RFR: 8183546: [MVT] cleanup/improve vreturn convention implementation
Roland Westrelin
rwestrel at redhat.com
Wed Jul 5 07:33:19 UTC 2017
http://cr.openjdk.java.net/~roland/valhalla/vreturn-improv/webrev.00/
This patch:
- reworks the verification logic in
SharedRuntime::store_value_type_fields_to_buf() to address the crash
that Paul encountered
- changes the vreturn convention so if we return the klass pointer +
fields, the klass pointer is tagged by setting its least significant
bit. This way it's cheaper for the caller to detect if it's getting an
oop, a buffered value or a list of fields back from the callee. (this
is based on a discussion with Fred)
- stores precomputed extended signature and vreturn registers in the
ValueKlass to not have to compute them every time they are
needed. This is also something Fred suggested. I considered
initializaing those fields on first use but came to the conclusion it
would make things too complicated. For instance the vreturn registers
are sometimes use at a point where the thread can't safepoint making
it impossible to use a metadata Array.
Roland.
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