[vm/doc] Add documentation describing AOT code size analysis

mkustermann · commit-bot@chromium.org · commit e7b3d2955359 · 2019-08-12T12:08:35.000Z
This adds runtime/docs/aot_binary_size_analysis.md describing how to visualize the breakdown of generated code size from our AOT. Change-Id: I63ae3728db808532fad0ca178e1947e5b8280521 Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/112397 Reviewed-by: Michael Thomsen <mit@google.com> Commit-Queue: Martin Kustermann <kustermann@google.com>
diff --git a/runtime/docs/aot_binary_size_analysis.md b/runtime/docs/aot_binary_size_analysis.md
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+# AOT code size analysis
+
+The Dart VM's AOT compiler has support for emitting binary size information
+for all the code that gets generated. This information can then be visualized.
+
+## Telling the AOT compiler to generate binary size information
+
+Our AOT compiler accepts an extra `--print-instructions-sizes-to=sizes.json`
+flag. If supplied the AOT compiler will emit binary size information for all
+generated functions to `sizes.json`.
+
+This flag can be passed to `gen_snapshot` directly, or to the various wrapper
+scripts (e.g. `pkg/vm/tool/precompiler2`):
+
+```
+% tools/build.py -mrelease -ax64 runtime_kernel dart_precompiled_runtime
+% pkg/vm/tool/precompiler2 --print-instructions-sizes-to=hello_sizes.json hello.dart hello.dart.aot
+```
+
+## Visualizing the information from the binary size json file
+
+To visualize the information emitted by the AOT compiler one can use our binary
+size analysis tool:
+
+```
+% dart pkg/vm/bin/run_binary_size_analysis.dart hello_sizes.json hello_sizes
+Generated file:///.../sdk/hello_sizes/index.html
+% chrome hello_sizes/index.html
+```
+
