[Metadata] Extend 'count' field of DISubrange to take a metadata node

Summary:
This patch extends the DISubrange 'count' field to take either a
(signed) constant integer value or a reference to a DILocalVariable
or DIGlobalVariable.

This is patch [1/3] in a series to extend LLVM's DISubrange Metadata
node to support debugging of C99 variable length arrays and vectors with
runtime length like the Scalable Vector Extension for AArch64. It is
also a first step towards representing more complex cases like arrays
in Fortran.

Reviewers: echristo, pcc, aprantl, dexonsmith, clayborg, kristof.beyls, dblaikie

Reviewed By: aprantl

Subscribers: rnk, probinson, fhahn, aemerson, rengolin, JDevlieghere, llvm-commits

Differential Revision: https://reviews.llvm.org/D41695

llvm-svn: 323313

llvm/docs/LangRef.rst

@@ -4310,6 +4310,8 @@ DISubrange
 
 ``DISubrange`` nodes are the elements for ``DW_TAG_array_type`` variants of
 :ref:`DICompositeType`. ``count: -1`` indicates an empty array.
+``count: !9`` describes the count with a :ref:`DILocalVariable`.
+``count: !11`` describes the count with a :ref:`DIGlobalVariable`.
 
 .. code-block:: llvm
 
@@ -4317,6 +4319,20 @@ DISubrange
     !1 = !DISubrange(count: 5, lowerBound: 1) ; array counting from 1
     !2 = !DISubrange(count: -1) ; empty array.
 
+    ; Scopes used in rest of example
+    !6 = !DIFile(filename: "vla.c", directory: "/path/to/file")
+    !7 = distinct !DICompileUnit(language: DW_LANG_C99, ...
+    !8 = distinct !DISubprogram(name: "foo", scope: !7, file: !6, line: 5, ...
+
+    ; Use of local variable as count value
+    !9 = !DIBasicType(name: "int", size: 32, encoding: DW_ATE_signed)
+    !10 = !DILocalVariable(name: "count", scope: !8, file: !6, line: 42, type: !9)
+    !11 = !DISubrange(count !10, lowerBound: 0)
+
+    ; Use of global variable as count value
+    !12 = !DIGlobalVariable(name: "count", scope: !8, file: !6, line: 22, type: !9)
+    !13 = !DISubrange(count !12, lowerBound: 0)
+
 .. _DIEnumerator:
 
 DIEnumerator

llvm/include/llvm/IR/DIBuilder.h

@@ -503,6 +503,7 @@ namespace llvm {
     /// Create a descriptor for a value range.  This
     /// implicitly uniques the values returned.
     DISubrange *getOrCreateSubrange(int64_t Lo, int64_t Count);
+    DISubrange *getOrCreateSubrange(int64_t Lo, Metadata *CountNode);
 
     /// Create a new descriptor for the specified variable.
     /// \param Context     Variable scope.

llvm/include/llvm/IR/DebugInfoMetadata.h

@@ -18,11 +18,13 @@
 #include "llvm/ADT/BitmaskEnum.h"
 #include "llvm/ADT/None.h"
 #include "llvm/ADT/Optional.h"
+#include "llvm/ADT/PointerUnion.h"
 #include "llvm/ADT/STLExtras.h"
 #include "llvm/ADT/SmallVector.h"
 #include "llvm/ADT/StringRef.h"
 #include "llvm/ADT/iterator_range.h"
 #include "llvm/BinaryFormat/Dwarf.h"
+#include "llvm/IR/Constants.h"
 #include "llvm/IR/Metadata.h"
 #include "llvm/Support/Casting.h"
 #include <cassert>
@@ -332,31 +334,53 @@ class DISubrange : public DINode {
   friend class LLVMContextImpl;
   friend class MDNode;
 
-  int64_t Count;
   int64_t LowerBound;
 
-  DISubrange(LLVMContext &C, StorageType Storage, int64_t Count,
-             int64_t LowerBound)
-      : DINode(C, DISubrangeKind, Storage, dwarf::DW_TAG_subrange_type, None),
-        Count(Count), LowerBound(LowerBound) {}
+  DISubrange(LLVMContext &C, StorageType Storage, Metadata *Node,
+             int64_t LowerBound, ArrayRef<Metadata *> Ops)
+      : DINode(C, DISubrangeKind, Storage, dwarf::DW_TAG_subrange_type, Ops),
+        LowerBound(LowerBound) {}
+
   ~DISubrange() = default;
 
   static DISubrange *getImpl(LLVMContext &Context, int64_t Count,
                              int64_t LowerBound, StorageType Storage,
                              bool ShouldCreate = true);
 
+  static DISubrange *getImpl(LLVMContext &Context, Metadata *CountNode,
+                             int64_t LowerBound, StorageType Storage,
+                             bool ShouldCreate = true);
+
   TempDISubrange cloneImpl() const {
-    return getTemporary(getContext(), getCount(), getLowerBound());
+    return getTemporary(getContext(), getRawCountNode(), getLowerBound());
   }
 
 public:
   DEFINE_MDNODE_GET(DISubrange, (int64_t Count, int64_t LowerBound = 0),
                     (Count, LowerBound))
 
+  DEFINE_MDNODE_GET(DISubrange, (Metadata *CountNode, int64_t LowerBound = 0),
+                    (CountNode, LowerBound))
+
   TempDISubrange clone() const { return cloneImpl(); }
 
   int64_t getLowerBound() const { return LowerBound; }
-  int64_t getCount() const { return Count; }
+
+  Metadata *getRawCountNode() const {
+    return getOperand(0).get();
+  }
+
+  typedef PointerUnion<ConstantInt*, DIVariable*> CountType;
+
+  CountType getCount() const {
+    if (auto *MD = dyn_cast<ConstantAsMetadata>(getRawCountNode()))
+      return CountType(cast<ConstantInt>(MD->getValue()));
+
+    if (auto *DV = dyn_cast<DIVariable>(getRawCountNode()))
+      return CountType(DV);
+
+    return CountType();
+  }
 
   static bool classof(const Metadata *MD) {
     return MD->getMetadataID() == DISubrangeKind;

llvm/lib/AsmParser/LLParser.cpp

@@ -3492,6 +3492,39 @@ template <class FieldTy> struct MDFieldImpl {
       : Val(std::move(Default)), Seen(false) {}
 };
 
+/// Structure to represent an optional metadata field that
+/// can be of either type (A or B) and encapsulates the
+/// MD<typeofA>Field and MD<typeofB>Field structs, so not
+/// to reimplement the specifics for representing each Field.
+template <class FieldTypeA, class FieldTypeB> struct MDEitherFieldImpl {
+  typedef MDEitherFieldImpl<FieldTypeA, FieldTypeB> ImplTy;
+  FieldTypeA A;
+  FieldTypeB B;
+  bool Seen;
+
+  enum {
+    IsInvalid = 0,
+    IsTypeA = 1,
+    IsTypeB = 2
+  } WhatIs;
+
+  void assign(FieldTypeA A) {
+    Seen = true;
+    this->A = std::move(A);
+    WhatIs = IsTypeA;
+  }
+
+  void assign(FieldTypeB B) {
+    Seen = true;
+    this->B = std::move(B);
+    WhatIs = IsTypeB;
+  }
+
+  explicit MDEitherFieldImpl(FieldTypeA DefaultA, FieldTypeB DefaultB)
+      : A(std::move(DefaultA)), B(std::move(DefaultB)), Seen(false),
+        WhatIs(IsInvalid) {}
+};
+
 struct MDUnsignedField : public MDFieldImpl<uint64_t> {
   uint64_t Max;
 
@@ -3582,6 +3615,26 @@ struct ChecksumKindField : public MDFieldImpl<DIFile::ChecksumKind> {
   ChecksumKindField(DIFile::ChecksumKind CSKind) : ImplTy(CSKind) {}
 };
 
+struct MDSignedOrMDField : MDEitherFieldImpl<MDSignedField, MDField> {
+  MDSignedOrMDField(int64_t Default = 0, bool AllowNull = true)
+      : ImplTy(MDSignedField(Default), MDField(AllowNull)) {}
+
+  MDSignedOrMDField(int64_t Default, int64_t Min, int64_t Max,
+                    bool AllowNull = true)
+      : ImplTy(MDSignedField(Default, Min, Max), MDField(AllowNull)) {}
+
+  bool isMDSignedField() const { return WhatIs == IsTypeA; }
+  bool isMDField() const { return WhatIs == IsTypeB; }
+  int64_t getMDSignedValue() const {
+    assert(isMDSignedField() && "Wrong field type");
+    return A.Val;
+  }
+  Metadata *getMDFieldValue() const {
+    assert(isMDField() && "Wrong field type");
+    return B.Val;
+  }
+};
+
 } // end anonymous namespace
 
 namespace llvm {
@@ -3835,6 +3888,29 @@ bool LLParser::ParseMDField(LocTy Loc, StringRef Name, MDField &Result) {
   return false;
 }
 
+template <>
+bool LLParser::ParseMDField(LocTy Loc, StringRef Name,
+                            MDSignedOrMDField &Result) {
+  // Try to parse a signed int.
+  if (Lex.getKind() == lltok::APSInt) {
+    MDSignedField Res = Result.A;
+    if (!ParseMDField(Loc, Name, Res)) {
+      Result.assign(Res);
+      return false;
+    }
+    return true;
+  }
+
+  // Otherwise, try to parse as an MDField.
+  MDField Res = Result.B;
+  if (!ParseMDField(Loc, Name, Res)) {
+    Result.assign(Res);
+    return false;
+  }
+
+  return true;
+}
+
 template <>
 bool LLParser::ParseMDField(LocTy Loc, StringRef Name, MDStringField &Result) {
   LocTy ValueLoc = Lex.getLoc();
@@ -3979,14 +4055,23 @@ bool LLParser::ParseGenericDINode(MDNode *&Result, bool IsDistinct) {
 
 /// ParseDISubrange:
 ///   ::= !DISubrange(count: 30, lowerBound: 2)
+///   ::= !DISubrange(count: !node, lowerBound: 2)
 bool LLParser::ParseDISubrange(MDNode *&Result, bool IsDistinct) {
 #define VISIT_MD_FIELDS(OPTIONAL, REQUIRED)                                    \
-  REQUIRED(count, MDSignedField, (-1, -1, INT64_MAX));                         \
+  REQUIRED(count, MDSignedOrMDField, (-1, -1, INT64_MAX, false));              \
   OPTIONAL(lowerBound, MDSignedField, );
   PARSE_MD_FIELDS();
 #undef VISIT_MD_FIELDS
 
-  Result = GET_OR_DISTINCT(DISubrange, (Context, count.Val, lowerBound.Val));
+  if (count.isMDSignedField())
+    Result = GET_OR_DISTINCT(
+        DISubrange, (Context, count.getMDSignedValue(), lowerBound.Val));
+  else if (count.isMDField())
+    Result = GET_OR_DISTINCT(
+        DISubrange, (Context, count.getMDFieldValue(), lowerBound.Val));
+  else
+    return true;
+
   return false;
 }
 

llvm/lib/Bitcode/Reader/MetadataLoader.cpp

@@ -1174,14 +1174,25 @@ Error MetadataLoader::MetadataLoaderImpl::parseOneMetadata(
     break;
   }
   case bitc::METADATA_SUBRANGE: {
-    if (Record.size() != 3)
-      return error("Invalid record");
+    Metadata *Val = nullptr;
+    // Operand 'count' is interpreted as:
+    // - Signed integer (version 0)
+    // - Metadata node  (version 1)
+    switch (Record[0] >> 1) {
+    case 0:
+      Val = GET_OR_DISTINCT(DISubrange,
+                            (Context, Record[1], unrotateSign(Record.back())));
+      break;
+    case 1:
+      Val = GET_OR_DISTINCT(DISubrange, (Context, getMDOrNull(Record[1]),
+                                         unrotateSign(Record.back())));
+      break;
+    default:
+      return error("Invalid record: Unsupported version of DISubrange");
+    }
 
-    IsDistinct = Record[0];
-    MetadataList.assignValue(
-        GET_OR_DISTINCT(DISubrange,
-                        (Context, Record[1], unrotateSign(Record[2]))),
-        NextMetadataNo);
+    MetadataList.assignValue(Val, NextMetadataNo);
+    IsDistinct = Record[0] & 1;
     NextMetadataNo++;
     break;
   }

llvm/lib/Bitcode/Writer/BitcodeWriter.cpp

@@ -1442,8 +1442,9 @@ static uint64_t rotateSign(int64_t I) {
 void ModuleBitcodeWriter::writeDISubrange(const DISubrange *N,
                                           SmallVectorImpl<uint64_t> &Record,
                                           unsigned Abbrev) {
-  Record.push_back(N->isDistinct());
-  Record.push_back(N->getCount());
+  const uint64_t Version = 1 << 1;
+  Record.push_back((uint64_t)N->isDistinct() | Version);
+  Record.push_back(VE.getMetadataOrNullID(N->getRawCountNode()));
   Record.push_back(rotateSign(N->getLowerBound()));
 
   Stream.EmitRecord(bitc::METADATA_SUBRANGE, Record, Abbrev);

llvm/lib/CodeGen/AsmPrinter/CodeViewDebug.cpp

@@ -1325,7 +1325,9 @@ TypeIndex CodeViewDebug::lowerTypeArray(const DICompositeType *Ty) {
     const DISubrange *Subrange = cast<DISubrange>(Element);
     assert(Subrange->getLowerBound() == 0 &&
            "codeview doesn't support subranges with lower bounds");
-    int64_t Count = Subrange->getCount();
+    int64_t Count = -1;
+    if (auto *CI = Subrange->getCount().dyn_cast<ConstantInt*>())
+      Count = CI->getSExtValue();
 
     // Forward declarations of arrays without a size and VLAs use a count of -1.
     // Emit a count of zero in these cases to match what MSVC does for arrays

llvm/lib/CodeGen/AsmPrinter/DwarfUnit.cpp

@@ -1328,7 +1328,9 @@ void DwarfUnit::constructSubrangeDIE(DIE &Buffer, const DISubrange *SR,
   // DW_AT_lower_bound and DW_AT_count attributes.
   int64_t LowerBound = SR->getLowerBound();
   int64_t DefaultLowerBound = getDefaultLowerBound();
-  int64_t Count = SR->getCount();
+  int64_t Count = -1;
+  if (auto *CI = SR->getCount().dyn_cast<ConstantInt*>())
+    Count = CI->getSExtValue();
 
   if (DefaultLowerBound == -1 || LowerBound != DefaultLowerBound)
     addUInt(DW_Subrange, dwarf::DW_AT_lower_bound, None, LowerBound);

llvm/lib/IR/AsmWriter.cpp

@@ -1621,10 +1621,15 @@ static void writeDILocation(raw_ostream &Out, const DILocation *DL,
 }
 
 static void writeDISubrange(raw_ostream &Out, const DISubrange *N,
-                            TypePrinting *, SlotTracker *, const Module *) {
+                            TypePrinting *TypePrinter, SlotTracker *Machine,
+                            const Module *Context) {
   Out << "!DISubrange(";
-  MDFieldPrinter Printer(Out);
-  Printer.printInt("count", N->getCount(), /* ShouldSkipZero */ false);
+  MDFieldPrinter Printer(Out, TypePrinter, Machine, Context);
+  if (auto *CE = N->getCount().dyn_cast<ConstantInt*>())
+    Printer.printInt("count", CE->getSExtValue(), /* ShouldSkipZero */ false);
+  else
+    Printer.printMetadata("count", N->getCount().dyn_cast<DIVariable*>(),
+                          /*ShouldSkipNull */ false);
   Printer.printInt("lowerBound", N->getLowerBound());
   Out << ")";
 }

llvm/lib/IR/DIBuilder.cpp

@@ -582,6 +582,10 @@ DISubrange *DIBuilder::getOrCreateSubrange(int64_t Lo, int64_t Count) {
   return DISubrange::get(VMContext, Count, Lo);
 }
 
+DISubrange *DIBuilder::getOrCreateSubrange(int64_t Lo, Metadata *CountNode) {
+  return DISubrange::get(VMContext, CountNode, Lo);
+}
+
 static void checkGlobalVariableScope(DIScope *Context) {
 #ifndef NDEBUG
   if (auto *CT =

llvm/lib/IR/DebugInfoMetadata.cpp

@@ -249,8 +249,17 @@ void GenericDINode::recalculateHash() {
 
 DISubrange *DISubrange::getImpl(LLVMContext &Context, int64_t Count, int64_t Lo,
                                 StorageType Storage, bool ShouldCreate) {
-  DEFINE_GETIMPL_LOOKUP(DISubrange, (Count, Lo));
-  DEFINE_GETIMPL_STORE_NO_OPS(DISubrange, (Count, Lo));
+  auto *CountNode = ConstantAsMetadata::get(
+      ConstantInt::getSigned(Type::getInt64Ty(Context), Count));
+  return getImpl(Context, CountNode, Lo, Storage, ShouldCreate);
+}
+
+DISubrange *DISubrange::getImpl(LLVMContext &Context, Metadata *CountNode,
+                                int64_t Lo, StorageType Storage,
+                                bool ShouldCreate) {
+  DEFINE_GETIMPL_LOOKUP(DISubrange, (CountNode, Lo));
+  Metadata *Ops[] = { CountNode };
+  DEFINE_GETIMPL_STORE(DISubrange, (CountNode, Lo), Ops);
 }
 
 DIEnumerator *DIEnumerator::getImpl(LLVMContext &Context, int64_t Value,

llvm/lib/IR/LLVMContextImpl.h

@@ -321,19 +321,34 @@ template <> struct MDNodeKeyImpl<GenericDINode> : MDNodeOpsKey {
 };
 
 template <> struct MDNodeKeyImpl<DISubrange> {
-  int64_t Count;
+  Metadata *CountNode;
   int64_t LowerBound;
 
-  MDNodeKeyImpl(int64_t Count, int64_t LowerBound)
-      : Count(Count), LowerBound(LowerBound) {}
+  MDNodeKeyImpl(Metadata *CountNode, int64_t LowerBound)
+      : CountNode(CountNode), LowerBound(LowerBound) {}
   MDNodeKeyImpl(const DISubrange *N)
-      : Count(N->getCount()), LowerBound(N->getLowerBound()) {}
+      : CountNode(N->getRawCountNode()),
+        LowerBound(N->getLowerBound()) {}
 
   bool isKeyOf(const DISubrange *RHS) const {
-    return Count == RHS->getCount() && LowerBound == RHS->getLowerBound();
+    if (LowerBound != RHS->getLowerBound())
+      return false;
+
+    if (auto *RHSCount = RHS->getCount().dyn_cast<ConstantInt*>())
+      if (auto *MD = dyn_cast<ConstantAsMetadata>(CountNode))
+        if (RHSCount->getSExtValue() ==
+            cast<ConstantInt>(MD->getValue())->getSExtValue())
+          return true;
+
+    return CountNode == RHS->getRawCountNode();
   }
 
-  unsigned getHashValue() const { return hash_combine(Count, LowerBound); }
+  unsigned getHashValue() const {
+    if (auto *MD = dyn_cast<ConstantAsMetadata>(CountNode))
+      return hash_combine(cast<ConstantInt>(MD->getValue())->getSExtValue(),
+                          LowerBound);
+    return hash_combine(CountNode, LowerBound);
+  }
 };
 
 template <> struct MDNodeKeyImpl<DIEnumerator> {

llvm/lib/IR/Verifier.cpp

@@ -868,7 +868,12 @@ void Verifier::visitDIScope(const DIScope &N) {
 
 void Verifier::visitDISubrange(const DISubrange &N) {
   AssertDI(N.getTag() == dwarf::DW_TAG_subrange_type, "invalid tag", &N);
-  AssertDI(N.getCount() >= -1, "invalid subrange count", &N);
+  auto Count = N.getCount();
+  AssertDI(Count, "Count must either be a signed constant or a DIVariable",
+           &N);
+  AssertDI(!Count.is<ConstantInt*>() ||
+               Count.get<ConstantInt*>()->getSExtValue() >= -1,
+           "invalid subrange count", &N);
 }
 
 void Verifier::visitDIEnumerator(const DIEnumerator &N) {

llvm/test/Assembler/invalid-disubrange-count-node.ll

@@ -0,0 +1,4 @@
+; RUN: not llvm-as < %s -disable-output 2>&1 | FileCheck %s
+
+; CHECK: [[@LINE+1]]:{{[0-9]+}}: error: 'count' cannot be null
+!0 = !DISubrange(count: null)

llvm/test/Bitcode/disubrange-v0.ll

@@ -0,0 +1,41 @@
+; Check that a DISubrange built with an older version of LLVM is correctly restored.
+; RUN: llvm-dis < %s.bc | FileCheck %s
+; RUN: llvm-dis < %s.bc | llvm-as | llvm-dis | FileCheck %s
+
+define void @foo(i32 %n) {
+entry:
+  %array = alloca i32, i64 42, align 16
+  call void @llvm.dbg.declare(metadata i32* %array, metadata !19, metadata !12), !dbg !18
+  ret void
+}
+
+declare void @llvm.dbg.declare(metadata, metadata, metadata) #1
+
+!llvm.dbg.cu = !{!0}
+!llvm.module.flags = !{!3, !4, !5}
+!llvm.ident = !{!6}
+
+!0 = distinct !DICompileUnit(language: DW_LANG_C99, file: !1, producer: "clang version 5.0.1", isOptimized: false, runtimeVersion: 0, emissionKind: FullDebug, enums: !2)
+!1 = !DIFile(filename: "vla.c", directory: "/path/to")
+!2 = !{}
+!3 = !{i32 2, !"Dwarf Version", i32 4}
+!4 = !{i32 2, !"Debug Info Version", i32 3}
+!5 = !{i32 1, !"wchar_size", i32 4}
+!6 = !{!"clang version 5.0.1"}
+!7 = distinct !DISubprogram(name: "foo", scope: !1, file: !1, line: 20, type: !8, isLocal: false, isDefinition: true, scopeLine: 20, flags: DIFlagPrototyped, isOptimized: false, unit: !0, variables: !11)
+!8 = !DISubroutineType(types: !9)
+!9 = !{null, !10}
+!10 = !DIBasicType(name: "int", size: 32, encoding: DW_ATE_signed)
+!11 = !{!16, !19}
+!12 = !DIExpression()
+!16 = !DILocalVariable(name: "vla_expr", scope: !7, file: !1, line: 21, type: !17)
+!17 = !DIBasicType(name: "long unsigned int", size: 64, encoding: DW_ATE_unsigned)
+!18 = !DILocation(line: 21, column: 7, scope: !7)
+!19 = !DILocalVariable(name: "array", scope: !7, file: !1, line: 21, type: !20)
+!20 = !DICompositeType(tag: DW_TAG_array_type, baseType: !10, align: 32, elements: !21)
+!21 = !{!22}
+; CHECK-DAG: ![[NODE:[0-9]+]] = !DILocalVariable(name: "array"
+; CHECK-DAG: ![[CONST:[0-9]+]] = !DISubrange(count: 42, lowerBound: 1)
+; CHECK-DAG: ![[MULTI:[0-9]+]] = !{![[CONST]]}
+; CHECK-DAG: elements: ![[MULTI]]
+!22 = !DISubrange(count: 42, lowerBound: 1)

llvm/test/Bitcode/disubrange.ll

@@ -0,0 +1,49 @@
+; Check that the DISubrange 'count' reference is correctly uniqued and restored,
+; since it can take the value of either a signed integer or a DIVariable.
+; RUN: llvm-as < %s | llvm-dis | FileCheck %s
+
+define void @foo(i32 %n) {
+entry:
+  %0 = zext i32 %n to i64
+  %vla = alloca i32, i64 %0, align 16
+  call void @llvm.dbg.declare(metadata i32* %vla, metadata !19, metadata !12), !dbg !18
+  ret void
+}
+
+declare void @llvm.dbg.declare(metadata, metadata, metadata) #1
+
+!llvm.dbg.cu = !{!0}
+!llvm.module.flags = !{!3, !4, !5}
+!llvm.ident = !{!6}
+
+!0 = distinct !DICompileUnit(language: DW_LANG_C99, file: !1, producer: "clang version 5.0.1", isOptimized: false, runtimeVersion: 0, emissionKind: FullDebug, enums: !2)
+!1 = !DIFile(filename: "vla.c", directory: "/path/to")
+!2 = !{}
+!3 = !{i32 2, !"Dwarf Version", i32 4}
+!4 = !{i32 2, !"Debug Info Version", i32 3}
+!5 = !{i32 1, !"wchar_size", i32 4}
+!6 = !{!"clang version 5.0.1"}
+!7 = distinct !DISubprogram(name: "foo", scope: !1, file: !1, line: 20, type: !8, isLocal: false, isDefinition: true, scopeLine: 20, flags: DIFlagPrototyped, isOptimized: false, unit: !0, variables: !11)
+!8 = !DISubroutineType(types: !9)
+!9 = !{null, !10}
+!10 = !DIBasicType(name: "int", size: 32, encoding: DW_ATE_signed)
+!11 = !{!16, !19}
+!12 = !DIExpression()
+!16 = !DILocalVariable(name: "vla_expr", scope: !7, file: !1, line: 21, type: !17)
+!17 = !DIBasicType(name: "long unsigned int", size: 64, encoding: DW_ATE_unsigned)
+!18 = !DILocation(line: 21, column: 7, scope: !7)
+!19 = !DILocalVariable(name: "vla", scope: !7, file: !1, line: 21, type: !20)
+!20 = !DICompositeType(tag: DW_TAG_array_type, baseType: !10, align: 32, elements: !21)
+!21 = !{!22, !23, !24, !25, !26, !27}
+
+; CHECK-DAG: ![[NODE:[0-9]+]] = !DILocalVariable(name: "vla_expr"
+; CHECK-DAG: ![[RANGE:[0-9]+]] = !DISubrange(count: ![[NODE]])
+; CHECK-DAG: ![[CONST:[0-9]+]] = !DISubrange(count: 16)
+; CHECK-DAG: ![[MULTI:[0-9]+]] = !{![[RANGE]], ![[RANGE]], ![[CONST]], ![[CONST]], ![[CONST]], ![[CONST]]}
+; CHECK-DAG: elements: ![[MULTI]]
+!22 = !DISubrange(count: !16)
+!23 = !DISubrange(count: !16)
+!24 = !DISubrange(count: 16)
+!25 = !DISubrange(count: i16 16)
+!26 = !DISubrange(count: i32 16)
+!27 = !DISubrange(count: i64 16)

llvm/test/Verifier/invalid-disubrange-count-node.ll

@@ -0,0 +1,37 @@
+; RUN: llvm-as < %s -disable-output 2>&1 | FileCheck %s
+
+define void @foo(i32 %n) {
+entry:
+  %0 = zext i32 %n to i64
+  %vla = alloca i32, i64 %0, align 16
+  call void @llvm.dbg.declare(metadata i32* %vla, metadata !19, metadata !12), !dbg !18
+  ret void
+}
+
+declare void @llvm.dbg.declare(metadata, metadata, metadata) #1
+
+!llvm.dbg.cu = !{!0}
+!llvm.module.flags = !{!3, !4, !5}
+!llvm.ident = !{!6}
+
+!0 = distinct !DICompileUnit(language: DW_LANG_C99, file: !1, producer: "clang version 5.0.1", isOptimized: false, runtimeVersion: 0, emissionKind: FullDebug, enums: !2)
+!1 = !DIFile(filename: "vla.c", directory: "/path/to")
+!2 = !{}
+!3 = !{i32 2, !"Dwarf Version", i32 4}
+!4 = !{i32 2, !"Debug Info Version", i32 3}
+!5 = !{i32 1, !"wchar_size", i32 4}
+!6 = !{!"clang version 5.0.1"}
+!7 = distinct !DISubprogram(name: "foo", scope: !1, file: !1, line: 20, type: !8, isLocal: false, isDefinition: true, scopeLine: 20, flags: DIFlagPrototyped, isOptimized: false, unit: !0, variables: !11)
+!8 = !DISubroutineType(types: !9)
+!9 = !{null, !10}
+!10 = !DIBasicType(name: "int", size: 32, encoding: DW_ATE_signed)
+!11 = !{!16, !19}
+!12 = !DIExpression()
+!16 = !DILocalVariable(name: "vla_expr", scope: !7, file: !1, line: 21, type: !17)
+!17 = !DIBasicType(name: "long unsigned int", size: 64, encoding: DW_ATE_unsigned)
+!18 = !DILocation(line: 21, column: 7, scope: !7)
+!19 = !DILocalVariable(name: "vla", scope: !7, file: !1, line: 21, type: !20)
+!20 = !DICompositeType(tag: DW_TAG_array_type, baseType: !10, align: 32, elements: !21)
+!21 = !{!22}
+; CHECK: Count must either be a signed constant or a DIVariable
+!22 = !DISubrange(count: !17)

llvm/unittests/IR/MetadataTest.cpp

@@ -932,8 +932,11 @@ typedef MetadataTest DISubrangeTest;
 
 TEST_F(DISubrangeTest, get) {
   auto *N = DISubrange::get(Context, 5, 7);
+  auto Count = N->getCount();
   EXPECT_EQ(dwarf::DW_TAG_subrange_type, N->getTag());
-  EXPECT_EQ(5, N->getCount());
+  ASSERT_TRUE(Count);
+  ASSERT_TRUE(Count.is<ConstantInt*>());
+  EXPECT_EQ(5, Count.get<ConstantInt*>()->getSExtValue());
   EXPECT_EQ(7, N->getLowerBound());
   EXPECT_EQ(N, DISubrange::get(Context, 5, 7));
   EXPECT_EQ(DISubrange::get(Context, 5, 0), DISubrange::get(Context, 5));
@@ -944,12 +947,34 @@ TEST_F(DISubrangeTest, get) {
 
 TEST_F(DISubrangeTest, getEmptyArray) {
   auto *N = DISubrange::get(Context, -1, 0);
+  auto Count = N->getCount();
   EXPECT_EQ(dwarf::DW_TAG_subrange_type, N->getTag());
-  EXPECT_EQ(-1, N->getCount());
+  ASSERT_TRUE(Count);
+  ASSERT_TRUE(Count.is<ConstantInt*>());
+  EXPECT_EQ(-1, Count.get<ConstantInt*>()->getSExtValue());
   EXPECT_EQ(0, N->getLowerBound());
   EXPECT_EQ(N, DISubrange::get(Context, -1, 0));
 }
 
+TEST_F(DISubrangeTest, getVariableCount) {
+  DILocalScope *Scope = getSubprogram();
+  DIFile *File = getFile();
+  DIType *Type = getDerivedType();
+  DINode::DIFlags Flags = static_cast<DINode::DIFlags>(7);
+  auto *VlaExpr = DILocalVariable::get(Context, Scope, "vla_expr", File, 8,
+                                       Type, 2, Flags, 8);
+
+  auto *N = DISubrange::get(Context, VlaExpr, 0);
+  auto Count = N->getCount();
+  ASSERT_TRUE(Count);
+  ASSERT_TRUE(Count.is<DIVariable*>());
+  EXPECT_EQ(VlaExpr, Count.get<DIVariable*>());
+  ASSERT_TRUE(isa<DIVariable>(N->getRawCountNode()));
+  EXPECT_EQ(0, N->getLowerBound());
+  EXPECT_EQ("vla_expr", Count.get<DIVariable*>()->getName());
+  EXPECT_EQ(N, DISubrange::get(Context, VlaExpr, 0));
+}
+
 typedef MetadataTest DIEnumeratorTest;
 
 TEST_F(DIEnumeratorTest, get) {