Index: lib/CodeGen/MachineBlockPlacement.cpp
===================================================================
--- lib/CodeGen/MachineBlockPlacement.cpp
+++ lib/CodeGen/MachineBlockPlacement.cpp
@@ -957,6 +957,7 @@
     return Result;
   }
 
+  bool ComputeBestB = true;
   // Did we pick the triangle edge? If tail-duplication is profitable, do
   // that instead. Otherwise merge the triangle edge now while we know it is
   // optimal.
@@ -978,10 +979,18 @@
       Result.ShouldTailDup = true;
       return Result;
     }
+    // If any of the BestA.Dest's successor is outside of the Trellis, we should
+    // not use BestB as it may not be optimal.
+    for (MachineBasicBlock *Succ : BestA.Dest->successors())
+      if (!Successors.count(Succ)) {
+        ComputeBestB = false;
+        break;
+      }
   }
-  // We have already computed the optimal edge for the other side of the
-  // trellis.
-  ComputedEdges[BestB.Src] = { BestB.Dest, false };
+  if (ComputeBestB)
+    // We have already computed the optimal edge for the other side of the
+    // trellis.
+    ComputedEdges[BestB.Src] = { BestB.Dest, false };
 
   auto TrellisSucc = BestA.Dest;
   DEBUG(BranchProbability SuccProb = getAdjustedProbability(
Index: test/CodeGen/PowerPC/tail-dup-layout.ll
===================================================================
--- test/CodeGen/PowerPC/tail-dup-layout.ll
+++ test/CodeGen/PowerPC/tail-dup-layout.ll
@@ -474,6 +474,52 @@
   ret void
 }
 
+; Verify that in the triangular trellis case, if there is hot successor
+; outside of trellis, we should be able to connect them by not connecting
+; the triagular edges.
+; CHECK-LABEL: trellis_triangle
+; CHECK: # %entry
+; CHECK: # %b
+; CHECK: # %d
+; CHECK: # %ret
+; CHECK: # %c
+; CHECK: # %e
+define void @trellis_no_triangle(i32 %tag) {
+entry:
+  br label %a
+a:
+  call void @a()
+  call void @a()
+  %tagbits.a = and i32 %tag, 3
+  %tagbits.a.eq0 = icmp eq i32 %tagbits.a, 0
+  br i1 %tagbits.a.eq0, label %b, label %c, !prof !8 ; 98 to 2
+b:
+  call void @b()
+  call void @b()
+  %tagbits.b = and i32 %tag, 12
+  %tagbits.b.eq1 = icmp eq i32 %tagbits.b, 8
+  br i1 %tagbits.b.eq1, label %d, label %e, !prof !9 ; 97 to 1
+d:
+  call void @d()
+  call void @d()
+  %tagbits.d = and i32 %tag, 48
+  %tagbits.d.eq1 = icmp eq i32 %tagbits.d, 32
+  br i1 %tagbits.d.eq1, label %ret, label %e, !prof !10 ; 96 to 2
+c:
+  call void @c()
+  call void @c()
+  %tagbits.c = and i32 %tag, 12
+  %tagbits.c.eq0 = icmp eq i32 %tagbits.c, 0
+  br i1 %tagbits.c.eq0, label %d, label %e, !prof !2 ; 1 to 1
+e:
+  call void @e()
+  call void @e()
+  br label %ret
+ret:
+  call void @f()
+  ret void
+}
+
 declare void @a()
 declare void @b()
 declare void @c()
@@ -492,3 +538,6 @@
 !5 = !{!"branch_weights", i32 2, i32 8}
 !6 = !{!"branch_weights", i32 3, i32 4}
 !7 = !{!"branch_weights", i32 4, i32 2}
+!8 = !{!"branch_weights", i32 98, i32 2}
+!9 = !{!"branch_weights", i32 97, i32 1}
+!10 = !{!"branch_weights", i32 96, i32 2}