[llvm] [LV] Vectorize early exit loops with multiple exits. (PR #174864)

[David Sherwood via llvm-commits]

================
@@ -3949,75 +3949,150 @@ void VPlanTransforms::convertToConcreteRecipes(VPlan &Plan) {
     R->eraseFromParent();
 }
 
-void VPlanTransforms::handleUncountableEarlyExit(VPBasicBlock *EarlyExitingVPBB,
-                                                 VPBasicBlock *EarlyExitVPBB,
-                                                 VPlan &Plan,
-                                                 VPBasicBlock *HeaderVPBB,
-                                                 VPBasicBlock *LatchVPBB) {
-  auto *MiddleVPBB = cast<VPBasicBlock>(LatchVPBB->getSuccessors()[0]);
-  if (!EarlyExitVPBB->getSinglePredecessor() &&
-      EarlyExitVPBB->getPredecessors()[1] == MiddleVPBB) {
-    assert(EarlyExitVPBB->getNumPredecessors() == 2 &&
-           EarlyExitVPBB->getPredecessors()[0] == EarlyExitingVPBB &&
-           "unsupported early exit VPBB");
-    // Early exit operand should always be last phi operand. If EarlyExitVPBB
-    // has two predecessors and EarlyExitingVPBB is the first, swap the operands
-    // of the phis.
-    for (VPRecipeBase &R : EarlyExitVPBB->phis())
-      cast<VPIRPhi>(&R)->swapOperands();
-  }
+void VPlanTransforms::handleUncountableEarlyExits(VPlan &Plan,
+                                                  VPBasicBlock *HeaderVPBB,
+                                                  VPBasicBlock *LatchVPBB,
+                                                  VPBasicBlock *MiddleVPBB) {
+  struct EarlyExitInfo {
+    VPBasicBlock *EarlyExitingVPBB;
+    VPIRBasicBlock *EarlyExitVPBB;
+    VPValue *CondToExit;
+  };
 
   VPBuilder Builder(LatchVPBB->getTerminator());
-  VPBlockBase *TrueSucc = EarlyExitingVPBB->getSuccessors()[0];
-  assert(match(EarlyExitingVPBB->getTerminator(), m_BranchOnCond()) &&
-         "Terminator must be be BranchOnCond");
-  VPValue *CondOfEarlyExitingVPBB =
-      EarlyExitingVPBB->getTerminator()->getOperand(0);
-  auto *CondToEarlyExit = TrueSucc == EarlyExitVPBB
-                              ? CondOfEarlyExitingVPBB
-                              : Builder.createNot(CondOfEarlyExitingVPBB);
-
-  // Create a BranchOnTwoConds in the latch that branches to:
-  // [0] vector.early.exit, [1] middle block, [2] header (continue looping).
-  VPValue *IsEarlyExitTaken =
-      Builder.createNaryOp(VPInstruction::AnyOf, {CondToEarlyExit});
-  VPBasicBlock *VectorEarlyExitVPBB =
-      Plan.createVPBasicBlock("vector.early.exit");
-  VectorEarlyExitVPBB->setParent(EarlyExitVPBB->getParent());
-
-  VPBlockUtils::connectBlocks(VectorEarlyExitVPBB, EarlyExitVPBB);
-
-  // Update the exit phis in the early exit block.
-  VPBuilder MiddleBuilder(MiddleVPBB);
-  VPBuilder EarlyExitB(VectorEarlyExitVPBB);
-  for (VPRecipeBase &R : EarlyExitVPBB->phis()) {
-    auto *ExitIRI = cast<VPIRPhi>(&R);
-    // Early exit operand should always be last, i.e., 0 if EarlyExitVPBB has
-    // a single predecessor and 1 if it has two.
-    unsigned EarlyExitIdx = ExitIRI->getNumOperands() - 1;
-    if (ExitIRI->getNumOperands() != 1) {
-      // The first of two operands corresponds to the latch exit, via MiddleVPBB
-      // predecessor. Extract its final lane.
-      ExitIRI->extractLastLaneOfLastPartOfFirstOperand(MiddleBuilder);
+  SmallVector<EarlyExitInfo> Exits;
+  for (VPIRBasicBlock *EB : Plan.getExitBlocks()) {
+    for (VPBlockBase *Pred : to_vector(EB->getPredecessors())) {
+      if (Pred == MiddleVPBB)
+        continue;
+      // Collect condition for this early exit.
+      auto *EarlyExitingVPBB = cast<VPBasicBlock>(Pred);
+      VPBlockBase *TrueSucc = EarlyExitingVPBB->getSuccessors()[0];
+      assert(match(EarlyExitingVPBB->getTerminator(), m_BranchOnCond()) &&
----------------
david-arm wrote:

Is it worth just always calling match here so that you can also obtain the condition? For example, something like:

```
  VPValue *CondOfEarlyExitingVPBB;
  [[maybe_unused]] bool Matched = match(EarlyExitingVPBB->getTerminator(), m_BranchOnCond(CondOfEarlyExitingVPBB));
  assert(Matched && "Terminator must be BranchOnCond");
```

https://github.com/llvm/llvm-project/pull/174864