Index: lib/CodeGen/LiveRegUnits.cpp
===================================================================
--- lib/CodeGen/LiveRegUnits.cpp
+++ lib/CodeGen/LiveRegUnits.cpp
@@ -130,8 +130,9 @@
     // To get the live-outs we simply merge the live-ins of all successors.
     for (const MachineBasicBlock *Succ : MBB.successors())
       addBlockLiveIns(*this, *Succ);
-  } else if (MBB.isReturnBlock()) {
-    // For the return block: Add all callee saved registers.
+  } else if (MBB.isReturnBlock() || !MF.getFunction().doesNotThrow()) {
+    // For the return block, or a block whose end should be unreachable in a
+    // function which might throw: Add all callee saved registers.
     const MachineFrameInfo &MFI = MF.getFrameInfo();
     if (MFI.isCalleeSavedInfoValid())
       addCalleeSavedRegs(*this, MF);
Index: test/CodeGen/ARM/register-scavenger-exceptions.mir
===================================================================
--- /dev/null
+++ test/CodeGen/ARM/register-scavenger-exceptions.mir
@@ -0,0 +1,85 @@
+# RUN: llc -o - %s -run-pass=prologepilog | FileCheck %s
+
+--- |
+  target datalayout = "e-m:e-p:32:32-i64:64-v128:64:128-a:0:32-n32-S64"
+  target triple = "armv7--none-eabi"
+
+  define hidden void @_Z3foov(i32 %P0, ...) {
+  entry:
+    %V1 = alloca [4075 x i8], align 8
+    %tmp3 = alloca i8, i32 undef, align 8
+    unreachable
+  }
+
+  define hidden void @_Z3bazv(i32 %P0, ...) nounwind {
+  entry:
+    %V1 = alloca [4075 x i8], align 8
+    %tmp3 = alloca i8, i32 undef, align 8
+    unreachable
+  }
+
+  declare dso_local void @_Z3barv() noreturn
+  declare dso_local i8* @__cxa_allocate_exception(i32)
+  declare dso_local void @__cxa_throw(i8*, i8*, i8*)
+
+...
+---
+# Check that the register scavenger does pick r5 (not preserved in prolog) for
+# materialising a stack frame address when the function ends in throwing an
+# exception.
+# CHECK: $sp = frame-setup STMDB_UPD $sp, 14, $noreg, killed $r4, killed $r10, killed $r11, killed $lr
+# CHECK-NOT: $r5
+name:            _Z3foov
+stack:
+  - { id: 0, name: V1, type: default, offset: 0, size: 5000, alignment: 8,
+      stack-id: 0, callee-saved-register: '', callee-saved-restored: true,
+      local-offset: -4080, debug-info-variable: '', debug-info-expression: '',
+      debug-info-location: '' }
+  - { id: 1, name: tmp3, type: variable-sized, offset: 0, alignment: 1,
+      stack-id: 0, callee-saved-register: '', callee-saved-restored: true,
+      local-offset: -4112, debug-info-variable: '', debug-info-expression: '',
+      debug-info-location: '' }
+  - { id: 2, name: '', type: spill-slot, offset: 0, size: 4, alignment: 4,
+      stack-id: 0, callee-saved-register: '', callee-saved-restored: true,
+      debug-info-variable: '', debug-info-expression: '', debug-info-location: '' }
+body:             |
+  bb.0.entry:
+
+    $r0 = MOVi 0, 14, $noreg, $noreg
+    $r1 = MOVi 0, 14, $noreg, $noreg
+    $r2 = MOVi 0, 14, $noreg, $noreg
+    $r3 = MOVi 0, 14, $noreg, $noreg
+    $r4 = MOVi 0, 14, $noreg, $noreg
+    STRi12 killed $lr, %stack.2, 0, 14, $noreg :: (store 4 into %stack.2)
+    BL @_Z3barv, csr_aapcs, implicit-def dead $lr, implicit $sp, implicit killed $r0, implicit killed $r1, implicit killed $r2, implicit killed $r3, implicit killed $r4, implicit-def $sp
+
+...
+# In a nounwind function, we can use non-saved registers in blocks with
+# unreachable ends.
+# CHECK: $sp = frame-setup STMDB_UPD $sp, 14, $noreg, killed $r4, killed $r10, killed $r11, killed $lr
+# CHECK: $r5 = SUBri killed $r11, 4096
+name:            _Z3bazv
+stack:
+  - { id: 0, name: V1, type: default, offset: 0, size: 5000, alignment: 8,
+      stack-id: 0, callee-saved-register: '', callee-saved-restored: true,
+      local-offset: -4080, debug-info-variable: '', debug-info-expression: '',
+      debug-info-location: '' }
+  - { id: 1, name: tmp3, type: variable-sized, offset: 0, alignment: 1,
+      stack-id: 0, callee-saved-register: '', callee-saved-restored: true,
+      local-offset: -4112, debug-info-variable: '', debug-info-expression: '',
+      debug-info-location: '' }
+  - { id: 2, name: '', type: spill-slot, offset: 0, size: 4, alignment: 4,
+      stack-id: 0, callee-saved-register: '', callee-saved-restored: true,
+      debug-info-variable: '', debug-info-expression: '', debug-info-location: '' }
+body:             |
+  bb.0.entry:
+
+    $r0 = MOVi 0, 14, $noreg, $noreg
+    $r1 = MOVi 0, 14, $noreg, $noreg
+    $r2 = MOVi 0, 14, $noreg, $noreg
+    $r3 = MOVi 0, 14, $noreg, $noreg
+    $r4 = MOVi 0, 14, $noreg, $noreg
+    STRi12 killed $lr, %stack.2, 0, 14, $noreg :: (store 4 into %stack.2)
+    BL @_Z3barv, csr_aapcs, implicit-def dead $lr, implicit $sp, implicit killed $r0, implicit killed $r1, implicit killed $r2, implicit killed $r3, implicit killed $r4, implicit-def $sp
+
+...