[llvm] [Verifier] Add checks for loop metadata nodes (PR #182252)

[Matt Arsenault via llvm-commits]

================
@@ -1145,6 +1146,61 @@ void Verifier::visitMDNode(const MDNode &MD, AreDebugLocsAllowed AllowLocs) {
   Check(MD.isResolved(), "All nodes should be resolved!", &MD);
 }
 
+// Loop attributes that require exactly two operands (name + i1).
+static const char *const LoopBooleanAttributeNames[] = {
+    "llvm.loop.distribute.enable",
+    "llvm.loop.vectorize.enable",
+};
+
+// Loop attributes that allow only a single operand (just the name).
+// TODO: This is not an exhaustive list and can also include attributes
+//       like llvm.loop.licm_versioning.disable.
+static const char *const LoopSingleOperandAttributeNames[] = {
+    "llvm.loop.unroll.disable",
+    "llvm.loop.unroll.enable",
+    "llvm.loop.unroll.full",
+    "llvm.loop.unroll_and_jam.enable",
+    "llvm.loop.unroll_and_jam.disable",
+};
+
+void Verifier::verifyLoopMetadata(const MDNode *LoopID) {
+  // Allow empty loop metadata (!{}) so the verifier does not crash on malformed
+  // IR; skip further checks.
+  if (LoopID->getNumOperands() == 0)
+    return;
+  Check(LoopID->getNumOperands() >= 1,
+        "llvm.loop metadata must have at least one operand", LoopID);
+  for (const MDOperand &Op : llvm::drop_begin(LoopID->operands())) {
+    MDNode *Option = dyn_cast<MDNode>(Op);
+    if (!Option || Option->getNumOperands() < 1)
+      continue;
+    MDString *Name = dyn_cast<MDString>(Option->getOperand(0));
+    if (!Name)
+      continue;
+    StringRef AttrName = Name->getString();
+
+    // Verify single-operand attributes.
+    if (llvm::is_contained(LoopSingleOperandAttributeNames, AttrName)) {
+      Check(Option->getNumOperands() == 1,
+            "llvm.loop attribute must have exactly one operand", Option);
----------------
arsenm wrote:

This isn't an attribute, don't call it one

https://github.com/llvm/llvm-project/pull/182252