This reverts commit 0859ac5866a0228f5607dd329f83f4a9622dedcc.

This caused a couple test failures, likely due to a mid-air collision.
Reverting for now to get the tree back to green and allow the original
author to run UTC/friends and verify the output.

This maybe a bug which is introduced by commit
6749ae36b4a33769e7a77cf812d7cd0a908ae3b9, and has been present ever
since.
In this case, `OtherReg` always overlaps with `DstReg` cause they from
the `Copy` all.

Enables the terminal rule for remaining targets

Before llvm20, (void)__sync_fetch_and_add(...) always generates locked
xadd insns. In linux kernel upstream discussion [1], it is found that
for arm64 architecture, the original semantics of
(void)__sync_fetch_and_add(...), i.e., __atomic_fetch_add(...), is
preferred in order for jit to emit proper native barrier insns.

In llvm commits [2] and [3], (void)__sync_fetch_and_add(...) will
generate the following insns:
  - for cpu v1/v2: locked xadd insns to keep backward compatibility
  - for cpu v3/v4: __atomic_fetch_add() insns

To ensure proper barrier semantics for (void)__sync_fetch_and_add(...),
cpu v3/v4 is recommended.

This patch enables cpu=v3 as the default cpu version. For users wanting
to use cpu v1, -mcpu=v1 needs to be explicitly added to clang/llc
command line.

  [1]
https://lore.kernel.org/bpf/ZqqiQQWRnz7H93Hc@google.com/T/#mb68d67bc8f39e35a0c3db52468b9de59b79f021f
  [2] https://github.com/llvm/llvm-project/pull/101428
  [3] https://github.com/llvm/llvm-project/pull/106494

Internal label names never occur in the symbol table, so when using an
object streamer, there's no point in constructing these names and then
adding them to hash tables -- they are never visible in the output.

It's not possible to reuse createTempSymbol, because on BPF has a
different prefix for globals and basic blocks right now.

The issue is uncovered by #47698: for IR files without a target triple,
-mtriple= specifies the full target triple while -march= merely sets the
architecture part of the default target triple, leaving a target triple which
may not make sense, e.g. riscv64-apple-darwin.

Therefore, -march= is error-prone and not recommended for tests without a target
triple. The issue has been benign as we recognize $unknown-apple-darwin as ELF instead
of rejecting it outrightly.

This reverts commit 122efef8ee9be57055d204d52c38700fe933c033.

- Patch fixed to not reuse definitions from predecessors in EH landing pads.
- Late review suggestions (by MaskRay) have been addressed.
- M68k/pipeline.ll test updated.
- Init captures added in processBlock() to avoid capturing structured bindings.
- RISCV has this disabled for now.

Original commit message:

A new pass MachineLateInstrsCleanup is added to be run after PEI.

This is a simple pass that removes redundant and identical instructions
whenever found by scanning the MF once while keeping track of register
definitions in a map. These instructions are typically immediate loads
resulting from rematerialization, and address loads emitted by target in
eliminateFrameInde().

This is enabled by default, but a target could easily disable it by means of
'disablePass(&MachineLateInstrsCleanupID);'.

This late cleanup is naturally not "optimal" in removing instructions as it
is done by looking at phys-regs, but still quite effective. It would be
desirable to improve other parts of CodeGen and avoid these redundant
instructions in the first place, but there are no ideas for this yet.

Differential Revision: https://reviews.llvm.org/D123394

Reviewed By: RKSimon, foad, craig.topper, arsenm, asb

This reverts commit 17db0de330f943833296ae72e26fa988bba39cb3.

Some more bots got broken - need to investigate.

Init captures added in processBlock() to avoid capturing structured bindings,
which caused the build problems (with clang).

RISCV has this disabled for now until problems relating to post RA pseudo
expansions are resolved.

Temporarily revert and fix buildbot failure.

This reverts commit 6d12599fd4134c1da63198c74a25490d28c733f6.