Sketch re-compiled when unnecessary

[weswitt]

Describe the problem

When using make & makefiles a build followed immediately by another build causes nothing to be compiled or linked because make honors timestamps when building the dependency graph. The arduino-cli does not seem to do this. If i do a compile and then immediately another compile it rebuild the binary the second time. This is unnecessary and consumes time & processing power. Arduido-cli should behave like make.

To reproduce

Do a compile and the immediately another compile.

Expected behavior

The second compile should exit without doing anything.

Arduino CLI version

arduino-cli Version: 0.29.0 Commit: 76251df Date: 2022-11-17T09:21:37Z

Operating system

Windows

Operating system version

Windows 11

Additional context

Additional reports

• Avoid unnecessary compiling when clicking "Upload" button #2015

Issue checklist

• I searched for previous reports in the issue tracker
• I verified the problem still occurs when using the nightly build
• My report contains all necessary details

[scottchiefbaker]

What's the status on this? I'm getting bit by this also.

[umbynos]

Actually the compile process does compile different "parts" of a sketch:

• the core
• the libraries
• the user code (the sketch)

The first two already use a caching mechanism. The sketch currently does not have this behavior. Unfortunately, it's not that easy because the library detection can't be cached.

[weswitt]

can't? i don't think so. it's amazing how make has done this for decades.

[cmaglie]

can't? i don't think so. it's amazing how make has done this for decades.

Just to give some context: the slow part is the automatic library detection, the difference between a Makefile and a sketch is that with a Makefile the used libraries are given (it's the user's duty to write the paths manually or with the aid of other tools like cmake/automake). With a sketch, the libraries are automatically discovered.

Moving to a more pragmatic example, this is how a clean compile looks like:

~/Arduino/Blink$ LANG=en arduino-cli compile -b arduino:avr:uno --clean -v
FQBN: arduino:avr:uno
Using board 'uno' from platform in folder: /home/megabug/.arduino15/packages/arduino/hardware/avr/1.8.6
Using core 'arduino' from platform in folder: /home/megabug/.arduino15/packages/arduino/hardware/avr/1.8.6

Detecting libraries used...
/home/megabug/.arduino15/packages/arduino/tools/avr-gcc/7.3.0-atmel3.6.1-arduino7/bin/avr-g++ -c -g -Os -w -std=gnu++11 -fpermissive -fno-exceptions -ffunction-sections -fdata-sections -fno-threadsafe-statics -Wno-error=narrowing -flto -w -x c++ -E -CC -mmcu=atmega328p -DF_CPU=16000000L -DARDUINO=10607 -DARDUINO_AVR_UNO -DARDUINO_ARCH_AVR -I/home/megabug/.arduino15/packages/arduino/hardware/avr/1.8.6/cores/arduino -I/home/megabug/.arduino15/packages/arduino/hardware/avr/1.8.6/variants/standard /tmp/arduino/sketches/002050EAA7EFB9A4FC451CDFBC0FA2D3/sketch/Blink.ino.cpp -o /dev/null
Alternatives for Wire.h: [Arduino_Threads@0.0.1 Wire@1.0]
ResolveLibrary(Wire.h)
  -> candidates: [Arduino_Threads@0.0.1 Wire@1.0]
/home/megabug/.arduino15/packages/arduino/tools/avr-gcc/7.3.0-atmel3.6.1-arduino7/bin/avr-g++ -c -g -Os -w -std=gnu++11 -fpermissive -fno-exceptions -ffunction-sections -fdata-sections -fno-threadsafe-statics -Wno-error=narrowing -flto -w -x c++ -E -CC -mmcu=atmega328p -DF_CPU=16000000L -DARDUINO=10607 -DARDUINO_AVR_UNO -DARDUINO_ARCH_AVR -I/home/megabug/.arduino15/packages/arduino/hardware/avr/1.8.6/cores/arduino -I/home/megabug/.arduino15/packages/arduino/hardware/avr/1.8.6/variants/standard -I/home/megabug/.arduino15/packages/arduino/hardware/avr/1.8.6/libraries/Wire/src /tmp/arduino/sketches/002050EAA7EFB9A4FC451CDFBC0FA2D3/sketch/Blink.ino.cpp -o /dev/null
/home/megabug/.arduino15/packages/arduino/tools/avr-gcc/7.3.0-atmel3.6.1-arduino7/bin/avr-g++ -c -g -Os -w -std=gnu++11 -fpermissive -fno-exceptions -ffunction-sections -fdata-sections -fno-threadsafe-statics -Wno-error=narrowing -flto -w -x c++ -E -CC -mmcu=atmega328p -DF_CPU=16000000L -DARDUINO=10607 -DARDUINO_AVR_UNO -DARDUINO_ARCH_AVR -I/home/megabug/.arduino15/packages/arduino/hardware/avr/1.8.6/cores/arduino -I/home/megabug/.arduino15/packages/arduino/hardware/avr/1.8.6/variants/standard -I/home/megabug/.arduino15/packages/arduino/hardware/avr/1.8.6/libraries/Wire/src /home/megabug/.arduino15/packages/arduino/hardware/avr/1.8.6/libraries/Wire/src/Wire.cpp -o /dev/null
/home/megabug/.arduino15/packages/arduino/tools/avr-gcc/7.3.0-atmel3.6.1-arduino7/bin/avr-g++ -c -g -Os -w -std=gnu++11 -fpermissive -fno-exceptions -ffunction-sections -fdata-sections -fno-threadsafe-statics -Wno-error=narrowing -flto -w -x c++ -E -CC -mmcu=atmega328p -DF_CPU=16000000L -DARDUINO=10607 -DARDUINO_AVR_UNO -DARDUINO_ARCH_AVR -I/home/megabug/.arduino15/packages/arduino/hardware/avr/1.8.6/cores/arduino -I/home/megabug/.arduino15/packages/arduino/hardware/avr/1.8.6/variants/standard -I/home/megabug/.arduino15/packages/arduino/hardware/avr/1.8.6/libraries/Wire/src /home/megabug/.arduino15/packages/arduino/hardware/avr/1.8.6/libraries/Wire/src/utility/twi.c -o /dev/null
Generating function prototypes...
/home/megabug/.arduino15/packages/arduino/tools/avr-gcc/7.3.0-atmel3.6.1-arduino7/bin/avr-g++ -c -g -Os -w -std=gnu++11 -fpermissive -fno-exceptions -ffunction-sections -fdata-sections -fno-threadsafe-statics -Wno-error=narrowing -flto -w -x c++ -E -CC -mmcu=atmega328p -DF_CPU=16000000L -DARDUINO=10607 -DARDUINO_AVR_UNO -DARDUINO_ARCH_AVR -I/home/megabug/.arduino15/packages/arduino/hardware/avr/1.8.6/cores/arduino -I/home/megabug/.arduino15/packages/arduino/hardware/avr/1.8.6/variants/standard -I/home/megabug/.arduino15/packages/arduino/hardware/avr/1.8.6/libraries/Wire/src /tmp/arduino/sketches/002050EAA7EFB9A4FC451CDFBC0FA2D3/sketch/Blink.ino.cpp -o /tmp/arduino/sketches/002050EAA7EFB9A4FC451CDFBC0FA2D3/preproc/sketch_merged.cpp
/home/megabug/.arduino15/packages/builtin/tools/ctags/5.8-arduino11/ctags -u --language-force=c++ -f - --c++-kinds=svpf --fields=KSTtzns --line-directives /tmp/arduino/sketches/002050EAA7EFB9A4FC451CDFBC0FA2D3/preproc/sketch_merged.cpp
Compiling sketch...
/home/megabug/.arduino15/packages/arduino/tools/avr-gcc/7.3.0-atmel3.6.1-arduino7/bin/avr-g++ -c -g -Os -w -std=gnu++11 -fpermissive -fno-exceptions -ffunction-sections -fdata-sections -fno-threadsafe-statics -Wno-error=narrowing -MMD -flto -mmcu=atmega328p -DF_CPU=16000000L -DARDUINO=10607 -DARDUINO_AVR_UNO -DARDUINO_ARCH_AVR -I/home/megabug/.arduino15/packages/arduino/hardware/avr/1.8.6/cores/arduino -I/home/megabug/.arduino15/packages/arduino/hardware/avr/1.8.6/variants/standard -I/home/megabug/.arduino15/packages/arduino/hardware/avr/1.8.6/libraries/Wire/src /tmp/arduino/sketches/002050EAA7EFB9A4FC451CDFBC0FA2D3/sketch/Blink.ino.cpp -o /tmp/arduino/sketches/002050EAA7EFB9A4FC451CDFBC0FA2D3/sketch/Blink.ino.cpp.o
Compiling libraries...
Compiling library "Wire"
/home/megabug/.arduino15/packages/arduino/tools/avr-gcc/7.3.0-atmel3.6.1-arduino7/bin/avr-g++ -c -g -Os -w -std=gnu++11 -fpermissive -fno-exceptions -ffunction-sections -fdata-sections -fno-threadsafe-statics -Wno-error=narrowing -MMD -flto -mmcu=atmega328p -DF_CPU=16000000L -DARDUINO=10607 -DARDUINO_AVR_UNO -DARDUINO_ARCH_AVR -I/home/megabug/.arduino15/packages/arduino/hardware/avr/1.8.6/cores/arduino -I/home/megabug/.arduino15/packages/arduino/hardware/avr/1.8.6/variants/standard -I/home/megabug/.arduino15/packages/arduino/hardware/avr/1.8.6/libraries/Wire/src /home/megabug/.arduino15/packages/arduino/hardware/avr/1.8.6/libraries/Wire/src/Wire.cpp -o /tmp/arduino/sketches/002050EAA7EFB9A4FC451CDFBC0FA2D3/libraries/Wire/Wire.cpp.o
/home/megabug/.arduino15/packages/arduino/tools/avr-gcc/7.3.0-atmel3.6.1-arduino7/bin/avr-gcc -c -g -Os -w -std=gnu11 -ffunction-sections -fdata-sections -MMD -flto -fno-fat-lto-objects -mmcu=atmega328p -DF_CPU=16000000L -DARDUINO=10607 -DARDUINO_AVR_UNO -DARDUINO_ARCH_AVR -I/home/megabug/.arduino15/packages/arduino/hardware/avr/1.8.6/cores/arduino -I/home/megabug/.arduino15/packages/arduino/hardware/avr/1.8.6/variants/standard -I/home/megabug/.arduino15/packages/arduino/hardware/avr/1.8.6/libraries/Wire/src /home/megabug/.arduino15/packages/arduino/hardware/avr/1.8.6/libraries/Wire/src/utility/twi.c -o /tmp/arduino/sketches/002050EAA7EFB9A4FC451CDFBC0FA2D3/libraries/Wire/utility/twi.c.o
Compiling core...
/home/megabug/.arduino15/packages/arduino/tools/avr-gcc/7.3.0-atmel3.6.1-arduino7/bin/avr-g++ -c -g -Os -w -std=gnu++11 -fpermissive -fno-exceptions -ffunction-sections -fdata-sections -fno-threadsafe-statics -Wno-error=narrowing -MMD -flto -mmcu=atmega328p -DF_CPU=16000000L -DARDUINO=10607 -DARDUINO_AVR_UNO -DARDUINO_ARCH_AVR -I/home/megabug/.arduino15/packages/arduino/hardware/avr/1.8.6/cores/arduino -I/home/megabug/.arduino15/packages/arduino/hardware/avr/1.8.6/variants/standard /home/megabug/.arduino15/packages/arduino/hardware/avr/1.8.6/cores/arduino/HardwareSerial0.cpp -o /tmp/arduino/sketches/002050EAA7EFB9A4FC451CDFBC0FA2D3/core/HardwareSerial0.cpp.o
/home/megabug/.arduino15/packages/arduino/tools/avr-gcc/7.3.0-atmel3.6.1-arduino7/bin/avr-g++ -c -g -Os -w -std=gnu++11 -fpermissive -fno-exceptions -ffunction-sections -fdata-sections -fno-threadsafe-statics -Wno-error=narrowing -MMD -flto -mmcu=atmega328p -DF_CPU=16000000L -DARDUINO=10607 -DARDUINO_AVR_UNO -DARDUINO_ARCH_AVR -I/home/megabug/.arduino15/packages/arduino/hardware/avr/1.8.6/cores/arduino -I/home/megabug/.arduino15/packages/arduino/hardware/avr/1.8.6/variants/standard /home/megabug/.arduino15/packages/arduino/hardware/avr/1.8.6/cores/arduino/IPAddress.cpp -o /tmp/arduino/sketches/002050EAA7EFB9A4FC451CDFBC0FA2D3/core/IPAddress.cpp.o
/home/megabug/.arduino15/packages/arduino/tools/avr-gcc/7.3.0-atmel3.6.1-arduino7/bin/avr-g++ -c -g -Os -w -std=gnu++11 -fpermissive -fno-exceptions -ffunction-sections -fdata-sections -fno-threadsafe-statics -Wno-error=narrowing -MMD -flto -mmcu=atmega328p -DF_CPU=16000000L -DARDUINO=10607 -DARDUINO_AVR_UNO -DARDUINO_ARCH_AVR -I/home/megabug/.arduino15/packages/arduino/hardware/avr/1.8.6/cores/arduino -I/home/megabug/.arduino15/packages/arduino/hardware/avr/1.8.6/variants/standard /home/megabug/.arduino15/packages/arduino/hardware/avr/1.8.6/cores/arduino/HardwareSerial.cpp -o /tmp/arduino/sketches/002050EAA7EFB9A4FC451CDFBC0FA2D3/core/HardwareSerial.cpp.o
/home/megabug/.arduino15/packages/arduino/tools/avr-gcc/7.3.0-atmel3.6.1-arduino7/bin/avr-g++ -c -g -Os -w -std=gnu++11 -fpermissive -fno-exceptions -ffunction-sections -fdata-sections -fno-threadsafe-statics -Wno-error=narrowing -MMD -flto -mmcu=atmega328p -DF_CPU=16000000L -DARDUINO=10607 -DARDUINO_AVR_UNO -DARDUINO_ARCH_AVR -I/home/megabug/.arduino15/packages/arduino/hardware/avr/1.8.6/cores/arduino -I/home/megabug/.arduino15/packages/arduino/hardware/avr/1.8.6/variants/standard /home/megabug/.arduino15/packages/arduino/hardware/avr/1.8.6/cores/arduino/HardwareSerial2.cpp -o /tmp/arduino/sketches/002050EAA7EFB9A4FC451CDFBC0FA2D3/core/HardwareSerial2.cpp.o
/home/megabug/.arduino15/packages/arduino/tools/avr-gcc/7.3.0-atmel3.6.1-arduino7/bin/avr-g++ -c -g -Os -w -std=gnu++11 -fpermissive -fno-exceptions -ffunction-sections -fdata-sections -fno-threadsafe-statics -Wno-error=narrowing -MMD -flto -mmcu=atmega328p -DF_CPU=16000000L -DARDUINO=10607 -DARDUINO_AVR_UNO -DARDUINO_ARCH_AVR -I/home/megabug/.arduino15/packages/arduino/hardware/avr/1.8.6/cores/arduino -I/home/megabug/.arduino15/packages/arduino/hardware/avr/1.8.6/variants/standard /home/megabug/.arduino15/packages/arduino/hardware/avr/1.8.6/cores/arduino/CDC.cpp -o /tmp/arduino/sketches/002050EAA7EFB9A4FC451CDFBC0FA2D3/core/CDC.cpp.o
/home/megabug/.arduino15/packages/arduino/tools/avr-gcc/7.3.0-atmel3.6.1-arduino7/bin/avr-g++ -c -g -Os -w -std=gnu++11 -fpermissive -fno-exceptions -ffunction-sections -fdata-sections -fno-threadsafe-statics -Wno-error=narrowing -MMD -flto -mmcu=atmega328p -DF_CPU=16000000L -DARDUINO=10607 -DARDUINO_AVR_UNO -DARDUINO_ARCH_AVR -I/home/megabug/.arduino15/packages/arduino/hardware/avr/1.8.6/cores/arduino -I/home/megabug/.arduino15/packages/arduino/hardware/avr/1.8.6/variants/standard /home/megabug/.arduino15/packages/arduino/hardware/avr/1.8.6/cores/arduino/PluggableUSB.cpp -o /tmp/arduino/sketches/002050EAA7EFB9A4FC451CDFBC0FA2D3/core/PluggableUSB.cpp.o
/home/megabug/.arduino15/packages/arduino/tools/avr-gcc/7.3.0-atmel3.6.1-arduino7/bin/avr-g++ -c -g -Os -w -std=gnu++11 -fpermissive -fno-exceptions -ffunction-sections -fdata-sections -fno-threadsafe-statics -Wno-error=narrowing -MMD -flto -mmcu=atmega328p -DF_CPU=16000000L -DARDUINO=10607 -DARDUINO_AVR_UNO -DARDUINO_ARCH_AVR -I/home/megabug/.arduino15/packages/arduino/hardware/avr/1.8.6/cores/arduino -I/home/megabug/.arduino15/packages/arduino/hardware/avr/1.8.6/variants/standard /home/megabug/.arduino15/packages/arduino/hardware/avr/1.8.6/cores/arduino/HardwareSerial3.cpp -o /tmp/arduino/sketches/002050EAA7EFB9A4FC451CDFBC0FA2D3/core/HardwareSerial3.cpp.o
/home/megabug/.arduino15/packages/arduino/tools/avr-gcc/7.3.0-atmel3.6.1-arduino7/bin/avr-g++ -c -g -Os -w -std=gnu++11 -fpermissive -fno-exceptions -ffunction-sections -fdata-sections -fno-threadsafe-statics -Wno-error=narrowing -MMD -flto -mmcu=atmega328p -DF_CPU=16000000L -DARDUINO=10607 -DARDUINO_AVR_UNO -DARDUINO_ARCH_AVR -I/home/megabug/.arduino15/packages/arduino/hardware/avr/1.8.6/cores/arduino -I/home/megabug/.arduino15/packages/arduino/hardware/avr/1.8.6/variants/standard /home/megabug/.arduino15/packages/arduino/hardware/avr/1.8.6/cores/arduino/HardwareSerial1.cpp -o /tmp/arduino/sketches/002050EAA7EFB9A4FC451CDFBC0FA2D3/core/HardwareSerial1.cpp.o
/home/megabug/.arduino15/packages/arduino/tools/avr-gcc/7.3.0-atmel3.6.1-arduino7/bin/avr-g++ -c -g -Os -w -std=gnu++11 -fpermissive -fno-exceptions -ffunction-sections -fdata-sections -fno-threadsafe-statics -Wno-error=narrowing -MMD -flto -mmcu=atmega328p -DF_CPU=16000000L -DARDUINO=10607 -DARDUINO_AVR_UNO -DARDUINO_ARCH_AVR -I/home/megabug/.arduino15/packages/arduino/hardware/avr/1.8.6/cores/arduino -I/home/megabug/.arduino15/packages/arduino/hardware/avr/1.8.6/variants/standard /home/megabug/.arduino15/packages/arduino/hardware/avr/1.8.6/cores/arduino/Tone.cpp -o /tmp/arduino/sketches/002050EAA7EFB9A4FC451CDFBC0FA2D3/core/Tone.cpp.o
/home/megabug/.arduino15/packages/arduino/tools/avr-gcc/7.3.0-atmel3.6.1-arduino7/bin/avr-g++ -c -g -Os -w -std=gnu++11 -fpermissive -fno-exceptions -ffunction-sections -fdata-sections -fno-threadsafe-statics -Wno-error=narrowing -MMD -flto -mmcu=atmega328p -DF_CPU=16000000L -DARDUINO=10607 -DARDUINO_AVR_UNO -DARDUINO_ARCH_AVR -I/home/megabug/.arduino15/packages/arduino/hardware/avr/1.8.6/cores/arduino -I/home/megabug/.arduino15/packages/arduino/hardware/avr/1.8.6/variants/standard /home/megabug/.arduino15/packages/arduino/hardware/avr/1.8.6/cores/arduino/Print.cpp -o /tmp/arduino/sketches/002050EAA7EFB9A4FC451CDFBC0FA2D3/core/Print.cpp.o
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/home/megabug/.arduino15/packages/arduino/tools/avr-gcc/7.3.0-atmel3.6.1-arduino7/bin/avr-g++ -c -g -Os -w -std=gnu++11 -fpermissive -fno-exceptions -ffunction-sections -fdata-sections -fno-threadsafe-statics -Wno-error=narrowing -MMD -flto -mmcu=atmega328p -DF_CPU=16000000L -DARDUINO=10607 -DARDUINO_AVR_UNO -DARDUINO_ARCH_AVR -I/home/megabug/.arduino15/packages/arduino/hardware/avr/1.8.6/cores/arduino -I/home/megabug/.arduino15/packages/arduino/hardware/avr/1.8.6/variants/standard /home/megabug/.arduino15/packages/arduino/hardware/avr/1.8.6/cores/arduino/WMath.cpp -o /tmp/arduino/sketches/002050EAA7EFB9A4FC451CDFBC0FA2D3/core/WMath.cpp.o
/home/megabug/.arduino15/packages/arduino/tools/avr-gcc/7.3.0-atmel3.6.1-arduino7/bin/avr-g++ -c -g -Os -w -std=gnu++11 -fpermissive -fno-exceptions -ffunction-sections -fdata-sections -fno-threadsafe-statics -Wno-error=narrowing -MMD -flto -mmcu=atmega328p -DF_CPU=16000000L -DARDUINO=10607 -DARDUINO_AVR_UNO -DARDUINO_ARCH_AVR -I/home/megabug/.arduino15/packages/arduino/hardware/avr/1.8.6/cores/arduino -I/home/megabug/.arduino15/packages/arduino/hardware/avr/1.8.6/variants/standard /home/megabug/.arduino15/packages/arduino/hardware/avr/1.8.6/cores/arduino/WString.cpp -o /tmp/arduino/sketches/002050EAA7EFB9A4FC451CDFBC0FA2D3/core/WString.cpp.o
/home/megabug/.arduino15/packages/arduino/tools/avr-gcc/7.3.0-atmel3.6.1-arduino7/bin/avr-g++ -c -g -Os -w -std=gnu++11 -fpermissive -fno-exceptions -ffunction-sections -fdata-sections -fno-threadsafe-statics -Wno-error=narrowing -MMD -flto -mmcu=atmega328p -DF_CPU=16000000L -DARDUINO=10607 -DARDUINO_AVR_UNO -DARDUINO_ARCH_AVR -I/home/megabug/.arduino15/packages/arduino/hardware/avr/1.8.6/cores/arduino -I/home/megabug/.arduino15/packages/arduino/hardware/avr/1.8.6/variants/standard /home/megabug/.arduino15/packages/arduino/hardware/avr/1.8.6/cores/arduino/abi.cpp -o /tmp/arduino/sketches/002050EAA7EFB9A4FC451CDFBC0FA2D3/core/abi.cpp.o
/home/megabug/.arduino15/packages/arduino/tools/avr-gcc/7.3.0-atmel3.6.1-arduino7/bin/avr-gcc -c -g -Os -w -std=gnu11 -ffunction-sections -fdata-sections -MMD -flto -fno-fat-lto-objects -mmcu=atmega328p -DF_CPU=16000000L -DARDUINO=10607 -DARDUINO_AVR_UNO -DARDUINO_ARCH_AVR -I/home/megabug/.arduino15/packages/arduino/hardware/avr/1.8.6/cores/arduino -I/home/megabug/.arduino15/packages/arduino/hardware/avr/1.8.6/variants/standard /home/megabug/.arduino15/packages/arduino/hardware/avr/1.8.6/cores/arduino/hooks.c -o /tmp/arduino/sketches/002050EAA7EFB9A4FC451CDFBC0FA2D3/core/hooks.c.o
/home/megabug/.arduino15/packages/arduino/tools/avr-gcc/7.3.0-atmel3.6.1-arduino7/bin/avr-g++ -c -g -Os -w -std=gnu++11 -fpermissive -fno-exceptions -ffunction-sections -fdata-sections -fno-threadsafe-statics -Wno-error=narrowing -MMD -flto -mmcu=atmega328p -DF_CPU=16000000L -DARDUINO=10607 -DARDUINO_AVR_UNO -DARDUINO_ARCH_AVR -I/home/megabug/.arduino15/packages/arduino/hardware/avr/1.8.6/cores/arduino -I/home/megabug/.arduino15/packages/arduino/hardware/avr/1.8.6/variants/standard /home/megabug/.arduino15/packages/arduino/hardware/avr/1.8.6/cores/arduino/main.cpp -o /tmp/arduino/sketches/002050EAA7EFB9A4FC451CDFBC0FA2D3/core/main.cpp.o
/home/megabug/.arduino15/packages/arduino/tools/avr-gcc/7.3.0-atmel3.6.1-arduino7/bin/avr-g++ -c -g -Os -w -std=gnu++11 -fpermissive -fno-exceptions -ffunction-sections -fdata-sections -fno-threadsafe-statics -Wno-error=narrowing -MMD -flto -mmcu=atmega328p -DF_CPU=16000000L -DARDUINO=10607 -DARDUINO_AVR_UNO -DARDUINO_ARCH_AVR -I/home/megabug/.arduino15/packages/arduino/hardware/avr/1.8.6/cores/arduino -I/home/megabug/.arduino15/packages/arduino/hardware/avr/1.8.6/variants/standard /home/megabug/.arduino15/packages/arduino/hardware/avr/1.8.6/cores/arduino/new.cpp -o /tmp/arduino/sketches/002050EAA7EFB9A4FC451CDFBC0FA2D3/core/new.cpp.o
/home/megabug/.arduino15/packages/arduino/tools/avr-gcc/7.3.0-atmel3.6.1-arduino7/bin/avr-gcc -c -g -Os -w -std=gnu11 -ffunction-sections -fdata-sections -MMD -flto -fno-fat-lto-objects -mmcu=atmega328p -DF_CPU=16000000L -DARDUINO=10607 -DARDUINO_AVR_UNO -DARDUINO_ARCH_AVR -I/home/megabug/.arduino15/packages/arduino/hardware/avr/1.8.6/cores/arduino -I/home/megabug/.arduino15/packages/arduino/hardware/avr/1.8.6/variants/standard /home/megabug/.arduino15/packages/arduino/hardware/avr/1.8.6/cores/arduino/wiring.c -o /tmp/arduino/sketches/002050EAA7EFB9A4FC451CDFBC0FA2D3/core/wiring.c.o
/home/megabug/.arduino15/packages/arduino/tools/avr-gcc/7.3.0-atmel3.6.1-arduino7/bin/avr-gcc -c -g -Os -w -std=gnu11 -ffunction-sections -fdata-sections -MMD -flto -fno-fat-lto-objects -mmcu=atmega328p -DF_CPU=16000000L -DARDUINO=10607 -DARDUINO_AVR_UNO -DARDUINO_ARCH_AVR -I/home/megabug/.arduino15/packages/arduino/hardware/avr/1.8.6/cores/arduino -I/home/megabug/.arduino15/packages/arduino/hardware/avr/1.8.6/variants/standard /home/megabug/.arduino15/packages/arduino/hardware/avr/1.8.6/cores/arduino/wiring_analog.c -o /tmp/arduino/sketches/002050EAA7EFB9A4FC451CDFBC0FA2D3/core/wiring_analog.c.o
/home/megabug/.arduino15/packages/arduino/tools/avr-gcc/7.3.0-atmel3.6.1-arduino7/bin/avr-gcc -c -g -Os -w -std=gnu11 -ffunction-sections -fdata-sections -MMD -flto -fno-fat-lto-objects -mmcu=atmega328p -DF_CPU=16000000L -DARDUINO=10607 -DARDUINO_AVR_UNO -DARDUINO_ARCH_AVR -I/home/megabug/.arduino15/packages/arduino/hardware/avr/1.8.6/cores/arduino -I/home/megabug/.arduino15/packages/arduino/hardware/avr/1.8.6/variants/standard /home/megabug/.arduino15/packages/arduino/hardware/avr/1.8.6/cores/arduino/wiring_digital.c -o /tmp/arduino/sketches/002050EAA7EFB9A4FC451CDFBC0FA2D3/core/wiring_digital.c.o
/home/megabug/.arduino15/packages/arduino/tools/avr-gcc/7.3.0-atmel3.6.1-arduino7/bin/avr-gcc -c -g -x assembler-with-cpp -flto -MMD -mmcu=atmega328p -DF_CPU=16000000L -DARDUINO=10607 -DARDUINO_AVR_UNO -DARDUINO_ARCH_AVR -I/home/megabug/.arduino15/packages/arduino/hardware/avr/1.8.6/cores/arduino -I/home/megabug/.arduino15/packages/arduino/hardware/avr/1.8.6/variants/standard /home/megabug/.arduino15/packages/arduino/hardware/avr/1.8.6/cores/arduino/wiring_pulse.S -o /tmp/arduino/sketches/002050EAA7EFB9A4FC451CDFBC0FA2D3/core/wiring_pulse.S.o
/home/megabug/.arduino15/packages/arduino/tools/avr-gcc/7.3.0-atmel3.6.1-arduino7/bin/avr-gcc -c -g -Os -w -std=gnu11 -ffunction-sections -fdata-sections -MMD -flto -fno-fat-lto-objects -mmcu=atmega328p -DF_CPU=16000000L -DARDUINO=10607 -DARDUINO_AVR_UNO -DARDUINO_ARCH_AVR -I/home/megabug/.arduino15/packages/arduino/hardware/avr/1.8.6/cores/arduino -I/home/megabug/.arduino15/packages/arduino/hardware/avr/1.8.6/variants/standard /home/megabug/.arduino15/packages/arduino/hardware/avr/1.8.6/cores/arduino/wiring_pulse.c -o /tmp/arduino/sketches/002050EAA7EFB9A4FC451CDFBC0FA2D3/core/wiring_pulse.c.o
/home/megabug/.arduino15/packages/arduino/tools/avr-gcc/7.3.0-atmel3.6.1-arduino7/bin/avr-gcc -c -g -Os -w -std=gnu11 -ffunction-sections -fdata-sections -MMD -flto -fno-fat-lto-objects -mmcu=atmega328p -DF_CPU=16000000L -DARDUINO=10607 -DARDUINO_AVR_UNO -DARDUINO_ARCH_AVR -I/home/megabug/.arduino15/packages/arduino/hardware/avr/1.8.6/cores/arduino -I/home/megabug/.arduino15/packages/arduino/hardware/avr/1.8.6/variants/standard /home/megabug/.arduino15/packages/arduino/hardware/avr/1.8.6/cores/arduino/wiring_shift.c -o /tmp/arduino/sketches/002050EAA7EFB9A4FC451CDFBC0FA2D3/core/wiring_shift.c.o
/home/megabug/.arduino15/packages/arduino/tools/avr-gcc/7.3.0-atmel3.6.1-arduino7/bin/avr-gcc-ar rcs /tmp/arduino/sketches/002050EAA7EFB9A4FC451CDFBC0FA2D3/core/core.a /tmp/arduino/sketches/002050EAA7EFB9A4FC451CDFBC0FA2D3/core/CDC.cpp.o
/home/megabug/.arduino15/packages/arduino/tools/avr-gcc/7.3.0-atmel3.6.1-arduino7/bin/avr-gcc-ar rcs /tmp/arduino/sketches/002050EAA7EFB9A4FC451CDFBC0FA2D3/core/core.a /tmp/arduino/sketches/002050EAA7EFB9A4FC451CDFBC0FA2D3/core/HardwareSerial.cpp.o
/home/megabug/.arduino15/packages/arduino/tools/avr-gcc/7.3.0-atmel3.6.1-arduino7/bin/avr-gcc-ar rcs /tmp/arduino/sketches/002050EAA7EFB9A4FC451CDFBC0FA2D3/core/core.a /tmp/arduino/sketches/002050EAA7EFB9A4FC451CDFBC0FA2D3/core/HardwareSerial0.cpp.o
/home/megabug/.arduino15/packages/arduino/tools/avr-gcc/7.3.0-atmel3.6.1-arduino7/bin/avr-gcc-ar rcs /tmp/arduino/sketches/002050EAA7EFB9A4FC451CDFBC0FA2D3/core/core.a /tmp/arduino/sketches/002050EAA7EFB9A4FC451CDFBC0FA2D3/core/HardwareSerial1.cpp.o
/home/megabug/.arduino15/packages/arduino/tools/avr-gcc/7.3.0-atmel3.6.1-arduino7/bin/avr-gcc-ar rcs /tmp/arduino/sketches/002050EAA7EFB9A4FC451CDFBC0FA2D3/core/core.a /tmp/arduino/sketches/002050EAA7EFB9A4FC451CDFBC0FA2D3/core/HardwareSerial2.cpp.o
/home/megabug/.arduino15/packages/arduino/tools/avr-gcc/7.3.0-atmel3.6.1-arduino7/bin/avr-gcc-ar rcs /tmp/arduino/sketches/002050EAA7EFB9A4FC451CDFBC0FA2D3/core/core.a /tmp/arduino/sketches/002050EAA7EFB9A4FC451CDFBC0FA2D3/core/HardwareSerial3.cpp.o
/home/megabug/.arduino15/packages/arduino/tools/avr-gcc/7.3.0-atmel3.6.1-arduino7/bin/avr-gcc-ar rcs /tmp/arduino/sketches/002050EAA7EFB9A4FC451CDFBC0FA2D3/core/core.a /tmp/arduino/sketches/002050EAA7EFB9A4FC451CDFBC0FA2D3/core/IPAddress.cpp.o
/home/megabug/.arduino15/packages/arduino/tools/avr-gcc/7.3.0-atmel3.6.1-arduino7/bin/avr-gcc-ar rcs /tmp/arduino/sketches/002050EAA7EFB9A4FC451CDFBC0FA2D3/core/core.a /tmp/arduino/sketches/002050EAA7EFB9A4FC451CDFBC0FA2D3/core/PluggableUSB.cpp.o
/home/megabug/.arduino15/packages/arduino/tools/avr-gcc/7.3.0-atmel3.6.1-arduino7/bin/avr-gcc-ar rcs /tmp/arduino/sketches/002050EAA7EFB9A4FC451CDFBC0FA2D3/core/core.a /tmp/arduino/sketches/002050EAA7EFB9A4FC451CDFBC0FA2D3/core/Print.cpp.o
/home/megabug/.arduino15/packages/arduino/tools/avr-gcc/7.3.0-atmel3.6.1-arduino7/bin/avr-gcc-ar rcs /tmp/arduino/sketches/002050EAA7EFB9A4FC451CDFBC0FA2D3/core/core.a /tmp/arduino/sketches/002050EAA7EFB9A4FC451CDFBC0FA2D3/core/Stream.cpp.o
/home/megabug/.arduino15/packages/arduino/tools/avr-gcc/7.3.0-atmel3.6.1-arduino7/bin/avr-gcc-ar rcs /tmp/arduino/sketches/002050EAA7EFB9A4FC451CDFBC0FA2D3/core/core.a /tmp/arduino/sketches/002050EAA7EFB9A4FC451CDFBC0FA2D3/core/Tone.cpp.o
/home/megabug/.arduino15/packages/arduino/tools/avr-gcc/7.3.0-atmel3.6.1-arduino7/bin/avr-gcc-ar rcs /tmp/arduino/sketches/002050EAA7EFB9A4FC451CDFBC0FA2D3/core/core.a /tmp/arduino/sketches/002050EAA7EFB9A4FC451CDFBC0FA2D3/core/USBCore.cpp.o
/home/megabug/.arduino15/packages/arduino/tools/avr-gcc/7.3.0-atmel3.6.1-arduino7/bin/avr-gcc-ar rcs /tmp/arduino/sketches/002050EAA7EFB9A4FC451CDFBC0FA2D3/core/core.a /tmp/arduino/sketches/002050EAA7EFB9A4FC451CDFBC0FA2D3/core/WInterrupts.c.o
/home/megabug/.arduino15/packages/arduino/tools/avr-gcc/7.3.0-atmel3.6.1-arduino7/bin/avr-gcc-ar rcs /tmp/arduino/sketches/002050EAA7EFB9A4FC451CDFBC0FA2D3/core/core.a /tmp/arduino/sketches/002050EAA7EFB9A4FC451CDFBC0FA2D3/core/WMath.cpp.o
/home/megabug/.arduino15/packages/arduino/tools/avr-gcc/7.3.0-atmel3.6.1-arduino7/bin/avr-gcc-ar rcs /tmp/arduino/sketches/002050EAA7EFB9A4FC451CDFBC0FA2D3/core/core.a /tmp/arduino/sketches/002050EAA7EFB9A4FC451CDFBC0FA2D3/core/WString.cpp.o
/home/megabug/.arduino15/packages/arduino/tools/avr-gcc/7.3.0-atmel3.6.1-arduino7/bin/avr-gcc-ar rcs /tmp/arduino/sketches/002050EAA7EFB9A4FC451CDFBC0FA2D3/core/core.a /tmp/arduino/sketches/002050EAA7EFB9A4FC451CDFBC0FA2D3/core/abi.cpp.o
/home/megabug/.arduino15/packages/arduino/tools/avr-gcc/7.3.0-atmel3.6.1-arduino7/bin/avr-gcc-ar rcs /tmp/arduino/sketches/002050EAA7EFB9A4FC451CDFBC0FA2D3/core/core.a /tmp/arduino/sketches/002050EAA7EFB9A4FC451CDFBC0FA2D3/core/hooks.c.o
/home/megabug/.arduino15/packages/arduino/tools/avr-gcc/7.3.0-atmel3.6.1-arduino7/bin/avr-gcc-ar rcs /tmp/arduino/sketches/002050EAA7EFB9A4FC451CDFBC0FA2D3/core/core.a /tmp/arduino/sketches/002050EAA7EFB9A4FC451CDFBC0FA2D3/core/main.cpp.o
/home/megabug/.arduino15/packages/arduino/tools/avr-gcc/7.3.0-atmel3.6.1-arduino7/bin/avr-gcc-ar rcs /tmp/arduino/sketches/002050EAA7EFB9A4FC451CDFBC0FA2D3/core/core.a /tmp/arduino/sketches/002050EAA7EFB9A4FC451CDFBC0FA2D3/core/new.cpp.o
/home/megabug/.arduino15/packages/arduino/tools/avr-gcc/7.3.0-atmel3.6.1-arduino7/bin/avr-gcc-ar rcs /tmp/arduino/sketches/002050EAA7EFB9A4FC451CDFBC0FA2D3/core/core.a /tmp/arduino/sketches/002050EAA7EFB9A4FC451CDFBC0FA2D3/core/wiring.c.o
/home/megabug/.arduino15/packages/arduino/tools/avr-gcc/7.3.0-atmel3.6.1-arduino7/bin/avr-gcc-ar rcs /tmp/arduino/sketches/002050EAA7EFB9A4FC451CDFBC0FA2D3/core/core.a /tmp/arduino/sketches/002050EAA7EFB9A4FC451CDFBC0FA2D3/core/wiring_analog.c.o
/home/megabug/.arduino15/packages/arduino/tools/avr-gcc/7.3.0-atmel3.6.1-arduino7/bin/avr-gcc-ar rcs /tmp/arduino/sketches/002050EAA7EFB9A4FC451CDFBC0FA2D3/core/core.a /tmp/arduino/sketches/002050EAA7EFB9A4FC451CDFBC0FA2D3/core/wiring_digital.c.o
/home/megabug/.arduino15/packages/arduino/tools/avr-gcc/7.3.0-atmel3.6.1-arduino7/bin/avr-gcc-ar rcs /tmp/arduino/sketches/002050EAA7EFB9A4FC451CDFBC0FA2D3/core/core.a /tmp/arduino/sketches/002050EAA7EFB9A4FC451CDFBC0FA2D3/core/wiring_pulse.S.o
/home/megabug/.arduino15/packages/arduino/tools/avr-gcc/7.3.0-atmel3.6.1-arduino7/bin/avr-gcc-ar rcs /tmp/arduino/sketches/002050EAA7EFB9A4FC451CDFBC0FA2D3/core/core.a /tmp/arduino/sketches/002050EAA7EFB9A4FC451CDFBC0FA2D3/core/wiring_pulse.c.o
/home/megabug/.arduino15/packages/arduino/tools/avr-gcc/7.3.0-atmel3.6.1-arduino7/bin/avr-gcc-ar rcs /tmp/arduino/sketches/002050EAA7EFB9A4FC451CDFBC0FA2D3/core/core.a /tmp/arduino/sketches/002050EAA7EFB9A4FC451CDFBC0FA2D3/core/wiring_shift.c.o
Archiving built core (caching) in: /tmp/arduino/cores/arduino_avr_uno_12e4cfbdc0590d50ab9cd20e50a4c3c5/core.a
Linking everything together...
/home/megabug/.arduino15/packages/arduino/tools/avr-gcc/7.3.0-atmel3.6.1-arduino7/bin/avr-gcc -w -Os -g -flto -fuse-linker-plugin -Wl,--gc-sections -mmcu=atmega328p -o /tmp/arduino/sketches/002050EAA7EFB9A4FC451CDFBC0FA2D3/Blink.ino.elf /tmp/arduino/sketches/002050EAA7EFB9A4FC451CDFBC0FA2D3/sketch/Blink.ino.cpp.o /tmp/arduino/sketches/002050EAA7EFB9A4FC451CDFBC0FA2D3/libraries/Wire/Wire.cpp.o /tmp/arduino/sketches/002050EAA7EFB9A4FC451CDFBC0FA2D3/libraries/Wire/utility/twi.c.o /tmp/arduino/sketches/002050EAA7EFB9A4FC451CDFBC0FA2D3/core/core.a -L/tmp/arduino/sketches/002050EAA7EFB9A4FC451CDFBC0FA2D3 -lm
/home/megabug/.arduino15/packages/arduino/tools/avr-gcc/7.3.0-atmel3.6.1-arduino7/bin/avr-objcopy -O ihex -j .eeprom --set-section-flags=.eeprom=alloc,load --no-change-warnings --change-section-lma .eeprom=0 /tmp/arduino/sketches/002050EAA7EFB9A4FC451CDFBC0FA2D3/Blink.ino.elf /tmp/arduino/sketches/002050EAA7EFB9A4FC451CDFBC0FA2D3/Blink.ino.eep
/home/megabug/.arduino15/packages/arduino/tools/avr-gcc/7.3.0-atmel3.6.1-arduino7/bin/avr-objcopy -O ihex -R .eeprom /tmp/arduino/sketches/002050EAA7EFB9A4FC451CDFBC0FA2D3/Blink.ino.elf /tmp/arduino/sketches/002050EAA7EFB9A4FC451CDFBC0FA2D3/Blink.ino.hex
Multiple libraries were found for "Wire.h"
  Used: /home/megabug/.arduino15/packages/arduino/hardware/avr/1.8.6/libraries/Wire
  Not used: /home/megabug/Workspace/Arduino_Threads
Using library Wire at version 1.0 in folder: /home/megabug/.arduino15/packages/arduino/hardware/avr/1.8.6/libraries/Wire 
/home/megabug/.arduino15/packages/arduino/tools/avr-gcc/7.3.0-atmel3.6.1-arduino7/bin/avr-size -A /tmp/arduino/sketches/002050EAA7EFB9A4FC451CDFBC0FA2D3/Blink.ino.elf
Sketch uses 1636 bytes (5%) of program storage space. Maximum is 32256 bytes.
Global variables use 122 bytes (5%) of dynamic memory, leaving 1926 bytes for local variables. Maximum is 2048 bytes.

Used library Version Path                                                                       
Wire         1.0     /home/megabug/.arduino15/packages/arduino/hardware/avr/1.8.6/libraries/Wire

Used platform Version Path                                                        
arduino:avr   1.8.6   /home/megabug/.arduino15/packages/arduino/hardware/avr/1.8.6
~/Arduino/Blink$

and this is the same compile after immediately re-running it:

~/Arduino/Blink$ LANG=en arduino-cli compile -b arduino:avr:uno -v
FQBN: arduino:avr:uno
Using board 'uno' from platform in folder: /home/megabug/.arduino15/packages/arduino/hardware/avr/1.8.6
Using core 'arduino' from platform in folder: /home/megabug/.arduino15/packages/arduino/hardware/avr/1.8.6

Detecting libraries used...
/home/megabug/.arduino15/packages/arduino/tools/avr-gcc/7.3.0-atmel3.6.1-arduino7/bin/avr-g++ -c -g -Os -w -std=gnu++11 -fpermissive -fno-exceptions -ffunction-sections -fdata-sections -fno-threadsafe-statics -Wno-error=narrowing -flto -w -x c++ -E -CC -mmcu=atmega328p -DF_CPU=16000000L -DARDUINO=10607 -DARDUINO_AVR_UNO -DARDUINO_ARCH_AVR -I/home/megabug/.arduino15/packages/arduino/hardware/avr/1.8.6/cores/arduino -I/home/megabug/.arduino15/packages/arduino/hardware/avr/1.8.6/variants/standard /tmp/arduino/sketches/002050EAA7EFB9A4FC451CDFBC0FA2D3/sketch/Blink.ino.cpp -o /dev/null
Alternatives for Wire.h: [Arduino_Threads@0.0.1 Wire@1.0]
ResolveLibrary(Wire.h)
  -> candidates: [Arduino_Threads@0.0.1 Wire@1.0]
/home/megabug/.arduino15/packages/arduino/tools/avr-gcc/7.3.0-atmel3.6.1-arduino7/bin/avr-g++ -c -g -Os -w -std=gnu++11 -fpermissive -fno-exceptions -ffunction-sections -fdata-sections -fno-threadsafe-statics -Wno-error=narrowing -flto -w -x c++ -E -CC -mmcu=atmega328p -DF_CPU=16000000L -DARDUINO=10607 -DARDUINO_AVR_UNO -DARDUINO_ARCH_AVR -I/home/megabug/.arduino15/packages/arduino/hardware/avr/1.8.6/cores/arduino -I/home/megabug/.arduino15/packages/arduino/hardware/avr/1.8.6/variants/standard -I/home/megabug/.arduino15/packages/arduino/hardware/avr/1.8.6/libraries/Wire/src /tmp/arduino/sketches/002050EAA7EFB9A4FC451CDFBC0FA2D3/sketch/Blink.ino.cpp -o /dev/null
Using cached library dependencies for file: /home/megabug/.arduino15/packages/arduino/hardware/avr/1.8.6/libraries/Wire/src/Wire.cpp
Using cached library dependencies for file: /home/megabug/.arduino15/packages/arduino/hardware/avr/1.8.6/libraries/Wire/src/utility/twi.c
Generating function prototypes...
/home/megabug/.arduino15/packages/arduino/tools/avr-gcc/7.3.0-atmel3.6.1-arduino7/bin/avr-g++ -c -g -Os -w -std=gnu++11 -fpermissive -fno-exceptions -ffunction-sections -fdata-sections -fno-threadsafe-statics -Wno-error=narrowing -flto -w -x c++ -E -CC -mmcu=atmega328p -DF_CPU=16000000L -DARDUINO=10607 -DARDUINO_AVR_UNO -DARDUINO_ARCH_AVR -I/home/megabug/.arduino15/packages/arduino/hardware/avr/1.8.6/cores/arduino -I/home/megabug/.arduino15/packages/arduino/hardware/avr/1.8.6/variants/standard -I/home/megabug/.arduino15/packages/arduino/hardware/avr/1.8.6/libraries/Wire/src /tmp/arduino/sketches/002050EAA7EFB9A4FC451CDFBC0FA2D3/sketch/Blink.ino.cpp -o /tmp/arduino/sketches/002050EAA7EFB9A4FC451CDFBC0FA2D3/preproc/sketch_merged.cpp
/home/megabug/.arduino15/packages/builtin/tools/ctags/5.8-arduino11/ctags -u --language-force=c++ -f - --c++-kinds=svpf --fields=KSTtzns --line-directives /tmp/arduino/sketches/002050EAA7EFB9A4FC451CDFBC0FA2D3/preproc/sketch_merged.cpp
Compiling sketch...
/home/megabug/.arduino15/packages/arduino/tools/avr-gcc/7.3.0-atmel3.6.1-arduino7/bin/avr-g++ -c -g -Os -w -std=gnu++11 -fpermissive -fno-exceptions -ffunction-sections -fdata-sections -fno-threadsafe-statics -Wno-error=narrowing -MMD -flto -mmcu=atmega328p -DF_CPU=16000000L -DARDUINO=10607 -DARDUINO_AVR_UNO -DARDUINO_ARCH_AVR -I/home/megabug/.arduino15/packages/arduino/hardware/avr/1.8.6/cores/arduino -I/home/megabug/.arduino15/packages/arduino/hardware/avr/1.8.6/variants/standard -I/home/megabug/.arduino15/packages/arduino/hardware/avr/1.8.6/libraries/Wire/src /tmp/arduino/sketches/002050EAA7EFB9A4FC451CDFBC0FA2D3/sketch/Blink.ino.cpp -o /tmp/arduino/sketches/002050EAA7EFB9A4FC451CDFBC0FA2D3/sketch/Blink.ino.cpp.o
Compiling libraries...
Compiling library "Wire"
Using previously compiled file: /tmp/arduino/sketches/002050EAA7EFB9A4FC451CDFBC0FA2D3/libraries/Wire/utility/twi.c.o
Using previously compiled file: /tmp/arduino/sketches/002050EAA7EFB9A4FC451CDFBC0FA2D3/libraries/Wire/Wire.cpp.o
Compiling core...
Using precompiled core: /tmp/arduino/cores/arduino_avr_uno_12e4cfbdc0590d50ab9cd20e50a4c3c5/core.a
Linking everything together...
/home/megabug/.arduino15/packages/arduino/tools/avr-gcc/7.3.0-atmel3.6.1-arduino7/bin/avr-gcc -w -Os -g -flto -fuse-linker-plugin -Wl,--gc-sections -mmcu=atmega328p -o /tmp/arduino/sketches/002050EAA7EFB9A4FC451CDFBC0FA2D3/Blink.ino.elf /tmp/arduino/sketches/002050EAA7EFB9A4FC451CDFBC0FA2D3/sketch/Blink.ino.cpp.o /tmp/arduino/sketches/002050EAA7EFB9A4FC451CDFBC0FA2D3/libraries/Wire/Wire.cpp.o /tmp/arduino/sketches/002050EAA7EFB9A4FC451CDFBC0FA2D3/libraries/Wire/utility/twi.c.o /tmp/arduino/sketches/002050EAA7EFB9A4FC451CDFBC0FA2D3/../../cores/arduino_avr_uno_12e4cfbdc0590d50ab9cd20e50a4c3c5/core.a -L/tmp/arduino/sketches/002050EAA7EFB9A4FC451CDFBC0FA2D3 -lm
/home/megabug/.arduino15/packages/arduino/tools/avr-gcc/7.3.0-atmel3.6.1-arduino7/bin/avr-objcopy -O ihex -j .eeprom --set-section-flags=.eeprom=alloc,load --no-change-warnings --change-section-lma .eeprom=0 /tmp/arduino/sketches/002050EAA7EFB9A4FC451CDFBC0FA2D3/Blink.ino.elf /tmp/arduino/sketches/002050EAA7EFB9A4FC451CDFBC0FA2D3/Blink.ino.eep
/home/megabug/.arduino15/packages/arduino/tools/avr-gcc/7.3.0-atmel3.6.1-arduino7/bin/avr-objcopy -O ihex -R .eeprom /tmp/arduino/sketches/002050EAA7EFB9A4FC451CDFBC0FA2D3/Blink.ino.elf /tmp/arduino/sketches/002050EAA7EFB9A4FC451CDFBC0FA2D3/Blink.ino.hex
Multiple libraries were found for "Wire.h"
  Used: /home/megabug/.arduino15/packages/arduino/hardware/avr/1.8.6/libraries/Wire
  Not used: /home/megabug/Workspace/Arduino_Threads
Using library Wire at version 1.0 in folder: /home/megabug/.arduino15/packages/arduino/hardware/avr/1.8.6/libraries/Wire 
/home/megabug/.arduino15/packages/arduino/tools/avr-gcc/7.3.0-atmel3.6.1-arduino7/bin/avr-size -A /tmp/arduino/sketches/002050EAA7EFB9A4FC451CDFBC0FA2D3/Blink.ino.elf
Sketch uses 1636 bytes (5%) of program storage space. Maximum is 32256 bytes.
Global variables use 122 bytes (5%) of dynamic memory, leaving 1926 bytes for local variables. Maximum is 2048 bytes.

Used library Version Path                                                                       
Wire         1.0     /home/megabug/.arduino15/packages/arduino/hardware/avr/1.8.6/libraries/Wire

Used platform Version Path                                                        
arduino:avr   1.8.6   /home/megabug/.arduino15/packages/arduino/hardware/avr/1.8.6

The second run is resuing almost everything from the cache except on:

1. The Detecting libraries used... phase. This is the slowest. It's also not easy to fully cache and/or parallelize, because it actually requires running gcc -E on the sketch to check if there are missing includes (the installed libraries may have changed in the meantime). The same process must be done on all the compilation units in the included libraries: this may become very long if there are hundreds of files.
2. The sketch itself is compiled and linked again even if there are no changes.

About problem 2: this could be surely improved even if the gain is very little compared to the overall compilation time. I opened #2204 to track this one.

About problem 1: there is an interesting tentative here #1735 but it's flaky, BTW it gave some ideas to work on to actually get to a correct solution, I made a preparatory PR here #1766 to clean up the library resolution code in preparation of a bigger refactoring.

[weswitt]

and i consider the automatic library detection a gimmick and unnecessary. as the author of the code i know exactly which libraries i'm using can can easily declare their use. have a faster, more efficient build is WAY more important than library detection.

[apos]

THIS IS SO ANNOYING. Really. Together with the exhaustive compilation times, not just on Windows, also on Linux for V. 2x - this is not acceptable.

Wherever I can, I use now PlatformIO. Unfortunately, this is not possible with every Arduino project.

This problem persists now a long time. Sorry - this can not be accepted. The Arduino IDE is for beginners and should not sugest, C compiling takes forever. I am doing programming now for a long time (decades), but I never saw such a poor implementation. Normally, I would not post such negative thoughts. But the problem is: this simple facts, which EVERY other IDE has solved for ages, still exists.