VM: Support phis with pair representations.

runtime/vm/intermediate_language_ia32.cc

Index: runtime/vm/intermediate_language_ia32.cc
diff --git a/runtime/vm/intermediate_language_ia32.cc b/runtime/vm/intermediate_language_ia32.cc
index e0bfb7f48534340d1b489a42a927445e74f2453b..d75867c357705ec4cc10110a54ae0e4fb90a53d2 100644
--- a/runtime/vm/intermediate_language_ia32.cc
+++ b/runtime/vm/intermediate_language_ia32.cc
@@ -6088,7 +6088,7 @@ void ShiftMintOpInstr::EmitNativeCode(FlowGraphCompiler* compiler) {
           __ movl(left_lo, left_hi);  // Shift by 32.
           __ sarl(left_hi, Immediate(31));  // Sign extend left hi.
           if (shift > 32) {
-            __ sarl(left_lo, Immediate(shift - 32));
+            __ sarl(left_lo, Immediate(shift > 63 ? 31 : shift - 32));
           }
         } else {
           __ shrdl(left_lo, left_hi, Immediate(shift));
@@ -6097,6 +6097,7 @@ void ShiftMintOpInstr::EmitNativeCode(FlowGraphCompiler* compiler) {
         break;
       }
       case Token::kSHL: {
+        ASSERT(shift < 64);
         if (can_overflow()) {
           Register temp1 = locs()->temp(0).reg();
           Register temp2 = locs()->temp(1).reg();