RFR: 8292329: Enable CDS shared heap for zero builds [v2]

[Erik Joelsson]

On Tue, 23 Aug 2022 22:08:10 GMT, Erik Joelsson <erikj at openjdk.org> wrote:

>> @erikj79 I couldn't get it to work. I believe the following is evaluated only once, so `$(JVM_VARIANT)` is bound to the value when HotspotCommon.gmk is loaded:
>> 
>> 
>> check-jvm-feature = \
>>   $(strip \
>>     $(if $(filter-out $(VALID_JVM_FEATURES), $1), \
>>       $(error Internal error: Invalid feature tested: $1)) \
>>     $(if $(filter $1, $(JVM_FEATURES_$(JVM_VARIANT))), true, false))
>> 
>> 
>> So I would need to run a submake in order to get this function to behave differently for each variant. That's going to be complicated in order to support multiple JVM variants per build.
>> 
>> I heard that we are going to remove multiple variant support (?), so maybe this is not worth it.
>
> The suggested code should be something like this, note the double `$$` in the call.
> 
> Suggestion:
> 
>   $1_$2_CDS_DUMP_FLAGS := $$(CDS_DUMP_FLAGS)
>   ifeq ($$(call check-jvm-feature, g1gc), true)
>     $1_$2_CDS_DUMP_FLAGS += -XX:+UseG1GC
>   endif

I just realized that check-jvm-feature is only defined in HotspotCommon.gmk, which isn't included here (and can't really be either without modifications). Sorry to lead you on a wild goose chase. Unless Magnus can think of a reasonable way of exposing that macro here, I think your current solution is good enough.

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PR: https://git.openjdk.org/jdk/pull/9984