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

[Ashley Coleman via llvm-commits]

================
@@ -823,8 +827,153 @@ DXILBindingMap::findByUse(const Value *Key) const {
 
 //===----------------------------------------------------------------------===//
 
+static bool isUpdateCounterIntrinsic(Function &F) {
+  return F.getIntrinsicID() == Intrinsic::dx_resource_updatecounter;
+}
+
+void DXILResourceCounterDirectionMap::populate(Module &M, DXILBindingMap &DBM) {
+  std::vector<std::tuple<dxil::ResourceBindingInfo, ResourceCounterDirection,
+                         const Function *, const CallInst *>>
+      DiagCounterDirs;
+
+  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)
+        DiagCounterDirs.emplace_back(RBInfo, Direction, &F, CI);
+    }
+  }
+
+  // An entry that is not in the map is considered unknown so its wasted
+  // overhead and increased complexity to keep an entry explicitly marked
+  // unknown
+  const auto RemoveEnd = std::remove_if(
+      DiagCounterDirs.begin(), DiagCounterDirs.end(), [](const auto &Item) {
+        return std::get<ResourceCounterDirection>(Item) ==
+               ResourceCounterDirection::Unknown;
+      });
+
+  // Sort by the Binding and Direction for fast lookup
+  std::sort(DiagCounterDirs.begin(), RemoveEnd,
+            [](const auto &LHS, const auto &RHS) {
+              const auto L = std::pair{std::get<dxil::ResourceBindingInfo>(LHS),
+                                       std::get<ResourceCounterDirection>(LHS)};
+              const auto R = std::pair{std::get<dxil::ResourceBindingInfo>(RHS),
+                                       std::get<ResourceCounterDirection>(RHS)};
+              return L < R;
+            });
+
+  // Remove the duplicate entries. Since direction is considered for equality
+  // a unique resource with more than one direction will not be deduped.
+  const auto UniqueEnd = std::unique(
+      DiagCounterDirs.begin(), RemoveEnd, [](const auto &LHS, const auto &RHS) {
+        const auto L = std::pair{std::get<dxil::ResourceBindingInfo>(LHS),
+                                 std::get<ResourceCounterDirection>(LHS)};
+        const auto R = std::pair{std::get<dxil::ResourceBindingInfo>(RHS),
+                                 std::get<ResourceCounterDirection>(RHS)};
+        return L == R;
+      });
+
+  // Actually erase the items invalidated by remove_if + unique
+  DiagCounterDirs.erase(UniqueEnd, DiagCounterDirs.end());
+
+  // If any duplicate entries still exist at this point then it must be a
+  // resource that was both incremented and decremented which is not allowed.
+  // Mark all those entries as invalid.
+  {
+    auto DupFirst = DiagCounterDirs.begin();
+    auto DupNext = DupFirst + 1;
+    auto DupLast = DiagCounterDirs.end();
+    for (; DupFirst < DupLast && DupNext < DupLast; ++DupFirst, ++DupNext) {
+      if (std::get<dxil::ResourceBindingInfo>(*DupFirst) ==
+          std::get<dxil::ResourceBindingInfo>(*DupNext)) {
+        std::get<ResourceCounterDirection>(*DupFirst) =
+            ResourceCounterDirection::Invalid;
+        std::get<ResourceCounterDirection>(*DupNext) =
+            ResourceCounterDirection::Invalid;
+      }
+    }
+  }
+
+  // Raise an error for every invalid entry
+  for (const auto Entry : DiagCounterDirs) {
+    ResourceCounterDirection Dir = std::get<ResourceCounterDirection>(Entry);
+    const Function *F = std::get<const Function *>(Entry);
+    const CallInst *CI = std::get<const CallInst *>(Entry);
+
+    if (Dir != ResourceCounterDirection::Invalid)
+      continue;
+
+    StringRef Message = "RWStructuredBuffers may increment or decrement their "
+                        "counters, but not both.";
+    M.getContext().diagnose(
+        DiagnosticInfoGenericWithLoc(Message, *F, CI->getDebugLoc()));
----------------
V-FEXrt wrote:

Looks to be fairly arbitrary what it does. Here are some links:

https://godbolt.org/z/cns8ToYGb
https://godbolt.org/z/o9qz4fdaG
https://godbolt.org/z/cKdbzdcKn
https://godbolt.org/z/7W8YTbfsx

I thought it might be picking the direction with the least total number of uses but
https://godbolt.org/z/qnG9ahdrr
disproves that


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