VM: Support phis with pair representations.

runtime/vm/intermediate_language_arm.cc

Index: runtime/vm/intermediate_language_arm.cc
diff --git a/runtime/vm/intermediate_language_arm.cc b/runtime/vm/intermediate_language_arm.cc
index 026d0ed938dd24e31d6e6318895c900dd38f3d84..06f3988208f34eb2d517a5903c0c695df63b68f6 100644
--- a/runtime/vm/intermediate_language_arm.cc
+++ b/runtime/vm/intermediate_language_arm.cc
@@ -6221,14 +6221,17 @@ void ShiftMintOpInstr::EmitNativeCode(FlowGraphCompiler* compiler) {
         } else {
           if (shift == 32) {
             __ mov(out_lo, Operand(left_hi));
-          } else {
+          } else if (shift < 64) {
             __ Asr(out_lo, left_hi, Operand(shift - 32));
+          } else {
+            __ Asr(out_lo, left_hi, Operand(31));
           }
           __ Asr(out_hi, left_hi, Operand(31));
         }
         break;
       }
       case Token::kSHL: {
+        ASSERT(shift < 64);
         if (shift < 32) {
           __ Lsr(out_hi, left_lo, Operand(32 - shift));
           __ orr(out_hi, out_hi, Operand(left_hi, LSL, shift));