Index: lib/Target/ARM/ARMCallingConv.td
===================================================================
--- lib/Target/ARM/ARMCallingConv.td
+++ lib/Target/ARM/ARMCallingConv.td
@@ -142,6 +142,9 @@
   // Handles byval parameters.
   CCIfByVal<CCPassByVal<4, 4>>,
 
+  // The 'nest' parameter, if any, is passed in R12.
+  CCIfNest<CCAssignToReg<[R12]>>,
+
   // Handle all vector types as either f64 or v2f64.
   CCIfType<[v1i64, v2i32, v4i16, v8i8, v2f32], CCBitConvertToType<f64>>,
   CCIfType<[v2i64, v4i32, v8i16, v16i8, v4f32], CCBitConvertToType<v2f64>>,
Index: test/CodeGen/ARM/nest-register.ll
===================================================================
--- /dev/null
+++ test/CodeGen/ARM/nest-register.ll
@@ -0,0 +1,21 @@
+; RUN: llc -mtriple=arm-eabi %s -o - | FileCheck %s
+
+; Tests that the 'nest' parameter attribute causes the relevant parameter to be
+; passed in the right register.
+
+define i8* @nest_receiver(i8* nest %arg) nounwind {
+; CHECK-LABEL: nest_receiver:
+; CHECK: @ BB#0:
+; CHECK-NEXT: mov r0, r12
+; CHECK-NEXT: mov pc, lr
+        ret i8* %arg
+}
+
+define i8* @nest_caller(i8* %arg) nounwind {
+; CHECK-LABEL: nest_caller:
+; CHECK: mov r12, r0
+; CHECK-NEXT: bl nest_receiver
+; CHECK: mov pc, lr
+        %result = call i8* @nest_receiver(i8* nest %arg)
+        ret i8* %result
+}