Optionally use 31-bits SMI value for 64-bit system

src/x64/debug-x64.cc

Index: src/x64/debug-x64.cc
diff --git a/src/x64/debug-x64.cc b/src/x64/debug-x64.cc
index a337b0d052f7252ea1baa0e3b1d0bfe608fd87a7..8de11f256a3fdd04d3da56ceb40625c5dcbf1e39 100644
--- a/src/x64/debug-x64.cc
+++ b/src/x64/debug-x64.cc
@@ -127,11 +127,19 @@ static void Generate_DebugBreakCallHelper(MacroAssembler* masm,
       // Store the 64-bit value as two smis.
       if ((non_object_regs & (1 << r)) != 0) {
         __ movq(kScratchRegister, reg);
+#if !V8_USE_31_BITS_SMI_VALUE
         __ Integer32ToSmi(reg, reg);
         __ push(reg);
         __ sar(kScratchRegister, Immediate(32));
         __ Integer32ToSmi(kScratchRegister, kScratchRegister);
         __ push(kScratchRegister);
+#else
+        __ shr(reg, Immediate(63));
+        __ shll(reg, Immediate(1));
+        __ push(reg);
+        __ shl(kScratchRegister, Immediate(1));
+        __ push(kScratchRegister);
+#endif
       }
     }
 
@@ -157,11 +165,18 @@ static void Generate_DebugBreakCallHelper(MacroAssembler* masm,
       // Reconstruct the 64-bit value from two smis.
       if ((non_object_regs & (1 << r)) != 0) {
         __ pop(kScratchRegister);
+#if !V8_USE_31_BITS_SMI_VALUE
         __ SmiToInteger32(kScratchRegister, kScratchRegister);
         __ shl(kScratchRegister, Immediate(32));
         __ pop(reg);
         __ SmiToInteger32(reg, reg);
         __ or_(reg, kScratchRegister);
+#else
+        __ shr(kScratchRegister, Immediate(1));
+        __ pop(reg);
+        __ shl(reg, Immediate(62));
+        __ or_(reg, kScratchRegister);
+#endif
       }
     }