On 10/07/2015 02:26 AM, Richard Biener wrote:
Hmm, other passes avoid all this by not removing edges or blocks
themselves but leaving that to cfgcleanup. They simply replace the
condition in GIMPLE_CONDs or the switch value in GIMPLE_SWITCHes and
let cleanup_control_expr_graph do the hard part of the job.
Now - I don't know how that would interact with jump threads
covering those paths, that is, what kind of "mess" jump threading
would produce with the conditions/switches mangled that way.
The other nice thing is that CFG cleanup properly deals with loop
structure changes.
Threading will handle it correctly as that's essentially how we handled
it until last week ;-)
The "problem" is the threader thread through those blocks. And while
that works correctly, it is quite wasteful in terms of compile time and
memory consumption due to the block duplication required to preserve
side effects. It also churns the blocks & ssa-names used in the
isolated regions which makes comparing debugging dumps before/after
threading much harder than it ought to be.
Jeff
