[llvm] [SCEV] Introduce SCEVUse, use it instead of const SCEV * (NFCI) (WIP). (PR #91961)

[Florian Hahn via llvm-commits]

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@@ -69,6 +69,99 @@ enum SCEVTypes : unsigned short;
 
 extern bool VerifySCEV;
 
+class SCEV;
+
+class SCEVUse : public PointerIntPair<const SCEV *, 2> {
+public:
+  SCEVUse() : PointerIntPair(nullptr, 0) {}
+  SCEVUse(const SCEV *S) : PointerIntPair(S, 0) {}
+  SCEVUse(const SCEV *S, int Flags) : PointerIntPair(S, Flags) {}
+
+  operator const SCEV *() const { return getPointer(); }
+  const SCEV *operator->() const { return getPointer(); }
+  const SCEV *operator->() { return getPointer(); }
+
+  void *getRawPointer() { return getOpaqueValue(); }
+
+  /// Print out the internal representation of this scalar to the specified
+  /// stream.  This should really only be used for debugging purposes.
+  void print(raw_ostream &OS) const;
+
+  /// This method is used for debugging.
+  void dump() const;
+};
+
+template <> struct PointerLikeTypeTraits<SCEVUse> {
+  static inline void *getAsVoidPointer(SCEVUse U) { return U.getOpaqueValue(); }
+  static inline SCEVUse getFromVoidPointer(void *P) {
+    SCEVUse U;
+    U.setFromOpaqueValue(P);
+    return U;
+  }
+
+  /// Note, we assume here that void* is related to raw malloc'ed memory and
+  /// that malloc returns objects at least 4-byte aligned. However, this may be
+  /// wrong, or pointers may be from something other than malloc. In this case,
+  /// you should specify a real typed pointer or avoid this template.
+  ///
+  /// All clients should use assertions to do a run-time check to ensure that
+  /// this is actually true.
+  static constexpr int NumLowBitsAvailable = 0;
+};
+
+template <> struct DenseMapInfo<SCEVUse> {
+  // The following should hold, but it would require T to be complete:
+  // static_assert(alignof(T) <= (1 << Log2MaxAlign),
+  //               "DenseMap does not support pointer keys requiring more than "
+  //               "Log2MaxAlign bits of alignment");
+  static constexpr uintptr_t Log2MaxAlign = 12;
+
+  static inline SCEVUse getEmptyKey() {
+    uintptr_t Val = static_cast<uintptr_t>(-1);
+    Val <<= Log2MaxAlign;
+    return PointerLikeTypeTraits<SCEVUse>::getFromVoidPointer((void *)Val);
+  }
+
+  static inline SCEVUse getTombstoneKey() {
+    uintptr_t Val = static_cast<uintptr_t>(-2);
+    Val <<= Log2MaxAlign;
+    return PointerLikeTypeTraits<SCEVUse>::getFromVoidPointer((void *)Val);
+  }
+
+  static unsigned getHashValue(SCEVUse U) {
+    void *PtrVal = PointerLikeTypeTraits<SCEVUse>::getAsVoidPointer(U);
+    return (unsigned((uintptr_t)PtrVal) >> 4) ^
+           (unsigned((uintptr_t)PtrVal) >> 9);
+  }
+
+  static bool isEqual(const SCEVUse LHS, const SCEVUse RHS) {
+    return LHS == RHS;
+  }
+};
+
+template <typename To> [[nodiscard]] inline decltype(auto) dyn_cast(SCEVUse U) {
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fhahn wrote:

So far I've not managed to get CastInfo to work as needed, but I'll look into it more

https://github.com/llvm/llvm-project/pull/91961