riscv,x86: Stop using the arch Nop machine instruction unnecessarily.

That particular ExtMachInst is a convenient placeholder, but a value
of 0 in RISCV or a static uninitialized ExtMachInst (which will
therefore be all zeroes) on x86 works just as well, and removes the
need for an ISA specific constant.

Also, the idea of a universal Nop doesn't always make sense since it
could be that what, exactly, doesn't do anything depends on context
which would be lost on a constant value of an ExtMachInst. For
instance, the value of an ExtMachInst that makes sense might depend on
what mode the CPU was in, etc.

Change-Id: I1f1a43a5c607a667e11b79bcf6e059e4f7141b3f
Reviewed-on: https://gem5-review.googlesource.com/6825
Reviewed-by: Gabe Black <gabeblack@google.com>
Reviewed-by: Alec Roelke <ar4jc@virginia.edu>
Maintainer: Gabe Black <gabeblack@google.com>

style: remove trailing whitespace

Result of running 'hg m5style --skip-all --fix-white -a'.

GCC: Get everything working with gcc 4.6.1.

And by "everything" I mean all the quick regressions.

X86: Consolidate extra microop flags into one parameter.

This single parameter replaces the collection of bools that set up various
flavors of microops. A flag parameter also allows other flags to be set like
the serialize before/after flags, etc., without having to change the
constructor.

X86: Get rid of the unused getAllocator on the python base microop class.

This function is always overridden, and doesn't actually have the right
signature.

copyright: Change HP copyright on x86 code to be more friendly

X86: Take limitted advantage of the compilers type checking for microop operands.

X86: Autogenerate macroop generateDisassemble function.

X86: Set the delayed commit flag in x86 microops appropriately.

X86: Create a handy way to access labels from the ROM in microcode.

X86: Make X86's microcode ROM actually do something.

X86: Move the fp microops to their own file with their own base classes in C++ and python.

X86: Major rework of how regop microops are generated.
The new implementation uses metaclass, and gives a lot more precise control
with a lot less verbosity. The flags/no flags reg/imm variants are all handled
by the same python class now which supplies a constructor to the right C++
class based on context.

Pull some hard coded base classes out of the isa description.

Move load/store microops into their own file. They still don't do anything, though.

Make microOp vs microop and macroOp vs macroop capitilization consistent.

src/arch/x86/isa/macroop.isa:
Make microOp vs microop and macroOp vs macroop capitilization consistent. Also fill out the emulation environment handling a little more, and use an object to pass around output code.
src/arch/x86/isa/microops/base.isa:
Make microOp vs microop and macroOp vs macroop capitilization consistent. Also adjust python to C++ bool translation.

Fix the formatting on a comment.

Make limm (load immediate) microop

Reworking x86's microcode system. This is a work in progress, and X86 doesn't compile.

src/arch/x86/isa/decoder/one_byte_opcodes.isa:
src/arch/x86/isa/macroop.isa:
src/arch/x86/isa/main.isa:
src/arch/x86/isa/microasm.isa:
src/arch/x86/isa/microops/base.isa:
src/arch/x86/isa/microops/microops.isa:
src/arch/x86/isa/operands.isa:
src/arch/x86/isa/microops/regop.isa:
src/arch/x86/isa/microops/specop.isa:
Reworking x86's microcode system

Reworked x86 a bit

Consolidated the microcode assembler to help separate it from more x86-centric stuff.

Refactored the x86 isa description some more. There should be more seperation between x86 specific parts, and those parts which are implemented in the isa description but could eventually be moved elsewhere.

The process of going from an instruction definition to an instruction to be returned by the decoder has been fleshed out more. The following steps describe how an instruction implementation becomes a StaticInst.

1. Microops are created. These are StaticInsts use templates to provide a basic form of polymorphism without having to make the microassembler smarter.
2. An instruction class is created which has a "templated" microcode program as it's docstring. The template parameters are refernced with ^ following by a number.
3. An instruction in the decoder references an instruction template using it's mnemonic. The parameters to it's format end up replacing the placeholders. These parameters describe a source for an operand which could be memory, a register, or an immediate. It it's a register, the register index is used. If it's memory, eventually a load/store will be pre/postpended to the instruction template and it's destination register will be used in place of the ^. If it's an immediate, the immediate is used. Some operand types, specifically those that come from the ModRM byte, need to be decoded further into memory vs. register versions. This is accomplished by making the decode_block text for these instructions another case statement based off ModRM.
4. Once all of the template parameters have been handled, the instruction goes throw the microcode assembler which resolves labels and creates a list of python op objects. If an operand is a register, it uses a % prefix, an immediate uses $, and a label uses @. If the operand is just letters, numbers, and underscores, it can appear immediately after the prefix. If it's not, it can be encolsed in non nested {}s.
5. If there is a single "op" object (which corresponds to a single microop) the decoder is set up to return it directly. If not, a macroop wrapper is created around it.

In the future, I'm considering seperating the operand type specialization from the template substitution step. A problem this introduces is that either the template arguments need to be kept around for the specialization step, or they need to be re-extracted. Re-extraction might be the way to go so that the operand formats can be coded directly into the micro assembler template without having to pass them in as parameters. I don't know if that's actually useful, though.

src/arch/x86/isa/decoder/one_byte_opcodes.isa:
src/arch/x86/isa/microasm.isa:
src/arch/x86/isa/microops/microops.isa:
src/arch/x86/isa/operands.isa:
src/arch/x86/isa/microops/base.isa:
Implemented polymorphic microops and changed around the microcode assembler syntax.