https://gcc.gnu.org/bugzilla/show_bug.cgi?id=99966
Andrew Macleod <amacleod at redhat dot com> changed:
What |Removed |Added
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CC| |amacleod at redhat dot com
--- Comment #2 from Andrew Macleod <amacleod at redhat dot com> ---
looking at VRP2:
the initial assert provides:
Relational : (start_4(D) < end_5(D))
Relational : (_16 > start_4(D))
Relational : (end_5(D) <= _16)
unfortunately, the loop back edge is:
i_12 = i_17 + 1;
if (end_5(D) != i_12)
goto <bb 5>; [89.00%]
else
goto <bb 8>; [11.00%]
so it only registers what it knows from the branch:
Relational : (i_12 != end_5(D))
so when it gets to the bounds check at:
if (i_12 >= _16)
goto <bb 6>; [0.04%]
else
goto <bb 10>; [99.96%]
It doesn't really know the answer. If the loop branch had remained
if (i_12 < end_5) instead of being changed, then we would instead get the
relation:
Relational : (i_12 < end_5(D))
which combined with the earlier Relational : (end_5(D) <= _16), should register
the transitive relation (i_12 < _16), and enable removal of the check.
This is transformed in ivopts, which runs after vrp1. A quick check shows at
VRP1 time, the bounds are still using the < format...
In fact... running with --param=vrp1-mode=ranger registers this exact
transitive relation, and produces:
Relational : (i_2 < _16)
Relational : (i_2 < end_5(D))
<bb 6> [local count: 952547451]:
if (0 != 0)
goto <bb 7>; [0.04%]
else
goto <bb 8>; [99.96%]
and eliminates the bounds check.
So we can close this PR when we turn ranger on by default for VRP1.
