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

[Erik Joelsson]

On Tue, 23 Aug 2022 21:42:00 GMT, Ioi Lam <iklam at openjdk.org> wrote:

>> Oh, the loop is already there, it's jus the naming of the variable. I think we should adjust that so the check-jvm-feature macro can be used.
>
> @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

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