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

["rguenth at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>]

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

--- Comment #10 from Richard Biener <rguenth at gcc dot gnu.org> ---
(In reply to Andrew Macleod from comment #9)
> Created attachment 57620 [details]
> proposed patch
> 
> Does this solve your problem if there is an active ranger?  it bootstraps
> with no regressions

I'll check what it does.

> ITs pretty minimal, and basically we invokes the cache's version of
> range_of_expr if there is no context.   I tweaked it such that if there is
> no context, and the def has not been calculated yet, it calls range_of_def,
> and combines it with any SSA_NAME_RANGE_INFO that may have pre-existed.  All
> without invoking any new lookups.
> 
> This seems relatively harmless and does not spawn new dynamic lookups.   As
> long as it resolves your issue...   If it still does not work, and we
> require the def to actually be evaluated, I will look into that. we prpbably
> should do that anyway.  There appears to be a cycle when this is invoked
> from the loop analysis, probably because folding of PHIs uses loop info...
> and back and forth we go.

Yeah, I ran into this as well.

> I'd probably need to add a flag to the ranger
> instantiation to tell it to avoid using loop info.

I've quickly tried to detect active discovery in SCEV but it wasn't as easy
as I thought.

> Are we looking to fix this in this release?

I think the full evaluation has to wait for stage1 because of that recursion
issue.  I'm also sure we're going to need ways to _not_ do this, so maybe
a clearer separation in the API is warranted.  As I see it when you call
range_of_expr without context you get the same result as if using the
global range query so maybe it should be a different API from the start
(the one that is now without context) and range_of_expr without context
using a conservative default (the definition point).