RFR: 8236714: enable link-time section-gc for linux to remove unused code

[David Holmes]

Hi Matthias,

On 16/01/2020 6:10 pm, Baesken, Matthias wrote:
> Hi David, sure we can introduce a way to switch this on/off.

Thanks.

> There is already something similar for the link-time optimization (flto) , see the feature
> 
> JvmFeatures.gmk
> 180 ifeq ($(call check-jvm-feature, link-time-opt), true)
> 190 ifeq ($(call check-jvm-feature, link-time-opt), false)
> 
> hotspot.m4
> 29 static-build link-time-opt aot jfr"
> 502 JVM_FEATURES_link_time_opt="link-time-opt"

Yep familiar with that from Minimal VM and SE Embedded days :)

> Should we have  "link-time-gc"  additionally to   " link-time-opt"  ?   (however it  would  be a  bit misleading   that it is a "JVM" feature , but except linux s390x  it is only changing the build of the JDK libs) .

I agree the definition of this as a "JVM" feature is a bit 
odd/misleading. Perhaps the build folk have a suggestion on how to 
refactor this kind of option into something more general? In the 
meantime having link-time-gc sit alongside link-time-opt seems 
acceptable to me.

Thanks,
David

> Best regards, Matthias
> 
> 
> 
>>
>> Hi Matthias,
>>
>> I have reservations about turning this on by default and with no way to
>> control it. This seems like it should be something you have to opt-in to
>> initially while we gain some experience with it and ensure there are no
>> unexpected side-effects. After that it could be enabled by default.
>>
>