[NFC] Add a specialization of DenseMapInfo for SmallVector (#140380)

Equivalent to the three existing uses I found which were all pointers.
Implementing the general pattern so SmallVector<int> etc will work as
well.

Added to the SmallVector.h header as opposed to DenseMapInfo.h following
the StringRef.h and SmallBitVector.h prior art.

Noticed while writing an unrelated patch which currently wants a map
from small vectors to other things and cleaner to generalise than add
another specialisation to said patch.

Author: JonChesterfield

llvm/include/llvm/ADT/SmallVector.h

@@ -14,6 +14,7 @@
 #ifndef LLVM_ADT_SMALLVECTOR_H
 #define LLVM_ADT_SMALLVECTOR_H
 
+#include "llvm/ADT/DenseMapInfo.h"
 #include "llvm/Support/Compiler.h"
 #include <algorithm>
 #include <cassert>
@@ -1319,6 +1320,26 @@ extern template class llvm::SmallVectorBase<uint32_t>;
 extern template class llvm::SmallVectorBase<uint64_t>;
 #endif
 
+// Provide DenseMapInfo for SmallVector of a type which has info.
+template <typename T, unsigned N> struct DenseMapInfo<llvm::SmallVector<T, N>> {
+  static SmallVector<T, N> getEmptyKey() {
+    return {DenseMapInfo<T>::getEmptyKey()};
+  }
+
+  static SmallVector<T, N> getTombstoneKey() {
+    return {DenseMapInfo<T>::getTombstoneKey()};
+  }
+
+  static unsigned getHashValue(const SmallVector<T, N> &V) {
+    return static_cast<unsigned>(hash_combine_range(V));
+  }
+
+  static bool isEqual(const SmallVector<T, N> &LHS,
+                      const SmallVector<T, N> &RHS) {
+    return LHS == RHS;
+  }
+};
+
 } // end namespace llvm
 
 namespace std {

llvm/lib/Transforms/Scalar/LoopStrengthReduce.cpp

@@ -1275,38 +1275,13 @@ struct LSRFixup {
   void dump() const;
 };
 
-/// A DenseMapInfo implementation for holding DenseMaps and DenseSets of sorted
-/// SmallVectors of const SCEV*.
-struct UniquifierDenseMapInfo {
-  static SmallVector<const SCEV *, 4> getEmptyKey() {
-    SmallVector<const SCEV *, 4>  V;
-    V.push_back(reinterpret_cast<const SCEV *>(-1));
-    return V;
-  }
-
-  static SmallVector<const SCEV *, 4> getTombstoneKey() {
-    SmallVector<const SCEV *, 4> V;
-    V.push_back(reinterpret_cast<const SCEV *>(-2));
-    return V;
-  }
-
-  static unsigned getHashValue(const SmallVector<const SCEV *, 4> &V) {
-    return static_cast<unsigned>(hash_combine_range(V));
-  }
-
-  static bool isEqual(const SmallVector<const SCEV *, 4> &LHS,
-                      const SmallVector<const SCEV *, 4> &RHS) {
-    return LHS == RHS;
-  }
-};
-
 /// This class holds the state that LSR keeps for each use in IVUsers, as well
 /// as uses invented by LSR itself. It includes information about what kinds of
 /// things can be folded into the user, information about the user itself, and
 /// information about how the use may be satisfied.  TODO: Represent multiple
 /// users of the same expression in common?
 class LSRUse {
-  DenseSet<SmallVector<const SCEV *, 4>, UniquifierDenseMapInfo> Uniquifier;
+  DenseSet<SmallVector<const SCEV *, 4>> Uniquifier;
 
 public:
   /// An enum for a kind of use, indicating what types of scaled and immediate
@@ -4754,8 +4729,7 @@ void LSRInstance::FilterOutUndesirableDedicatedRegisters() {
 
   // Collect the best formula for each unique set of shared registers. This
   // is reset for each use.
-  using BestFormulaeTy =
-      DenseMap<SmallVector<const SCEV *, 4>, size_t, UniquifierDenseMapInfo>;
+  using BestFormulaeTy = DenseMap<SmallVector<const SCEV *, 4>, size_t>;
 
   BestFormulaeTy BestFormulae;
 

llvm/lib/Transforms/Vectorize/VPlanSLP.h

@@ -73,30 +73,8 @@ class VPInterleavedAccessInfo {
 class VPlanSlp {
   enum class OpMode { Failed, Load, Opcode };
 
-  /// A DenseMapInfo implementation for using SmallVector<VPValue *, 4> as
-  /// DenseMap keys.
-  struct BundleDenseMapInfo {
-    static SmallVector<VPValue *, 4> getEmptyKey() {
-      return {reinterpret_cast<VPValue *>(-1)};
-    }
-
-    static SmallVector<VPValue *, 4> getTombstoneKey() {
-      return {reinterpret_cast<VPValue *>(-2)};
-    }
-
-    static unsigned getHashValue(const SmallVector<VPValue *, 4> &V) {
-      return static_cast<unsigned>(hash_combine_range(V));
-    }
-
-    static bool isEqual(const SmallVector<VPValue *, 4> &LHS,
-                        const SmallVector<VPValue *, 4> &RHS) {
-      return LHS == RHS;
-    }
-  };
-
   /// Mapping of values in the original VPlan to a combined VPInstruction.
-  DenseMap<SmallVector<VPValue *, 4>, VPInstruction *, BundleDenseMapInfo>
-      BundleToCombined;
+  DenseMap<SmallVector<VPValue *, 4>, VPInstruction *> BundleToCombined;
 
   VPInterleavedAccessInfo &IAI;