Index: lib/CodeGen/MIRCanonicalizerPass.cpp
===================================================================
--- lib/CodeGen/MIRCanonicalizerPass.cpp
+++ lib/CodeGen/MIRCanonicalizerPass.cpp
@@ -131,7 +131,43 @@
   return ~0U;
 }
 
-static bool rescheduleCanonically(MachineBasicBlock *MBB) {
+static bool
+rescheduleLexographically(std::vector<MachineInstr *> instructions,
+                          MachineBasicBlock *MBB,
+                          std::function<MachineBasicBlock::iterator()> getPos) {
+
+  bool Changed = false;
+  std::map<std::string, MachineInstr*> StringInstrMap;
+
+  for (auto *II : instructions) {
+    std::string S;
+    raw_string_ostream OS(S);
+    II->print(OS);
+    OS.flush();
+
+    // Trim the assignment, or start from the begining in the case of a store.
+    const size_t i = S.find("=");
+    StringInstrMap.insert({(i == std::string::npos) ? S : S.substr(i), II});
+  }
+
+  for (auto &II : StringInstrMap) {
+
+    DEBUG({
+      dbgs() << "Splicing ";
+      II.second->dump();
+      dbgs() << " right before: ";
+      getPos()->dump();
+    });
+
+    Changed = true;
+    MBB->splice(getPos(), MBB, II.second);
+  }
+
+  return Changed;
+}
+
+static bool rescheduleCanonically(unsigned &PseudoIdempotentInstCount,
+                                  MachineBasicBlock *MBB) {
 
   bool Changed = false;
 
@@ -153,13 +189,60 @@
     Instructions.push_back(&MI);
   }
 
+  std::vector<MachineInstr *> PseudoIdempotentInstructions;
+  std::vector<unsigned> PhysRegDefs;
+  for (auto *II : Instructions) {
+    for (unsigned i = 1; i < II->getNumOperands(); i++) {
+      MachineOperand &MO = II->getOperand(i);
+      if (!MO.isReg())
+        continue;
+
+      if (TargetRegisterInfo::isVirtualRegister(MO.getReg()))
+        continue;
+
+      if (!MO.isDef())
+        continue;
+
+      PhysRegDefs.push_back(MO.getReg());
+    }
+  }
+
   for (auto *II : Instructions) {
     if (II->getNumOperands() == 0)
       continue;
+    if (II->mayLoad()) {
+      continue;
+    }
+    if (II->mayStore()) {
+      continue;
+    }
 
     MachineOperand &MO = II->getOperand(0);
     if (!MO.isReg() || !TargetRegisterInfo::isVirtualRegister(MO.getReg()))
       continue;
+    if (!MO.isDef())
+      continue;
+
+    bool IsPseudoIdempotent = true;
+    for (unsigned i = 1; i < II->getNumOperands(); i++) {
+      if (II->getOperand(i).isReg()) {
+        if (!TargetRegisterInfo::isVirtualRegister(
+                II->getOperand(i).getReg())) {
+          if (llvm::find(PhysRegDefs, II->getOperand(i).getReg()) ==
+              PhysRegDefs.end()) {
+            continue;
+          }
+        }
+
+        IsPseudoIdempotent = false;
+        break;
+      }
+    }
+
+    if (IsPseudoIdempotent) {
+      PseudoIdempotentInstructions.push_back(II);
+      continue;
+    }
 
     DEBUG(dbgs() << "Operand " << 0 << " of "; II->dump(); MO.dump(););
 
@@ -194,9 +277,6 @@
       if (DefI != BBE && UseI != BBE)
         break;
 
-      if ((&*BBI != Def) && (&*BBI != UseToBringDefCloserTo))
-        continue;
-
       if (&*BBI == Def) {
         DefI = BBI;
         continue;
@@ -222,6 +302,12 @@
     MBB->splice(UseI, MBB, DefI);
   }
 
+  PseudoIdempotentInstCount = PseudoIdempotentInstructions.size();
+  DEBUG(dbgs() << "Rescheduling Idempotent Instructions Lexographically.";);
+  Changed |= rescheduleLexographically(
+      PseudoIdempotentInstructions, MBB,
+      [&]() -> MachineBasicBlock::iterator { return MBB->begin(); });
+
   return Changed;
 }
 
@@ -517,7 +603,8 @@
   DEBUG(dbgs() << "\n\n NEW BASIC BLOCK: " << MBB->getName() << "\n\n";);
 
   DEBUG(dbgs() << "MBB Before Scheduling:\n"; MBB->dump(););
-  Changed |= rescheduleCanonically(MBB);
+  unsigned PseudoIdempotentInstCount = 0;
+  Changed |= rescheduleCanonically(PseudoIdempotentInstCount, MBB);
   DEBUG(dbgs() << "MBB After Scheduling:\n"; MBB->dump(););
 
   std::vector<MachineInstr *> Candidates = populateCandidates(MBB);
@@ -579,6 +666,38 @@
 
   auto VRegRenameMap = GetVRegRenameMap(VRegs, renamedInOtherBB, MRI, DummyRC);
   Changed |= doVRegRenaming(renamedInOtherBB, VRegRenameMap, MRI);
+
+  // Here we renumber the def vregs for the idempotent instructions from the top
+  // of the MachineBasicBlock so that they are named in the order that we sorted
+  // them alphabetically. If there's less than two idempotent instructions we
+  // don't bother with this step because it doesn't seem to have a lot of value
+  // in real world cases we've tried.
+  if (PseudoIdempotentInstCount >= 2) {
+    Changed = true;
+    unsigned i = 0;
+    unsigned gap = 1;
+    SkipVRegs(gap, MRI, DummyRC);
+
+    for (auto &MI : *MBB) {
+
+      if (i++ >= PseudoIdempotentInstCount) {
+        break;
+      }
+
+      unsigned vRegToRename = MI.getOperand(0).getReg();
+      auto Rename = MRI.createVirtualRegister(MRI.getRegClass(vRegToRename));
+
+      std::vector<MachineOperand *> RenameMOs;
+      for (auto &MO : MRI.reg_operands(vRegToRename)) {
+        RenameMOs.push_back(&MO);
+      }
+
+      for (auto *MO : RenameMOs) {
+        MO->setReg(Rename);
+      }
+    }
+  }
+
   Changed |= doDefKillClear(MBB);
 
   DEBUG(dbgs() << "Updated MachineBasicBlock:\n"; MBB->dump(); dbgs() << "\n";);
@@ -622,4 +741,3 @@
 
   return Changed;
 }
-
Index: test/CodeGen/MIR/AArch64/mirCanonIdempotent.mir
===================================================================
--- /dev/null
+++ test/CodeGen/MIR/AArch64/mirCanonIdempotent.mir
@@ -0,0 +1,116 @@
+# RUN: llc -mtriple=arm64-apple-ios11.0.0 -o - -run-pass mir-canonicalizer %s | FileCheck %s
+# These Idempotent instructions are sorted alphabetically (based on after the '=')
+# CHECK: %4353:gpr64 = MOVi64imm 4617315517961601024
+# CHECK: %4354:gpr32 = MOVi32imm 408
+# CHECK: %4355:gpr64all = IMPLICIT_DEF
+# CHECK: %4356:fpr64 = FMOVDi 20
+# CHECK: %4357:fpr64 = FMOVDi 112
+...
+---
+name: Proc8
+stack:
+  - { id: 0, type: default, offset: 0, size: 4, alignment: 4,
+      stack-id: 0, callee-saved-register: '', callee-saved-restored: true,
+      local-offset: -4, di-variable: '', di-expression: '', di-location: '' }
+  - { id: 1, type: default, offset: 0, size: 8, alignment: 8,
+      stack-id: 0, callee-saved-register: '', callee-saved-restored: true,
+      local-offset: -16, di-variable: '', di-expression: '', di-location: '' }
+  - { id: 2, type: default, offset: 0, size: 8, alignment: 8,
+      stack-id: 0, callee-saved-register: '', callee-saved-restored: true,
+      local-offset: -24, di-variable: '', di-expression: '', di-location: '' }
+  - { id: 3, type: default, offset: 0, size: 8, alignment: 8,
+      stack-id: 0, callee-saved-register: '', callee-saved-restored: true,
+      local-offset: -32, di-variable: '', di-expression: '', di-location: '' }
+  - { id: 4, type: default, offset: 0, size: 8, alignment: 8,
+      stack-id: 0, callee-saved-register: '', callee-saved-restored: true,
+      local-offset: -40, di-variable: '', di-expression: '', di-location: '' }
+  - { id: 5, type: default, offset: 0, size: 8, alignment: 8,
+      stack-id: 0, callee-saved-register: '', callee-saved-restored: true,
+      local-offset: -48, di-variable: '', di-expression: '', di-location: '' }
+  - { id: 6, type: default, offset: 0, size: 8, alignment: 8,
+      stack-id: 0, callee-saved-register: '', callee-saved-restored: true,
+      local-offset: -56, di-variable: '', di-expression: '', di-location: '' }
+constants:
+body: |
+  bb.0:
+    liveins: $x0, $x1, $d0, $d1
+
+    %3:fpr64 = COPY $d1
+    %2:fpr64 = COPY $d0
+    %1:gpr64 = COPY $x1
+    %0:gpr64common = COPY $x0
+    STRXui %0, %stack.1, 0 :: (store 8)
+    STRXui %1, %stack.2, 0 :: (store 8)
+    STRDui %2, %stack.3, 0 :: (store 8)
+    STRDui %3, %stack.4, 0 :: (store 8)
+
+    %4:fpr64 = FMOVDi 20
+    %5:fpr64 = FADDDrr %2, killed %4
+    STRDui %5, %stack.5, 0 :: (store 8)
+
+    %6:gpr32 = FCVTZSUWDr %5
+    STRDroW %3, %0, killed %6, 1, 1
+
+    %7:gpr64common = LDRXui %stack.1, 0 :: (dereferenceable load 8)
+    %8:fpr64 = LDRDui %stack.5, 0 :: (dereferenceable load 8)
+
+    %9:gpr32common = FCVTZSUWDr killed %8
+    %10:fpr64 = LDRDroW %7, %9, 1, 1
+
+    %11:gpr32common = ADDWri %9, 1, 0
+    STRDroW killed %10, %7, killed %11, 1, 1
+
+    %12:fpr64 = LDRDui %stack.5, 0 :: (dereferenceable load 8)
+    %13:gpr64common = LDRXui %stack.1, 0 :: (dereferenceable load 8)
+
+    %14:gpr32common = FCVTZSUWDr %12
+    %15:gpr32common = ADDWri killed %14, 30, 0
+    STRDroW %12, killed %13, killed %15, 1, 1
+
+    %16:fpr64 = LDRDui %stack.5, 0 :: (dereferenceable load 8)
+    STRDui killed %16, %stack.6, 0 :: (store 8)
+
+    %19:fpr64 = FMOVDi 112
+    %46:gpr32 = MOVi32imm 408
+    %43:fpr64 = LDRDui %stack.5, 0 :: (dereferenceable load 8)
+    %44:gpr64 = LDRXui %stack.2, 0 :: (dereferenceable load 8)
+
+    %45:gpr32 = FCVTZSUWDr %43
+    %47:gpr64common = SMADDLrrr killed %45, %46, killed %44
+    %48:fpr64 = LDRDui %stack.6, 0 :: (dereferenceable load 8)
+
+    %49:gpr32 = FCVTZSUWDr killed %48
+    STRDroW %43, killed %47, killed %49, 1, 1
+
+    %21:gpr64 = LDRXui %stack.2, 0 :: (dereferenceable load 8)
+    %22:fpr64 = LDRDui %stack.5, 0 :: (dereferenceable load 8)
+
+    %23:gpr32 = FCVTZSUWDr killed %22
+    %24:gpr32 = MOVi32imm 408
+    %25:gpr64common = SMADDLrrr %23, %24, killed %21
+    %26:gpr64sp = ADDXrx killed %25, %23, 51
+    %27:fpr64 = LDURDi %26, -8
+    %29:fpr64 = FADDDrr killed %27, %19
+    STURDi killed %29, %26, -8
+
+    %30:gpr64common = LDRXui %stack.1, 0 :: (dereferenceable load 8)
+    %31:fpr64 = LDRDui %stack.5, 0 :: (dereferenceable load 8)
+
+    %32:gpr32common = FCVTZSUWDr killed %31
+    %34:gpr64all = IMPLICIT_DEF
+    %33:gpr64 = INSERT_SUBREG %34, %32, %subreg.sub_32
+    %35:gpr64 = SBFMXri killed %33, 61, 31
+    %36:fpr64 = LDRDroX killed %30, %35, 0, 0
+    %37:gpr64 = LDRXui %stack.2, 0 :: (dereferenceable load 8)
+
+    %38:gpr32common = ADDWri %32, 20, 0
+    %39:gpr64common = SMADDLrrr killed %38, %24, killed %37
+    STRDroX killed %36, killed %39, %35, 0, 0
+
+    %40:gpr64 = MOVi64imm 4617315517961601024
+
+    %42:gpr32 = LDRWui %stack.0, 0 :: (dereferenceable load 8)
+    $w0 = COPY %42
+    RET_ReallyLR implicit $w0
+
+...