Index: lib/CodeGen/PeepholeOptimizer.cpp
===================================================================
--- lib/CodeGen/PeepholeOptimizer.cpp
+++ lib/CodeGen/PeepholeOptimizer.cpp
@@ -1111,7 +1111,8 @@
 getNewSource(MachineRegisterInfo *MRI, const TargetInstrInfo *TII,
              RegSubRegPair Def,
              const PeepholeOptimizer::RewriteMapTy &RewriteMap,
-             bool HandleMultipleSources = true) {
+             bool HandleMultipleSources = true,
+             bool Recursing = false) {
   RegSubRegPair LookupSrc(Def.Reg, Def.SubReg);
   while (true) {
     ValueTrackerResult Res = RewriteMap.lookup(LookupSrc);
@@ -1131,13 +1132,17 @@
     if (!HandleMultipleSources)
       break;
 
+    if (Recursing)
+      return LookupSrc;
+
     // Multiple sources, recurse into each source to find a new source
     // for it. Then, rewrite the PHI accordingly to its new edges.
     SmallVector<RegSubRegPair, 4> NewPHISrcs;
     for (unsigned i = 0; i < NumSrcs; ++i) {
       RegSubRegPair PHISrc(Res.getSrcReg(i), Res.getSrcSubReg(i));
       NewPHISrcs.push_back(
-          getNewSource(MRI, TII, PHISrc, RewriteMap, HandleMultipleSources));
+          getNewSource(MRI, TII, PHISrc, RewriteMap,
+                       HandleMultipleSources, true));
     }
 
     // Build the new PHI node and return its def register as the new source.
Index: test/CodeGen/AArch64/peephole-recursion.mir
===================================================================
--- /dev/null
+++ test/CodeGen/AArch64/peephole-recursion.mir
@@ -0,0 +1,134 @@
+# RUN: llc -o - %s -run-pass=peephole-opt | FileCheck %s
+# Make sure this doesn't crash
+# CHECK: COPY %r0
+
+--- |
+  target datalayout = "e-m:e-p:32:32-i64:64-v128:64:128-a:0:32-n32-S64"
+  target triple = "thumbv8--linux-gnueabi"
+  
+  define i32 @test() {
+  entry:
+    ret i32 0
+  }
+
+...
+---
+name:            test
+tracksRegLiveness: true
+body:             |
+  bb.0:
+    successors: %bb.2(0x80000000)
+    liveins: $r0
+
+    $0:rgpr = COPY $r0
+    t2B %bb.2, 14, $noreg
+  
+  bb.1:
+    successors: %bb.18(0x30000000), %bb.12(0x50000000)
+  
+    %7:rgpr = PHI $0, %bb.4, $10, %bb.2
+    t2CMPrr $0, $0, 14, $noreg, implicit-def $cpsr
+    t2Bcc %bb.18, 0, $cpsr
+    t2B %bb.12, 14, $noreg
+  
+  bb.2:
+    successors: %bb.1(0x30000000)
+  
+    $10:rgpr = PHI $0, %bb.0, $291, %bb.58
+    t2B %bb.1, 14, $noreg
+  
+  bb.4:
+    successors: %bb.1(0x7c000000)
+    t2B %bb.1, 14, $noreg
+  
+  bb.9:
+    %54:gpr = PHI $0, %bb.38, $271, %bb.59
+    %563:spr = VMOVSR %54, 14, $noreg
+    tBX_RET 14, $noreg
+  
+  bb.12:
+    successors: %bb.18(0x7c000000)
+  
+  bb.18:
+    successors: %bb.25(0x50000000)
+  
+    %91:rgpr = PHI $0, %bb.12, %7, %bb.1
+    t2B %bb.25, 14, $noreg
+  
+  bb.24:
+    successors: %bb.25(0x7c000000)
+    t2B %bb.25, 14, $noreg
+  
+  bb.25:
+    successors: %bb.26(0x50000000)
+    $127:rgpr = PHI $0, %bb.18, %91, %bb.24
+  
+  bb.26:
+    successors: %bb.32(0x7c000000)
+  
+    t2B %bb.32, 14, $noreg
+  
+  bb.31:
+    successors: %bb.32(0x7c000000)
+  
+  bb.32:
+    successors: %bb.39(0x50000000)
+    $163:rgpr = PHI $0, %bb.26, $127, %bb.31
+    t2B %bb.39, 14, $noreg
+  
+  bb.38:
+    successors: %bb.39(0x7c000000), %bb.9(0x04000000)
+  
+    t2CMPrr $0, $0, 14, $noreg, implicit-def $cpsr
+    t2Bcc %bb.9, 1, $cpsr
+  
+  bb.39:
+    successors: %bb.46(0x50000000)
+  
+    $199:rgpr = PHI $0, %bb.32, $163, %bb.38
+    t2B %bb.46, 14, $noreg
+  
+  bb.45:
+    successors: %bb.46(0x7c000000)
+  
+  bb.46:
+    successors: %bb.47(0x50000000)
+  
+    $235:rgpr = PHI $0, %bb.39, $199, %bb.45
+  
+  bb.47:
+    successors: %bb.53(0x7c000000)
+  
+    t2B %bb.53, 14, $noreg
+  
+  bb.52:
+    successors: %bb.53(0x7c000000)
+  
+  bb.53:
+    successors: %bb.59(0x30000000), %bb.54(0x50000000)
+  
+    $271:rgpr = PHI $0, %bb.47, $235, %bb.52
+    t2CMPrr $0, $0, 14, $noreg, implicit-def $cpsr
+    t2Bcc %bb.59, 0, $cpsr
+  
+  bb.54:
+    successors: %bb.57(0x40000000), %bb.58(0x40000000)
+  
+    t2CMPrr $0, $0, 14, $noreg, implicit-def $cpsr
+    t2Bcc %bb.58, 9, $cpsr
+  
+  bb.57:
+    successors: %bb.58(0x80000000)
+  
+  bb.58:
+    successors: %bb.2(0x7c000000)
+  
+    $291:gpr = PHI $271, %bb.54, $0, %bb.57
+    t2B %bb.2, 14, $noreg
+  
+  bb.59:
+    successors: %bb.9(0x04000000)
+  
+    t2B %bb.9, 14, $noreg
+
+...