[clang] nonblocking/nonallocating attributes: 2nd pass caller/callee analysis (PR #99656)

[Erich Keane via cfe-commits]

================
@@ -4932,6 +4938,78 @@ class FunctionEffectsRef {
   void dump(llvm::raw_ostream &OS) const;
 };
 
+/// A mutable set of FunctionEffect::Kind.
+class FunctionEffectKindSet {
+  // For now this only needs to be a bitmap.
+  constexpr static size_t EndBitPos = 8;
+  using KindBitsT = std::bitset<EndBitPos>;
+
+  KindBitsT KindBits{};
+
+  explicit FunctionEffectKindSet(KindBitsT KB) : KindBits(KB) {}
+
+  constexpr static size_t kindToPos(FunctionEffect::Kind K) {
+    return size_t(K);
+  }
+
+public:
+  FunctionEffectKindSet() = default;
+  explicit FunctionEffectKindSet(FunctionEffectsRef FX) { insert(FX); }
+
+  // Iterates through the bits which are set.
+  class iterator {
+    const FunctionEffectKindSet *Outer = nullptr;
+    size_t Idx = 0;
+
+    // If Idx does not reference a set bit, advance it until it does,
+    // or until it reaches EndBitPos.
+    void advanceToNextSetBit() {
+      while (Idx < EndBitPos && !Outer->KindBits.test(Idx))
+        ++Idx;
+    }
+
+  public:
+    iterator();
+    iterator(const FunctionEffectKindSet &O, size_t I) : Outer(&O), Idx(I) {
+      advanceToNextSetBit();
+    }
+    bool operator==(const iterator &Other) const { return Idx == Other.Idx; }
+    bool operator!=(const iterator &Other) const { return Idx != Other.Idx; }
+
+    iterator operator++() {
+      ++Idx;
+      advanceToNextSetBit();
+      return *this;
+    }
+
+    FunctionEffect operator*() const {
+      assert(Idx < EndBitPos);
----------------
erichkeane wrote:

```suggestion
      assert(Idx < EndBitPos && "Dereference of end iterator");
```

https://github.com/llvm/llvm-project/pull/99656