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[wasm] Set flutter_runtime_mode in tools/gn to_gn_wasm_args - #193407
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This fixes an issue where Wasm builds implicitly defaulted to debug runtime mode under GN by propagating args.runtime_mode into gn_args['flutter_runtime_mode']. This correctly resolves #16PD4 where release wimp.wasm was built with IMPELLER_DEBUG=1.
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This pull request updates the GN build configuration for Web/Wasm targets to set the flutter_runtime_mode argument based on the runtime mode, and adds corresponding unit tests in gn_test.py. Feedback suggests wrapping several long lines in the test file to comply with the 80-character limit of the Google Python Style Guide.
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Sep 29, 2026
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OMG, is this why the check framebuffer stuff is still showing up in profiles?? Let me know what the perf looks like after this change!
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…13104) Manual roll requested by [email protected] flutter/flutter@d649d2b...e89fd0a 2026-10-01 [email protected] Manual roll ICU from 6ebb40c59477 to 5aa526207171 (2 revisions) (flutter/flutter#193661) 2026-10-01 [email protected] fix(web): hash source maps before rewriting sourceMappingURL with --web-content-hash (flutter/flutter#193614) 2026-10-01 [email protected] [flutter_tools] Bootstrap DeviceManager in ToolDependencies (flutter/flutter#193524) 2026-10-01 [email protected] [wasm] Set flutter_runtime_mode in tools/gn to_gn_wasm_args (flutter/flutter#193407) 2026-10-01 [email protected] Remove remaining `download_jdk` references (flutter/flutter#193562) 2026-10-01 [email protected] Synchronize dart2wasm feature probes in roll script and flutter_bootstrap.js (flutter/flutter#193271) 2026-10-01 [email protected] [web] Unskip web tests that now pass in gestures, services, and widgets (flutter/flutter#193512) 2026-10-01 [email protected] Roll Fuchsia Test Scripts from whZAV1mfT-Rdc0rQ8... to fCNknap4ZI0AMcvIf... (flutter/flutter#193640) 2026-10-01 [email protected] Roll Skia from 0575a37d0619 to f2d68e0b8863 (2 revisions) (flutter/flutter#193621) 2026-10-01 [email protected] perf(widgets): use const <Never>{} in InheritedModelElement and avoid redundant casts in RenderObjectElement.update (flutter/flutter#192913) 2026-10-01 [email protected] [web] Unskip and strengthen missing glyph tofu test on Wimp (flutter/flutter#193426) 2026-10-01 [email protected] [flutter_tools] Fix `flutter drive -d chrome` hanging on web (flutter/flutter#193459) 2026-10-01 [email protected] [web] Fix hang when Chromium cannot bind remote debugging port (flutter/flutter#193461) 2026-10-01 [email protected] [flutter_tools] Bundle data assets from hooks in flutter test (flutter/flutter#193435) 2026-10-01 [email protected] Roll Packages from 0ba9a82 to d5ec6db (11 revisions) (flutter/flutter#193641) 2026-10-01 [email protected] Revert: [flutter_tools] Fix DTD "Stream already subscribed" error and wait for analysis over DTD in widget preview (flutter/flutter#193637) 2026-10-01 [email protected] Roll Skia from 6182a3cf8f98 to 0575a37d0619 (5 revisions) (flutter/flutter#193613) 2026-10-01 [email protected] [flutter_tools] Fix DTD "Stream already subscribed" error and wait for analysis over DTD in widget preview (flutter/flutter#192930) 2026-09-30 [email protected] [Impeller] Sample the render target rect in offscreen advanced blends (flutter/flutter#192988) 2026-09-30 [email protected] Roll Skia from 01524014dff5 to 6182a3cf8f98 (11 revisions) (flutter/flutter#193594) 2026-09-30 [email protected] [web] Use Xvfb -displayfd and clean up Xvfb after Firefox test suites (flutter/flutter#193510) 2026-09-30 [email protected] Fixes bug where sibling node fail to update size (flutter/flutter#191220) 2026-09-30 [email protected] Roll Skia from c7b323126bf0 to 01524014dff5 (3 revisions) (flutter/flutter#193577) 2026-09-30 [email protected] Remove some Undefined Behavior from run_customer_testing_tests.dart. (flutter/flutter#193582) 2026-09-30 [email protected] Fix pointer id/coordinate mismatch in Android platform view multi-touch (flutter/flutter#191631) 2026-09-30 [email protected] Roll Packages from 3c6ce59 to 0ba9a82 (11 revisions) (flutter/flutter#193578) 2026-09-30 [email protected] Fix unresolved doc comment references in dev/ tooling (flutter/flutter#193501) If this roll has caused a breakage, revert this CL and set the roller to dry run mode using the controls here: https://autoroll.skia.org/r/flutter-packages Please CC [email protected],[email protected] on the revert to ensure that a human is aware of the problem. To file a bug in Packages: https://github.com/flutter/flutter/issues/new/choose To report a problem with the AutoRoller itself, please file a bug: https://issues.skia.org/issues/new?component=1389291&template=1850622 Documentation for the AutoRoller is here: https://skia.googlesource.com/buildbot/+doc/main/autoroll/README.md
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Rationale
In
engine/src/flutter/tools/gn,to_gn_args()checksif args.target_os == 'wasm' or args.web:, delegates toto_gn_wasm_args(), and returns early before reaching the linegn_args['flutter_runtime_mode'] = runtime_mode.Because
to_gn_wasm_args()never mapped the argument back intogn_args,flutter_runtime_modefalls back to"debug"during GN evaluation for all--webengine targets. This evaluatesimpeller_debug = true(IMPELLER_DEBUG=1macro) globally in C++ for Web Impeller release builds. This defect was driving 50+ synchronousglCheckFramebufferStatus()calls per frame onbouncy@128(and 500+ calls per frame on multi-pass blur/filter workloads) during Web Impeller benchmarking.Summary of Changes
args.runtime_modeintogn_args['flutter_runtime_mode']insideto_gn_wasm_args()intools/gn.tools/gn_test.py(test_get_out_dirandtest_to_gn_args) verifyingflutter_runtime_modeand output directories acrossdebug,profile, andreleasefor--weband--target-os=wasm.Verification & Empirical Performance Delta (
wimp.wasmwasm_release)tools/gn_test.pywith 100% pass on all 5 test cases.wimp.wasm(wasm_release) locally before and after this change and benchmarked both single-pass and multi-pass offscreen workloads (?effects=multipass, wrapping each leaf node inColorFiltered+ClipRect+BackdropFilter5px Gaussian blur +Opacity):IMPELLER_DEBUG=1)IMPELLER_DEBUG=0)wimp.wasmUncompressed / Gzipped Size3,608,411 B/1,463,726 B3,599,401 B/1,457,944 B-9,010 B/-5,782 B-0.25%/-0.40%bouncy@128(single-pass)glCheckFramebufferStatus/ frame58(2.83%worker CPU)0-100.0%bouncy_multipass@16(wimp_st)glCheckFramebufferStatus/ frame1480-100.0%bouncy_multipass@16(wimp_st) Raster Time (ms/frame)273.40 ms210.28 ms-63.12 ms(-23.1%)1.30xfasterbouncy_multipass@32(wimp_st)glCheckFramebufferStatus/ frame2680-100.0%bouncy_multipass@32(wimp_st) Raster Time (ms/frame)286.61 ms203.44 ms-83.16 ms(-29.0%)1.41xfasterbouncy_multipass@64(wimp_st)glCheckFramebufferStatus/ frame5020-100.0%bouncy_multipass@64(wimp_st) Raster Time (ms/frame)364.64 ms246.61 ms-118.03 ms(-32.4%)1.48xfasterbouncy_multipass@64(wimp_mt)glCheckFramebufferStatus/ frame5030-100.0%bouncy_multipass@64(wimp_mt) Raster Time (ms/frame)380.41 ms256.95 ms-123.46 ms(-32.5%)1.48xfasterbouncy_multipass@64(--disable-gl-drawing-for-tests,wimp_st)228.21 ms42.31 ms-185.90 ms(-81.5%)5.39xfasterFixes #193406
Pre-launch Checklist
///).