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

[Shilei Tian via llvm-commits]

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@@ -5785,6 +5793,136 @@ struct AAPointerInfo : public AbstractAttribute {
     AK_MUST_READ_WRITE = AK_MUST | AK_R | AK_W,
   };
 
+  /// A helper containing a list of offsets computed for a Use. Ideally this
+  /// list should be strictly ascending, but we ensure that only when we
+  /// actually translate the list of offsets to a RangeList.
+  struct OffsetInfo {
+    using VecTy = SmallVector<AA::RangeTy>;
+    // A map to store depth 1 predecessors per offset.
+    using OriginsTy = SmallVector<SmallPtrSet<Value *, 4>>;
+    using const_iterator = VecTy::const_iterator;
+    OriginsTy Origins;
+    VecTy Ranges;
+
+    const_iterator begin() const { return Ranges.begin(); }
+    const_iterator end() const { return Ranges.end(); }
+
+    bool operator==(const OffsetInfo &RHS) const {
+      return Ranges == RHS.Ranges && Origins == RHS.Origins;
+    }
+
+    bool operator!=(const OffsetInfo &RHS) const { return !(*this == RHS); }
+
+    void insert(AA::RangeTy Range, Value &V) {
+
+      auto *It = std::find(Ranges.begin(), Ranges.end(), Range);
+
+      // Offset exists in Offsets map
+      if (It != Ranges.end()) {
+        size_t Index = It - Ranges.begin();
+        if (Index < Origins.size())
+          Origins[Index].insert(&V);
+      } else {
+        Ranges.push_back(Range);
+        Origins.emplace_back();
+        Origins.back().insert(&V);
+      }
+    }
+
+    void setSizeAll(uint64_t Size) {
+      for (auto &Range : Ranges)
+        Range.Size = Size;
+    }
+
+    void getOnlyOffsets(SmallVector<int64_t> &Offsets) {
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shiltian wrote:

put document on those functions that are not trivial to understand by their names

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