RFR: 8290529: C2: assert(BoolTest(btest).is_canonical()) failure

[Vladimir Kozlov]

On Tue, 19 Jul 2022 12:28:10 GMT, Roland Westrelin <roland at openjdk.org> wrote:

> For the test case:
> 
> 1) In Parse::do_if(), tst0 is:
> 
> (Bool#lt (CmpU 0 Parm0))
> 
> 2) transformed by gvn in tst:
> 
> (Bool#gt (CmpU Parm0 0))
> 
> 3) That test is not canonical and is negated and retransformed which
> results in:
> 
> (Bool#eq (CmpI Parm0 0))
> 
> The assert fires because that test is not canonical either.
> 
> The root cause I think is that the (CmpU .. 0) -> (CmpI .. 0) only
> triggers if the condition of the CmpU is canonical (and results in a
> non canonical test). Tweaking it so it applies even if the condition
> is not leads to the following change in the steps above:
> 
> 2) (Bool#ne (CmpI Parm0 0))
> 
> which is a canonical test.

Changes are good. If possible add IR framework test.

src/hotspot/share/opto/subnode.cpp line 1621:

> 1619:   }
> 1620: 
> 1621:   // Change x u< 1 or x u<= 0 to x == 0

Update comment.

-------------

PR: https://git.openjdk.org/jdk/pull/9553