RFR: 8161265: [JVMCI] EnableJVMCI should only be required when its not implied by other flags

[Christian Thalinger]

> On Jul 13, 2016, at 10:24 AM, Doug Simon <doug.simon at oracle.com> wrote:
> 
>> 
>> On 13 Jul 2016, at 21:36, Doug Simon <doug.simon at oracle.com> wrote:
>> 
>>> 
>>> On 13 Jul 2016, at 20:32, Christian Thalinger <cthalinger at twitter.com> wrote:
>>> 
>>> 
>>> 
>>>> On Jul 12, 2016, at 11:20 PM, Doug Simon <doug.simon at oracle.com> wrote:
>>>> 
>>>> The -XX:+EnableJVMCI option 1) unlocks code paths in the VM related to JVMCI and 2) is required to unlock all other JVMCI options. However, 1 could be achieved by specific JVMCI options without requiring 2. Since JVMCI is experimental, these options already require -XX:+UnlockExperimentalVMOptions. Having to unlock them twice is redundant and makes for unnecessarily long command lines. For example:
>>>> 
>>>> java -XX:+UnlockExperimentalVMOptions -XX:+EnableJVMCI -XX:+UseJVMCICompiler ...
>>>> 
>>>> could be:
>>>> 
>>>> java -XX:+UnlockExperimentalVMOptions -XX:+UseJVMCICompiler ...
>>>> 
>>>> This webrev removes the need for specifying -XX:+EnableJVMCI for these options:
>>>> 
>>>> UseJVMCICompiler
>>> 
>>> Totally makes sense for this one.
>>> 
>>>> JVMCITraceLevel
>>>> JVMCICounterSize
>>>> JVMCICountersExcludeCompiler
>>>> JVMCIUseFastLocking
>>>> JVMCINMethodSizeLimit
>>>> TraceUncollectedSpeculations
>>> 
>>> Not so sure about these.
>> 
>> Ok, Tom also commented offline that these should still require EnableJVMCI. That is, EnableJVMCI is still explicitly required to enable hosted-only JVMCI compilation. I can see why this makes sense and am preparing another webrev now.
> 
> Done - I updated the original web rev.

Generally it looks good now but...  Your patch definitely makes the logic simpler but it also adds this dependency:
+// IMPLEMENTATION NOTE: When adding to the set of JVMCI options, ensure
+// JVMCIGlobals::check_jvmci_flags_are_consistent is adjusted appropriately
Not sure if that is a step forward.

> 
> -Doug

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