[VPlan] Preserve debug location when creating branch.

Update createEmptyBasicBlock to preserve the debug location of the
previous terminator.

Author: fhahn

llvm/lib/Transforms/Vectorize/VPlan.cpp

@@ -280,8 +280,10 @@ VPBasicBlock::createEmptyBasicBlock(VPTransformState::CFGState &CFG) {
     if (isa<UnreachableInst>(PredBBTerminator)) {
       assert(PredVPSuccessors.size() == 1 &&
              "Predecessor ending w/o branch must have single successor.");
+      DebugLoc DL = PredBBTerminator->getDebugLoc();
       PredBBTerminator->eraseFromParent();
-      BranchInst::Create(NewBB, PredBB);
+      auto *Br = BranchInst::Create(NewBB, PredBB);
+      Br->setDebugLoc(DL);
     } else {
       assert(PredVPSuccessors.size() == 2 &&
              "Predecessor ending with branch must have two successors.");

llvm/test/Transforms/LoopVectorize/debugloc.ll

@@ -70,8 +70,7 @@ define i32 @test_debug_loc_on_branch_in_loop(i32* noalias %src, i32* noalias %ds
 ; CHECK-NEXT: pred.store.if:
 ; CHECK-NEXT:   [[GEP:%.+]] = getelementptr inbounds i32, i32* %dst, i64 {{.+}}, !dbg [[LOC3]]
 ; CHECK-NEXT:   store i32 0, i32* [[GEP]], align 4, !dbg [[LOC3]]
-; CHECK-NEXT:   br label %pred.store.continue
-; CHECK-NOT:  !dbg
+; CHECK-NEXT:   br label %pred.store.continue, !dbg [[LOC3]]
 ; CHECK-EMPTY:
 ;
 entry: