RFR: 8256215: Shenandoah: re-organize saving/restoring machine state in assembler code [v2]

[Aleksey Shipilev]

> $ CONF=linux-x86-server-fastdebug make images run-test TEST=compiler/c1/Test6855215.java TEST_VM_OPTS="-XX:+UseShenandoahGC"
> 
> # Internal Error (/home/shade/trunks/jdk/src/hotspot/cpu/x86/assembler_x86.cpp:3047), pid=1427307, tid=1427311
> # Error: assert(VM_Version::supports_sse2()) failed
> 
> V [libjvm.so+0x53f9e8] Assembler::movsd(Address, XMMRegisterImpl*)+0x168
> V [libjvm.so+0x14647bd] save_xmm_registers(MacroAssembler*)+0x9d
> V [libjvm.so+0x1465d8f] ShenandoahBarrierSetAssembler::load_reference_barrier(MacroAssembler*, RegisterImpl*, Address, ShenandoahBarrierSet::AccessKind)+0x91f
> 
> This only affects x86_32, as x86_64 uses at least UseSSE >= 2 at all times.
> 
> Additional testing:
>  - [ ] `tier1`, Linux x86_64 `-XX:+UseShenandoahGC`
>  - [ ] `tier1`, Linux x86_32 `-XX:+UseShenandoahGC`
>  - [ ] `tier1`, Linux x86_32 `-XX:+UseShenandoahGC -XX:UseSSE=0`
>  - [ ] `tier1`, Linux x86_32 `-XX:+UseShenandoahGC -XX:UseSSE=1`

Aleksey Shipilev has updated the pull request incrementally with one additional commit since the last revision:

  Drop FP reg saves for arraycopy (current behavior)

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

Changes:
  - all: https://git.openjdk.java.net/jdk/pull/1172/files
  - new: https://git.openjdk.java.net/jdk/pull/1172/files/b4db69e5..489c0db7

Webrevs:
 - full: https://webrevs.openjdk.java.net/?repo=jdk&pr=1172&range=01
 - incr: https://webrevs.openjdk.java.net/?repo=jdk&pr=1172&range=00-01

  Stats: 2 lines in 1 file changed: 0 ins; 0 del; 2 mod
  Patch: https://git.openjdk.java.net/jdk/pull/1172.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/1172/head:pull/1172

PR: https://git.openjdk.java.net/jdk/pull/1172