[15] RFR(M): 8236493: C2: Inconsistent known instance type information after EA

[Tobias Hartmann]

Hi,

please review the following patch:
https://bugs.openjdk.java.net/browse/JDK-8236493
http://cr.openjdk.java.net/~thartmann/8236493/webrev.00/

While working on 8233164, I've noticed that escape analysis does not set known instance type
information for LoadNodes and their users if the loaded object does not escape but that information
is only (incrementally) propagated during IGVN. That's a problem because depending on the sequence
in which nodes on the worklist are processed, optimizations might still see the not-yet-updated (and
therefore incorrect) type. For example, another LoadNode optimization might rely on it's memory
input to be a general memory slice and re-wire it's inputs accordingly (ignoring known instance type
memory), when it is really reading from a known instance.

For a detailed description of an instance of such a problem, see my RFR for 8233164 [1]. There, the
type of a CastPPNode is not updated (yet) and a Load user is incorrectly re-wired.

To catch this case before things go horribly wrong, I've added an assert to
Node::raise_bottom_type(). Reverting the fix for 8233164 now immediately triggers the assert because
the known instance id of a DecodeNNode is only updated during IGVN [2]. All new tests in
TestInstanceIdPropagation.java trigger the assert as well.

The fix is to always eagerly propagate that information during EA. If an object loaded from the
field of a non-escaping object is also non-escaping, we need to propagate that information.

Thanks,
Tobias

[1] https://mail.openjdk.java.net/pipermail/hotspot-compiler-dev/2019-December/036616.html

[2] Failure with TestArrayCopyMemoryChain.java when reverting fix for 8233164:

 300	Proj	===  288  [[ 301  305  312 ]] #5 !jvms: TestArrayCopyMemoryChain::test2 @ bci:25
 305	CheckCastPP	===  302  300  [[ 385  316 ]]  #byte[int:1]:NotNull:exact *,iid=288 !jvms:
TestArrayCopyMemoryChain::test2 @ bci:25
 385	EncodeP	=== _  305  [[ 387  403 ]]  #narrowoop: byte[int:1]:NotNull:exact *,iid=288 !orig=[402]
!jvms: TestArrayCopyMemoryChain$Wrapper::<init> @ bci:11 TestArrayCopyMemoryChain::test2 @ bci:41
 403 >	DecodeN	=== _  385  [[ 494  420 ]]  #byte[int:1]:NotNull:exact *,iid=288 !jvms:
TestArrayCopyMemoryChain::test2 @ bci:48
 494	CastPP	===  486  403  [[ 526  514 ]]  #byte[int:>=0]:NotNull:exact * !jvms:
TestArrayCopyMemoryChain::test2 @ bci:71
 420	CallStaticJava	===  404  327  341  8  9 ( 419  1  1  1  64  1  1  1  403  257  43  64  11  230
) [[ 421 ]] # Static uncommon_trap(reason='intrinsic_or_type_checked_inlining'
action='make_not_entrant' debug_id='0')  void ( int ) C=0.000100 TestArrayCopyMemoryChain::test2 @
bci:61 !jvms: TestArrayCopyMemoryChain::test2 @ bci:61
# To suppress the following error report, specify this argument
# after -XX: or in .hotspotrc:  SuppressErrorAt=/node.cpp:1088
#
# A fatal error has been detected by the Java Runtime Environment:
#
#  Internal Error (/oracle/jdk_jdk/open/src/hotspot/share/opto/node.cpp:1088), pid=6482, tid=6496
#  assert(false) failed: Known instance type should have been set during EA