RFR: 8305895: Implement JEP 450: Compact Object Headers (Experimental) [v26]

[Roberto Castañeda Lozano]

On Tue, 8 Oct 2024 16:30:56 GMT, Roman Kennke <rkennke at openjdk.org> wrote:

>> Turns out I can also reproduce the issue on my linux-x64 machine (Intel Core i7-9850H), simply running:
>> 
>> `make run-test TEST="java/lang/String/IndexOf.java" CONF=linux-x64-debug`
>> 
>> In this case I get:
>> 
>> 
>> #
>> # A fatal error has been detected by the Java Runtime Environment:
>> #
>> #  Internal Error (codeBuffer.hpp:200), pid=51958, tid=51975
>> #  assert(allocates2(pc)) failed: not in CodeBuffer memory: 0x00007c2778843560 <= 0x00007c27788543b3 <= 0x00007c27788543b0
>> 
>> 
>> A few more details of my processor:
>> 
>> family 6 model 158 stepping 13
>> flags: fpu vme de pse tsc msr pae mce cx8 apic sep mtrr pge mca cmov pat pse36 clflush dts acpi mmx fxsr sse sse2 ss ht tm pbe syscall nx pdpe1gb rdtscp lm constant_tsc art arch_perfmon pebs bts rep_good nopl xtopology nonstop_tsc cpuid aperfmperf pni pclmulqdq dtes64 monitor ds_cpl vmx smx est tm2 ssse3 sdbg fma cx16 xtpr pdcm pcid sse4_1 sse4_2 x2apic movbe popcnt tsc_deadline_timer aes xsave avx f16c rdrand lahf_lm abm 3dnowprefetch cpuid_fault epb ssbd ibrs ibpb stibp ibrs_enhanced tpr_shadow flexpriority ept vpid ept_ad fsgsbase tsc_adjust bmi1 avx2 smep bmi2 erms invpcid mpx rdseed adx smap clflushopt intel_pt xsaveopt xsavec xgetbv1 xsaves dtherm ida arat pln pts hwp hwp_notify hwp_act_window hwp_epp vnmi md_clear flush_l1d arch_capabilities
>
> Oh! We need to increase the compiler stub size for the indexOf changes. Strange that it blows up like this, I was sure there was a better check for this somewhere. I changed it like this, let me know if you agree that this is the correct fix:
> https://github.com/openjdk/jdk/pull/20677/commits/b289ef885816958d9806c76f473b10e34a39e247

That seems to work, thanks @rkennke!

Since the [indexOf changes](https://github.com/openjdk/jdk/pull/20677/files#diff-ae1139bb5342494f9761e04389b090c543391bfdd7817af1625e854357c96e63) are complex and affect the default JVM configuration, they should be subject to the same level of scrutiny as if they were a standalone RFE, i.e. approved by at least a second reviewer. @sviswa7 could someone else at Intel have a second look and explicitly approve them?

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

PR Review Comment: https://git.openjdk.org/jdk/pull/20677#discussion_r1792911644