RFR (S): 8140343: SEGV in DirectivesStack::getMatchingDirective

[Christian Thalinger]

> On Oct 24, 2015, at 1:49 AM, Nils Eliasson <nils.eliasson at oracle.com> wrote:
> 
> 
> On 2015-10-23 22:39, Christian Thalinger wrote:
>>> On Oct 22, 2015, at 11:03 PM, Nils Eliasson <nils.eliasson at oracle.com> wrote:
>>> 
>>> Hi all,
>>> 
>>> This fixes a bug when using a compiler that doesn't have compiler directives. This is a temporary fix using the default directive for c1.
>> What are the default directives for C1 and C2?  This fix is for JVMCI compilers and JVMCI compilers can only replace C2 in a tiered configuration.  Depending on what they are, wouldn’t it make more sense to use C2’s default directives?
> 
> The default directive is a directive that is always installed, always enabled and contains all the default values from vmflags and compile commands. This is the directive all compilations are using if no additional directives are installed.

Alright, but then I am confused that you said “default directive for c1”.  Anyway, it’s good.

>> 
>>> In the future permanent fix all compilers will have directives by default.
>> How would that look like?
> 
> Long story. It is an internal implementation detail to the structure of compiler directives. Right now there is a bit of an overhead adding a new compiler, even if only a single flag is used. The idea is to have all directives contain all flags for all compilers - it might sound expensive but will actually be more efficient. The most common use case is only having the default directive, and in this case the common flags wouldn't have to be duplicated for each compiler. The profit in the JVMCI case is that all the common flags are valid and usable without any workaround. The improvement is straightforward and wont affect any use site but is big enough not to be the fix of this bug.

Ok.

> 
> //Nils
> 
> 
>>> bug: https://bugs.openjdk.java.net/browse/JDK-8140343
>>> webrev: http://cr.openjdk.java.net/~neliasso/8140343/webrev.01/
>>> 
>>> Please review,
>>> Nils
>