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

Pavel Labath taught me that clang-format sorts headers automatically
using llvm's rules, and it's better not to have spaces between

So in this diff I'm removing those spaces and formatting them as well.

I used `clang-format -i` to format these files.

As discusses offline with @jj10305, we are updating some naming used throughout the code, specially in the json schema

- traceBuffer -> iptTrace
- core -> cpu

Differential Revision: https://reviews.llvm.org/D127817

This applies the changes requested for diff 12.

- use DenseMap<ConstString, _> instead of std::unordered_map<ConstString, _>, which is more idiomatic and possibly performant.
- deduplicate some code in Trace.cpp by using helper functions for fetching in maps
- stop using size and offset when fetching binary data, because we in fact read the entire buffers all the time. If we ever need streaming, we can implement it then. Now, the size is used only to check that we are getting the correct amount of data. This is useful because in some cases determining the size doesn't involve fetching the actual data.
- added back the x86_64 macro to the perf tests
- added more documentation
- simplified some file handling
- fixed some comments

Differential Revision: https://reviews.llvm.org/D127752

This improves several things and addresses comments up to the diff [11] in this stack.

- Simplify many functions to receive less parameters that they can identify easily
- Create Storage classes for Trace and TraceIntelPT that can make it easier to reason about what can change with live process refreshes and what cannot.
- Don't cache the perf zero conversion numbers in lldb-server to make sure we get the most up-to-date numbers.
- Move the thread identifaction from context switches to the bundle parser, to leave TraceIntelPT simpler. This also makes sure that the constructor of TraceIntelPT is invoked when the entire data has been checked to be correct.
- Normalize all bundle paths before the Processes, Threads and Modules are created, so that they can assume that all paths are correct and absolute
- Fix some issues in the tests. Now they all pass.
- return the specific instance when constructing PerThread and MultiCore processor tracers.
- Properly implement IntelPTMultiCoreTrace::TraceStart.
- Improve some comments.
- Use the typedef ContextSwitchTrace more often for clarity.
- Move CreateContextSwitchTracePerfEvent to Perf.h as a utility function.
- Synchronize better the state of the context switch and the intel pt
perf events.
- Use a booblean instead of an enum for the PerfEvent state.

Differential Revision: https://reviews.llvm.org/D127456

:q!
This diff is massive, but it's because it connects the client with lldb-server
and also ensures that the postmortem case works.

- Flatten the postmortem trace schema. The reason is that the schema has become quite complex due to the new multicore case, which defeats the original purpose of having a schema that could work for every trace plug-in. At this point, it's better that each trace plug-in defines it's own full schema. This means that the only common field is "type".
-- Because of this new approach, I merged the "common" trace load and saving functionalities into the IntelPT one. This simplified the code quite a bit. If we eventually implement another trace plug-in, we can see then what we could reuse.
-- The new schema, which is flattened, has now better comments and is parsed better. A change I did was to disallow hex addresses, because they are a bit error prone. I'm asking now to print the address in decimal.
-- Renamed "intel" to "GenuineIntel" in the schema because that's what you see in /proc/cpuinfo.
- Implemented reading the context switch trace data buffer. I had to do
some refactors to do that cleanly.
-- A major change that I did here was to simplify the perf_event circular buffer reading logic. It was too complex. Maybe the original Intel author had something different in mind.
- Implemented all the necessary bits to read trace.json files with per-core data.
- Implemented all the necessary bits to save to disk per-core trace session.
- Added a test that ensures that parsing and saving to disk works.

Differential Revision: https://reviews.llvm.org/D126015

- Add collection of context switches per cpu grouped with the per-cpu intel pt traces.
- Move the state handling from the interl pt trace class to the PerfEvent one.
- Add support for stopping and enabling perf event groups.
- Return context switch entries as part of the jLLDBTraceGetState response.
- Move the triggers of whenever the process stopped or resumed. Now the will-resume notification is in a better location, which will ensure that we'll capture the instructions that will be executed.
- Remove IntelPTSingleBufferTraceUP. The unique pointer was useless.
- Add unit tests

Differential Revision: https://reviews.llvm.org/D125897

When tracing on per-core mode, we are tracing all processes, which means
that after hitting a breakpoint, our process will stop running (thus
producing no more tracing data) but other processes will continue
writing to our trace buffers. This causes a big data loss for our trace.
As a way to remediate this, I'm adding some logic to pause and unpause
tracing based on the target's state. The earlier we do it the better,
however, I'm not adding the trigger at the earliest possible point for
simplicity of this diff. Later we can improve that part.

Differential Revision: https://reviews.llvm.org/D124962