[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

3 files changed, 74 insertions, 0 deletions

diff --git a/llvm/lib/IR/AsmWriter.cpp b/llvm/lib/IR/AsmWriter.cpp
index 4c6e3e3788b..ec4663018bd 100644
--- a/llvm/lib/IR/AsmWriter.cpp
+++ b/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);
 }
 
diff --git a/llvm/lib/IR/Attributes.cpp b/llvm/lib/IR/Attributes.cpp
index 3b1140ab542..b97afb6f4a6 100644
--- a/llvm/lib/IR/Attributes.cpp
+++ b/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
 //===----------------------------------------------------------------------===//
diff --git a/llvm/lib/IR/Globals.cpp b/llvm/lib/IR/Globals.cpp
index 5f338f58d94..5fbf51e0089 100644
--- a/llvm/lib/IR/Globals.cpp
+++ b/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());
   }
 }