llvm.module.flags = !{!6, !7}
+!llvm.ident = !{!8}
+
+!0 = distinct !DICompileUnit(language: DW_LANG_Fortran90, file: !1, producer: "PGI Fortran", isOptimized: false, runtimeVersion: 2, emissionKind: FullDebug, retainedTypes: !14, globals: !3)
+!1 = !DIFile(filename: "none.f90", directory: "/not/here/")
+!2 = distinct !DIGlobalVariable(scope: !5, name: "c", file: !1, type: !12, isDefinition: true)
+!3 = !{!13, !15}
+!4 = distinct !DIGlobalVariable(scope: !5, name: "COMMON /foo/", file: !1, line: 4, isLocal: false, isDefinition: true, type: !12)
+!5 = !DICommonBlock(scope: !9, declaration: !4, name: "a", file: !1, line: 4)
+!6 = !{i32 2, !"Dwarf Version", i32 4}
+!7 = !{i32 2, !"Debug Info Version", i32 3}
+!8 = !{!"PGI Fortran"}
+!9 = distinct !DISubprogram(name: "s", scope: !0, file: !1, line: 1, type: !10, isLocal: false, isDefinition: true, unit: !0)
+!10 = !DISubroutineType(types: !11)
+!11 = !{!12, !12}
+!12 = !DIBasicType(name: "int", size: 32)
+!13 = !DIGlobalVariableExpression(var: !4, expr: !DIExpression())
+!14 = !{!12, !10}
+!15 = !DIGlobalVariableExpression(var: !2, expr: !DIExpression(DW_OP_plus_uconst, 4))