AVR core 1.6.23 (IDE 1.8.7) LTO + debugger symbols crash

[ImpulseAdventure]

Hi --

I am encountering an internal compiler error in the latest Arduino AVR core (1.6.23) with IDE 1.8.7.

After much debugging, it appears to be related to the inclusion of the debugger symbols (-g) flag in the avr-gcc call (perhaps with LTO concurrently enabled).

Testcase

To help others reproduce the issue, I have created an isolated testcase:

• https://github.com/ImpulseAdventure/Arduino-LTO-Error

Error Output

The output was generated from the following setup:

• Arduino IDE: 1.8.7 on Windows 10
• Board Package: Arduino AVR Boards 1.6.23
• Board: Arduino UNO

Linking everything together...
"C:\\Program Files (x86)\\Arduino\\hardware\\tools\\avr/bin/avr-gcc" -Os -g -flto -fuse-linker-plugin -Wl,--gc-sections -mmcu=atmega328p -o "C:\\Users\\Cal\\AppData\\Local\\Temp\\arduino_build_528560/test-lto.ino.elf" "C:\\Users\\Cal\\AppData\\Local\\Temp\\arduino_build_528560\\sketch\\MyLib.c.o" "C:\\Users\\Cal\\AppData\\Local\\Temp\\arduino_build_528560\\sketch\\test-lto.ino.cpp.o" "C:\\Users\\Cal\\AppData\\Local\\Temp\\arduino_build_528560/core\\core.a" "-LC:\\Users\\Cal\\AppData\\Local\\Temp\\arduino_build_528560" -lm

lto1.exe: internal compiler error: in splice_child_die, at dwarf2out.c:4905
Please submit a full bug report,
with preprocessed source if appropriate.
See <http://gcc.gnu.org/bugs.html> for instructions.
lto-wrapper.exe: fatal error: C:\Program Files (x86)\Arduino\hardware\tools\avr/bin/avr-gcc returned 1 exit status

Other Test Results

Arduino IDE	Arduino AVR Boards	Extra Mods	Result
1.8.7	1.6.23		Fail
1.8.7	1.6.22		Fail
1.8.7	1.6.21		OK
1.8.5			OK
1.8.7	1.6.23	Disable -g	OK

• In the last test case, debugger symbol generation was disabled by removing the -g flag from platform.txt: compiler.c.flags.

Related Issues

• I note that AVR core 1.6.22 (IDE 1.8.6) crashes avr-gcc compiler (5.4.0) when F() string is assigned to a static variable #39 results in a similar crash message, but the triggering code is very different

Please let me know if further details may help root-cause the issue.

Thank you for your time,
Cal

[facchinm]

Hi @ImpulseAdventure ,
we are keeping track of this issue "family" here arduino/Arduino#7949 .
They are all related with a combination of lto, gcc 5.4.0 and Windows as host OS.
#39 instead is cross OS but related too.
We are evaluating to switch to gcc 7.3.0 (plus some patches); you can test it easily following these instructions; it would be cool if you could test your sketch with the new compiler and report the results there (or here).
Thanks for the perfect report!

[ImpulseAdventure]

Thank you @facchinm — I will give my testcase a try using gcc 7.3.0 / core 1.6.208 in the next few days and report back.

[ImpulseAdventure]

Confirmed as resolved in gcc 7.3.0 / core 1.6.208. Thank you for the workaround.
I presume the IDE's toolchain update may be some time off, so will guide users to rollback to Arduino AVR Boards 1.21 in the interim. Thanks!

[ImpulseAdventure]

For reference, the recently released Arduino IDE 1.8.10 (with Arduino AVR Boards 1.8.1) appears to have resolved the LTO issue.