[lldb] Defer checking CFA memory region (#7877) #8037
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To support stepping in Swift async code, LLDB uses the memory region (ie stack vs heap) of the Canonical Frame Address (CFA) to identify when an async function calls a synchronous function. But this has resulted in a performance regression, as determining the memory region of the CFA is not free, and eagerly performing this query for every `StackID`, particularly during backtracing/unwinding – when stepping is not yet occurring, is wasteful. This change proposes a solution that defers the memory region query until required to perform stepping logic. The logic that checks heaps vs stacks was moved into `ThreadPlan`, the only place that currently needs to make that determination. Performing this check in `ThreadPlan` provides access to the process, allowing stack/heap determination to happen as needed. Previously, the stack/heap determination was made eagerly when the `StackID` was constructed. rdar://117505613 (cherry-picked from commit c58c369)
kastiglione
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To support stepping in Swift async code, LLDB uses the memory region (ie stack vs heap)
of the Canonical Frame Address (CFA) to identify when an async function calls a
synchronous function.
But this has resulted in a performance regression, as determining the memory region of
the CFA is not free, and eagerly performing this query for every
StackID,particularly during backtracing/unwinding – when stepping is not yet occurring, is
wasteful.
This change proposes a solution that defers the memory region query until required to
perform stepping logic. The logic that checks heaps vs stacks was moved into
ThreadPlan, the only place that currently needs to make that determination.Performing this check in
ThreadPlanprovides access to the process, allowingstack/heap determination to happen as needed. Previously, the stack/heap determination
was made eagerly when the
StackIDwas constructed.rdar://117505613
(cherry-picked from commit c58c369)