Following discussions in #110443, and the following earlier discussions
in https://lists.llvm.org/pipermail/llvm-dev/2017-October/117907.html,
https://reviews.llvm.org/D38482, https://reviews.llvm.org/D38489, this
PR attempts to overhaul the `TargetMachine` and `LLVMTargetMachine`
interface classes. More specifically:
1. Makes `TargetMachine` the only class implemented under
`TargetMachine.h` in the `Target` library.
2. `TargetMachine` contains target-specific interface functions that
relate to IR/CodeGen/MC constructs, whereas before (at least on paper)
it was supposed to have only IR/MC constructs. Any Target that doesn't
want to use the independent code generator simply does not implement
them, and returns either `false` or `nullptr`.
3. Renames `LLVMTargetMachine` to `CodeGenCommonTMImpl`. This renaming
aims to make the purpose of `LLVMTargetMachine` clearer. Its interface
was moved under the CodeGen library, to further emphasis its usage in
Targets that use CodeGen directly.
4. Makes `TargetMachine` the only interface used across LLVM and its
projects. With these changes, `CodeGenCommonTMImpl` is simply a set of
shared function implementations of `TargetMachine`, and CodeGen users
don't need to static cast to `LLVMTargetMachine` every time they need a
CodeGen-specific feature of the `TargetMachine`.
5. More importantly, does not change any requirements regarding library
linking.

cc @arsenm @aeubanks

This will make it easy for callers to see issues with and fix up calls
to createTargetMachine after a future change to the params of
TargetMachine.

This matches other nearby enums.

For downstream users, this should be a fairly straightforward
replacement,
e.g. s/CodeGenOpt::Aggressive/CodeGenOptLevel::Aggressive
or s/CGFT_/CodeGenFileType::

All hardware address spaces on AVR can be freely cast between (they keep
the same bit pattern). They just aren't dereferenceable when they're in
a different address space as they really do point to a separate address
space.

This is supported in avr-gcc: https://godbolt.org/z/9Gfvhnhv9

avr-gcc also supports the `__memx` address space which is 24 bits. We
don't support this address space yet but I've added a safeguard just in
case.

Differential Revison: https://reviews.llvm.org/D142107

This fixes what I consider to be an API flaw I've tripped over
multiple times. The point this is constructed isn't well defined, so
depending on where this is first called, you can conclude different
information based on the MachineFunction. For example, the AMDGPU
implementation inspected the MachineFrameInfo on construction for the
stack objects and if the frame has calls. This kind of worked in
SelectionDAG which visited all allocas up front, but broke in
GlobalISel which hasn't visited any of the IR when arguments are
lowered.

I've run into similar problems before with the MIR parser and trying
to make use of other MachineFunction fields, so I think it's best to
just categorically disallow dependency on the MachineFunction state in
the constructor and to always construct this at the same time as the
MachineFunction itself.

A missing feature I still could use is a way to access an custom
analysis pass on the IR here.

The current inconsistency confuse contributors which coding guidlines to follow.
It would be better to have it consistent using clang-format tool.

Reviewed By: mhjacobson

Differential Revision: https://reviews.llvm.org/D109270

Reviewed By: mhjacobson, benshi001

Differential Revision: https://reviews.llvm.org/D107853

to reflect the new license.

We understand that people may be surprised that we're moving the header
entirely to discuss the new license. We checked this carefully with the
Foundation's lawyer and we believe this is the correct approach.

Essentially, all code in the project is now made available by the LLVM
project under our new license, so you will see that the license headers
include that license only. Some of our contributors have contributed
code under our old license, and accordingly, we have retained a copy of
our old license notice in the top-level files in each project and
repository.

llvm-svn: 351636

Reverting to investigate layering effects of MCJIT not linking
libCodeGen but using TargetMachine::getNameWithPrefix() breaking the
lldb bots.

This reverts commit r315633.

llvm-svn: 315637