Index: lib/CodeGen/MachineScheduler.cpp
===================================================================
--- lib/CodeGen/MachineScheduler.cpp
+++ lib/CodeGen/MachineScheduler.cpp
@@ -1533,6 +1533,52 @@
   return false;
 }
 
+/// Check dependencies in \p DAG whether \p Node0 can be schedule immediately
+/// before \p Node1.
+static bool canScheduleAdjacent(ScheduleDAGInstrs &DAG, const SUnit &Node0,
+                                const SUnit &Node1) {
+  // This is only a barebones implementation right now, limited to
+  // Node1==ExitSU. (This could be extended by employing
+  // ScheduleDAGMI.Topo.isReachable() queries on Node0 successors in the future)
+  assert(&Node1 == &DAG.ExitSU && "Only implemented for ExitSU node");
+  for (const SDep &Succ : Node0.Succs) {
+    if (Succ.getSUnit() != &Node1)
+      return false;
+  }
+  return true;
+}
+
+/// Add artificial edges to force adjacent scheduling of \p Node0 and \p Node1.
+static void addFusionEdges(ScheduleDAGMI &DAG, SUnit &Node0, SUnit &Node1) {
+  assert(&Node1 == &DAG.ExitSU &&
+         "addFusionEdges() only implemented for Node1 == ExitSU");
+  // This is simpler than the general case: We only need an artifical edge from
+  // roots and predecessors of ExitSU to Node0.
+  for (SDep &PredDep : DAG.ExitSU.Preds) {
+    SUnit &SU = *PredDep.getSUnit();
+    if (&SU == &Node0)
+      continue;
+
+    bool NeedEdge = true;
+    for (const SDep &SuccDep : SU.Succs) {
+      if (SuccDep.isWeak())
+        continue;
+      const SUnit &Succ = *SuccDep.getSUnit();
+      if (&Succ != &DAG.ExitSU) {
+        NeedEdge = false;
+        break;
+      }
+    }
+    if (NeedEdge)
+      DAG.addEdge(&Node0, SDep(&SU, SDep::Artificial));
+  }
+
+  for (SUnit &SU : DAG.SUnits) {
+    if (SU.NumSuccsLeft == 0 && &SU != &Node0)
+      DAG.addEdge(&Node0, SDep(&SU, SDep::Artificial));
+  }
+}
+
 /// \brief Callback from DAG postProcessing to create cluster edges to encourage
 /// fused operations.
 void MacroFusion::apply(ScheduleDAGInstrs *DAGInstrs) {
@@ -1556,17 +1602,12 @@
     if (!TII.shouldScheduleAdjacent(*Pred, *Branch))
       continue;
 
-    // Create a single weak edge from SU to ExitSU. The only effect is to cause
-    // bottom-up scheduling to heavily prioritize the clustered SU.  There is no
-    // need to copy predecessor edges from ExitSU to SU, since top-down
-    // scheduling cannot prioritize ExitSU anyway. To defer top-down scheduling
-    // of SU, we could create an artificial edge from the deepest root, but it
-    // hasn't been needed yet.
-    bool Success = DAG->addEdge(&ExitSU, SDep(&SU, SDep::Cluster));
-    (void)Success;
-    assert(Success && "No DAG nodes should be reachable from ExitSU");
-
-    DEBUG(dbgs() << "Macro Fuse SU(" << SU.NodeNum << ")\n");
+    if (!canScheduleAdjacent(*DAG, SU, ExitSU))
+      continue;
+
+    DEBUG(dbgs() << "Macro Fuse SU(" << SU.NodeNum << ") and SU("
+          << ExitSU.NodeNum << ")\n");
+    addFusionEdges(*DAG, SU, ExitSU);
     break;
   }
 }
@@ -3267,7 +3308,12 @@
 
 /// Create a generic scheduler with no vreg liveness or DAG mutation passes.
 static ScheduleDAGInstrs *createGenericSchedPostRA(MachineSchedContext *C) {
-  return new ScheduleDAGMI(C, make_unique<PostGenericScheduler>(C), /*IsPostRA=*/true);
+  ScheduleDAGMI *DAG =
+    new ScheduleDAGMI(C, make_unique<PostGenericScheduler>(C),
+                      /*IsPostRA=*/true);
+  if (EnableMacroFusion)
+    DAG->addMutation(createMacroFusionDAGMutation(DAG->TII, DAG->TRI));
+  return DAG;
 }
 
 //===----------------------------------------------------------------------===//
Index: test/CodeGen/AArch64/postmisched-fusion.mir
===================================================================
--- /dev/null
+++ test/CodeGen/AArch64/postmisched-fusion.mir
@@ -0,0 +1,23 @@
+# RUN: llc -o - %s -mtriple=aarch64-- -mcpu=cyclone -enable-post-misched -run-pass=postmisched | FileCheck %s
+# Test that the post machine scheduler respects macro op fusion.
+--- |
+  define void @func0() { ret void }
+...
+---
+# CHECK-LABEL: name: func0
+# CHECK: %xzr = SUBSXri{{.*}}implicit-def %nzcv
+# CHECK-NEXT: Bcc {{.*}}implicit killed %nzcv
+name: func0
+body: |
+  bb.0:
+    successors: %bb.1, %bb.2
+    %x8 = IMPLICIT_DEF
+    %x9 = LDRXui %x8, 0 :: (load 8)
+    dead %xzr = SUBSXri %x8, 0, 0, implicit def %nzcv
+    %x10 = ADDXri %x9, 13, 0
+    Bcc 1, %bb.1, implicit killed %nzcv
+    B %bb.2
+
+  bb.1:
+  bb.2:
+...