On 28 November 2013 09:29, Eric Anholt <e...@anholt.net> wrote: > Paul Berry <stereotype...@gmail.com> writes: > > > If an ir_loop has a non-null "counter" field, the variable referred to > > by this field is implicitly read and written by the loop. We need to > > account for this in ir_variable_refcount, otherwise there is a danger > > we will try to dead-code-eliminate the loop counter variable. > > > > Note: at the moment the dead code elimination bug doesn't occur due to > > a bug in ir_hierarchical_visitor: it doesn't visit the "counter" > > field, so dead code elimination doesn't treat it as a candidate for > > elimination. But the patch to follow will fix that bug, so we need to > > fix ir_variable_refcount first in order to avoid breaking dead code > > elimination. > > This series is: > > Reviewed-by: Eric Anholt <e...@anholt.net> > > I wish loop_control.cpp would make loop->control informational, and not > muck with the existing control flow in the loop. That way we could just > ignore loop->control in the backend, and it would only get used by loop > unrolling. I'm pretty sure I've seen loops where both loop controls > (loop->control and the original variable) end up getting used, and it's > something that's going to be hard for the backend to fix back up. >
Yeah, we talked about this on Tuesday. I'm working on a patch series to fix up this mess.
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