- Do not call pass initialization from pass constructors.
- Instead, pass initialization should happen in the `initializeAnalysis`
function.
- https://github.com/llvm/llvm-project/issues/111767

I'm planning to remove StringRef::equals in favor of
StringRef::operator==.

- StringRef::operator==/!= outnumber StringRef::equals by a factor of
  53 under llvm/ in terms of their usage.

- The elimination of StringRef::equals brings StringRef closer to
  std::string_view, which has operator== but not equals.

- S == "foo" is more readable than S.equals("foo"), especially for
  !Long.Expression.equals("str") vs Long.Expression != "str".

Primary change is to add a flag `--pretty-pgo-analysis-map` to
llvm-readobj and llvm-objdump that prints block frequencies and branch
probabilities in the same manner as BFI and BPI respectively. This can
be helpful if you are manually inspecting the outputs from the tools.

In order to print, I moved the `printBlockFreqImpl` function from
Analysis to Support and renamed it to `printRelativeBlockFreq`.

- Refactor the (Machine)BlockFrequencyInfo::printBlockFreq functions
into a `PrintBlockFreq()` function returning a `Printable` object. This
simplifies usage as it can be directly piped to a `raw_ostream` like
`dbgs() << PrintBlockFreq(MBFI, Freq) << '\n';`.
- Previously there was an interesting behavior where
`BlockFrequencyInfoImpl` stores frequencies both as a `Scaled64` number
and as an `uint64_t`. Most algorithms use the `BlockFrequency`
abstraction with the integers, the print function for basic blocks
printed the `Scaled64` number potentially showing higher accuracy than
was used by the algorithm. This changes things to only print
`BlockFrequency` values.
- Replace some instances of `dbgs() << Freq.getFrequency()` with the new
function.

The `BlockFrequency` class abstracts `uint64_t` frequency values. Use it
more consistently in various APIs and disable implicit conversion to
make usage more consistent and explicit.

- Use `BlockFrequency Freq` parameter for `setBlockFreq`,
`getProfileCountFromFreq` and `setBlockFreqAndScale` functions.
- Return `BlockFrequency` in `getEntryFreq()` functions.
- While on it change some `const BlockFrequency& Freq` parameters to
plain `BlockFreqency Freq`.
- Mark `BlockFrequency(uint64_t)` constructor as explicit.
- Add missing `BlockFrequency::operator!=`.
- Remove `uint64_t BlockFreqency::getMaxFrequency()`.
- Add `BlockFrequency BlockFrequency::max()` function.

When debugging and using debug-pass-manager (e.g. in regression tests)
we prefer a consistent order in which analysis passes are executed.
But when for example doing

  return MyClass(AM.getResult<LoopAnalysis>(F),
                 AM.getResult<DominatorTreeAnalysis>(F));

then the order in which LoopAnalysis and DominatorTreeAnalysis isn't
guaranteed, and might for example depend on which compiler that is
used when building LLVM.

I've not scanned the full source tree, but this fixes some occurances
of the above pattern found in lib/Analysis.

This problem was discussed briefly in review for D146206.

I've converted all known uses of None to std::nullopt, so we no longer
need to include None.h.

This is part of an effort to migrate from llvm::Optional to
std::optional:

https://discourse.llvm.org/t/deprecating-llvm-optional-x-hasvalue-getvalue-getvalueor/63716

This patch mechanically replaces None with std::nullopt where the
compiler would warn if None were deprecated.  The intent is to reduce
the amount of manual work required in migrating from Optional to
std::optional.

This is part of an effort to migrate from llvm::Optional to
std::optional:

https://discourse.llvm.org/t/deprecating-llvm-optional-x-hasvalue-getvalue-getvalueor/63716

Number of lines output by preprocessor:
before: 1065940348
after:  1065307662

Discourse thread: https://discourse.llvm.org/t/include-what-you-use-include-cleanup
Differential Revision: https://reviews.llvm.org/D120659