[llvm] [LV] Use ExtractLane(LastActiveLane, V) live outs when tail-folding. (PR #149042)

[Luke Lau via llvm-commits]

================
@@ -221,6 +225,44 @@ bool VPlanVerifier::verifyEVLRecipe(const VPInstruction &EVL) const {
   });
 }
 
+bool VPlanVerifier::verifyLastActiveLaneRecipe(
+    const VPInstruction &LastActiveLane) const {
+  assert(LastActiveLane.getOpcode() == VPInstruction::LastActiveLane &&
+         "must be called with VPInstruction::LastActiveLane");
+
+  if (LastActiveLane.getNumOperands() < 1) {
+    errs() << "LastActiveLane must have at least one operand\n";
+    return false;
+  }
+
+  const VPlan &Plan = *LastActiveLane.getParent()->getPlan();
+  // All operands must be prefix-mask. Currently we check for header masks or
+  // EVL-derived masks, as those are currently the only operands in practice,
+  // but this may need updating in the future..
+  for (VPValue *Op : LastActiveLane.operands()) {
+    if (vputils::isHeaderMask(Op, Plan))
+      continue;
+
+    // Masks derived from EVL are also fine.
+    auto BroadcastOrEVL =
+        m_CombineOr(m_Broadcast(m_VPValue()), m_EVL(m_VPValue()));
----------------
lukel97 wrote:

Should this be
```suggestion
        m_CombineOr(m_Broadcast(m_EVL(m_VPValue())), m_EVL(m_VPValue()));
```

https://github.com/llvm/llvm-project/pull/149042