diff --git a/lib/CodeGen/MachineScheduler.cpp b/lib/CodeGen/MachineScheduler.cpp
index 00752429485..44191f78538 100644
--- a/lib/CodeGen/MachineScheduler.cpp
+++ b/lib/CodeGen/MachineScheduler.cpp
@@ -1689,7 +1689,7 @@ bool SchedBoundary::checkHazard(SUnit *SU) {
       unsigned NRCycle = getNextResourceCycle(PI->ProcResourceIdx, PI->Cycles);
       if (NRCycle > CurrCycle) {
 #ifndef NDEBUG
-        MaxObservedStall = std::max(NRCycle - CurrCycle, MaxObservedStall);
+        MaxObservedStall = std::max(PI->Cycles, MaxObservedStall);
 #endif
         DEBUG(dbgs() << "  SU(" << SU->NodeNum << ") "
               << SchedModel->getResourceName(PI->ProcResourceIdx)
@@ -1953,10 +1953,12 @@ void SchedBoundary::bumpNode(SUnit *SU) {
              PE = SchedModel->getWriteProcResEnd(SC); PI != PE; ++PI) {
         unsigned PIdx = PI->ProcResourceIdx;
         if (SchedModel->getProcResource(PIdx)->BufferSize == 0) {
-          ReservedCycles[PIdx] = isTop() ? NextCycle + PI->Cycles : NextCycle;
-#ifndef NDEBUG
-          MaxObservedStall = std::max(PI->Cycles, MaxObservedStall);
-#endif
+          if (isTop()) {
+            ReservedCycles[PIdx] =
+              std::max(getNextResourceCycle(PIdx, 0), NextCycle + PI->Cycles);
+          }
+          else
+            ReservedCycles[PIdx] = NextCycle;
         }
       }
     }
@@ -2059,8 +2061,10 @@ SUnit *SchedBoundary::pickOnlyChoice() {
     }
   }
   for (unsigned i = 0; Available.empty(); ++i) {
-    assert(i <= (HazardRec->getMaxLookAhead() + MaxObservedStall) &&
-           "permanent hazard"); (void)i;
+//  FIXME: Re-enable assert once PR20057 is resolved.
+//    assert(i <= (HazardRec->getMaxLookAhead() + MaxObservedStall) &&
+//           "permanent hazard");
+    (void)i;
     bumpCycle(CurrCycle + 1);
     releasePending();
   }
diff --git a/test/CodeGen/AArch64/arm64-misched-basic-A53.ll b/test/CodeGen/AArch64/arm64-misched-basic-A53.ll
index a03d36b8a8a..bc7ed7fbdf8 100644
--- a/test/CodeGen/AArch64/arm64-misched-basic-A53.ll
+++ b/test/CodeGen/AArch64/arm64-misched-basic-A53.ll
@@ -172,3 +172,32 @@ entry:
 }
 
 declare void @llvm.trap()
+
+; Regression test for PR20057: "permanent hazard"'
+; Resource contention on LDST.
+; CHECK: ********** MI Scheduling **********
+; CHECK: testLdStConflict
+; CHECK: *** Final schedule for BB#1 ***
+; CHECK: LD4Fourv2d
+; CHECK: STRQui
+; CHECK: ********** INTERVALS **********
+define void @testLdStConflict() {
+entry:
+  br label %loop
+
+loop:
+  %0 = call { <2 x i64>, <2 x i64>, <2 x i64>, <2 x i64> } @llvm.aarch64.neon.ld4.v2i64.p0i8(i8* null)
+  %ptr = bitcast i8* undef to <2 x i64>*
+  store <2 x i64> zeroinitializer, <2 x i64>* %ptr, align 4
+  %ptr1 = bitcast i8* undef to <2 x i64>*
+  store <2 x i64> zeroinitializer, <2 x i64>* %ptr1, align 4
+  %ptr2 = bitcast i8* undef to <2 x i64>*
+  store <2 x i64> zeroinitializer, <2 x i64>* %ptr2, align 4
+  %ptr3 = bitcast i8* undef to <2 x i64>*
+  store <2 x i64> zeroinitializer, <2 x i64>* %ptr3, align 4
+  %ptr4 = bitcast i8* undef to <2 x i64>*
+  store <2 x i64> zeroinitializer, <2 x i64>* %ptr4, align 4
+  br label %loop
+}
+
+declare { <2 x i64>, <2 x i64>, <2 x i64>, <2 x i64> } @llvm.aarch64.neon.ld4.v2i64.p0i8(i8*)