RFR(sh/jdk8): Fix register allocation for thread register is 32bit LRB

[Zhengyu Gu]

On 12/1/20 2:46 PM, Roman Kennke wrote:
> This is a shenandoah/jdk8-specific fix. SFX barriers caused the 
> regression that the thread register in 32bit clashes with the index 
> register of the source address. Apparently, registers are shuffled 
> differently in later JDK interpreters. With a little bit of 
> experimentation I found that we can use rsi instead in JDK8.
> 
> http://cr.openjdk.java.net/~rkennke/shjdk8-fix32-regalloc-thread/webrev.00/
> 
> Testing: hotspot_gc_shenandoah (x86_32) and specjvm fast run. This 
> should catch mistakes there reliably, because all of the interpreter is 
> generated at the start, any clashes should be caught by the assert.
> 
> Ok?


  144   Register thread = rsi;
  145   if (thread == dst) {
  146     thread = rbx;
  147   }
  148   assert_different_registers(dst, src.base(), src.index(), thread);

Line#145 never true, Line#145 - 147 should be removed.

-Zhengyu

> 
> Thanks,
> Roman
>