[llvm] [SLP] Make getSameOpcode support different instructions if they have same semantics. (PR #112181)

[Alexey Bataev via llvm-commits]

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@@ -834,6 +834,105 @@ struct InstructionsState {
 
 } // end anonymous namespace
 
+struct InterchangeableInstruction {
+  unsigned Opcode;
+  SmallVector<Value *> Ops;
+  template <class... ArgTypes>
+  InterchangeableInstruction(unsigned Opcode, ArgTypes &&...Args)
+      : Opcode(Opcode), Ops{std::forward<decltype(Args)>(Args)...} {}
+};
+
+bool operator<(const InterchangeableInstruction &LHS,
+               const InterchangeableInstruction &RHS) {
+  return LHS.Opcode < RHS.Opcode;
+}
+
+/// \returns a list of interchangeable instructions which \p I can be converted
+/// to.
+/// e.g.,
+/// x << y -> x * (2^y)
+/// x << 1 -> x *   2
+/// x << 0 -> x *   1   -> x - 0 -> x + 0 -> x & 11...1 -> x | 0
+///           x *   0                     -> x & 0
+///           x *  -1   -> 0 - x
+/// TODO: support more patterns
+static SmallVector<InterchangeableInstruction, 6>
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alexey-bataev wrote:

Better to use `SmallVector<InterchangeableInstruction>`

https://github.com/llvm/llvm-project/pull/112181