[jdk16] RFR: 8258384: AArch64: SVE verify_ptrue fails on some tests

[Ningsheng Jian]

After applying [1], some Vector API tests fail with SIGILL on SVE
system. The SIGILL was triggered by verify_ptrue before c2 compiled
function returns, which means that the preserved p7 register (as ptrue)
has been clobbered before returning to c2 compiled code. (p7 is not
preserved cross function calls, and system calls [2]).

Currently we try to reinitialize ptrue at each entrypoint of returning
from non-c2 compiled code, which indicating possible C or system calls.
However, there's still one entrypoint missing, exception handling, as
we may jump to c2 compiled code for exception handler. See
OptoRuntime::generate_exception_blob().

Adding reinitialize_ptrue before jumping back to c2 compiled code in
generate_exception_blob() could solve those Vector API test failures.
Actually I had that in my initial test patch [3], I don't know why I
missed that in final patch... I reran tests with the same approach of
[3] and found that there's still something missing, the
nmethod_entry_barrier() in c2 function prolog. The barrier may call to
runtime code (see generate_method_entry_barrier()). To reduce the risk
of missing such reinitialize_ptrue in newly added code in future, I
think it would be better to do the reinitialize in
pop_call_clobbered_registers().

P.S. the SIGILL message is also not clear, it should print detailed
message as indicated by MacroAssembler::stop() call. This is caused by
JDK-8255711 removing the message printing code. This patch also adds it
back, so that it could print detailed message for abort.

Tested with tier1-3 on SVE hardware. Also verified with the same
approach of patch [3] with jtreg tests hotspot_all_no_apps and
jdk:tier1-3 passed without incorrect ptrue value assertion failure.

[1] https://github.com/openjdk/jdk/pull/1621
[2] https://github.com/torvalds/linux/blob/master/Documentation/arm64/sve.rst
[3] http://cr.openjdk.java.net/~njian/8231441/0001-RFC-Block-one-caller-save-register-for-C2.patch

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Commit messages:
 - 8258384: AArch64: SVE verify_ptrue fails on some tests

Changes: https://git.openjdk.java.net/jdk16/pull/50/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk16&pr=50&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8258384
  Stats: 54 lines in 7 files changed: 21 ins; 16 del; 17 mod
  Patch: https://git.openjdk.java.net/jdk16/pull/50.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk16 pull/50/head:pull/50

PR: https://git.openjdk.java.net/jdk16/pull/50