alpha,arm,mips,power,riscv,sparc,x86,cpu: Get rid of ISA_HAS_DELAY_SLOT.

This constant is, first, a #define, and second only used in one place.

In that one place, it appears that the code it guards is no longer
necessary in general. It was originally written to avoid refetching a
block of data that you're still in, even if you've moved slightly
farther in it because you're skipping the next instruction due to an
annulled branch delay slot. In reality however, in SPARC, the one ISA
I'm aware of which has this sort of branching behavior, the PC state
object will correctly determine that no branch is happening in these
cases. Code lower down in the loop will then recompute where fetching
should continue based on the next PC, automatically skipping the
annulled branch slot without misinterpretting the gap as a branch.

This change therefore also removes this block of code.

Change-Id: I820ebc9df10aeb4fcb69c12f6a784e9ec616743c
Reviewed-on: https://gem5-review.googlesource.com/6821
Reviewed-by: Andreas Sandberg <andreas.sandberg@arm.com>
Maintainer: Andreas Sandberg <andreas.sandberg@arm.com>

alpha,arm,mips,power,riscv,sparc,x86: Get rid of TheISA::NoopMachInst.

It's no longer used.

Change-Id: I4a71bcb214f1bb186b92ef50841eca635e6701c5
Reviewed-on: https://gem5-review.googlesource.com/6826
Reviewed-by: Gabe Black <gabeblack@google.com>
Maintainer: Gabe Black <gabeblack@google.com>

arch: Cleanup unused ISA traits constants

This patch prunes unused values, and also unifies how the values are
defined (not using an enum for ALPHA), aligning the use of int vs Addr
etc.

The patch also removes the duplication of PageBytes/PageShift and
VMPageSize/LogVMPageSize. For all ISAs the two pairs had identical
values and the latter has been removed.

ISA: generic Linux thread info support

This patch takes the Linux thread info support scattered across
different ISA implementations (currently in ARM, ALPHA, and MIPS), and
unifies them into a single file.

Adds a few more helper functions to read out TGID, mm, etc.

ISA-specific information (e.g., ALPHA PCBB register) is now moved to
the corresponding isa_traits.hh files.

ISA: Back-out NoopMachInst as a StaticInstPtr change.

ISA: Turn the ExtMachInst NoopMachinst into the StaticInstPtr NoopStaticInst.

This eliminates a use of the ExtMachInst type outside of the ISAs.

StaticInst: Merge StaticInst and StaticInstBase.

Having two StaticInst classes, one nominally ISA dependent and the other ISA
dependent, has not been historically useful and makes the StaticInst class
more complicated that it needs to be. This change merges StaticInstBase into
StaticInst.

Make commenting on close namespace brackets consistent.

Ran all the source files through 'perl -pi' with this script:

s|\s*(};?\s*)?/\*\s*(end\s*)?namespace\s*(\S+)\s*\*/(\s*})?|} // namespace $3|;
s|\s*};?\s*//\s*(end\s*)?namespace\s*(\S+)\s*|} // namespace $2\n|;
s|\s*};?\s*//\s*(\S+)\s*namespace\s*|} // namespace $1\n|;

Also did a little manual editing on some of the arch/*/isa_traits.hh files
and src/SConscript.

O3PCU: Split loads and stores that cross cache line boundaries.

When each load or store is sent to the LSQ, we check whether it will cross a
cache line boundary and, if so, split it in two. This creates two TLB
translations and two memory requests. Care has to be taken if the first
packet of a split load is sent but the second blocks the cache. Similarly,
for a store, if the first packet cannot be sent, we must store the second
one somewhere to retry later.

This modifies the LSQSenderState class to record both packets in a split
load or store.

Finally, a new const variable, HasUnalignedMemAcc, is added to each ISA
to indicate whether unaligned memory accesses are allowed. This is used
throughout the changed code so that compiler can optimise away code dealing
with split requests for ISAs that don't need them.

POWER: Add support for the Power ISA

This adds support for the 32-bit, big endian Power ISA. This supports both
integer and floating point instructions based on the Power ISA Book I v2.06.