RFR : JDK-8166110 : C2 crash in compiling method handles

Vladimir Ivanov vladimir.x.ivanov at oracle.com
Fri Feb 3 16:59:53 UTC 2017

The fix looks good.

More detailed description of the problem:

MH.invokeBasic() and MH.linkTo* signature-polymorphic are inherently 
unsafe. There are no type checks involved and it's user responsibility 
to ensure there are no type mismatches possible. They are available only 
to trusted code (in java.lang.invoke), which ensures the signatures 
always match.

Unfortunately, even though type mismatches aren't possible at runtime, 
JIT-compilers can encounter them in paradoxical situations. It usually 
happens when optimizing effectively dead code.

BoundMethodHandle.arg(I) demonstrates one of the problematic code shapes:

final Object arg(int i) {
     switch (speciesData().fieldType(i)) {
     case L_TYPE: return 
     case I_TYPE: return (int) 
     case J_TYPE: return (long) 
     case F_TYPE: return (float) 
     case D_TYPE: return (double) 

If C2 can constant fold speciesData().getters[i], it will try to inline 
through invokeBasic() on all execution paths, though only 1 of them is 
taken. On all other paths the signatures won't match and it can lead to 
type paradoxes on IR level though the code is effectively dead.

Though it was observed only with invokeBasic() and I don't see such 
situations is possible with MH.linkTo*(), for consistency the fix 
touches MH linkers as well.

Best regards,
Vladimir Ivanov

On 2/3/17 5:19 PM, Dmitry Chuyko wrote:
> Summary: some method handles can be used with actual parameters not
> matching their signatures. It's too expensive to check this on call but
> possible to check during inlining. Inlined MHs with wrong usage caused
> further assertion failures in debug builds. The fix adds checks for
> signatures match during MH inlining so it fails if they are not
> matching. New test checks linkToStatic and invokeBasic cases.
> Bug: https://bugs.openjdk.java.net/browse/JDK-8166110
> Webrev: http://cr.openjdk.java.net/~vlivanov/dchuyko/8166110/webrev.00/
> Testing: new test, Hotspot and JDK tests, promotion benchmarks.
> Thanks,
> -Dmitry

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