Following up from
https://discourse.llvm.org/t/improving-performance-of-multiple-threads-stepping-over-the-same-breakpoint/89637
When multiple threads are stopped at the same breakpoint, LLDB currently
steps each thread over the breakpoint one at a time. Each step requires
disabling the breakpoint, single-stepping one thread, and re-enabling
it, resulting in N disable/enable cycles and N individual vCont packets
for N threads.
Now we batch the step-over so that all threads at the same breakpoint
site are stepped together in a single vCont packet, with the breakpoint
disabled once at the start and re-enabled once after the last thread
finishes.
When we hit `WillResume` any leftover `StepOverBreakpoint` plans from a
previous cycle are popped with their re-enable side effect suppressed
via `SetReenabledBreakpointSite`, giving a clean slate.
`SetupToStepOverBreakpointIfNeeded` then creates fresh plans for all
threads that still need to step over a breakpoint, and these are grouped
by breakpoint address.
For groups with multiple threads, each plan is set to defer its
re-enable through `SetDeferReenableBreakpointSite`. Instead of
re-enabling the breakpoint directly when a plan completes, it calls
`ThreadFinishedSteppingOverBreakpoint`, which decrements a tracking
count per address. The breakpoint is only re-enabled when the count
reaches zero.
All threads in the largest group are resumed together in a single
batched vCont packet. If some threads don't complete their step in one
cycle, the pop-and-recreate logic naturally re-batches the remaining
threads on the next WillResume call.
Claude AI assisted in syntex fixes and making the comments more
understandable.
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Co-authored-by: Bar Soloveychik <barsolo@fb.com>
f45754b65e