[llvm] [LV][EVL] Support in-loop reduction using tail folding with EVL. (PR #90184)

[Mel Chen via llvm-commits]

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@@ -57,7 +57,55 @@ Value *VectorBuilder::createVectorInstruction(unsigned Opcode, Type *ReturnTy,
   auto VPID = VPIntrinsic::getForOpcode(Opcode);
   if (VPID == Intrinsic::not_intrinsic)
     return returnWithError<Value *>("No VPIntrinsic for this opcode");
+  return createVectorInstructionImpl(VPID, ReturnTy, InstOpArray, Name);
+}
+
+Value *VectorBuilder::createSimpleTargetReduction(RecurKind Kind, Type *ValTy,
+                                                  ArrayRef<Value *> InstOpArray,
+                                                  const Twine &Name) {
+  auto GetForRecurKind = [](RecurKind Kind) {
+    switch (Kind) {
+    case RecurKind::Add:
+      return Intrinsic::vp_reduce_add;
+    case RecurKind::Mul:
+      return Intrinsic::vp_reduce_mul;
+    case RecurKind::And:
+      return Intrinsic::vp_reduce_and;
+    case RecurKind::Or:
+      return Intrinsic::vp_reduce_or;
+    case RecurKind::Xor:
+      return Intrinsic::vp_reduce_xor;
+    case RecurKind::FMulAdd:
+    case RecurKind::FAdd:
+      return Intrinsic::vp_reduce_fadd;
+    case RecurKind::FMul:
+      return Intrinsic::vp_reduce_fmul;
+    case RecurKind::SMax:
+      return Intrinsic::vp_reduce_smax;
+    case RecurKind::SMin:
+      return Intrinsic::vp_reduce_smin;
+    case RecurKind::UMax:
+      return Intrinsic::vp_reduce_umax;
+    case RecurKind::UMin:
+      return Intrinsic::vp_reduce_umin;
+    case RecurKind::FMax:
+      return Intrinsic::vp_reduce_fmax;
+    case RecurKind::FMin:
+      return Intrinsic::vp_reduce_fmin;
+    default:
+      return Intrinsic::not_intrinsic;
+    }
+  };
+  auto VPID = getForRecurKind(Kind);
+  if (VPID == Intrinsic::not_intrinsic)
----------------
Mel-Chen wrote:

Using assert is indeed a more straightforward approach, but it seems like the class intends to support other functionalities as well.
```
enum class Behavior {
    // Abort if the requested VP intrinsic could not be created.
    // This is useful for strict consistency.
    ReportAndAbort = 0,

    // Return a default-initialized value if the requested VP intrinsic could
    // not be created.
    // This is useful for a defensive fallback to non-VP code.
    SilentlyReturnNone = 1,
  };
```
The original author seems to want to support 2 ways, both abort and return nullptr. 

https://github.com/llvm/llvm-project/pull/90184