X64: Made bit-fiddling fallback for double-to-int32 conversion.

src/x64/assembler-x64.h

 // Copyright (c) 1994-2006 Sun Microsystems Inc.
 // All Rights Reserved.
 //
 // Redistribution and use in source and binary forms, with or without
 // modification, are permitted provided that the following conditions are
 // met:
 //
 // - Redistributions of source code must retain the above copyright notice,
 // this list of conditions and the following disclaimer.
 //
@@ skipping 588 matching lines @@
   }
 
   void addq(Register dst, Immediate src) {
     immediate_arithmetic_op(0x0, dst, src);
   }
 
   void addq(const Operand& dst, Immediate src) {
     immediate_arithmetic_op(0x0, dst, src);
   }
 
+  void sbbl(Register dst, Register src) {
+    if (dst.low_bits() == 4) {  // Forces SIB byte if dst is base register.
+      arithmetic_op_32(0x19, src, dst);
+    } else {
+      arithmetic_op_32(0x1b, dst, src);
+    }
+  }
+
   void cmpb(Register dst, Immediate src) {
     immediate_arithmetic_op_8(0x7, dst, src);
   }
 
   void cmpb_al(Immediate src);
 
   void cmpb(Register dst, Register src) {
     arithmetic_op(0x3A, dst, src);
   }
 
@@ skipping 775 matching lines @@
  private:
   Assembler* assembler_;
 #ifdef DEBUG
   int space_before_;
 #endif
 };
 
 } }  // namespace v8::internal
 
 #endif  // V8_X64_ASSEMBLER_X64_H_