Index: llvm/trunk/lib/Target/ARM/ARMLoadStoreOptimizer.cpp
===================================================================
--- llvm/trunk/lib/Target/ARM/ARMLoadStoreOptimizer.cpp
+++ llvm/trunk/lib/Target/ARM/ARMLoadStoreOptimizer.cpp
@@ -1961,6 +1961,7 @@
     static char ID;
     ARMPreAllocLoadStoreOpt() : MachineFunctionPass(ID) {}
 
+    AliasAnalysis *AA;
     const DataLayout *TD;
     const TargetInstrInfo *TII;
     const TargetRegisterInfo *TRI;
@@ -1974,6 +1975,11 @@
       return ARM_PREALLOC_LOAD_STORE_OPT_NAME;
     }
 
+    virtual void getAnalysisUsage(AnalysisUsage &AU) const override {
+      AU.addRequired<AAResultsWrapperPass>();
+      MachineFunctionPass::getAnalysisUsage(AU);
+    }
+
   private:
     bool CanFormLdStDWord(MachineInstr *Op0, MachineInstr *Op1, DebugLoc &dl,
                           unsigned &NewOpc, unsigned &EvenReg,
@@ -2003,6 +2009,7 @@
   TRI = STI->getRegisterInfo();
   MRI = &Fn.getRegInfo();
   MF  = &Fn;
+  AA = &getAnalysis<AAResultsWrapperPass>().getAAResults();
 
   bool Modified = false;
   for (MachineBasicBlock &MFI : Fn)
@@ -2016,28 +2023,19 @@
                                       MachineBasicBlock::iterator E,
                                       SmallPtrSetImpl<MachineInstr*> &MemOps,
                                       SmallSet<unsigned, 4> &MemRegs,
-                                      const TargetRegisterInfo *TRI) {
+                                      const TargetRegisterInfo *TRI,
+                                      AliasAnalysis *AA) {
   // Are there stores / loads / calls between them?
-  // FIXME: This is overly conservative. We should make use of alias information
-  // some day.
   SmallSet<unsigned, 4> AddedRegPressure;
   while (++I != E) {
     if (I->isDebugValue() || MemOps.count(&*I))
       continue;
     if (I->isCall() || I->isTerminator() || I->hasUnmodeledSideEffects())
       return false;
-    if (isLd && I->mayStore())
-      return false;
-    if (!isLd) {
-      if (I->mayLoad())
-        return false;
-      // It's not safe to move the first 'str' down.
-      // str r1, [r0]
-      // strh r5, [r0]
-      // str r4, [r0, #+4]
-      if (I->mayStore())
-        return false;
-    }
+    if (I->mayStore() || (!isLd && I->mayLoad()))
+      for (MachineInstr *MemOp : MemOps)
+        if (I->mayAlias(AA, *MemOp, /*UseTBAA*/ false))
+          return false;
     for (unsigned j = 0, NumOps = I->getNumOperands(); j != NumOps; ++j) {
       MachineOperand &MO = I->getOperand(j);
       if (!MO.isReg())
@@ -2212,7 +2210,7 @@
       bool DoMove = (LastLoc - FirstLoc) <= NumMove*4; // FIXME: Tune this.
       if (DoMove)
         DoMove = IsSafeAndProfitableToMove(isLd, Base, FirstOp, LastOp,
-                                           MemOps, MemRegs, TRI);
+                                           MemOps, MemRegs, TRI, AA);
       if (!DoMove) {
         for (unsigned i = 0; i != NumMove; ++i)
           Ops.pop_back();
Index: llvm/trunk/test/CodeGen/ARM/ldrd.ll
===================================================================
--- llvm/trunk/test/CodeGen/ARM/ldrd.ll
+++ llvm/trunk/test/CodeGen/ARM/ldrd.ll
@@ -189,5 +189,23 @@
   ret i32* %p1
 }
 
+; CHECK-LABEL: ldrd_strd_aa:
+; NORMAL: ldrd [[TMP1:r[0-9]]], [[TMP2:r[0-9]]],
+; NORMAL: strd [[TMP1]], [[TMP2]],
+; CONSERVATIVE-NOT: ldrd
+; CONSERVATIVE-NOT: strd
+; CHECK: bx lr
+
+define void @ldrd_strd_aa(i32* noalias nocapture %x, i32* noalias nocapture readonly %y) {
+entry:
+  %0 = load i32, i32* %y, align 4
+  store i32 %0, i32* %x, align 4
+  %arrayidx2 = getelementptr inbounds i32, i32* %y, i32 1
+  %1 = load i32, i32* %arrayidx2, align 4
+  %arrayidx3 = getelementptr inbounds i32, i32* %x, i32 1
+  store i32 %1, i32* %arrayidx3, align 4
+  ret void
+}
+
 declare void @llvm.lifetime.start(i64, i8* nocapture) nounwind
 declare void @llvm.lifetime.end(i64, i8* nocapture) nounwind
Index: llvm/trunk/test/CodeGen/ARM/prera-ldst-aliasing.mir
===================================================================
--- llvm/trunk/test/CodeGen/ARM/prera-ldst-aliasing.mir
+++ llvm/trunk/test/CodeGen/ARM/prera-ldst-aliasing.mir
@@ -0,0 +1,40 @@
+# RUN: llc -run-pass arm-prera-ldst-opt %s -o - | FileCheck %s
+--- |
+  target triple = "thumbv7---eabi"
+
+  define void @ldrd_strd_aa(i32* noalias nocapture %x, i32* noalias nocapture readonly %y) {
+  entry:
+    %0 = load i32, i32* %y, align 4
+    store i32 %0, i32* %x, align 4
+    %arrayidx2 = getelementptr inbounds i32, i32* %y, i32 1
+    %1 = load i32, i32* %arrayidx2, align 4
+    %arrayidx3 = getelementptr inbounds i32, i32* %x, i32 1
+    store i32 %1, i32* %arrayidx3, align 4
+    ret void
+  }
+...
+---
+name:            ldrd_strd_aa
+alignment:       1
+tracksRegLiveness: true
+liveins:
+  - { reg: '%r0', virtual-reg: '%0' }
+  - { reg: '%r1', virtual-reg: '%1' }
+body:             |
+  bb.0.entry:
+    liveins: %r0, %r1
+
+    %1 : gpr = COPY %r1
+    %0 : gpr = COPY %r0
+    %2 : gpr = t2LDRi12 %1, 0, 14, _ :: (load 4 from %ir.y)
+    t2STRi12 killed %2, %0, 0, 14, _ :: (store 4 into %ir.x)
+    %3 : gpr = t2LDRi12 %1, 4, 14, _ :: (load 4 from %ir.arrayidx2)
+    t2STRi12 killed %3, %0, 4, 14, _ :: (store 4 into %ir.arrayidx3)
+    ; CHECK: t2LDRi12
+    ; CHECK-NEXT: t2LDRi12
+    ; CHECK-NEXT: t2STRi12
+    ; CHECK-NEXT: t2STRi12
+    tBX_RET 14, _
+
+...
+