IR: Add 'distinct' MDNodes to bitcode and assembly

Propagate whether `MDNode`s are 'distinct' through the other types of IR
(assembly and bitcode).  This adds the `distinct` keyword to assembly.

Currently, no one actually calls `MDNode::getDistinct()`, so these nodes
only get created for:

  - self-references, which are never uniqued, and
  - nodes whose operands are replaced that hit a uniquing collision.

The concept of distinct nodes is still not quite first-class, since
distinct-ness doesn't yet survive across `MapMetadata()`.

Part of PR22111.

llvm-svn: 225474

7 files changed, 26 insertions, 6 deletions

diff --git a/llvm/lib/AsmParser/LLLexer.cpp b/llvm/lib/AsmParser/LLLexer.cpp
index ca3c9e8b6f8..de5db1a4093 100644
--- a/llvm/lib/AsmParser/LLLexer.cpp
+++ b/llvm/lib/AsmParser/LLLexer.cpp
@@ -655,6 +655,9 @@ lltok::Kind LLLexer::LexIdentifier() {
   KEYWORD(x);
   KEYWORD(blockaddress);
 
+  // Metadata types.
+  KEYWORD(distinct);
+
   // Use-list order directives.
   KEYWORD(uselistorder);
   KEYWORD(uselistorder_bb);
diff --git a/llvm/lib/AsmParser/LLParser.cpp b/llvm/lib/AsmParser/LLParser.cpp
index 232c580b88f..bcb314dfbd7 100644
--- a/llvm/lib/AsmParser/LLParser.cpp
+++ b/llvm/lib/AsmParser/LLParser.cpp
@@ -618,8 +618,9 @@ bool LLParser::ParseStandaloneMetadata() {
   if (Lex.getKind() == lltok::Type)
     return TokError("unexpected type in metadata definition");
 
+  bool IsDistinct = EatIfPresent(lltok::kw_distinct);
   if (ParseToken(lltok::exclaim, "Expected '!' here") ||
-      ParseMDNode(Init))
+      ParseMDNode(Init, IsDistinct))
     return true;
 
   // See if this was forward referenced, if so, handle it.
@@ -2945,12 +2946,15 @@ bool LLParser::ParseGlobalValueVector(SmallVectorImpl<Constant *> &Elts) {
   return false;
 }
 
-bool LLParser::ParseMDNode(MDNode *&MD) {
+bool LLParser::ParseMDNode(MDNode *&MD, bool IsDistinct) {
   SmallVector<Metadata *, 16> Elts;
   if (ParseMDNodeVector(Elts))
     return true;
 
-  MD = MDNode::get(Context, Elts);
+  if (IsDistinct)
+    MD = MDNode::getDistinct(Context, Elts);
+  else
+    MD = MDNode::get(Context, Elts);
   return false;
 }
 
diff --git a/llvm/lib/AsmParser/LLParser.h b/llvm/lib/AsmParser/LLParser.h
index d8d272b500d..f1df5b8e54b 100644
--- a/llvm/lib/AsmParser/LLParser.h
+++ b/llvm/lib/AsmParser/LLParser.h
@@ -389,7 +389,7 @@ namespace llvm {
     bool ParseMetadataAsValue(Value *&V, PerFunctionState &PFS);
     bool ParseValueAsMetadata(Metadata *&MD, PerFunctionState *PFS);
     bool ParseMetadata(Metadata *&MD, PerFunctionState *PFS);
-    bool ParseMDNode(MDNode *&MD);
+    bool ParseMDNode(MDNode *&MD, bool IsDistinct = false);
     bool ParseMDNodeVector(SmallVectorImpl<Metadata *> &MDs);
     bool ParseInstructionMetadata(Instruction *Inst, PerFunctionState *PFS);
 
diff --git a/llvm/lib/AsmParser/LLToken.h b/llvm/lib/AsmParser/LLToken.h
index a2111ca96e9..4fb01824d9b 100644
--- a/llvm/lib/AsmParser/LLToken.h
+++ b/llvm/lib/AsmParser/LLToken.h
@@ -182,6 +182,9 @@ namespace lltok {
     kw_extractelement, kw_insertelement, kw_shufflevector,
     kw_extractvalue, kw_insertvalue, kw_blockaddress,
 
+    // Metadata types.
+    kw_distinct,
+
     // Use-list order directives.
     kw_uselistorder, kw_uselistorder_bb,
 
diff --git a/llvm/lib/Bitcode/Reader/BitcodeReader.cpp b/llvm/lib/Bitcode/Reader/BitcodeReader.cpp
index 7c7eebde1df..1792f8b8dd4 100644
--- a/llvm/lib/Bitcode/Reader/BitcodeReader.cpp
+++ b/llvm/lib/Bitcode/Reader/BitcodeReader.cpp
@@ -1106,6 +1106,7 @@ std::error_code BitcodeReader::ParseMetadata() {
     // Read a record.
     Record.clear();
     unsigned Code = Stream.readRecord(Entry.ID, Record);
+    bool IsDistinct = false;
     switch (Code) {
     default:  // Default behavior: ignore.
       break;
@@ -1196,12 +1197,17 @@ std::error_code BitcodeReader::ParseMetadata() {
           NextMDValueNo++);
       break;
     }
+    case bitc::METADATA_DISTINCT_NODE:
+      IsDistinct = true;
+      // fallthrough...
     case bitc::METADATA_NODE: {
       SmallVector<Metadata *, 8> Elts;
       Elts.reserve(Record.size());
       for (unsigned ID : Record)
         Elts.push_back(ID ? MDValueList.getValueFwdRef(ID - 1) : nullptr);
-      MDValueList.AssignValue(MDNode::get(Context, Elts), NextMDValueNo++);
+      MDValueList.AssignValue(IsDistinct ? MDNode::getDistinct(Context, Elts)
+                                         : MDNode::get(Context, Elts),
+                              NextMDValueNo++);
       break;
     }
     case bitc::METADATA_STRING: {
diff --git a/llvm/lib/Bitcode/Writer/BitcodeWriter.cpp b/llvm/lib/Bitcode/Writer/BitcodeWriter.cpp
index 2eb67219c8a..8152799bbce 100644
--- a/llvm/lib/Bitcode/Writer/BitcodeWriter.cpp
+++ b/llvm/lib/Bitcode/Writer/BitcodeWriter.cpp
@@ -773,7 +773,9 @@ static void WriteMDNode(const MDNode *N,
     assert(!isa<LocalAsMetadata>(MD) && "Unexpected function-local metadata");
     Record.push_back(VE.getMetadataID(MD) + 1);
   }
-  Stream.EmitRecord(bitc::METADATA_NODE, Record);
+  Stream.EmitRecord(N->isDistinct() ? bitc::METADATA_DISTINCT_NODE
+                                    : bitc::METADATA_NODE,
+                    Record);
   Record.clear();
 }
 
diff --git a/llvm/lib/IR/AsmWriter.cpp b/llvm/lib/IR/AsmWriter.cpp
index 175e20f9794..dc2c5934c2a 100644
--- a/llvm/lib/IR/AsmWriter.cpp
+++ b/llvm/lib/IR/AsmWriter.cpp
@@ -1253,6 +1253,8 @@ static void WriteMDNodeBodyInternal(raw_ostream &Out, const MDNode *Node,
                                     TypePrinting *TypePrinter,
                                     SlotTracker *Machine,
                                     const Module *Context) {
+  if (Node->isDistinct())
+    Out << "distinct ";
   Out << "!{";
   for (unsigned mi = 0, me = Node->getNumOperands(); mi != me; ++mi) {
     const Metadata *MD = Node->getOperand(mi);