[llvm] [SLP] Make getSameOpcode support interchangeable instructions. (PR #127450)

[Alexey Bataev via llvm-commits]

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@@ -813,6 +835,300 @@ static std::optional<unsigned> getExtractIndex(const Instruction *E) {
 }
 
 namespace {
+/// \returns true if \p Opcode is allowed as part of the main/alternate
+/// instruction for SLP vectorization.
+///
+/// Example of unsupported opcode is SDIV that can potentially cause UB if the
+/// "shuffled out" lane would result in division by zero.
+bool isValidForAlternation(unsigned Opcode) {
+  return !Instruction::isIntDivRem(Opcode);
+}
+
+/// Helper class that determines VL can use the same opcode.
+/// Alternate instruction is supported. In addition, it supports interchangeable
+/// instruction. An interchangeable instruction is an instruction that can be
+/// converted to another instruction with same semantics. For example, x << 1 is
+/// equal to x * 2. x * 1 is equal to x | 0.
+class BinOpSameOpcodeHelper {
+  using MaskType = std::uint_fast16_t;
+  // Sort SupportedOp because it is used by binary_search.
----------------
alexey-bataev wrote:

```suggestion
  /// Sort SupportedOp because it is used by binary_search.
```

https://github.com/llvm/llvm-project/pull/127450