[IR] Allow attributes with global variables

This patch extends llvm-ir to allow attributes to be set on global variables.
An RFC was sent out earlier by my colleague James Molloy: http://lists.llvm.org/pipermail/cfe-dev/2017-March/053100.html
A key part of that proposal was to extend LLVM-IR to carry attributes on global variables.
This generic feature could be useful for multiple purposes.
In our present context, it would be useful to carry user specified sections for bss/rodata/data.

Reviewed by: Jonathan Roelofs, Reid Kleckner
Differential Revision: https://reviews.llvm.org/D32009

llvm-svn: 302794

llvm/docs/LangRef.rst

@@ -641,8 +641,9 @@ assume that the globals are densely packed in their section and try to
 iterate over them as an array, alignment padding would break this
 iteration. The maximum alignment is ``1 << 29``.
 
-Globals can also have a :ref:`DLL storage class <dllstorageclass>` and
-an optional list of attached :ref:`metadata <metadata>`,
+Globals can also have a :ref:`DLL storage class <dllstorageclass>`,
+an optional :ref:`global attributes <glattrs>` and
+an optional list of attached :ref:`metadata <metadata>`.
 
 Variables and aliases can have a
 :ref:`Thread Local Storage Model <tls_model>`.
@@ -1624,6 +1625,14 @@ example:
     the ELF x86-64 abi, but it can be disabled for some compilation
     units.
 
+.. _glattrs:
+
+Global Attributes
+-----------------
+
+Attributes may be set to communicate additional information about a global variable.
+Unlike :ref:`function attributes <fnattrs>`, attributes on a global variable
+are grouped into a single :ref:`attribute group <attrgrp>`.
 
 .. _opbundles:
 

llvm/include/llvm/IR/Attributes.h

@@ -35,6 +35,7 @@ namespace llvm {
 class AttrBuilder;
 class AttributeImpl;
 class AttributeListImpl;
+class AttributeList;
 class AttributeSetNode;
 template<typename T> struct DenseMapInfo;
 class Function;
@@ -227,14 +228,51 @@ public:
   bool operator==(const AttributeSet &O) { return SetNode == O.SetNode; }
   bool operator!=(const AttributeSet &O) { return !(*this == O); }
 
+  /// Add an argument attribute. Because
+  /// attribute sets are immutable, this returns a new set.
+  AttributeSet addAttribute(LLVMContext &C,
+                            Attribute::AttrKind Kind) const;
+
+  /// Add a target-dependent attribute. Because
+  /// attribute sets are immutable, this returns a new set.
+  AttributeSet addAttribute(LLVMContext &C, StringRef Kind,
+                            StringRef Value = StringRef()) const;
+
+  /// Add attributes to the attribute set. Because
+  /// attribute sets are immutable, this returns a new set.
+  AttributeSet addAttributes(LLVMContext &C, AttributeSet AS) const;
+
+  /// Remove the specified attribute from this set. Because
+  /// attribute sets are immutable, this returns a new set.
+  AttributeSet removeAttribute(LLVMContext &C,
+                                Attribute::AttrKind Kind) const;
+
+  /// Remove the specified attribute from this set. Because
+  /// attribute sets are immutable, this returns a new set.
+  AttributeSet removeAttribute(LLVMContext &C,
+                                StringRef Kind) const;
+
+  /// Remove the specified attributes from this set. Because
+  /// attribute sets are immutable, this returns a new set.
+  AttributeSet removeAttributes(LLVMContext &C,
+                                 const AttrBuilder &AttrsToRemove) const;
+
+  /// Return the number of attributes in this set.
   unsigned getNumAttributes() const;
 
+  /// Return true if attributes exists in this set.
   bool hasAttributes() const { return SetNode != nullptr; }
 
+  /// Return true if the attribute exists in this set.
   bool hasAttribute(Attribute::AttrKind Kind) const;
+
+  /// Return true if the attribute exists in this set.
   bool hasAttribute(StringRef Kind) const;
 
+  /// Return the attribute object.
   Attribute getAttribute(Attribute::AttrKind Kind) const;
+
+  /// Return the target-dependent attribute object.
   Attribute getAttribute(StringRef Kind) const;
 
   unsigned getAlignment() const;
@@ -248,6 +286,9 @@ public:
 
   iterator begin() const;
   iterator end() const;
+#if !defined(NDEBUG) || defined(LLVM_ENABLE_DUMP)
+  void dump() const;
+#endif
 };
 
 //===----------------------------------------------------------------------===//

llvm/include/llvm/IR/GlobalVariable.h

@@ -24,6 +24,7 @@
 #include "llvm/ADT/Twine.h"
 #include "llvm/ADT/ilist_node.h"
 #include "llvm/IR/GlobalObject.h"
+#include "llvm/IR/Attributes.h"
 #include "llvm/IR/OperandTraits.h"
 #include "llvm/IR/Value.h"
 #include <cassert>
@@ -41,6 +42,7 @@ class DIGlobalVariableExpression;
 class GlobalVariable : public GlobalObject, public ilist_node<GlobalVariable> {
   friend class SymbolTableListTraits<GlobalVariable>;
 
+  AttributeSet Attrs;
   bool isConstantGlobal : 1;                   // Is this a global constant?
   bool isExternallyInitializedConstant : 1;    // Is this a global whose value
                                                // can change from its initial
@@ -178,6 +180,61 @@ public:
   /// Fill the vector with all debug info attachements.
   void getDebugInfo(SmallVectorImpl<DIGlobalVariableExpression *> &GVs) const;
 
+  /// Add attribute to this global.
+  void addAttribute(Attribute::AttrKind Kind) {
+    Attrs = Attrs.addAttribute(getContext(), Kind);
+  }
+
+  /// Add attribute to this global.
+  void addAttribute(StringRef Kind, StringRef Val = StringRef()) {
+    Attrs = Attrs.addAttribute(getContext(), Kind, Val);
+  }
+
+  /// Return true if the attribute exists.
+  bool hasAttribute(Attribute::AttrKind Kind) const {
+    return Attrs.hasAttribute(Kind);
+  }
+
+  /// Return true if the attribute exists.
+  bool hasAttribute(StringRef Kind) const {
+    return Attrs.hasAttribute(Kind);
+  }
+
+  /// Return true if any attributes exist.
+  bool hasAttributes() const {
+    return Attrs.hasAttributes();
+  }
+
+  /// Return the attribute object.
+  Attribute getAttribute(Attribute::AttrKind Kind) const {
+    return Attrs.getAttribute(Kind);
+  }
+
+  /// Return the attribute object.
+  Attribute getAttribute(StringRef Kind) const {
+    return Attrs.getAttribute(Kind);
+  }
+
+  /// Return the attribute set for this global
+  AttributeSet getAttributes() const {
+    return Attrs;
+  }
+
+  /// Return attribute set as list with index.
+  /// FIXME: This may not be required once ValueEnumerators
+  /// in bitcode-writer can enumerate attribute-set.
+  AttributeList getAttributesAsList(unsigned index) const {
+    if (!hasAttributes())
+      return AttributeList();
+    std::pair<unsigned, AttributeSet> AS[1] = {{index, Attrs}};
+    return AttributeList::get(getContext(), AS);
+  }
+
+  /// Set attribute list for this global
+  void setAttributes(AttributeSet A) {
+    Attrs = A;
+  }
+
   // Methods for support type inquiry through isa, cast, and dyn_cast:
   static inline bool classof(const Value *V) {
     return V->getValueID() == Value::GlobalVariableVal;

llvm/lib/AsmParser/LLParser.cpp

@@ -162,6 +162,10 @@ bool LLParser::ValidateEndOfModule() {
       AS = AS.addAttributes(Context, AttributeList::FunctionIndex,
                             AttributeSet::get(Context, FnAttrs));
       II->setAttributes(AS);
+    } else if (auto *GV = dyn_cast<GlobalVariable>(V)) {
+      AttrBuilder Attrs(GV->getAttributes());
+      Attrs.merge(B);
+      GV->setAttributes(AttributeSet::get(Context,Attrs));
     } else {
       llvm_unreachable("invalid object with forward attribute group reference");
     }
@@ -832,10 +836,10 @@ bool LLParser::parseIndirectSymbol(
 /// ParseGlobal
 ///   ::= GlobalVar '=' OptionalLinkage OptionalVisibility OptionalDLLStorageClass
 ///       OptionalThreadLocal OptionalUnnamedAddr OptionalAddrSpace
-///       OptionalExternallyInitialized GlobalType Type Const
+///       OptionalExternallyInitialized GlobalType Type Const OptionalAttrs
 ///   ::= OptionalLinkage OptionalVisibility OptionalDLLStorageClass
 ///       OptionalThreadLocal OptionalUnnamedAddr OptionalAddrSpace
-///       OptionalExternallyInitialized GlobalType Type Const
+///       OptionalExternallyInitialized GlobalType Type Const OptionalAttrs
 ///
 /// Everything up to and including OptionalUnnamedAddr has been parsed
 /// already.
@@ -950,6 +954,16 @@ bool LLParser::ParseGlobal(const std::string &Name, LocTy NameLoc,
     }
   }
 
+  AttrBuilder Attrs;
+  LocTy BuiltinLoc;
+  std::vector<unsigned> FwdRefAttrGrps;
+  if (ParseFnAttributeValuePairs(Attrs, FwdRefAttrGrps, false, BuiltinLoc))
+    return true;
+  if (Attrs.hasAttributes() || !FwdRefAttrGrps.empty()) {
+    GV->setAttributes(AttributeSet::get(Context, Attrs));
+    ForwardRefAttrGroups[GV] = FwdRefAttrGrps;
+  }
+
   return false;
 }
 

llvm/lib/Bitcode/Reader/BitcodeReader.cpp

@@ -2750,7 +2750,7 @@ Error BitcodeReader::parseComdatRecord(ArrayRef<uint64_t> Record) {
 Error BitcodeReader::parseGlobalVarRecord(ArrayRef<uint64_t> Record) {
   // v1: [pointer type, isconst, initid, linkage, alignment, section,
   // visibility, threadlocal, unnamed_addr, externally_initialized,
-  // dllstorageclass, comdat] (name in VST)
+  // dllstorageclass, comdat, attributes] (name in VST)
   // v2: [strtab_offset, strtab_size, v1]
   StringRef Name;
   std::tie(Name, Record) = readNameFromStrtab(Record);
@@ -2830,6 +2830,11 @@ Error BitcodeReader::parseGlobalVarRecord(ArrayRef<uint64_t> Record) {
   } else if (hasImplicitComdat(RawLinkage)) {
     NewGV->setComdat(reinterpret_cast<Comdat *>(1));
   }
+
+  if (Record.size() > 12) {
+    auto AS = getAttributes(Record[12]).getFnAttributes();
+    NewGV->setAttributes(AS);
+  }
   return Error::success();
 }
 

llvm/lib/Bitcode/Writer/BitcodeWriter.cpp

@@ -1109,7 +1109,7 @@ void ModuleBitcodeWriter::writeModuleInfo() {
     // GLOBALVAR: [strtab offset, strtab size, type, isconst, initid,
     //             linkage, alignment, section, visibility, threadlocal,
     //             unnamed_addr, externally_initialized, dllstorageclass,
-    //             comdat]
+    //             comdat, attributes]
     Vals.push_back(StrtabBuilder.add(GV.getName()));
     Vals.push_back(GV.getName().size());
     Vals.push_back(VE.getTypeID(GV.getValueType()));
@@ -1124,13 +1124,17 @@ void ModuleBitcodeWriter::writeModuleInfo() {
         GV.getUnnamedAddr() != GlobalValue::UnnamedAddr::None ||
         GV.isExternallyInitialized() ||
         GV.getDLLStorageClass() != GlobalValue::DefaultStorageClass ||
-        GV.hasComdat()) {
+        GV.hasComdat() ||
+        GV.hasAttributes()) {
       Vals.push_back(getEncodedVisibility(GV));
       Vals.push_back(getEncodedThreadLocalMode(GV));
       Vals.push_back(getEncodedUnnamedAddr(GV));
       Vals.push_back(GV.isExternallyInitialized());
       Vals.push_back(getEncodedDLLStorageClass(GV));
       Vals.push_back(GV.hasComdat() ? VE.getComdatID(GV.getComdat()) : 0);
+
+      auto AL = GV.getAttributesAsList(AttributeList::FunctionIndex);
+      Vals.push_back(VE.getAttributeListID(AL));
     } else {
       AbbrevToUse = SimpleGVarAbbrev;
     }

llvm/lib/Bitcode/Writer/ValueEnumerator.cpp

@@ -314,10 +314,13 @@ ValueEnumerator::ValueEnumerator(const Module &M,
   // Remember what is the cutoff between globalvalue's and other constants.
   unsigned FirstConstant = Values.size();
 
-  // Enumerate the global variable initializers.
-  for (const GlobalVariable &GV : M.globals())
+  // Enumerate the global variable initializers and attributes.
+  for (const GlobalVariable &GV : M.globals()) {
     if (GV.hasInitializer())
       EnumerateValue(GV.getInitializer());
+    if (GV.hasAttributes())
+      EnumerateAttributes(GV.getAttributesAsList(AttributeList::FunctionIndex));
+  }
 
   // Enumerate the aliasees.
   for (const GlobalAlias &GA : M.aliases())

llvm/lib/IR/AsmWriter.cpp

@@ -805,6 +805,9 @@ void SlotTracker::processModule() {
     if (!Var.hasName())
       CreateModuleSlot(&Var);
     processGlobalObjectMetadata(Var);
+    auto Attrs = Var.getAttributes();
+    if (Attrs.hasAttributes())
+      CreateAttributeSetSlot(Attrs);
   }
 
   for (const GlobalAlias &A : TheModule->aliases()) {
@@ -2502,6 +2505,10 @@ void AssemblyWriter::printGlobal(const GlobalVariable *GV) {
   GV->getAllMetadata(MDs);
   printMetadataAttachments(MDs, ", ");
 
+  auto Attrs = GV->getAttributes();
+  if (Attrs.hasAttributes())
+    Out << " #" << Machine.getAttributeGroupSlot(Attrs);
+
   printInfoComment(*GV);
 }
 

llvm/lib/IR/Attributes.cpp

@@ -504,6 +504,64 @@ AttributeSet AttributeSet::get(LLVMContext &C, ArrayRef<Attribute> Attrs) {
   return AttributeSet(AttributeSetNode::get(C, Attrs));
 }
 
+AttributeSet AttributeSet::addAttribute(LLVMContext &C,
+                          Attribute::AttrKind Kind) const {
+  if (hasAttribute(Kind)) return *this;
+  AttrBuilder B;
+  B.addAttribute(Kind);
+  return addAttributes(C, AttributeSet::get(C, B));
+}
+
+AttributeSet AttributeSet::addAttribute(LLVMContext &C, StringRef Kind,
+                          StringRef Value) const {
+  AttrBuilder B;
+  B.addAttribute(Kind, Value);
+  return addAttributes(C, AttributeSet::get(C, B));
+}
+
+AttributeSet AttributeSet::addAttributes(LLVMContext &C,
+                                         const AttributeSet AS) const {
+  if (!hasAttributes())
+    return AS;
+
+  if (!AS.hasAttributes())
+    return *this;
+
+  AttrBuilder B(AS);
+  for (Attribute I : *this)
+    B.addAttribute(I);
+
+ return get(C, B);
+}
+
+AttributeSet AttributeSet::removeAttribute(LLVMContext &C,
+                                             Attribute::AttrKind Kind) const {
+  if (!hasAttribute(Kind)) return *this;
+  AttrBuilder B;
+  B.addAttribute(Kind);
+  return removeAttributes(C, B);
+}
+
+AttributeSet AttributeSet::removeAttribute(LLVMContext &C,
+                                             StringRef Kind) const {
+  if (!hasAttribute(Kind)) return *this;
+  AttrBuilder B;
+  B.addAttribute(Kind);
+  return removeAttributes(C, B);
+}
+
+AttributeSet AttributeSet::removeAttributes(LLVMContext &C,
+                                              const AttrBuilder &Attrs) const {
+
+  // FIXME it is not obvious how this should work for alignment.
+  // For now, say we can't pass in alignment, which no current use does.
+  assert(!Attrs.hasAlignmentAttr() && "Attempt to change alignment!");
+
+  AttrBuilder B(*this);
+  B.remove(Attrs);
+  return get(C, B);
+}
+
 unsigned AttributeSet::getNumAttributes() const {
   return SetNode ? SetNode->getNumAttributes() : 0;
 }
@@ -557,6 +615,14 @@ AttributeSet::iterator AttributeSet::end() const {
   return SetNode ? SetNode->end() : nullptr;
 }
 
+#if !defined(NDEBUG) || defined(LLVM_ENABLE_DUMP)
+LLVM_DUMP_METHOD void AttributeSet::dump() const {
+  dbgs() << "AS =\n";
+    dbgs() << "  { ";
+    dbgs() << getAsString(true) << " }\n";
+}
+#endif
+
 //===----------------------------------------------------------------------===//
 // AttributeSetNode Definition
 //===----------------------------------------------------------------------===//

llvm/lib/IR/Globals.cpp

@@ -338,6 +338,7 @@ void GlobalVariable::copyAttributesFrom(const GlobalValue *Src) {
   if (const GlobalVariable *SrcVar = dyn_cast<GlobalVariable>(Src)) {
     setThreadLocalMode(SrcVar->getThreadLocalMode());
     setExternallyInitialized(SrcVar->isExternallyInitialized());
+    setAttributes(SrcVar->getAttributes());
   }
 }
 

llvm/test/Assembler/globalvariable-attributes.ll

@@ -0,0 +1,19 @@
+; RUN: llvm-as < %s | llvm-dis | llvm-as | llvm-dis | FileCheck %s
+
+@g1 = global i32 7 "key" = "value" "key2" = "value2"
+@g2 = global i32 2, align 4 "key3" = "value3"
+@g3 = global i32 2 #0
+@g4 = global i32 2, align 4 "key5" = "value5" #0
+
+attributes #0 = { "string" = "value" nobuiltin norecurse }
+
+; CHECK: @g1 = global i32 7 #0
+; CHECK: @g2 = global i32 2, align 4 #1
+; CHECK: @g3 = global i32 2 #2
+; CHECK: @g4 = global i32 2, align 4 #3
+
+; CHECK: attributes #0 = { "key"="value" "key2"="value2" }
+; CHECK: attributes #1 = { "key3"="value3" }
+; CHECK: attributes #2 = { nobuiltin norecurse "string"="value" }
+; CHECK: attributes #3 = { nobuiltin norecurse "key5"="value5" "string"="value" }
+

llvm/test/Bitcode/globalvariable-attributes.ll

@@ -0,0 +1,19 @@
+; RUN: llvm-as < %s | llvm-dis | FileCheck %s
+
+@g1 = global i32 7 "key" = "value" "key2" = "value2"
+@g2 = global i32 2, align 4 "key3" = "value3"
+@g3 = global i32 2 #0
+@g4 = global i32 2, align 4 "key5" = "value5" #0
+
+attributes #0 = { "string" = "value" nobuiltin norecurse }
+
+; CHECK: @g1 = global i32 7 #0
+; CHECK: @g2 = global i32 2, align 4 #1
+; CHECK: @g3 = global i32 2 #2
+; CHECK: @g4 = global i32 2, align 4 #3
+
+; CHECK: attributes #0 = { "key"="value" "key2"="value2" }
+; CHECK: attributes #1 = { "key3"="value3" }
+; CHECK: attributes #2 = { nobuiltin norecurse "string"="value" }
+; CHECK: attributes #3 = { nobuiltin norecurse "key5"="value5" "string"="value" }
+