[llvm] [HLSL] Analyze update counter usage (PR #130356)

[Finn Plummer via llvm-commits]

================
@@ -823,8 +825,92 @@ DXILBindingMap::findByUse(const Value *Key) const {
 
 //===----------------------------------------------------------------------===//
 
+static bool isUpdateCounterIntrinsic(Function &F) {
+  return F.getIntrinsicID() == Intrinsic::dx_resource_updatecounter;
+}
+
+void DXILResourceCounterDirectionMap::populate(Module &M,
+                                               ModuleAnalysisManager &AM) {
+  DXILBindingMap &DBM = AM.getResult<DXILResourceBindingAnalysis>(M);
+  CounterDirections.clear();
+
+  for (Function &F : M.functions()) {
+    if (!isUpdateCounterIntrinsic(F))
+      continue;
+
+    for (const User *U : F.users()) {
+      const CallInst *CI = dyn_cast<CallInst>(U);
+      assert(CI && "Users of dx_resource_updateCounter must be call instrs");
+
+      // Determine if the use is an increment or decrement
+      Value *CountArg = CI->getArgOperand(1);
+      ConstantInt *CountValue = dyn_cast<ConstantInt>(CountArg);
+      int64_t CountLiteral = CountValue->getSExtValue();
+
+      ResourceCounterDirection Direction = ResourceCounterDirection::Unknown;
+      if (CountLiteral > 0) {
+        Direction = ResourceCounterDirection::Increment;
+      }
+      if (CountLiteral < 0) {
+        Direction = ResourceCounterDirection::Decrement;
+      }
+
+      // Collect all potential creation points for the handle arg
+      Value *HandleArg = CI->getArgOperand(0);
+      SmallVector<dxil::ResourceBindingInfo> RBInfos = DBM.findByUse(HandleArg);
+      for (const dxil::ResourceBindingInfo RBInfo : RBInfos) {
+        CounterDirections.emplace_back(RBInfo, Direction);
+      }
+    }
+  }
+
+  // An entry that is not in the map is considered unknown so its wasted
----------------
inbelic wrote:

Is it possible to also not `emplace_back` an unknown direction above, rather than add it and then remove it? Further, then we could probably remove that enum and just use an optional

https://github.com/llvm/llvm-project/pull/130356