[llvm] [SLP] SLP's copyable elements based upon Main/Alt operations. (PR #124242)

[Alexey Bataev via llvm-commits]

================
@@ -7687,6 +7930,59 @@ static bool isAlternateInstruction(const Instruction *I,
                                    const Instruction *AltOp,
                                    const TargetLibraryInfo &TLI);
 
+bool BoUpSLP::canRepresentAsCopyable(const InstructionsState &S,
+                                     ArrayRef<Value *> VL) {
+  unsigned Opcode0 = S.getOpcode();
+  unsigned Opcode1 = S.getAltOpcode();
+  DenseMap<unsigned, unsigned> AltOps;
+  SmallVector<unsigned> MainAltOps;
+  unsigned Operand;
+  Instruction *NewAlt = nullptr;
+
+  if (isCopyableOp(VL, S.getMainOp(), S.getAltOp()))
+    return true;
+  if ((isa<BinaryOperator>(S.getMainOp()) && Opcode0 == Opcode1) ||
+      (!isValidForAlternation(Opcode0) || !isValidForAlternation(Opcode1)) ||
+      !tryToRepresentAsInstArg(S.getOpcode(), S.getAltOp()) ||
+      !tryToRepresentAsInstArg(S.getAltOpcode(), S.getMainOp()))
+    return false;
+  for (unsigned I = 0, VF = VL.size(); I < VF; ++I) {
+    Instruction *Inst = dyn_cast<Instruction>(VL[I]);
+    if (!Inst)
+      return false;
+    if (Inst->getOpcode() == Opcode0) {
+      for (unsigned Op : seq<unsigned>(0, S.getMainOp()->getNumOperands())) {
+        Instruction *Inst1 = dyn_cast<Instruction>(Inst->getOperand(Op));
+        if (!Inst1)
+          continue;
+        if (Inst1->getOpcode() == Opcode0)
+          return false;
+        if (AltOps.contains(I) || (AltOps.size() && Op != Operand))
+          return false;
+        if (Inst1->getOpcode() == Opcode1) {
+          if (!AltOps.size())
+            Operand = Op;
+          AltOps[I] = Op;
+        } else {
+          if (!NewAlt) {
+            NewAlt = Inst1;
+            if (!tryToRepresentAsInstArg(S.getAltOpcode(), Inst1))
+              return false;
+          }
+          if (NewAlt->getOpcode() != Inst1->getOpcode())
+            return false;
+        }
+      }
+    } else if (Inst->getOpcode() == Opcode1) {
+      MainAltOps.push_back(I);
+    }
+  }
+  if (AltOps.size() > 0 && MainAltOps.size() > 0)
+    return true;
+
+  return false;
----------------
alexey-bataev wrote:

```suggestion
  return !AltOps.empty() && !MainAltOps.empty();
```

https://github.com/llvm/llvm-project/pull/124242