[llvm] [SeparateConstOffsetFromGEP] Decompose constant xor operand if possible (PR #135788)

[Juan Manuel Martinez Caamaño via llvm-commits]

================
@@ -486,6 +490,39 @@ class SeparateConstOffsetFromGEP {
   DenseMap<ExprKey, SmallVector<Instruction *, 2>> DominatingSubs;
 };
 
+/// A helper class that aims to convert xor operations into or operations when
+/// their operands are disjoint and the result is used in a GEP's index. This
+/// can then enable further GEP optimizations by effectively turning BaseVal |
+/// Const into BaseVal + Const when they are disjoint, which
+/// SeparateConstOffsetFromGEP can then process. This is a common pattern that
+/// sets up a grid of memory accesses across a wave where each thread acesses
+/// data at various offsets.
+class XorToOrDisjointTransformer {
+public:
+  XorToOrDisjointTransformer(Function &F, DominatorTree &DT,
+                             const DataLayout &DL)
+      : F(F), DT(DT), DL(DL) {}
+
+  bool run();
+
+private:
+  Function &F;
+  DominatorTree &DT;
+  const DataLayout &DL;
+  /// Maps a common operand to all Xor instructions
+  using XorOpList = SmallVector<std::pair<BinaryOperator *, APInt>, 8>;
+  using XorBaseValMap = DenseMap<Value *, XorOpList>;
+  XorBaseValMap XorGroups;
+
+  /// Checks if the given value has at least one GetElementPtr user
+  bool hasGEPUser(const Value *V) const;
----------------
jmmartinez wrote:

Function doesn't access the state of the object.
```suggestion
  static bool hasGEPUser(const Value *V);
```

https://github.com/llvm/llvm-project/pull/135788