X64: Make all arithmetic ops, and a few other, try to avoid rsp and r12 as base register.

src/x64/assembler-x64.h

Index: src/x64/assembler-x64.h
diff --git a/src/x64/assembler-x64.h b/src/x64/assembler-x64.h
index 0f06c3c448c4ca5d93f9ec522f9f0e68a07fa445..b55a7b72631046bdf442cbcf36374b34acea2f80 100644
--- a/src/x64/assembler-x64.h
+++ b/src/x64/assembler-x64.h
@@ -567,11 +567,7 @@ class Assembler : public Malloced {
 
   // Arithmetics
   void addl(Register dst, Register src) {
-    if (dst.low_bits() == 4) {  // Forces SIB byte.
-      arithmetic_op_32(0x01, src, dst);
-    } else {
-      arithmetic_op_32(0x03, dst, src);
-    }
+    arithmetic_op_32(0x03, dst, src);
   }
 
   void addl(Register dst, Immediate src) {
@@ -607,11 +603,7 @@ class Assembler : public Malloced {
   }
 
   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);
-    }
+    arithmetic_op_32(0x1b, dst, src);
   }
 
   void cmpb(Register dst, Immediate src) {