RFC: DMH lambda form arguments by jlink

[Andrey Petushkov]

Dear JDK developers,

(I'm apologising if posted to wrong alias, please forward as appropriate)

The question is about lambda form cache, created by jlink. More precisely
by jdk/tools/jlink/internal/plugins/GenerateJLIClassesPlugin.java.
It appears to me that it has a bug in set of signatures, specifically in
attempt to create LF for invocation of invokevirtual type with signature of
"L_L" [1]. According to documentation [2] and supported by the code the
arguments to lambda form must be the arguments of the target method
prepended by DMH itself. Hence the invokevirtual linkage should always be
supplied with at least two oop arguments coming first (DMH and receiver)

If I'm correct this bug is totally harmless, since such lambda form
although buggy (the native wrapper for respective MethodHandle intrinsic
have register clash between receiver (receiver_reg) and MemberName
(member_reg) at [3]) it will never be actually used, because the actual MH
invoke will not have such signature. But for the sake of consistency I'd
rather remove the signature in question.

The problem is actually found by jtreg tests on aarch32 platform [4]
(please don't confuse with arm port) where it happen to exist assert
checking for mentioned register clash [5]

Will be happy if someone could confirm if this is indeed correct
description of what's happening or point to mistake in analysis, as
appropriate

Thanks,
Andrey

[1]
http://hg.openjdk.java.net/jdk/jdk/file/00bf1e66de11/src/jdk.jlink/share/classes/jdk/tools/jlink/internal/plugins/GenerateJLIClassesPlugin.java#l151
[2] https://wiki.openjdk.java.net/display/HotSpot/Direct+method+handles
[3]
http://hg.openjdk.java.net/jdk/jdk/file/00bf1e66de11/src/hotspot/cpu/x86/methodHandles_x86.cpp#l293
[4]
https://mail.openjdk.java.net/pipermail/aarch32-port-dev/2018-September/001093.html
[5]
http://cr.openjdk.java.net/~apetushkov/aarch32jdk11%2b28/src/hotspot/cpu/aarch32/methodHandles_aarch32.cpp.html
line
269