diff --git a/llvm/include/llvm/CodeGen/GlobalISel/Localizer.h b/llvm/include/llvm/CodeGen/GlobalISel/Localizer.h
--- a/llvm/include/llvm/CodeGen/GlobalISel/Localizer.h
+++ b/llvm/include/llvm/CodeGen/GlobalISel/Localizer.h
@@ -64,6 +64,11 @@
 
   typedef SmallSetVector<MachineInstr *, 32> LocalizedSetVecT;
 
+  /// If \p Op is a phi operand and not unique in that phi, that is,
+  /// there are other operands in the phi with the same register,
+  /// return true.
+  bool isNonUniquePhiValue(MachineOperand &Op) const;
+
   /// Do inter-block localization from the entry block.
   bool localizeInterBlock(MachineFunction &MF,
                           LocalizedSetVecT &LocalizedInstrs);
diff --git a/llvm/lib/CodeGen/GlobalISel/Localizer.cpp b/llvm/lib/CodeGen/GlobalISel/Localizer.cpp
--- a/llvm/lib/CodeGen/GlobalISel/Localizer.cpp
+++ b/llvm/lib/CodeGen/GlobalISel/Localizer.cpp
@@ -11,6 +11,7 @@
 
 #include "llvm/CodeGen/GlobalISel/Localizer.h"
 #include "llvm/ADT/DenseMap.h"
+#include "llvm/ADT/STLExtras.h"
 #include "llvm/Analysis/TargetTransformInfo.h"
 #include "llvm/CodeGen/MachineRegisterInfo.h"
 #include "llvm/CodeGen/TargetLowering.h"
@@ -56,6 +57,20 @@
   return InsertMBB == Def.getParent();
 }
 
+bool Localizer::isNonUniquePhiValue(MachineOperand &Op) const {
+  MachineInstr *MI = Op.getParent();
+  if (!MI->isPHI())
+    return false;
+
+  Register SrcReg = Op.getReg();
+  for (unsigned Idx = 1; Idx < MI->getNumOperands(); Idx += 2) {
+    auto &MO = MI->getOperand(Idx);
+    if (&MO != &Op && MO.isReg() && MO.getReg() == SrcReg)
+      return true;
+  }
+  return false;
+}
+
 bool Localizer::localizeInterBlock(MachineFunction &MF,
                                    LocalizedSetVecT &LocalizedInstrs) {
   bool Changed = false;
@@ -93,6 +108,14 @@
         LocalizedInstrs.insert(&MI);
         continue;
       }
+
+      // If the use is a phi operand that's not unique, don't try to localize.
+      // If we do, we can cause unnecessary instruction bloat by duplicating
+      // into each predecessor block, when the existing one is sufficient and
+      // allows for easier optimization later.
+      if (isNonUniquePhiValue(MOUse))
+        continue;
+
       LLVM_DEBUG(dbgs() << "Fixing non-local use\n");
       Changed = true;
       auto MBBAndReg = std::make_pair(InsertMBB, Reg);
diff --git a/llvm/test/CodeGen/AArch64/GlobalISel/localizer.mir b/llvm/test/CodeGen/AArch64/GlobalISel/localizer.mir
--- a/llvm/test/CodeGen/AArch64/GlobalISel/localizer.mir
+++ b/llvm/test/CodeGen/AArch64/GlobalISel/localizer.mir
@@ -56,7 +56,7 @@
 
   define void @test_inttoptr() { ret void }
   define void @many_local_use_intra_block() { ret void }
-
+  define void @non_local_phi_use_nonunique() { ret void }
 ...
 
 ---
@@ -564,3 +564,45 @@
     %6:gpr(s32) = G_ADD %0, %0
     %7:gpr(s32) = G_ADD %1, %1
 ...
+
+---
+name:            non_local_phi_use_nonunique
+legalized:       true
+regBankSelected: true
+tracksRegLiveness: true
+body:             |
+  ; CHECK-LABEL: name: non_local_phi_use_nonunique
+  ; CHECK: bb.0:
+  ; CHECK:   successors: %bb.1(0x40000000), %bb.2(0x40000000)
+  ; CHECK:   [[C:%[0-9]+]]:gpr(s32) = G_CONSTANT i32 1
+  ; CHECK:   [[ADD:%[0-9]+]]:gpr(s32) = G_ADD [[C]], [[C]]
+  ; CHECK:   %cmp:gpr(s32) = G_ICMP intpred(eq), [[ADD]](s32), [[C]]
+  ; CHECK:   %cond:gpr(s1) = G_TRUNC %cmp(s32)
+  ; CHECK:   G_BRCOND %cond(s1), %bb.1
+  ; CHECK:   G_BR %bb.2
+  ; CHECK: bb.1:
+  ; CHECK:   successors: %bb.2(0x80000000)
+  ; CHECK: bb.2:
+  ; CHECK:   [[PHI:%[0-9]+]]:gpr(s32) = G_PHI [[C]](s32), %bb.1
+  ; CHECK:   [[ADD1:%[0-9]+]]:gpr(s32) = G_ADD [[PHI]], [[PHI]]
+
+  ; Don't localize the 1 into bb.1, because there are multiple edges
+  ; using that register.
+
+  bb.0:
+    successors: %bb.1, %bb.2
+
+    %0:gpr(s32) = G_CONSTANT i32 1
+    %1:gpr(s32) = G_ADD %0, %0
+    %cmp:gpr(s32) = G_ICMP intpred(eq), %1(s32), %0
+    %cond:gpr(s1) = G_TRUNC %cmp(s32)
+    G_BRCOND %cond(s1), %bb.1
+    G_BR %bb.2
+
+  bb.1:
+    successors: %bb.2
+
+  bb.2:
+    %3:gpr(s32) = G_PHI %0(s32), %bb.1, %0(s32), %bb.0
+    %2:gpr(s32) = G_ADD %3, %3
+...