[Bug tree-optimization/114151] [14 Regression] weird and inefficient codegen and addressing modes since r14-9193

["amacleod at redhat dot com" <gcc-bugzilla@gcc.gnu.org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=114151

--- Comment #7 from Andrew Macleod <amacleod at redhat dot com> ---
(In reply to Richard Biener from comment #6)
> (In reply to Andrew Macleod from comment #5)
> > (In reply to rguenther@suse.de from comment #4)
> > 
> > > 
> > > What was definitely missing is consideration of POLY_INT_CSTs (and
> > > variable polys, as I think there's no range info for those).
> > > 
> > Ranger doesn't do anything with POLY_INTs, mostly because I didn't
> > understand them.  
> > 
> > > We do eventually want to improve how ranger behaves here.  I'm not sure
> > > why when we do not provide a context 'stmt' it can't see to compute
> > > a range valid at the SSA names point of definition?  (so basically
> > > compute the global range)
> > 
> > The call looks like it doesn't provide the stmt.  Without the stmt, all
> > ranger will ever provide is global ranges.
> > 
> > I think you are asking why, If there is no global range, it doesn't try to
> > compute one from the ssa_name_def_stmt?  Ranger does when it is active.  
> 
> I tried with an active ranger but that doesn't make a difference.  Basically
> I added enable_ranger () / disable_ranger () around the pass and thought
> that would "activate" it.  But looking at range_for_expr I don't see how
> that would make a difference without a provided stmt.
> 

It wouldn't. why isn't a context stmt being provided?

range_of_expr with no context stmt makes no attempt to calculate anything. This
is because one can get into a lot of trouble as it doesn't know whether the
expression you are calculating is even in the IL or just some detached tree
expression.

If you have an SSA NAME and want to actually calculate the value, you can use
range_of_stmt (range, SSA_NAME_DEF_STMT (name))  instead of range_of_expr ().

If you pass in a stmt as context, and the SSA_NAME you are asking about is the
LHS of the stmt, then range_of_expr will call range_of_stmt itself... but
again, it needs a context stmt in order to know its safe to do so.

In general, range_of_expr with no context will not calculate anything... When a
stmt for location context is provided, then its free to go an do whatever
calculations are required.