[VPlan] Use terminator debug loc for latch BranchOnCond.

Update VPlan to consistently use the latch branch debug location for the
latch branch in the vector loop, if there is one.

Author: fhahn

llvm/lib/Transforms/Vectorize/VPlanConstruction.cpp

@@ -437,9 +437,12 @@ static void addCanonicalIVRecipes(VPlan &Plan, VPBasicBlock *HeaderVPBB,
 
   // We are about to replace the branch to exit the region. Remove the original
   // BranchOnCond, if there is any.
+  DebugLoc LatchDL = DL;
   if (!LatchVPBB->empty() &&
-      match(&LatchVPBB->back(), m_BranchOnCond(m_VPValue())))
+      match(&LatchVPBB->back(), m_BranchOnCond(m_VPValue()))) {
+    LatchDL = LatchVPBB->getTerminator()->getDebugLoc();
     LatchVPBB->getTerminator()->eraseFromParent();
+  }
 
   VPBuilder Builder(LatchVPBB);
   // Add a VPInstruction to increment the scalar canonical IV by VF * UF.
@@ -452,7 +455,8 @@ static void addCanonicalIVRecipes(VPlan &Plan, VPBasicBlock *HeaderVPBB,
 
   // Add the BranchOnCount VPInstruction to the latch.
   Builder.createNaryOp(VPInstruction::BranchOnCount,
-                       {CanonicalIVIncrement, &Plan.getVectorTripCount()}, DL);
+                       {CanonicalIVIncrement, &Plan.getVectorTripCount()},
+                       LatchDL);
 }
 
 void VPlanTransforms::prepareForVectorization(

llvm/test/Transforms/LoopVectorize/dbg-outer-loop-vect.ll

@@ -30,8 +30,8 @@ define void @foo(ptr %h) !dbg !4 {
 ; CHECK-NEXT:    br i1 [[TMP6]], label [[FOR_COND_CLEANUP32]], label [[FOR_COND5_PREHEADER1]], !dbg [[DBG28]]
 ; CHECK:       vector.latch:
 ; CHECK-NEXT:    [[INDEX_NEXT]] = add nuw i64 [[INDEX]], 4, !dbg [[DBG222]]
-; CHECK-NEXT:    [[TMP9:%.*]] = icmp eq i64 [[INDEX_NEXT]], 20, !dbg [[DBG222]]
-; CHECK-NEXT:    br i1 [[TMP9]], label [[MIDDLE_BLOCK:%.*]], label [[VECTOR_BODY]], !dbg [[DBG222]], !llvm.loop [[LOOP29:![0-9]+]]
+; CHECK-NEXT:    [[TMP9:%.*]] = icmp eq i64 [[INDEX_NEXT]], 20, !dbg [[DBG21]]
+; CHECK-NEXT:    br i1 [[TMP9]], label [[MIDDLE_BLOCK:%.*]], label [[VECTOR_BODY]], !dbg [[DBG21]], !llvm.loop [[LOOP29:![0-9]+]]
 ; CHECK:       middle.block:
 ; CHECK-NEXT:    br i1 false, label [[EXIT:%.*]], label [[SCALAR_PH]], !dbg [[DBG21]]
 ; CHECK:       scalar.ph:

llvm/test/Transforms/LoopVectorize/debugloc.ll

@@ -14,9 +14,9 @@ target datalayout = "e-p:64:64:64-i1:8:8-i8:8:8-i16:16:16-i32:32:32-i64:64:64-f3
 ; CHECK:   load <2 x i32>, ptr {{.*}}, !dbg ![[LOC1]]
 ; CHECK:   add <2 x i32> {{.*}}, !dbg ![[LOC1]]
 ; CHECK:   add nuw i64 %index, 2, !dbg ![[LOC1]]
-; CHECK:   icmp eq i64 %index.next, %n.vec, !dbg ![[LOC1]]
+; CHECK:   icmp eq i64 %index.next, %n.vec, !dbg ![[BR_LOC:[0-9]+]]
 ; CHECK: middle.block
-; CHECK:   call i32 @llvm.vector.reduce.add.v2i32(<2 x i32> %{{.*}}), !dbg ![[BR_LOC:[0-9]+]]
+; CHECK:   call i32 @llvm.vector.reduce.add.v2i32(<2 x i32> %{{.*}}), !dbg ![[BR_LOC]]
 ; CHECK: for.body
 ; CHECK: br i1{{.*}}, label %for.body,{{.*}}, !dbg ![[BR_LOC]],