diff --git a/llvm/lib/Target/AMDGPU/SILoadStoreOptimizer.cpp b/llvm/lib/Target/AMDGPU/SILoadStoreOptimizer.cpp
--- a/llvm/lib/Target/AMDGPU/SILoadStoreOptimizer.cpp
+++ b/llvm/lib/Target/AMDGPU/SILoadStoreOptimizer.cpp
@@ -205,6 +205,8 @@
   MachineRegisterInfo *MRI = nullptr;
   AliasAnalysis *AA = nullptr;
   bool OptimizeAgain;
+  bool MergeableInvalid;
+  std::set<MachineInstr*> MIMovedList;
 
   static bool dmasksCanBeCombined(const CombineInfo &CI,
                                   const SIInstrInfo &TII,
@@ -269,6 +271,8 @@
   bool collectMergeableInsts(MachineBasicBlock &MBB,
                   std::list<std::list<CombineInfo> > &MergeableInsts) const;
 
+  bool isCleanMergeList(std::list<CombineInfo> &MergeList) const;
+
 public:
   static char ID;
 
@@ -278,7 +282,8 @@
 
   bool optimizeInstsWithSameBaseAddr(std::list<CombineInfo> &MergeList,
                                      bool &OptimizeListAgain);
-  bool optimizeBlock(std::list<std::list<CombineInfo> > &MergeableInsts);
+  bool optimizeBlock(std::list<std::list<CombineInfo> > &MergeableInsts,
+                     MachineBasicBlock &MBB);
 
   bool runOnMachineFunction(MachineFunction &MF) override;
 
@@ -583,12 +588,14 @@
 }
 
 static void moveInstsAfter(MachineBasicBlock::iterator I,
-                           ArrayRef<MachineInstr *> InstsToMove) {
+                           ArrayRef<MachineInstr *> InstsToMove,
+                           std::set<MachineInstr*> &MovedList) {
   MachineBasicBlock *MBB = I->getParent();
   ++I;
   for (MachineInstr *MI : InstsToMove) {
     MI->removeFromParent();
     MBB->insert(I, MI);
+    MovedList.insert(MI);
   }
 }
 
@@ -1056,7 +1063,7 @@
                             .add(*Dest1)
                             .addReg(DestReg, RegState::Kill, SubRegIdx1);
 
-  moveInstsAfter(Copy1, InstsToMove);
+  moveInstsAfter(Copy1, InstsToMove, MIMovedList);
 
   CI.I->eraseFromParent();
   Paired.I->eraseFromParent();
@@ -1140,7 +1147,7 @@
           .addImm(0)                                 // gds
           .cloneMergedMemRefs({&*CI.I, &*Paired.I});
 
-  moveInstsAfter(Write2, InstsToMove);
+  moveInstsAfter(Write2, InstsToMove, MIMovedList);
 
   CI.I->eraseFromParent();
   Paired.I->eraseFromParent();
@@ -1196,7 +1203,7 @@
                             .add(*Dest1)
                             .addReg(DestReg, RegState::Kill, SubRegIdx1);
 
-  moveInstsAfter(Copy1, InstsToMove);
+  moveInstsAfter(Copy1, InstsToMove, MIMovedList);
 
   CI.I->eraseFromParent();
   Paired.I->eraseFromParent();
@@ -1247,7 +1254,7 @@
                             .add(*Dest1)
                             .addReg(DestReg, RegState::Kill, SubRegIdx1);
 
-  moveInstsAfter(Copy1, InstsToMove);
+  moveInstsAfter(Copy1, InstsToMove, MIMovedList);
 
   CI.I->eraseFromParent();
   Paired.I->eraseFromParent();
@@ -1310,7 +1317,7 @@
                             .add(*Dest1)
                             .addReg(DestReg, RegState::Kill, SubRegIdx1);
 
-  moveInstsAfter(Copy1, InstsToMove);
+  moveInstsAfter(Copy1, InstsToMove, MIMovedList);
 
   CI.I->eraseFromParent();
   Paired.I->eraseFromParent();
@@ -1378,7 +1385,7 @@
                             .add(*Dest1)
                             .addReg(DestReg, RegState::Kill, SubRegIdx1);
 
-  moveInstsAfter(Copy1, InstsToMove);
+  moveInstsAfter(Copy1, InstsToMove, MIMovedList);
 
   CI.I->eraseFromParent();
   Paired.I->eraseFromParent();
@@ -1442,7 +1449,7 @@
           .addMemOperand(
               combineKnownAdjacentMMOs(*MBB->getParent(), MMOa, MMOb));
 
-  moveInstsAfter(MIB, InstsToMove);
+  moveInstsAfter(MIB, InstsToMove, MIMovedList);
 
   CI.I->eraseFromParent();
   Paired.I->eraseFromParent();
@@ -1601,7 +1608,7 @@
         .addImm(0)            // swz
         .addMemOperand(combineKnownAdjacentMMOs(*MBB->getParent(), MMOa, MMOb));
 
-  moveInstsAfter(MIB, InstsToMove);
+  moveInstsAfter(MIB, InstsToMove, MIMovedList);
 
   CI.I->eraseFromParent();
   Paired.I->eraseFromParent();
@@ -2001,17 +2008,32 @@
   return Modified;
 }
 
+bool SILoadStoreOptimizer::isCleanMergeList(std::list<CombineInfo> &MergeList) const {
+  for (auto I : MergeList) {
+    MachineInstr* MI = &*(I.I);
+    if (MIMovedList.count(MI))
+      return false;
+  }
+  return true;
+}
+
 // Scan through looking for adjacent LDS operations with constant offsets from
 // the same base register. We rely on the scheduler to do the hard work of
 // clustering nearby loads, and assume these are all adjacent.
 bool SILoadStoreOptimizer::optimizeBlock(
-                       std::list<std::list<CombineInfo> > &MergeableInsts) {
+                       std::list<std::list<CombineInfo> > &MergeableInsts,
+                       MachineBasicBlock &MBB) {
   bool Modified = false;
 
   for (std::list<std::list<CombineInfo>>::iterator I = MergeableInsts.begin(),
                                                    E = MergeableInsts.end(); I != E;) {
     std::list<CombineInfo> &MergeList = *I;
 
+    if (!isCleanMergeList(MergeList)) {
+      MergeableInvalid = true;
+      return Modified;
+    }
+
     bool OptimizeListAgain = false;
     if (!optimizeInstsWithSameBaseAddr(MergeList, OptimizeListAgain)) {
       // We weren't able to make any changes, so delete the list so we don't
@@ -2152,15 +2174,23 @@
 
   bool Modified = false;
 
-
   for (MachineBasicBlock &MBB : MF) {
-    std::list<std::list<CombineInfo> > MergeableInsts;
     // First pass: Collect list of all instructions we know how to merge.
-    Modified |= collectMergeableInsts(MBB, MergeableInsts);
     do {
-      OptimizeAgain = false;
-      Modified |= optimizeBlock(MergeableInsts);
-    } while (OptimizeAgain);
+      std::list<std::list<CombineInfo> > MergeableInsts;
+      Modified |= collectMergeableInsts(MBB, MergeableInsts);
+      MergeableInvalid = false;
+      MIMovedList.clear();
+
+      do {
+        OptimizeAgain = false;
+        Modified |= optimizeBlock(MergeableInsts, MBB);
+      } while (OptimizeAgain && !MergeableInvalid);
+
+      // Has a transformation occurred that invalidates the MergeableInsts list?
+      // This can happen if other mergeable instructions are moved when merging
+      // a different list
+    } while(MergeableInvalid);
   }
 
   return Modified;