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

[Alexey Bataev via llvm-commits]

================
@@ -813,6 +835,302 @@ 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) {
+  if (Instruction::isIntDivRem(Opcode))
+    return false;
+
+  return true;
+}
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alexey-bataev wrote:

```suggestion
bool isValidForAlternation(unsigned Opcode) {
  return !Instruction::isIntDivRem(Opcode);
}
```

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