[llvm] [InstCombine] Fold binary op of reductions. (PR #121567)

[Yingwei Zheng via llvm-commits]

================
@@ -2313,6 +2313,63 @@ Instruction *InstCombinerImpl::foldVectorBinop(BinaryOperator &Inst) {
   return nullptr;
 }
 
+static Intrinsic::ID getReductionForBinop(Instruction::BinaryOps Opc) {
+  switch (Opc) {
+  default:
+    break;
+  case Instruction::Add:
+    return Intrinsic::vector_reduce_add;
+  case Instruction::Mul:
+    return Intrinsic::vector_reduce_mul;
+  case Instruction::And:
+    return Intrinsic::vector_reduce_and;
+  case Instruction::Or:
+    return Intrinsic::vector_reduce_or;
+  case Instruction::Xor:
+    return Intrinsic::vector_reduce_xor;
+  }
+  return Intrinsic::not_intrinsic;
+}
+
+Instruction *InstCombinerImpl::foldBinopOfReductions(BinaryOperator &Inst) {
+  Instruction::BinaryOps BinOpOpc = Inst.getOpcode();
+  Intrinsic::ID ReductionIID = getReductionForBinop(BinOpOpc);
+  if (BinOpOpc == Instruction::Sub)
+    ReductionIID = Intrinsic::vector_reduce_add;
+  if (ReductionIID == Intrinsic::not_intrinsic)
+    return nullptr;
+
+  auto checkIntrinsicAndGetItsArgument = [](Value *V,
+                                            Intrinsic::ID IID) -> Value * {
+    IntrinsicInst *II = dyn_cast<IntrinsicInst>(V);
+    if (!II)
+      return nullptr;
+    if ((II->getIntrinsicID() == IID) && II->hasOneUse())
----------------
dtcxzyw wrote:

```suggestion
    if (II->getIntrinsicID() == IID && II->hasOneUse())
```

https://github.com/llvm/llvm-project/pull/121567