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From: "tnfchris at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
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Subject: [Bug target/105219] [12 Regression] SVE: Wrong code with -O3
 -msve-vector-bits=128 -mtune=thunderx
Date: Wed, 13 Apr 2022 11:34:24 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D105219

Tamar Christina <tnfchris at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Assignee|unassigned at gcc dot gnu.org      |tnfchris at gcc dot=
 gnu.org

--- Comment #9 from Tamar Christina <tnfchris at gcc dot gnu.org> ---
This was a bit annoying to track down...

So BB 68 gets merged into BB 51,

BB 51 is loading 4 ints 8 - 12 out of 14.

So after it there's still 2 ints left to process.  However it looks like the
compiler thinks that there can't be any more elements left.

It turns:

  next_mask_416 =3D .WHILE_ULT (12, bnd.38_326, { 0, 0, 0, 0 });
  if (next_mask_416 !=3D { 0, 0, 0, 0 })
    goto <bb 51>; [75.00%]
  else
    goto <bb 56>; [25.00%]

into

  next_mask_373 =3D .WHILE_ULT (12, bnd.38_326, { 0, 0, 0, 0 });
  goto <bb 56>; [100.00%]

where bb 56 is the lastb reduction bit.  So basically we're 2 scalar loop
iterations short.

This seems to indicate like Richi suggested that nb_iterations_upper_bound =
is
set wrong.

Perhaps it was confused with the profitability threshold which went from 14=
 to
12.

Mine.=