[Bug target/112787] Codegen regression of large GCC vector extensions when enabling SVE

[avieira at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=112787

avieira at gcc dot gnu.org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
     Ever confirmed|0                           |1
             Status|UNCONFIRMED                 |ASSIGNED
           Assignee|unassigned at gcc dot gnu.org      |avieira at gcc dot gnu.org
   Last reconfirmed|                            |2023-11-30
             Target|                            |aarch64

--- Comment #1 from avieira at gcc dot gnu.org ---
The problem is veclower tries to find the largest vector type it can use for a
particular element type, which when SVE is enabled without a specified vector
length will always be a VLA type.  This then fails the check of it having less
elements than the type being used to do the computation, given that a VLA
element count is never 'known_lt' a constant one.

I am currently testing a patch that makes sure the mode selected does not have
more elements than the type we are trying to compute, given that it wouldn't be
used anyway.