8054492: compiler/intrinsics/classcast/NullCheckDroppingsTest.java is an invalid test

[Vladimir Kozlov]

 > We either need some code in WhiteBox to check for a deoptimization
 > event properly or we should just remove this altogether.

 > So, thoughts?  Just delete the check?

No, we have to check that uncommon trap was hit. This is the main 
purpose of that test.

May be we should add an other method WHITE_BOX.wasMethodDeopted(method) 
which checks if method was deoptimized at least once.

Vladimir

On 5/21/15 3:03 AM, Andrew Haley wrote:
> On 05/20/2015 11:02 PM, Vladimir Kozlov wrote:
>> testVarClassCast tests deoptimization for javaMirror == null:
>>
>> void testVarClassCast(String s) {
>>       Class cl = (s == null) ? null : String.class;
>>       try {
>>           ssink = (String)cl.cast(svalue);
>>
>> Which is done in LibraryCallKit::inline_Class_cast() by:
>>
>> mirror = null_check(mirror);
>>
>> which has Deoptimization::Action_make_not_entrant.
>>
>> Unfortunately currently the test also pass because unstable_if is
>> generated for the first line:
>>
>> (s == null) ? null : String.class;
>>
>> If you run the test with TraceDoptimization (or LogCompilation) you will
>> see:
>>
>> Uncommon trap occurred in NullCheckDroppingsTest::testVarClassCast
>> (@0x000000010b0670d8) thread=26883 reason=unstable_if action=reinterpret
>> unloaded_class_index=-1
>
> Not quite the same.  I get a reason=null_check:
>
> Uncommon trap occurred in NullCheckDroppingsTest::testVarClassCast (@0x000003ff8d253e54) thread=4396243677696 reason=null_check action=maybe_recompile unloaded_class_index=-1
>
> Which comes from a SEGV here:
>
>    0x000003ff89253ca4: ldr	x0, [x10,#72]   ; implicit exception: dispatches to 0x000003ff89253e40
>
> which is the line
>
>              ssink = (String)cl.cast(svalue);
>
> I don't get a trap for unstable_if because there isn't one.  I just get
>
>    0x000003ff89253c90: cbz	x2, 0x000003ff89253e00   (this is java/lang/String  s)
>
> -->
>
>    0x000003ff89253e00: mov	x10, xzr
>    0x000003ff89253e04: b	0x000003ff89253ca0
>
> -->
>
>    0x000003ff89253ca0: lsl	x11, x11, #3    ;*getstatic svalue
>                                                  ; - NullCheckDroppingsTest::testVarClassCast at 13 (line 181)
>    0x000003ff89253ca4: ldr	x0, [x10,#72]   ; implicit exception: dispatches to 0x000003ff89253e40
>
> ... and then the trap for the null pointer exception.
>
> Andrew.
>