sparc: Pull most of the Nop format out of the ISA description.

The Nop format mostly just made instructions that inherited from the
Nop base class but with different mnemonics, so there doesn't need
to be very much dynamic content.

Change-Id: I1cf5e25ca8372f9b71f56d49756879c7545c9f6c
Reviewed-on: https://gem5-review.googlesource.com/5462
Reviewed-by: Gabe Black <gabeblack@google.com>
Maintainer: Gabe Black <gabeblack@google.com>

alpha,arm,mips,power,riscv,sparc,x86: Merge exec decl templates.

In the ISA instruction definitions, some classes were declared with
execute, etc., functions outside of the main template because they
had CPU specific signatures and would need to be duplicated with
each CPU plugged into them. Now that the instructions always just
use an ExecContext, there's no reason for those templates to be
separate. This change folds those templates together.

Change-Id: I13bda247d3d1cc07c0ea06968e48aa5b4aace7fa
Reviewed-on: https://gem5-review.googlesource.com/5401
Reviewed-by: Andreas Sandberg <andreas.sandberg@arm.com>
Reviewed-by: Alec Roelke <ar4jc@virginia.edu>
Maintainer: Andreas Sandberg <andreas.sandberg@arm.com>

alpha,arm,mips,power,riscv,sparc,x86,isa: De-specialize ExecContexts.

The ISA parser used to generate different copies of exec functions
for each exec context class a particular CPU wanted to use. That's
since been changed so that those functions take a pointer to the base
ExecContext, so the code which would generate those extra functions
can be removed, and some functions which used to be templated on an
ExecContext subclass can be untemplated, or minimally less templated.

Now that some functions aren't going to be instantiated multiple times
with different signatures, there are also opportunities to collapse
templates and make many instruction definitions simpler within the
parser. Since those changes will be less mechanical, they're left for
later changes and will probably be done in smaller increments.

Change-Id: I0015307bb02dfb9c60380b56d2a820f12169ebea
Reviewed-on: https://gem5-review.googlesource.com/5381
Reviewed-by: Andreas Sandberg <andreas.sandberg@arm.com>
Maintainer: Andreas Sandberg <andreas.sandberg@arm.com>

arch: teach ISA parser how to split code across files

This patch encompasses several interrelated and interdependent changes
to the ISA generation step. The end goal is to reduce the size of the
generated compilation units for instruction execution and decoding so
that batch compilation can proceed with all CPUs active without
exhausting physical memory.

The ISA parser (src/arch/isa_parser.py) has been improved so that it can
accept 'split [output_type];' directives at the top level of the grammar
and 'split(output_type)' python calls within 'exec {{ ... }}' blocks.
This has the effect of "splitting" the files into smaller compilation
units. I use air-quotes around "splitting" because the files themselves
are not split, but preprocessing directives are inserted to have the same
effect.

Architecturally, the ISA parser has had some changes in how it works.
In general, it emits code sooner. It doesn't generate per-CPU files,
and instead defers to the C preprocessor to create the duplicate copies
for each CPU type. Likewise there are more files emitted and the C
preprocessor does more substitution that used to be done by the ISA parser.

Finally, the build system (SCons) needs to be able to cope with a
dynamic list of source files coming out of the ISA parser. The changes
to the SCons{cript,truct} files support this. In broad strokes, the
targets requested on the command line are hidden from SCons until all
the build dependencies are determined, otherwise it would try, realize
it can't reach the goal, and terminate in failure. Since build steps
(i.e. running the ISA parser) must be taken to determine the file list,
several new build stages have been inserted at the very start of the
build. First, the build dependencies from the ISA parser will be emitted
to arch/$ISA/generated/inc.d, which is then read by a new SCons builder
to finalize the dependencies. (Once inc.d exists, the ISA parser will not
need to be run to complete this step.) Once the dependencies are known,
the 'Environments' are made by the makeEnv() function. This function used
to be called before the build began but now happens during the build.
It is easy to see that this step is quite slow; this is a known issue
and it's important to realize that it was already slow, but there was
no obvious cause to attribute it to since nothing was displayed to the
terminal. Since new steps that used to be performed serially are now in a
potentially-parallel build phase, the pathname handling in the SCons scripts
has been tightened up to deal with chdir() race conditions. In general,
pathnames are computed earlier and more likely to be stored, passed around,
and processed as absolute paths rather than relative paths. In the end,
some of these issues had to be fixed by inserting serializing dependencies
in the build.

Minor note:
For the null ISA, we just provide a dummy inc.d so SCons is never
compelled to try to generate it. While it seems slightly wrong to have
anything in src/arch/*/generated (i.e. a non-generated 'generated' file),
it's by far the simplest solution.

SPARC: Clean up some historical style issues.

SPARC: Make nops have the IsNop flag set.
In O3, a nop is used to carry faults down the pipeline that didn't originate
from an instruction. If the instruction doesn't do anything, that is just
returns NoFault, but doesn't have IsNop set, the NoFault will overwrite the
fault that's being sent down and nothing will happen.

Changes to the isa_parser and affected files to fix an indexing problem with split execute instructions and miscregs aliasing with integer registers.

src/arch/isa_parser.py:
Rearranged things so that classes with more than one execute function treat operands properly.
1. Eliminated the CodeBlock class
2. Created a SubOperandList
3. Redefined how InstObjParams is constructed

To define an InstObjParam, you can either pass in a single code literal which will be named "code", or you can pass in a dictionary of code snippets which will be substituted into the Templates. In order to get this to work, there is a new restriction that each template has only one function in it. These changes should only affect memory instructions which have regular and split execute functions.

Also changed the MiscRegs so that they use the instrunctions srcReg and destReg arrays.
src/arch/sparc/isa/formats/basic.isa:
src/arch/sparc/isa/formats/branch.isa:
src/arch/sparc/isa/formats/integerop.isa:
src/arch/sparc/isa/formats/mem/basicmem.isa:
src/arch/sparc/isa/formats/mem/blockmem.isa:
src/arch/sparc/isa/formats/mem/util.isa:
src/arch/sparc/isa/formats/nop.isa:
src/arch/sparc/isa/formats/priv.isa:
src/arch/sparc/isa/formats/trap.isa:
Rearranged to work with new InstObjParam scheme.
src/cpu/o3/sparc/dyn_inst.hh:
Added functions to access the miscregs using the indexes from instructions srcReg and destReg arrays. Also changed the names of the other accessors so that they have the suffix "Operand" if they use those arrays.
src/cpu/simple/base.hh:
Added functions to access the miscregs using the indexes from instructions srcReg and destReg arrays.

Fix to SPARC Nop class for multiple CPU models.

src/arch/sparc/isa/formats/nop.isa:
Fix nop header so we can compile with multiple CPU models.
(Former code re-defined Nop object for each model.)

New directory structure:
- simulator source now in 'src' subdirectory
- imported files from 'ext' repository
- support building in arbitrary places, including
outside of the source tree. See comment at top
of SConstruct file for more details.
Regression tests are temporarily disabled; that
syetem needs more extensive revisions.

SConstruct:
Update for new directory structure.
Modify to support build trees that are not subdirectories
of the source tree. See comment at top of file for
more details.
Regression tests are temporarily disabled.
src/arch/SConscript:
src/arch/isa_parser.py:
src/python/SConscript:
Update for new directory structure.