RFR: 8293660: Fix frame::sender_for_compiled_frame frame size assert

[Aleksey Shipilev]

The condition and assert messages are contradicting each other here:


frame frame::sender_for_compiled_frame(RegisterMap* map) const {
  ...
  assert(_cb->frame_size() >= 0, "must have non-zero frame size");
  intptr_t* sender_sp = unextended_sp() + _cb->frame_size();


I found this in x86_32 Loom port, where a entry generator bug caused zero-sized frames. I believe the assert message is correct, and the condition is not: sender SP should be different from (unextended) SP. In fact, if allowed to proceed, the tests can then fail the later assert, assuming `sp() == unextended_sp()`:


  assert(sender_sp != sp(), "must have changed");


This code predates OpenJDK history, and assert was copy-pasted in this form to many arches. 

Additional testing:
 - [x] Linux x86_64 fastdebug `tier1`

-------------

Commit messages:
 - Fix

Changes: https://git.openjdk.org/jdk/pull/10242/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=10242&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8293660
  Stats: 4 lines in 4 files changed: 0 ins; 0 del; 4 mod
  Patch: https://git.openjdk.org/jdk/pull/10242.diff
  Fetch: git fetch https://git.openjdk.org/jdk pull/10242/head:pull/10242

PR: https://git.openjdk.org/jdk/pull/10242