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..89c166ce7476db802dc31129c9c6910b06b435d7 100644
--- a/runtime/vm/intermediate_language_arm.cc
+++ b/runtime/vm/intermediate_language_arm.cc
@@ -6221,8 +6221,10 @@ 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));

[regis, 2015/10/06 17:37:24]

The fix looks good if the constant right shift amount can really be >= 64.

[Florian Schneider, 2015/10/07 09:44:11]

Yes, the regression test shows that this can be the case. The result of such an
operation is either 0 or -1, so no need to deoptimize.

           }
           __ Asr(out_hi, left_hi, Operand(31));
         }