[llvm] [Attributor]: AApointerInfo - store the full chain of instructions that make up the access (PR #96526)

[Shilei Tian via llvm-commits]

================
@@ -926,10 +933,95 @@ struct AA::PointerInfo::State : public AbstractState {
   BooleanState BS;
 };
 
+AAPointerInfo::AccessPathSetTy *AA::PointerInfo::State::findAllAccessPaths(
+    AAPointerInfo::OffsetInfoMapTy &OffsetInfoMap, Instruction *LocalI) {
+  AAPointerInfo::AccessPathSetTy *AccessPathsSet =
+      new AAPointerInfo::AccessPathSetTy();
+
+  // Store the instruction and its storage (i.e, which path it belongs to)
+  // on the stack.
+  // We also store the visited map on the stack.
+  // Since we want to find new paths, we want to make sure an instruction is
+  // not visited twice on the same path. However, we can visit the same
+  // instruction more that once if it exists on different paths.
+  using VisitedTy = SmallPtrSet<Value *, 4>;
+  using StackElementTy =
+      std::tuple<Value *, AAPointerInfo::AccessPathTy *, VisitedTy>;
+
+  SmallVector<StackElementTy, 16> Stack;
+
+  // Populate the stack with elements.
+  for (auto *It = LocalI->op_begin(); It != LocalI->op_end(); It++) {
+    Value *V = cast<Value>(It);
+    if (!OffsetInfoMap.contains(V))
+      continue;
+
+    SmallPtrSet<Value *, 4> LocalVisitedMap;
+    AAPointerInfo::AccessPathTy *NewPath = new AAPointerInfo::AccessPathTy();
+    AccessPathsSet->insert(NewPath);
+    NewPath->push_back(LocalI);
+    Stack.push_back(std::make_tuple(V, NewPath, LocalVisitedMap));
+  }
+
+  while (!Stack.empty()) {
+    auto Entry = Stack.pop_back_val();
+    Value *Top = std::get<0>(Entry);
+    AAPointerInfo::AccessPathTy *CurrentChain = std::get<1>(Entry);
+    auto &Visited = std::get<2>(Entry);
+
+    if (!OffsetInfoMap.contains(Top))
+      continue;
+
+    if (!Visited.insert(Top).second)
+      continue;
+
+    CurrentChain->push_back(Top);
+    auto OI = OffsetInfoMap.lookup(Top);
+    auto &Origins = OI.Origins;
+
+    SmallPtrSet<Value *, 16> Successors;
+    for (auto &Origin : Origins) {
+      for (auto *Val : Origin) {
+        // Since we store depth 1 predecessors in our Origins map
+        // We can be sure that we hit termination condition if the
+        // Successor is the current instruction.
+        if (Val != Top)
+          Successors.insert(Val);
+      }
+    }
+
+    if (Successors.empty())
+      continue;
+
+    // Create new paths to be forked
+    SmallVector<AAPointerInfo::AccessPathTy *> NewPaths;
+    NewPaths.push_back(CurrentChain);
+    for (size_t Index = 1; Index < Successors.size(); Index++) {
+      AAPointerInfo::AccessPathTy *NewPath = new AAPointerInfo::AccessPathTy(
----------------
shiltian wrote:

Placement new, like `RQITy *RQIPtr = new (A.Allocator) RQITy(RQI.From, RQI.To);`.

https://github.com/llvm/llvm-project/pull/96526