review (S) for 6663854: assert(n != __null,"Bad immediate dominator info.") in C2 with -Xcomp

[Tom Rodriguez]

Oops.  http://cr.openjdk.java.net/~never/6663854

tom

On Feb 17, 2010, at 2:30 PM, Tom Rodriguez wrote:

> 6663854: assert(n != __null,"Bad immediate dominator info.") in C2 with -Xcomp
> Reviewed-by:
> 
> This is another instance of the ConvI2L problem with type information
> being raised to a point that it's no longer true, like the bug
> 6659207, resulting in top being returned and some code path being
> mistakenly killed.  The same style of fix for 6659207 won't work in
> this case because there's no option to bailout if the types won't
> work.  Instead we strip the constrained type off the ConvI2L as it is
> pushed up.  The test case was automatically generated and I couldn't
> simplify it any further so it's pretty horrific looking.  Tested with
> test case and confirmed that stripping the type doesn't affect the
> code quality for scimark which is very sensitive to the loss of the
> type information on ConvI2Ls used in address expressions.
> 
> src/share/vm/opto/split_if.cpp
> test/compiler/6663854/Test6663854.java