Add option to enable LTO easily

[drashna]

and disable features that cause compilation errors when LTO is enabled.

Added to tmk_core/common.mk rather than common_features.mk, since it's not really a feature.

[yanfali]

Maybe add a warning about what you are disabling

[drashna]

I should probably add docs for this too....
That would be a better place for the warnings.

[mtei]

Previously, the advice you gave was to add #define DISABLE_LEADER to config.h. Is this not necessary now?

#3546 (comment)

[drashna]

Previously, the advice you gave was to add #define DISABLE_LEADER to config.h. Is this not necessary now?

At the time, it was true. However, it's since been moved into it's own "feature" that is off by default, and only enabled if you add LEADER_ENABLE=yes to the makefile settings.

Also, the only reason I have it turning off the macros and functions is that enabling LTO can/will break those features.

[mtei]

I see.

FYI, there are also the following ways.

tmk_core/common.mk:

ifeq ($(strip $(LINK_TIME_OPTIMIZATION_ENABLE)), yes)
	    EXTRAFLAGS += -flto
	    POST_CONFIG_H += $(TMK_DIR)/post_config.h
	    TMK_COMMON_DEFS += -DLINK_TIME_OPTIMIZATION_ENABLE
endif

tmk_core/post_config.h:

#pragma once
#ifdef LINK_TIME_OPTIMIZATION_ENABLE
  #define NO_ACTION_MACRO
  #define NO_ACTION_FUNCTION
  #ifdef LEADER_ENABLE
    #error  some error message
  #endif
#endif

[drashna]

@mtei That would definitely work. But there is no reason to disable Leader Keys here. In fact, I think doing so is a bad idea, actually. I think that we should use the "lightest touch" here, and not disable anything, unless it's needed (aka it's breaking something).

[mtei]

OK, you are right. I do not know the relationship between LTO and LEADER_ENABLE. Just simply, if you need collision detection, just let you know that there is a way.

[vomindoraan]

Consider LTO_ENABLE instead of LINK_TIME_OPTIMIZATION_ENABLE.

[mtei]

ifeq ($(filter $(LTO_ENABLE) $(LINK_TIME_OPTIMIZATION_ENABLE),yes), yes)

[mechmerlin]

Thanks!