RFR: 8025856 - Fix typos in the GC code

[Vladimir Kozlov]

New comment is correct, uncommon traps are generated as call with one 
input parameter - trap_reason.

Thanks,
Vladimir

On 1/22/14 7:43 PM, Krystal Mok wrote:
> Hi John,
>
> On Wed, Jan 22, 2014 at 6:50 PM, John Coomes <John.Coomes at oracle.com
> <mailto:John.Coomes at oracle.com>> wrote:
>
>     opto/runtime.cpp:
>
>         fields[TypeFunc::Parms+0] = TypeInt::INT; // trap_reason (deopt
>     reason and action)
>
>         The comment you added is not obviously correct; did someone from
>         the compiler team check this?  If the comment is correct, the code
>         is crazily obscure!
>
> Yes, I proposed this change. The old comment had been out of date even
> before JDK6.
>
> duke at 0:
> line 392 of
> http://hg.openjdk.java.net/hsx/hotspot-main/hotspot/file/a61af66fc99e/src/share/vm/opto/runtime.cpp
>
> The corresponding runtime call goes through
> SharedRuntime::uncommon_trap_blob to:
>
> Deoptimization::UnrollBlock* Deoptimization::uncommon_trap(JavaThread*
> thread, jint trap_request)
>
> The "thread" argument came from uncommon_trap_blob; the "trap_request"
> argument came from constant embedded in compiled code.
> And this "trap_request" is the thing described by
> OptoRuntime::uncommon_trap_Type().
>
> Back in JDK1.4.2-ish or maybe even earlier, the signature of this
> function was:
>
> Deoptimization::UnrollBlock*, Deoptimization::uncommon_trap(JavaThread*
> thread, jint unloaded_class_index)
>
> where "unloaded_class_index" was a constant pool index of a class if >=
> 0, or other deopt cases if < 0.
>
> I'm not sure when it changed to its current form... waiting for someone
> else to share the history :-)
> Maybe the comment had been out of date longer then I thought.
>
> Speaking of this, the comment
> in SharedRuntime::generate_uncommon_trap_blob() is also out of date:
>
> e.g. hotspot/src/cpu/x86/vm/sharedRuntime_x86_64.cpp
>
>    // compiler left unloaded_class_index in j_rarg0 move to where the
>    // runtime expects it.
>    __ movl(c_rarg1, j_rarg0);
>
> "unloaded_class_index" should be "trap_reason" now.
>
>
>     -John
>
>     --
>     John Coomes                            Oracle, MS USCA22-3??
>     john.coomes at oracle.com <mailto:john.coomes at oracle.com>
>        4220 Network Circle
>     408-276-7048 <tel:408-276-7048>                           Santa
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>
>