This removes ThreadSafeContext::Lock, ThreadSafeContext::getLock, and
ThreadSafeContext::getContext, and replaces them with a
ThreadSafeContext::withContextDo method (and const override).

The new method can be used to access an existing
ThreadSafeContext-wrapped LLVMContext in a safe way:

ThreadSafeContext TSCtx = ... ;
TSCtx.withContextDo([](LLVMContext *Ctx) {
  // this closure has exclusive access to Ctx.
});

The new API enforces correct locking, whereas the old APIs relied on
manual locking (which almost no in-tree code preformed, relying instead
on incidental exclusive access to the ThreadSafeContext).

When specifying a weighted input file, the shell does not automatically
expand the tilde (`~`) character in the filename because the argument
is passed as a single string in the format `<weight>,<filename>`.

This commit fixes the issue by using `llvm::sys::fs::expand_tilde` to
explicitly resolve the tilde in the filename, ensuring that paths
like `~/path/to/file` are correctly handled.

Reapply "[NFC][DebugInfo][DWARF] Create new low-level dwarf library (#…
(#145959)
    
This reapplies cbf781f0bdf2f680abbe784faedeefd6f84c246e, with fixes for
the shared-library build and the unconventional sanitizer-runtime build.

Original Description:

This is the culmination of a series of changes described in [1].
    
Although somewhat large by line count, it is almost entirely mechanical,
creating a new library in DebugInfo/DWARF/LowLevel. This new library has
very minimal dependencies, allowing it to be used from more places than
the normal DebugInfo/DWARF library--in particular from MC.
    
1.
https://discourse.llvm.org/t/rfc-debuginfo-dwarf-refactor-into-to-lower-and-higher-level-libraries/86665/2

ArrayRef now has a new constructor that takes a parameter whose type
has data() and size().  This patch migrates:

  ArrayRef<T>(X.data(), X.size()

to:

  ArrayRef<T>(X)

…145081)"

This reverts commit cbf781f0bdf2f680abbe784faedeefd6f84c246e.

Breaks a couple of buildbots.

This is the culmination of a series of changes described in [1].
    
Although somewhat large by line count, it is almost entirely mechanical,
creating a new library in DebugInfo/DWARF/LowLevel. This new library has
very minimal dependencies, allowing it to be used from more places than
the normal DebugInfo/DWARF library--in particular from MC.
    
I am happy to put it in another location, or to structure it differently
if that makes sense. Some have suggested in BinaryFormat, but it is not
a great fit there. But if that makes more sense to the reviewers, I can
do that.
 
Another possibility would be to use pass-through headers to allow
clients who don't care to depend only on DebugInfo/DWARF. This would be
a much less invasive change, and perhaps easier for clients. But also a
system that hides details.

Either way, I'm open.

1.
https://discourse.llvm.org/t/rfc-debuginfo-dwarf-refactor-into-to-lower-and-higher-level-libraries/86665/2

Note that llvm::interleaved constructs a string with the elements from
a given range with a given separator.

This moves the MemoryAccess interface out of the ExecutorProcessControl
class and splits implementation classes InProcessMemoryManager and
SelfExecutorProcessControl out of ExecutorProcessControl.h and into
their own headers.

Similar to the existing implementations for X86 and PPC, support
symbolizing branch targets for AArch64. Do not omit the address for ADRP
as the target is typically not at an intended location.

Pull Request: https://github.com/llvm/llvm-project/pull/145009

Dynamic relocations are expensive on ELF/Linux platforms because they
are applied in userspace on process startup. Therefore, it is worth
optimizing them to make PIE and PIC dylib builds faster. In +asserts
builds (non-NDEBUG), nikic identified these schedule class name string
pointers as the leading source of dynamic relocations. [1]

This change uses llvm::StringTable and the StringToOffsetTable TableGen
helper to turn the string pointers into 32-bit offsets into a separate
character array.

The number of dynamic relocations is reduced by ~60%:
❯ llvm-readelf --dyn-relocations lib/libLLVM.so | wc -l
381376 # before
155156 # after

The test suite time is modestly affected, but I'm running on a shared
noisy workstation VM with a ton of cores:
https://gist.github.com/rnk/f38882c2fe2e63d0eb58b8fffeab69de
Testing Time: 100.88s   # before
Testing Time: 78.50s. # after
Testing Time: 96.25s.  # before again

I haven't used any fancy hyperfine/denoising tools, but I think the
result is clearly visible and we should ship it.

[1] https://gist.github.com/nikic/554f0a544ca15d5219788f1030f78c5a