RFR(S): 8243670: Unexpected test result caused by C2 MergeMemNode::Ideal

[Tobias Hartmann]

Hi Felix,

On 15.06.20 11:13, Yangfei (Felix) wrote:
> I see the logic is also triggered for non-OSR compiles with the reduced test case.
> But it didn't trigger a bug in that case even through the logic didn't do the right thing.
> 
> My initial patch removes the logic and no performance impact witnessed for specjbb2017. 
> Since the code is there from day one, maybe it's hard to find out. 

Even if the change introduces a regression (for example, blocking some loop optimization due to
useless memory merges not being removed), I think it's unlikely to show in SPECjbb.

To get a sense of how often this code is triggered, you could simply add an assert or log code and
run the jtreg compiler tests.

Best regards,
Tobias