Granular optimisation settings

PlatformIO Core
2

As per documentation on Advanced Scripting, it’s possible to arbitrarily modify the compiler flags of any file.

Example:

[env:nucleo_g071rb]
platform = ststm32
board = nucleo_g071rb
framework = arduino
build_type = debug 
extra_scripts = pre:modify_debug.py

and modify_debug.py in the root of the project

Import("env")

def exchange_debug_for_optimize_flag(node):
    # ignore certain files that are supposed to 
    # retain -Og
    sources_keep_debugging_info = [
        "main.cpp"
    ]
    #print("Node %s env.GetBuildType()=%s" % (node.name, str(env.GetBuildType())))
    # calculate compiler flags without optimization flags
    old_cflags = env["CCFLAGS"]
    new_cflags = [opt for opt in old_cflags if opt != "-Og" and opt != "-Os"]
    if node.name in sources_keep_debugging_info:
        new_cflags += ["-Og", "-g3", "-ggdb3"]
        return env.Object(
            node,
            CCFLAGS=new_cflags
        )
    else:
        new_cflags += ["-Os"]
        return env.Object(
            node,
            CCFLAGS=new_cflags
        )

# add modification functions to every file in build, but only for debug builds
if env.GetBuildType() == "debug":
    env.AddBuildMiddleware(exchange_debug_for_optimize_flag)

This will e.g. cause all files to be compiled with -Os, except the ones in the list sources_keep_debugging_info in which main.cpp is, which will get -Og -g3 -ggdb3. The whole thing is guarded by checking if the build type is “debug”, so the script does nothing during release build.

You can e.g. see that it works when you add build_type = debug in the platformio.ini to force a debug-mode compilation, and then use “Verbose Build” to see all compiler invocations.

For main.cpp

arm-none-eabi-g++ -o .pio\build\nucleo_g071rb\FrameworkArduino\main.cpp.o -c -std=gnu++14 -fno-threadsafe-statics -fno-rtti -fno-exceptions -fno-use-cxa-atexit -mcpu=cortex-m0plus -mthumb -ffunction-sections -fdata-sections -Wall -nostdlib --param max-inline-insns-single=500 -Og -g3 -ggdb3 -DPLATFORMIO=50200 […]

For all other files

arm-none-eabi-gcc -o .pio\build\nucleo_g071rb\FrameworkArduino\itoa.c.o -c -std=gnu11 -mcpu=cortex-m0plus -mthumb -ffunction-sections -fdata-sections -Wall -nostdlib --param max-inline-insns-single=500 -Os -DPLATFORMIO=50200 […]

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