[Vm-dev] ARM Cog progress

Tobias Pape Das.Linux at gmx.de
Sun Jun 7 16:35:42 UTC 2015


On 07.06.2015, at 17:58, tim Rowledge <tim at rowledge.org> wrote:

> 
> 
> On 07-06-2015, at 12:32 AM, Holger Freyther <holger at freyther.de> wrote:
>>> On 07 Jun 2015, at 01:25, tim Rowledge <tim at rowledge.org> wrote:
>>> 
>>> 
>>> GCC is such fun.
>> 
>> given the amount of warnings emitted during compilation, have you considered
>> that it might be the input given to gcc that is the issue here? ;)
> 
> I dunno; I get a total of 59 warnings when compiling the ARM Cog VM, none in the core vm code. I’d love to see it be 0. I rather suspect the world would come to an end if that happened.
> 
> On the other hand, I can’t see how it is acceptable for a compiler to produce code that blows up at one level of optimisation but not at another. Come to that I’m not sure why there are different levels; I can sort of see asking to optimise in different ways  - the NorCroft compiler for ARM can be asked to optimise for runtime speed or executable size, for example.
> 

not so uncommon:

gcc:
	-O0	no opt
	-O1	'Optimize' (= -O)
	-O2	'Optimize even more' 
	-O3	'Optimize yet more'
	-Os	'Optimize for size' (like -O2 minus size-increasing opts)
	-Ofast	'Disregard strict standards compliance'

clang: as gcc, plus

	-Oz 	'Like -Os (and thus -O2), but reduces code size further'
	(-O4	'currently like -O3')

	-flto	'Generate output files in LLVM formats, suitable for link time optimization'


Also: a lot of -f… flags

Best regards
	-Tobias


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