X86: Make fixed register operands ignore register index extensions from the REX prefix.

The only cases where this was the correct behavior are now handled with the
"B" operand type, and doing things this way was breaking some instructions,
notably a shift.

--HG--
extra : convert_revision : 072346d4f541edaceba7aecc26ba8d2cd756e481

src/arch/x86/isa/specialize.isa

@@ -138,9 +138,9 @@ let {{
                 #Figure out what to do with fixed register operands
                 #This is the index to use, so we should stick it some place.
                 if opType.reg in ("A", "B", "C", "D"):
-                    env.addReg("INTREG_R%sX | (REX_B << 3)" % opType.reg)
+                    env.addReg("INTREG_R%sX" % opType.reg)
                 else:
-                    env.addReg("INTREG_R%s | (REX_B << 3)" % opType.reg)
+                    env.addReg("INTREG_R%s" % opType.reg)
                 Name += "_R"
             elif opType.tag == "B":
                 # This refers to registers whose index is encoded as part of the opcode