Index: llvm/lib/Target/AArch64/AArch64LoadStoreOptimizer.cpp
===================================================================
--- llvm/lib/Target/AArch64/AArch64LoadStoreOptimizer.cpp
+++ llvm/lib/Target/AArch64/AArch64LoadStoreOptimizer.cpp
@@ -1515,6 +1515,32 @@
   return None;
 }
 
+// Returns a boolean that represents whether there exists a register
+// from FirstMI to the beginning of the block that can be renamed. If
+// one exists, we update Flags with its value.
+static bool updateFlagsWithRenameReg(
+    Optional<bool> MaybeCanRename, LdStPairFlags &Flags, MachineInstr &FirstMI,
+    MachineInstr &MI, LiveRegUnits &DefinedInBB, LiveRegUnits &UsedInBetween,
+    SmallPtrSetImpl<const TargetRegisterClass *> &RequiredClasses,
+    const TargetRegisterInfo *TRI) {
+  if (DebugCounter::shouldExecute(RegRenamingCounter)) {
+    if (!MaybeCanRename)
+      MaybeCanRename = {
+          canRenameUpToDef(FirstMI, UsedInBetween, RequiredClasses, TRI)};
+
+    if (*MaybeCanRename) {
+      Optional<MCPhysReg> MaybeRenameReg = tryToFindRegisterToRename(
+          FirstMI, MI, DefinedInBB, UsedInBetween, RequiredClasses, TRI);
+      if (MaybeRenameReg) {
+        Flags.setRenameReg(*MaybeRenameReg);
+        Flags.setMergeForward(true);
+        return true;
+      }
+    }
+  }
+  return false;
+}
+
 /// Scan the instructions looking for a load/store that can be combined with the
 /// current instruction into a wider equivalent or a load/store pair.
 MachineBasicBlock::iterator
@@ -1666,6 +1692,19 @@
             continue;
           }
         }
+
+        if (TRI->isSuperOrSubRegisterEq(Reg, getLdStRegOp(MI).getReg()) &&
+            ModifiedRegUnits.available(BaseReg) &&
+            UsedRegUnits.available(BaseReg)) {
+          bool FlagsHaveRenameReg = updateFlagsWithRenameReg(
+              MaybeCanRename, Flags, FirstMI, MI, DefinedInBB, UsedInBetween,
+              RequiredClasses, TRI);
+          if (FlagsHaveRenameReg) {
+            MBBIWithRenameReg = MBBI;
+            continue;
+          }
+        }
+
         // If the destination register of one load is the same register or a
         // sub/super register of the other load, bail and keep looking. A
         // load-pair instruction with both destination registers the same is
@@ -1715,21 +1754,11 @@
             return MBBI;
           }
 
-          if (DebugCounter::shouldExecute(RegRenamingCounter)) {
-            if (!MaybeCanRename)
-              MaybeCanRename = {canRenameUpToDef(FirstMI, UsedInBetween,
-                                                 RequiredClasses, TRI)};
-
-            if (*MaybeCanRename) {
-              Optional<MCPhysReg> MaybeRenameReg = tryToFindRegisterToRename(
-                  FirstMI, MI, DefinedInBB, UsedInBetween, RequiredClasses,
-                  TRI);
-              if (MaybeRenameReg) {
-                Flags.setRenameReg(*MaybeRenameReg);
-                Flags.setMergeForward(true);
-                MBBIWithRenameReg = MBBI;
-              }
-            }
+          bool FlagsHaveRenameReg = updateFlagsWithRenameReg(
+              MaybeCanRename, Flags, FirstMI, MI, DefinedInBB, UsedInBetween,
+              RequiredClasses, TRI);
+          if (FlagsHaveRenameReg) {
+            MBBIWithRenameReg = MBBI;
           }
         }
         // Unable to combine these instructions due to interference in between.
Index: llvm/test/CodeGen/AArch64/GlobalISel/byval-call.ll
===================================================================
--- llvm/test/CodeGen/AArch64/GlobalISel/byval-call.ll
+++ llvm/test/CodeGen/AArch64/GlobalISel/byval-call.ll
@@ -33,38 +33,30 @@
 ; CHECK-NEXT:    .cfi_offset w28, -16
 ; CHECK-NEXT:    .cfi_offset w30, -24
 ; CHECK-NEXT:    .cfi_offset w29, -32
-; CHECK-NEXT:    ldr q0, [x0]
-; CHECK-NEXT:    str q0, [sp]
+; CHECK-NEXT:    ldr q1, [x0]
 ; CHECK-NEXT:    ldr q0, [x0, #16]
-; CHECK-NEXT:    str q0, [sp, #16]
-; CHECK-NEXT:    ldr q0, [x0, #32]
-; CHECK-NEXT:    str q0, [sp, #32]
+; CHECK-NEXT:    stp q1, q0, [sp]
+; CHECK-NEXT:    ldr q1, [x0, #32]
 ; CHECK-NEXT:    ldr q0, [x0, #48]
-; CHECK-NEXT:    str q0, [sp, #48]
-; CHECK-NEXT:    ldr q0, [x0, #64]
-; CHECK-NEXT:    str q0, [sp, #64]
+; CHECK-NEXT:    stp q1, q0, [sp, #32]
+; CHECK-NEXT:    ldr q1, [x0, #64]
 ; CHECK-NEXT:    ldr q0, [x0, #80]
-; CHECK-NEXT:    str q0, [sp, #80]
-; CHECK-NEXT:    ldr q0, [x0, #96]
-; CHECK-NEXT:    str q0, [sp, #96]
+; CHECK-NEXT:    stp q1, q0, [sp, #64]
+; CHECK-NEXT:    ldr q1, [x0, #96]
 ; CHECK-NEXT:    ldr q0, [x0, #112]
-; CHECK-NEXT:    str q0, [sp, #112]
-; CHECK-NEXT:    ldr q0, [x0, #128]
-; CHECK-NEXT:    str q0, [sp, #128]
+; CHECK-NEXT:    stp q1, q0, [sp, #96]
+; CHECK-NEXT:    ldr q1, [x0, #128]
 ; CHECK-NEXT:    ldr q0, [x0, #144]
-; CHECK-NEXT:    str q0, [sp, #144]
-; CHECK-NEXT:    ldr q0, [x0, #160]
-; CHECK-NEXT:    str q0, [sp, #160]
+; CHECK-NEXT:    stp q1, q0, [sp, #128]
+; CHECK-NEXT:    ldr q1, [x0, #160]
 ; CHECK-NEXT:    ldr q0, [x0, #176]
-; CHECK-NEXT:    str q0, [sp, #176]
-; CHECK-NEXT:    ldr q0, [x0, #192]
-; CHECK-NEXT:    str q0, [sp, #192]
+; CHECK-NEXT:    stp q1, q0, [sp, #160]
+; CHECK-NEXT:    ldr q1, [x0, #192]
 ; CHECK-NEXT:    ldr q0, [x0, #208]
-; CHECK-NEXT:    str q0, [sp, #208]
-; CHECK-NEXT:    ldr q0, [x0, #224]
-; CHECK-NEXT:    str q0, [sp, #224]
+; CHECK-NEXT:    stp q1, q0, [sp, #192]
+; CHECK-NEXT:    ldr q1, [x0, #224]
 ; CHECK-NEXT:    ldr q0, [x0, #240]
-; CHECK-NEXT:    str q0, [sp, #240]
+; CHECK-NEXT:    stp q1, q0, [sp, #224]
 ; CHECK-NEXT:    bl byval_a64i32
 ; CHECK-NEXT:    ldr x28, [sp, #272] // 8-byte Folded Reload
 ; CHECK-NEXT:    ldp x29, x30, [sp, #256] // 16-byte Folded Reload
Index: llvm/test/CodeGen/AArch64/consthoist-gep.ll
===================================================================
--- llvm/test/CodeGen/AArch64/consthoist-gep.ll
+++ llvm/test/CodeGen/AArch64/consthoist-gep.ll
@@ -3,6 +3,8 @@
 ; CHECK-NOT: adrp    x10, global+332
 ; CHECK-NOT: add     x10, x10, :lo12:global+332
 ; CHECK: adrp    x10, global+528
+; CHECK-NEXT:  and w12, w8, #0xffffff
+; CHECK-NEXT:  ldr w8, [x11]
 ; CHECK-NEXT: add     x10, x10, :lo12:global+528
 
 %struct.blam = type { %struct.bar, %struct.bar.0, %struct.wobble, %struct.wombat, i8, i16, %struct.snork.2, %struct.foo, %struct.snork.3, %struct.wobble.4, %struct.quux, [9 x i16], %struct.spam, %struct.zot }
Index: llvm/test/CodeGen/AArch64/ldst-opt.ll
===================================================================
--- llvm/test/CodeGen/AArch64/ldst-opt.ll
+++ llvm/test/CodeGen/AArch64/ldst-opt.ll
@@ -1117,7 +1117,7 @@
 define void @post-indexed-sub-word(i32* %a, i32* %b, i64 %count) nounwind {
 ; CHECK-LABEL: post-indexed-sub-word
 ; CHECK: ldr w{{[0-9]+}}, [x{{[0-9]+}}], #-8
-; CHECK: str w{{[0-9]+}}, [x{{[0-9]+}}], #-8
+; CHECK: stp w{{[0-9]+}}, w{{[0-9]+}}, [x0, #-4]
   br label %for.body
 for.body:
   %phi1 = phi i32* [ %gep4, %for.body ], [ %b, %0 ]
@@ -1141,7 +1141,7 @@
 define void @post-indexed-sub-doubleword(i64* %a, i64* %b, i64 %count) nounwind {
 ; CHECK-LABEL: post-indexed-sub-doubleword
 ; CHECK: ldr x{{[0-9]+}}, [x{{[0-9]+}}], #-16
-; CHECK: str x{{[0-9]+}}, [x{{[0-9]+}}], #-16
+; CHECK: stp x{{[0-9]+}}, x{{[0-9]+}}, [x0, #-8]
   br label %for.body
 for.body:
   %phi1 = phi i64* [ %gep4, %for.body ], [ %b, %0 ]
@@ -1165,7 +1165,7 @@
 define void @post-indexed-sub-quadword(<2 x i64>* %a, <2 x i64>* %b, i64 %count) nounwind {
 ; CHECK-LABEL: post-indexed-sub-quadword
 ; CHECK: ldr q{{[0-9]+}}, [x{{[0-9]+}}], #-32
-; CHECK: str q{{[0-9]+}}, [x{{[0-9]+}}], #-32
+; CHECK: stp q{{[0-9]+}}, q{{[0-9]+}}, [x0, #-16]
   br label %for.body
 for.body:
   %phi1 = phi <2 x i64>* [ %gep4, %for.body ], [ %b, %0 ]
@@ -1189,7 +1189,7 @@
 define void @post-indexed-sub-float(float* %a, float* %b, i64 %count) nounwind {
 ; CHECK-LABEL: post-indexed-sub-float
 ; CHECK: ldr s{{[0-9]+}}, [x{{[0-9]+}}], #-8
-; CHECK: str s{{[0-9]+}}, [x{{[0-9]+}}], #-8
+; CHECK: stp s{{[0-9]+}}, s{{[0-9]+}}, [x0, #-4]
   br label %for.body
 for.body:
   %phi1 = phi float* [ %gep4, %for.body ], [ %b, %0 ]
@@ -1213,7 +1213,7 @@
 define void @post-indexed-sub-double(double* %a, double* %b, i64 %count) nounwind {
 ; CHECK-LABEL: post-indexed-sub-double
 ; CHECK: ldr d{{[0-9]+}}, [x{{[0-9]+}}], #-16
-; CHECK: str d{{[0-9]+}}, [x{{[0-9]+}}], #-16
+; CHECK: stp d{{[0-9]+}}, d{{[0-9]+}}, [x0, #-8]
   br label %for.body
 for.body:
   %phi1 = phi double* [ %gep4, %for.body ], [ %b, %0 ]
@@ -1237,7 +1237,7 @@
 define void @post-indexed-sub-doubleword-offset-min(i64* %a, i64* %b, i64 %count) nounwind {
 ; CHECK-LABEL: post-indexed-sub-doubleword-offset-min
 ; CHECK: ldr x{{[0-9]+}}, [x{{[0-9]+}}], #-256
-; CHECK: str x{{[0-9]+}}, [x{{[0-9]+}}], #-256
+; CHECK: stp x{{[0-9]+}}, x{{[0-9]+}}, [x0], #-256
   br label %for.body
 for.body:
   %phi1 = phi i64* [ %gep4, %for.body ], [ %b, %0 ]
@@ -1262,8 +1262,7 @@
 ; CHECK-LABEL: post-indexed-doubleword-offset-out-of-range
 ; CHECK: ldr x{{[0-9]+}}, [x{{[0-9]+}}]
 ; CHECK: add x{{[0-9]+}}, x{{[0-9]+}}, #256
-; CHECK: str x{{[0-9]+}}, [x{{[0-9]+}}]
-; CHECK: add x{{[0-9]+}}, x{{[0-9]+}}, #256
+; CHECK: stp x{{[0-9]+}}, x{{[0-9]+}}, [x0], #256
 
   br label %for.body
 for.body:
Index: llvm/test/CodeGen/AArch64/stp-opt-with-renaming.mir
===================================================================
--- llvm/test/CodeGen/AArch64/stp-opt-with-renaming.mir
+++ llvm/test/CodeGen/AArch64/stp-opt-with-renaming.mir
@@ -544,3 +544,161 @@
     RET undef $lr
 
 ...
+
+# During ISel, the order of load/store pairs can be optimized and changed
+# so that only a single register is used. Due to this register reuse, LDP/STPs
+# are not generated. These tests check that an STP instruction will be 
+# generated after register renaming is attempted.  
+... 
+---
+#
+# CHECK-LABEL: name: ldst32
+# CHECK: liveins: $x0, $x1
+# CHECK: $q1 = LDRQui renamable $x1, 1 :: (load 16)
+# CHECK-NEXT: renamable $q0 = LDRQui killed renamable $x1, 0 :: (load 16, align 32)
+# CHECK-NEXT: STPQi killed renamable $q0, killed $q1, killed renamable $x0, 0 :: (store 16, align 32)
+# CHECK-NEXT: RET undef $lr
+#
+name:            ldst32
+alignment:       4
+tracksRegLiveness: true
+liveins:
+  - { reg: '$x0', virtual-reg: '' }
+  - { reg: '$x1', virtual-reg: '' }
+frameInfo:
+  maxAlignment:    1
+  maxCallFrameSize: 0
+machineFunctionInfo:
+  hasRedZone:      false
+body:             |
+  bb.0.entry:
+    liveins: $x0, $x1
+    renamable $q0 = LDRQui renamable $x1, 1 :: (load 16)
+    STRQui killed renamable $q0, renamable $x0, 1 :: (store 16, basealign 32)
+    renamable $q0 = LDRQui killed renamable $x1, 0 :: (load 16, align 32)
+    STRQui killed renamable $q0, killed renamable $x0, 0 :: (store 16, align 32)
+    RET undef $lr
+
+...
+---
+#
+# CHECK-LABEL: name: ldst64
+# CHECK: liveins: $x0, $x1
+# CHECK: $q1 = LDRQui renamable $x1, 1 :: (load 16)
+# CHECK-NEXT: renamable $q0 = LDRQui killed renamable $x1, 0 :: (load 16, align 64)
+# CHECK-NEXT: STPQi killed renamable $q0, killed $q1, killed renamable $x0, 0 :: (store 16, align 64)
+# CHECK-NEXT: RET undef $lr
+#
+name:            ldst64
+alignment:       4
+tracksRegLiveness: true
+liveins:
+  - { reg: '$x0', virtual-reg: '' }
+  - { reg: '$x1', virtual-reg: '' }
+frameInfo:
+  maxAlignment:    1
+  maxCallFrameSize: 0
+machineFunctionInfo:
+  hasRedZone:      false
+body:             |
+  bb.0.entry:
+    liveins: $x0, $x1
+    renamable $q0 = LDRQui renamable $x1, 1 :: (load 16)
+    STRQui killed renamable $q0, renamable $x0, 1 :: (store 16, basealign 64)
+    renamable $q0 = LDRQui killed renamable $x1, 0 :: (load 16, align 64)
+    STRQui killed renamable $q0, killed renamable $x0, 0 :: (store 16, align 64)
+    RET undef $lr
+
+...
+---
+#
+# CHECK-LABEL: name: ldst128
+# CHECK: liveins: $x0, $x1
+# CHECK: $q1 = LDRQui renamable $x1, 1 :: (load 16)
+# CHECK-NEXT: renamable $q0 = LDRQui killed renamable $x1, 0 :: (load 16, align 128)
+# CHECK-NEXT: STPQi killed renamable $q0, killed $q1, killed renamable $x0, 0 :: (store 16, align 128)
+# CHECK-NEXT: RET undef $lr
+#
+name:            ldst128
+alignment:       4
+tracksRegLiveness: true
+liveins:
+  - { reg: '$x0', virtual-reg: '' }
+  - { reg: '$x1', virtual-reg: '' }
+frameInfo:
+  maxAlignment:    1
+  maxCallFrameSize: 0
+machineFunctionInfo:
+  hasRedZone:      false
+body:             |
+  bb.0.entry:
+    liveins: $x0, $x1
+    renamable $q0 = LDRQui renamable $x1, 1 :: (load 16)
+    STRQui killed renamable $q0, renamable $x0, 1 :: (store 16, basealign 128)
+    renamable $q0 = LDRQui killed renamable $x1, 0 :: (load 16, align 128)
+    STRQui killed renamable $q0, killed renamable $x0, 0 :: (store 16, align 128)
+    RET undef $lr
+
+... 
+---
+#
+# CHECK-LABEL: name: ldst-no-reg-available
+# CHECK: liveins: $x0, $x1, $q1, $q2, $q3, $q4, $q5, $q6, $q7, $q8, $q9, $q10
+# CHECK: renamable $q0 = LDRQui renamable $x1, 1 :: (load 16)
+# CHECK-NEXT: STRQui killed renamable $q0, renamable $x0, 1 :: (store 16, align 32)
+# CHECK-NEXT: renamable $q0 = LDRQui killed renamable $x1, 0 :: (load 16, align 32)
+# CHECK-NEXT: STRQui killed renamable $q0, killed renamable $x0, 0 :: (store 16, align 32)
+# CHECK-NEXT: RET undef $lr
+#
+name:            ldst-no-reg-available
+alignment:       4
+tracksRegLiveness: true
+liveins:
+  - { reg: '$x0' }
+  - { reg: '$x1' }
+frameInfo:
+  maxAlignment:    1
+  maxCallFrameSize: 0
+machineFunctionInfo:
+  hasRedZone:      false
+body:             |
+  bb.0.entry:
+    liveins: $x0, $x1, $q1, $q2, $q3, $q4, $q5, $q6, $q7, $q8, $q9, $q10
+    renamable $q0 = LDRQui renamable $x1, 1 :: (load 16)
+    STRQui killed renamable $q0, renamable $x0, 1 :: (store 16, basealign 32)
+    renamable $q0 = LDRQui killed renamable $x1, 0 :: (load 16, align 32)
+    STRQui killed renamable $q0, killed renamable $x0, 0 :: (store 16, align 32)
+    RET undef $lr
+
+... 
+---
+#
+# CHECK-LABEL: name: ldst-basereg-modified
+# CHECK: liveins: $x0, $x1
+# CHECK: renamable $q0 = LDRQui renamable $x1, 1 :: (load 16)
+# CHECK-NEXT: STRQui killed renamable $q0, renamable $x0, 1 :: (store 16, align 32)
+# CHECK-NEXT: renamable $q0 = LDRQui killed renamable $x1, 0 :: (load 16, align 32)
+# CHECK-NEXT: STRHHui $wzr, renamable $x0, 12 :: (store 2, align 8)
+# CHECK-NEXT: STRQui killed renamable $q0, killed renamable $x0, 0 :: (store 16, align 32)
+# CHECK-NEXT: RET undef $lr
+#
+name:            ldst-basereg-modified
+alignment:       4
+tracksRegLiveness: true
+liveins:
+  - { reg: '$x0' }
+  - { reg: '$x1' }
+frameInfo:
+  maxAlignment:    1
+  maxCallFrameSize: 0
+machineFunctionInfo:
+  hasRedZone:      false
+body:             |
+  bb.0.entry:
+    liveins: $x0, $x1
+    renamable $q0 = LDRQui renamable $x1, 1 :: (load 16)
+    STRQui killed renamable $q0, renamable $x0, 1 :: (store 16, basealign 32)
+    renamable $q0 = LDRQui killed renamable $x1, 0 :: (load 16, align 32)
+    STRHHui $wzr, renamable $x0, 12 :: (store 2, align 8)
+    STRQui killed renamable $q0, killed renamable $x0, 0 :: (store 16, align 32)
+    RET undef $lr