Revert "Use R0/R1 instead of R4/R5 for ARM eh_return return values"

lib/Target/ARM/ARMISelLowering.cpp

Index: lib/Target/ARM/ARMISelLowering.cpp
diff --git a/lib/Target/ARM/ARMISelLowering.cpp b/lib/Target/ARM/ARMISelLowering.cpp
index c516b42344df09c646939d1f12af2eafba038218..3e402d7a1c8e786381654e480b3d3385956c9eb5 100644
--- a/lib/Target/ARM/ARMISelLowering.cpp
+++ b/lib/Target/ARM/ARMISelLowering.cpp
@@ -765,16 +765,23 @@ ARMTargetLowering::ARMTargetLowering(const TargetMachine &TM,
   if (!Subtarget->isTargetMachO()) {
     // Non-MachO platforms may return values in these registers via the
     // personality function.
-    setExceptionPointerRegister(ARM::R0);
-    setExceptionSelectorRegister(ARM::R1);
-  }
+    // @LOCALMOD-START
+    if (Subtarget->isTargetNaCl()) {
+      // we use the first caller saved regs here
+      // c.f.: llvm-gcc/llvm-gcc-4.2/gcc/unwind-dw2.c::uw_install_context
+      // NOTE: these are related to the _Unwind_PNaClSetResult{0,1} functions
+      setExceptionPointerRegister(ARM::R4);
+      setExceptionSelectorRegister(ARM::R5);
+  
+      setOperationAction(ISD::FRAME_TO_ARGS_OFFSET, MVT::i32, Custom);
 
-  // @LOCALMOD-START
-  if (Subtarget->isTargetNaCl()) {
-    setOperationAction(ISD::FRAME_TO_ARGS_OFFSET, MVT::i32, Custom);
-    setOperationAction(ISD::EH_RETURN, MVT::Other, Custom);
+      setOperationAction(ISD::EH_RETURN, MVT::Other, Custom);
+    } else {
+      setExceptionPointerRegister(ARM::R0);
+      setExceptionSelectorRegister(ARM::R1);
+    }
+    // @LOCALMOD-END
   }
-  // @LOCALMOD-END
 
   if (Subtarget->getTargetTriple().isWindowsItaniumEnvironment())
     setOperationAction(ISD::DYNAMIC_STACKALLOC, MVT::i32, Custom);