Source lines for cpu samples present using --debug, but not using --profile

[CoderDake]

The CPU samples returned by getCpuSamples in devtools, are used to generate CPU profile data (which is used to populate the CPU profiler table).

When attached to the Flutter Gallery App run with --profile:

• the samples are parsed into stack frames here
• but the samples provided never have location?.line set.

On the other hand, when Flutter Gallery App is run with --debug:

• samples will have location?.line set.

The end result is that source lines only appear to work when running the target application in --debug mode.

Details

Reproduced on

Targets:

• MacOs
• android

Dev Tools was run on MacOs

My Dart Version

• Dart SDK Version (dart --version)
  • Dart SDK version: 2.18.0-34.0.dev (dev) (Tue Apr 19 01:34:32 2022 -0700) on "macos_x64"

[CoderDake]

@bkonyi this is one you may be able to help with

[bkonyi]

So I have this working now locally, but it has a non-negligible impact on the AOT snapshot size since we need to add token position information for each function (and if we wanted to be consistent, each field and class also) and line start arrays for each script.

Here's the sizes of the snapshots generated while building Flutter's image_list example:

-rw-r--r--   1 bkonyi  primarygroup  4965272 May  6 12:57 no_func_tokens.so
-rw-r--r--   1 bkonyi  primarygroup  5522328 May  6 12:47 with_func_tokens.so

For this relatively small application, we're seeing a 10% size regression, which is hardly ideal. If we really want to have line number information available for profiles (which I assume we do), we might need to consider other options (e.g., looking for the line/column information directly from the SourceLocation service objects rather than using token positions to map into the line starts arrays).