[13] 8221592: C2 compilation failed with assert(!q->is_MergeMem())

[Tobias Hartmann]

Hi Vladimir,

Sorry, I've already pushed this patch before you've sent the email (but for some reason, the
hgupdater didn't pick it up yet - maybe it's still down for maintenance).

On 29.04.19 09:15, Vladimir Ivanov wrote:
> src/hotspot/share/opto/parse1.cpp:
> 
> +  _gvn.transform(_exits.merged_memory());
> 
> I'm curious why the node isn't put on worklist when it is created/modified. It seems it should have
> solved the problem.

The 41744 Phi (see IR below) is created in Parse::build_exits() and intentionally not transformed
until do_exits() as this comment suggests:
http://hg.openjdk.java.net/jdk/jdk/file/2f4393ec54d4/src/hotspot/share/opto/parse1.cpp#l771

The MergeMem input is then added in return_current():
http://hg.openjdk.java.net/jdk/jdk/file/2f4393ec54d4/src/hotspot/share/opto/parse1.cpp#l2196

Putting the _exits.merged_memory() node on the igvn worklist during creation wouldn't help because
we don't execute a round of igvn between parsing of the inlined callee (where build_exits() creates
the node) and parsing of the caller (where the assert happens).

> Also, the code around usually does it a bit differently. For example, Parse::do_all_blocks():
> 
>         Node* result = _gvn.transform_no_reclaim(control());
>     ...
>         if (result != top()) {
>           record_for_igvn(result);

Do you mean that I should record the transformed _exits.merged_memory() for igvn in do_exits()? I
don't think that's necessary.

Thanks,
Tobias


 37057	MergeMem	=== _  1  37093  37094  1  1  37095  1  1  1  1  1  1  1  1  1  1  1  1  1  1  1  1
37096  1  1  37097  1  1  1  1  1  37098  37099  37100  37101  37102  37103  37104  37105  [[ 37058
37064  37070  37077  37083  19776  19759  19760  4968  4968  18862  41708  41716  41718  41726
41730  41738  41740  41748  41744 ]]  ...
 41744	Phi	===  41742  37057  [[ 41745 ]]  #memory  Memory: @BotPTR *+bot, idx=Bot; ...
 41745	MergeMem	=== _  1  41744  41751  1  1  41752  1  1  1  1  1  1  1  41753  1  1  1  1  1  1  1
 1  1  1  1  41754  [[ 41741 ]]  ...