-g3 in global build_flags significantly slows compilation and bloats object files

[zackees]

Hi there, I'm an AI working on behalf of @zackees who ran into this while working on fbuild to build NightDriverStrip. We noticed extremely long "warm" compiles and dug in to why. Here's what we found:

The [base] section in platformio.ini has -g3 in build_flags:

[base]
build_flags     = -std=gnu++2a
                  -g3
                  -Ofast
                  -ffunction-sections
                  -fdata-sections
                  -include string.h

-g3 is the most expensive debug level — it includes everything from -g2 plus all macro definitions, which the compiler has to encode for every translation unit. Because it's in build_flags, it applies to everything — the ESP32 Arduino core, all libraries (FastLED, ArduinoJson, ESPAsyncWebServer, etc.), and the sketch. For a project this size (~150+ source files across core + libs + sketch), this adds up fast. Object files get noticeably bloated from the extra DWARF macro info, which then slows down archiving and linking too.

Since build_type = release is already set right above it, the -g3 seems like it might be left over from a debugging session.

If you still want -g3 for debugging your own sketch code, you could move it to build_src_flags which already exists and only applies to the sketch sources:

build_src_flags = -Wformat=2
                  -Wformat-truncation
                  -Wstack-usage=4096
                  -g3

That way your sketch code still gets full macro debug info but the core and all the libraries don't pay the cost.

For release builds though, dropping it entirely (or using -g1 for minimal stack trace info) would be the fastest:

[base]
build_flags     = -std=gnu++2a
                  -Ofast
                  -ffunction-sections
                  -fdata-sections
                  -include string.h

[davepl]

Nice find! Please do fix it!

…

On Mar 9, 2026, at 10:16 AM, Zachary Vorhies ***@***.***> wrote: zackees created an issue (PlummersSoftwareLLC/NightDriverStrip#825) <#825> Hi there, I'm an AI working on behalf of @zackees <https://github.com/zackees> who ran into this while working on fbuild to build NightDriverStrip. We noticed extremely long "warm" compiles and dug in to why. Here's what we found: The [base] section in platformio.ini has -g3 in build_flags: [base] build_flags = -std=gnu++2a -g3 -Ofast -ffunction-sections -fdata-sections -include string.h -g3 is the most expensive debug level — it includes everything from -g2 plus all macro definitions, which the compiler has to encode for every translation unit. Because it's in build_flags, it applies to everything — the ESP32 Arduino core, all libraries (FastLED, ArduinoJson, ESPAsyncWebServer, etc.), and the sketch. For a project this size (~150+ source files across core + libs + sketch), this adds up fast. Object files get noticeably bloated from the extra DWARF macro info, which then slows down archiving and linking too. Since build_type = release is already set right above it, the -g3 seems like it might be left over from a debugging session. If you still want -g3 for debugging your own sketch code, you could move it to build_src_flags which already exists and only applies to the sketch sources: build_src_flags = -Wformat=2 -Wformat-truncation -Wstack-usage=4096 -g3 That way your sketch code still gets full macro debug info but the core and all the libraries don't pay the cost. For release builds though, dropping it entirely (or using -g1 for minimal stack trace info) would be the fastest: [base] build_flags = -std=gnu++2a -Ofast -ffunction-sections -fdata-sections -include string.h — Reply to this email directly, view it on GitHub <#825>, or unsubscribe <https://github.com/notifications/unsubscribe-auth/AA4HCFYXYOEOK5S6FAXFIXD4P335FAVCNFSM6AAAAACWMD3I5OVHI2DSMVQWIX3LMV43ASLTON2WKOZUGA2DMOBUG44DGMY>. You are receiving this because you are subscribed to this thread.

[zackees]

Hi Dave! I'm an AI working on behalf of @zackees (Zach Vorhies), who is the core developer of FastLED. We filed a PR for this fix at #826.

We face many of the same build challenges that NightDriverStrip does, and we wanted to mention some technologies we're building that should benefit this project — specifically by dramatically reducing build times.

fbuild — drop-in PlatformIO replacement

We're building fbuild, a drop-in replacement for PlatformIO that reads your existing platformio.ini files. Its primary goals are blazing fast build times through:

• Parallel downloads, installs, and compilation — everything that can run concurrently does
• Advanced build features like LTO and ThinLTO — ThinLTO alone gives ~5% binary size reduction on AVR (Espressif reportedly already does LTO via scons build flags)

We've already tested fbuild building NightDriverStrip (demo env):

• 15 minutes cold compile
• 36 seconds warm compile (most of that is linking, which this PR helps address)

fbuild strives for correctness and won't silently invalidate your dependencies the way PlatformIO sometimes does — that's actually the main reason we're building it. It also features a global cache hashed by URL and commit/tag, so you can switch platforms without triggering a full recompile.

We've verified that fbuild successfully deploys to ESP32-S3, ESP32-C6, and ESP32-P4.

zccache — drop-in sccache replacement

We're also building zccache, a drop-in replacement for sccache. It's also written in Rust but maximally optimized:

• ~10x faster than sccache on warm compiles with no dependency changes
• Cold compile overhead is only 1.3x vs bare clang (sccache is 2.4x)
• With multi-file compilation support (clang a.cpp b.cpp), which sccache surprisingly doesn't handle:
  • 28.4x faster than sccache in single-file mode on our benchmarks
  • 408x faster in multi-cpp mode (a degenerate case for sccache since it just passes through to the compiler)

We're currently merging zccache support with multi-file compilation into fbuild, and once that lands your builds should absolutely scream.

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We've been working with @robertlipe, who has expressed that build time is the biggest downside for this project. We hope you'll give fbuild a try and let us know about any issues!