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

[David Sherwood via llvm-commits]

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@@ -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) {
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david-arm wrote:

Is the middle block not easily available from the VPlan object, i.e. `getMiddleBlock()`? If this is a different middle block to the one returned by that function it's probably worth adding a comment explaining.

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