use option LTO

[Jason2866]

the option LTO saves a lot of flash space (reducing firmware size).
The change is tested and working for use with pioarduino the changes for ArduinoIDE are done accordingly but not tested (not using ArduinoIDE).
More Info Discord discussion https://discord.com/channels/1263397951829708871/1263397951829708874/1332807939395686472

@me-no-dev The PR as suggested.

[Jason2866]

Closing since compiling with LTO option is not possible with ArduinoIDE.
@me-no-dev Thx for testing!

[igrr]

Note that LTO is not compatible with linking rules which place certain object files into specific memory regions. For example, if IDF generates a linker script to place esp_timer.c.obj into IRAM, the rule may stop working after LTO gets enabled. This is the main reason why LTO is not enabled in IDF.

the option LTO saves a lot of flash space (reducing firmware size).

@Jason2866 could you please share some numbers, what size do you see with and without LTO in the tests you did?

[Jason2866]

@igrr For project Tasmota we have a size decrease from about 100k when compiling for esp32 (firmware size is ~2M). Similar size decrease has EspEasy.

[Jason2866]

Both projects had just minor small changes to do, to get it running with LTO.
Well imho the code creator is responsible for things you mentioned. Currently IDF just fails to compile itself when LTO is enabled. So there isn't a chance to hit the trap you showed ;-)