[llvm] [PGO] Add `llvm.loop.estimated_trip_count` metadata (PR #148758)

[Mircea Trofin via llvm-commits]

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@@ -201,34 +201,40 @@ void llvm::initializeLoopPassPass(PassRegistry &Registry) {
 }
 
 /// Create MDNode for input string.
-static MDNode *createStringMetadata(Loop *TheLoop, StringRef Name, unsigned V) {
+static MDNode *createStringMetadata(Loop *TheLoop, StringRef Name,
+                                    std::optional<unsigned> V) {
   LLVMContext &Context = TheLoop->getHeader()->getContext();
-  Metadata *MDs[] = {
-      MDString::get(Context, Name),
-      ConstantAsMetadata::get(ConstantInt::get(Type::getInt32Ty(Context), V))};
-  return MDNode::get(Context, MDs);
+  if (V) {
+    Metadata *MDs[] = {MDString::get(Context, Name),
+                       ConstantAsMetadata::get(
+                           ConstantInt::get(Type::getInt32Ty(Context), *V))};
+    return MDNode::get(Context, MDs);
+  }
+  return MDNode::get(Context, {MDString::get(Context, Name)});
 }
 
-/// Set input string into loop metadata by keeping other values intact.
-/// If the string is already in loop metadata update value if it is
-/// different.
-void llvm::addStringMetadataToLoop(Loop *TheLoop, const char *StringMD,
-                                   unsigned V) {
+bool llvm::addStringMetadataToLoop(Loop *TheLoop, const char *StringMD,
+                                   std::optional<unsigned> V) {
   SmallVector<Metadata *, 4> MDs(1);
   // If the loop already has metadata, retain it.
   MDNode *LoopID = TheLoop->getLoopID();
   if (LoopID) {
     for (unsigned i = 1, ie = LoopID->getNumOperands(); i < ie; ++i) {
       MDNode *Node = cast<MDNode>(LoopID->getOperand(i));
-      // If it is of form key = value, try to parse it.
-      if (Node->getNumOperands() == 2) {
+      // If it is of form key [= value], try to parse it.
+      unsigned NumOps = Node->getNumOperands();
+      if (NumOps == 1 || NumOps == 2) {
         MDString *S = dyn_cast<MDString>(Node->getOperand(0));
         if (S && S->getString() == StringMD) {
-          ConstantInt *IntMD =
-              mdconst::extract_or_null<ConstantInt>(Node->getOperand(1));
-          if (IntMD && IntMD->getSExtValue() == V)
-            // It is already in place. Do nothing.
-            return;
+          // If it is already in place, do nothing.
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mtrofin wrote:

if it's already in place and has the same value, right?

https://github.com/llvm/llvm-project/pull/148758