[VPlan] Simplify VPBuilder insert point when adding users in exit block.

Simplifies setting the insert point, addressing a TODO.

Author: fhahn

llvm/lib/Transforms/Vectorize/LoopVectorizationPlanner.h

@@ -69,6 +69,9 @@ class VPBuilder {
   VPBuilder() = default;
   VPBuilder(VPBasicBlock *InsertBB) { setInsertPoint(InsertBB); }
   VPBuilder(VPRecipeBase *InsertPt) { setInsertPoint(InsertPt); }
+  VPBuilder(VPBasicBlock *TheBB, VPBasicBlock::iterator IP) {
+    setInsertPoint(TheBB, IP);
+  }
 
   /// Clear the insertion point: created instructions will not be inserted into
   /// a block.

llvm/lib/Transforms/Vectorize/LoopVectorize.cpp

@@ -8691,14 +8691,7 @@ addUsersInExitBlock(VPlan &Plan,
       cast<VPBasicBlock>(Plan.getVectorLoopRegion()->getSingleSuccessor());
   BasicBlock *ExitBB =
       cast<VPIRBasicBlock>(MiddleVPBB->getSuccessors()[0])->getIRBasicBlock();
-  // TODO: set B to MiddleVPBB->getFirstNonPhi(), taking care of affected tests.
-  VPBuilder B(MiddleVPBB);
-  if (auto *Terminator = MiddleVPBB->getTerminator()) {
-    auto *Condition = dyn_cast<VPInstruction>(Terminator->getOperand(0));
-    assert((!Condition || Condition->getParent() == MiddleVPBB) &&
-           "Condition expected in MiddleVPBB");
-    B.setInsertPoint(Condition ? Condition : Terminator);
-  }
+  VPBuilder B(MiddleVPBB, MiddleVPBB->getFirstNonPhi());
 
   // Introduce VPUsers modeling the exit values.
   for (const auto &[ExitPhi, V] : ExitingValuesToFix) {

llvm/test/Transforms/LoopVectorize/first-order-recurrence-sink-replicate-region.ll

@@ -221,8 +221,8 @@ define i32 @sink_replicate_region_3_reduction(i32 %x, i8 %y, ptr %ptr) optsize {
 ; CHECK-EMPTY:
 ; CHECK-NEXT: middle.block:
 ; CHECK-NEXT:  EMIT vp<[[RED_RES:%.+]]> = compute-reduction-result ir<%and.red>, vp<[[SEL]]>
-; CHECK-NEXT:   EMIT vp<[[RESUME_1:%.+]]> = extract-from-end ir<%recur.next>, ir<1>
 ; CHECK-NEXT:   EMIT vp<[[RED_EX:%.+]]> = extract-from-end vp<[[RED_RES]]>, ir<1>
+; CHECK-NEXT:   EMIT vp<[[RESUME_1:%.+]]> = extract-from-end ir<%recur.next>, ir<1>
 ; CHECK-NEXT:   EMIT branch-on-cond ir<true>
 ; CHECK-NEXT: Successor(s): ir-bb<exit>, scalar.ph
 ; CHECK-EMPTY: