VM: Support phis with pair representations.

runtime/vm/intermediate_language_mips.cc

Index: runtime/vm/intermediate_language_mips.cc
diff --git a/runtime/vm/intermediate_language_mips.cc b/runtime/vm/intermediate_language_mips.cc
index 15fc876447e14290bcace045e6ef32ca99e79471..e381157f3a995b98cecc9647d3c430bfebc5f310 100644
--- a/runtime/vm/intermediate_language_mips.cc
+++ b/runtime/vm/intermediate_language_mips.cc
@@ -4931,12 +4931,19 @@ void ShiftMintOpInstr::EmitNativeCode(FlowGraphCompiler* compiler) {
           __ or_(out_lo, out_lo, TMP);
           __ sra(out_hi, left_hi, shift);
         } else {
-          __ sra(out_lo, left_hi, shift - 32);
+          if (shift == 32) {
+            __ mov(out_lo, left_hi);
+          } else if (shift < 64) {
+            __ sra(out_lo, left_hi, shift - 32);
+          } else {
+            __ sra(out_lo, left_hi, 31);
+          }
           __ sra(out_hi, left_hi, 31);
         }
         break;
       }
       case Token::kSHL: {
+        ASSERT(shift < 64);
         if (shift < 32) {
           __ srl(out_hi, left_lo, 32 - shift);
           __ sll(TMP, left_hi, shift);