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[lldb][swift] Filter await-resume funclets when setting breakpoints #8319

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[lldb][swift] Filter await-resume funclets when setting breakpoints #8319

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Commits on Mar 14, 2024

  1. [lldb] Allow languages to filter breakpoints set by line (llvm#83908) 

    Some languages may create artificial functions that have no real user
code, even though there is line table information for them. One such
case is with coroutine code that receives the CoroSplitter
transformation in LLVM IR. That code transformation creates many
different Functions, cloning one Instruction into many Instructions in
many different Functions and copying the associated debug locations.

It would be difficult to make that pass delete debug locations of cloned
instructions in a language agnostic way (is it even possible?), but LLDB
can ignore certain locations by querying its Language APIs and having it
decide based on, for example, mangling information.

(cherry picked from commit 0adccd1)
    @felipepiovezan
    felipepiovezan committed Mar 14, 2024
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  2. [lldb][swift] Filter await-resume funclets when setting breakpoints 

    These funclets only serve to `task_dealloc` previously allocated tasks when
returning from an async call, and immediately `task_switch` to the next
await-suspend funclet (which contains real user code).

By not filtering out these funclets, any breakpoint on a line with an async call
will cause execution to pause 3 times: once before the call, twice when
"returning" from the call, which makes for a confusing experience.

The patch does the filtering on `BreakpointResolver::SetSCMatchesByLine`, which
is the common code between BreakpointResolverFileLine and
BreakpointResolverFileRegex.

We also considered changing the debug line information in any of the many
different lowering stages the swift compiler, but this turned out to be very
complex to do in a targeted way; more often than not, a handful of early-IR
coroutine instructions get expanded into multiple function clones, all
inheriting the same debug line information. The current approach also has the
advantaged of being easily reversible if we decide to do so.
    @felipepiovezan
    felipepiovezan committed Mar 14, 2024
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