Fixed un-renamed CodeGenTargetMachineImpl Intheritances in Experimental Targets (#116290)

This PR fixes a set of build issues with experimental targets happened
in result of merging #111234 to mast

Fixed un-renamed CodeGenTargetMachineImpl Intheritances in Experimental Targets (#116290)

This PR fixes a set of build issues with experimental targets happened
in result of merging #111234 to master.

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Overhaul the TargetMachine and LLVMTargetMachine Classes (#111234)

Following discussions in #110443, and the following earlier discussions
in https://lists.llvm.org/pipermail/llvm-dev/2017-October/

Overhaul the TargetMachine and LLVMTargetMachine Classes (#111234)

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

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[MC] Forward declare ELFObjectWriter (#100989)

MCAssmembler: Move ELFHeaderEFlags to ELFObjectWriter

Now that MCELFStreamer can access ELFObjectWriter (commit
70c52b62c5669993e341664a63bfbe5245e32884), we can move ELFHeaderEFlags
there.

[MC] Make changeSection private

Using changeSection externally would cause `CurFrag` to be out of sync
of `SectionStack`. Remove some uses from MipsTargetStreamer.cpp.

[NC,MIPS] Avoid some registerSection calls

Similar to abbf3bce94e0848f746e39186d36ebb938c1c5de.

switchSection calls registerSection internally.

[Mips][NFC] Garbage collect unused code (#85499)

MIPS: fix emitDirectiveCpsetup on N32 (#80534)

In gas, .cpsetup may expand to one of two code sequences (one is related to `__gnu_local_gp`), depending on -mno-shared and -msym32.
Since Clang doesn

MIPS: fix emitDirectiveCpsetup on N32 (#80534)

In gas, .cpsetup may expand to one of two code sequences (one is related to `__gnu_local_gp`), depending on -mno-shared and -msym32.
Since Clang doesn't support -mno-shared or -msym32, .cpsetup expands to one code sequence.
The N32 condition incorrectly leads to the incorrect `__gnu_local_gp` code sequence.

```
00000000 <t1>:
0: ffbc0008 sd gp,8(sp)
4: 3c1c0000 lui gp,0x0
4: R_MIPS_HI16 __gnu_local_gp
8: 279c0000 addiu gp,gp,0
8: R_MIPS_LO16 __gnu_local_gp
```

Fixes: #52785

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Adjust includes in MCTargetDesc to avoid unnecessary CodeGen deps, NFC

These are small include-only changes in the X86, Mips, and SystemZ
backend that seem sufficiently small to commit separately wi

Adjust includes in MCTargetDesc to avoid unnecessary CodeGen deps, NFC

These are small include-only changes in the X86, Mips, and SystemZ
backend that seem sufficiently small to commit separately without
review.

See issue #64166 for more information about layering.

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Simplify with hasFeature. NFC

[NFC] Add helper method to ensure min alignment on MCSection

Follow up on D138653.

Differential Revision: https://reviews.llvm.org/D138686

[Alignment][NFC] Use Align in MCStreamer::emitValueToAlignment

Differential Revision: https://reviews.llvm.org/D138674

[Alignment][NFC] Use Align in MCStreamer::emitCodeAlignment

This patch makes code less readable but it will clean itself after all functions are converted.

Differential Revision: https://reviews.ll

[Alignment][NFC] Use Align in MCStreamer::emitCodeAlignment

This patch makes code less readable but it will clean itself after all functions are converted.

Differential Revision: https://reviews.llvm.org/D138665

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[reland][Alignment][NFC] Use the Align type in MCSection

Differential Revision: https://reviews.llvm.org/D138653

Revert D138653 [Alignment][NFC] Use the Align type in MCSection"

This breaks the bolt project.
This reverts commit 409f0dc4a420db1c6b259d5ae965a070c169d930.

[Alignment][NFC] Use the Align type in MCSection

Differential Revision: https://reviews.llvm.org/D138653

[MC] De-capitalize SwitchSection. NFC

Add SwitchSection to return switchSection. The API will be removed soon.

[MC] De-capitalize MCStreamer functions

Follow-up to c031378ce01b8485ba0ef486654bc9393c4ac024 .
The class is mostly consistent now.

[MIPS] Remove an incorrect microMIPS instruction alias

The microMIPS instruction set is compatible with the MIPS instruction
set at the assembly level but not in terms of encodings. `nop` in
microMI

[MIPS] Remove an incorrect microMIPS instruction alias

The microMIPS instruction set is compatible with the MIPS instruction
set at the assembly level but not in terms of encodings. `nop` in
microMIPS is a special case as it has the same encoding as `nop` for
MIPS.

Fix this error by reducing the usage of NOP in the MIPS backend such
that only that ISA correct variants are produced.

Differential Revision: https://reviews.llvm.org/D124716

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[MC] Fix letter case of some MCSection member functions

Cleanup LLVMMC headers

There's a few relevant forward declarations in there that may require downstream
adding explicit includes:

llvm/MC/MCContext.h no longer includes llvm/BinaryFormat/ELF.h, llv

Cleanup LLVMMC headers

There's a few relevant forward declarations in there that may require downstream
adding explicit includes:

llvm/MC/MCContext.h no longer includes llvm/BinaryFormat/ELF.h, llvm/MC/MCSubtargetInfo.h, llvm/MC/MCTargetOptions.h
llvm/MC/MCObjectStreamer.h no longer include llvm/MC/MCAssembler.h
llvm/MC/MCAssembler.h no longer includes llvm/MC/MCFixup.h, llvm/MC/MCFragment.h

Counting preprocessed lines required to rebuild llvm-project on my setup:
before: 1052436830
after: 1049293745

Which is significant and backs up the change in addition to the usual benefits of
decreasing coupling between headers and compilation units.

Discourse thread: https://discourse.llvm.org/t/include-what-you-use-include-cleanup
Differential Revision: https://reviews.llvm.org/D119244

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[MC] Add MCSubtargetInfo to MCAlignFragment

In preparation for passing the MCSubtargetInfo (STI) through to writeNops
so that it can use the STI in operation at the time, we need to record the
STI i

[MC] Add MCSubtargetInfo to MCAlignFragment

In preparation for passing the MCSubtargetInfo (STI) through to writeNops
so that it can use the STI in operation at the time, we need to record the
STI in operation when a MCAlignFragment may write nops as padding. The
STI is currently unused, a further patch will pass it through to
writeNops.

There are many places that can create an MCAlignFragment, in most cases
we can find out the STI in operation at the time. In a few places this
isn't possible as we are in initialisation or finalisation, or are
emitting constant pools. When possible I've tried to find the most
appropriate existing fragment to obtain the STI from, when none is
available use the per module STI.

For constant pools we don't actually need to use EmitCodeAlign as the
constant pools are data anyway so falling through into it via an
executable NOP is no better than falling through into data padding.

This is a prerequisite for D45962 which uses the STI to emit the
appropriate NOP for the STI. Which can differ per fragment.

Note that involves an interface change to InitSections. It is now
called initSections and requires a SubtargetInfo as a parameter.

Differential Revision: https://reviews.llvm.org/D45961

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[MC][ELF] Support for zero flag section groups

This change introduces support for zero flag ELF section groups to LLVM.
LLVM already supports COMDAT sections, which in ELF are a special type
of ELF

[MC][ELF] Support for zero flag section groups

This change introduces support for zero flag ELF section groups to LLVM.
LLVM already supports COMDAT sections, which in ELF are a special type
of ELF section groups. These are generally useful to enable linker GC
where you want a group of sections to always travel together, that is to
be either retained or discarded as a whole, but without the COMDAT
semantics. Other ELF assemblers already support zero flag ELF section
groups and this change helps us reach feature parity.

Differential Revision: https://reviews.llvm.org/D95851

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[mips] Implement .cpadd directive

This directive inserts code to add $gp to the argument's register when
support for position independent code is enabled.

For example, this code:
.cpadd $4
expand

[mips] Implement .cpadd directive

This directive inserts code to add $gp to the argument's register when
support for position independent code is enabled.

For example, this code:
.cpadd $4
expands to:
addu $4, $4, $gp

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[MIPS] Implement MIPS3D vector instructions

Patch by Michael Roe.

Differential Revision: https://reviews.llvm.org/D76247