Use isKnownNonNegative for information transfer. This can improve
results, in cases where ValueTracking can infer additional non-negative
info, e.g. for phi nodes.
This allows simplifying the check from
https://github.com/llvm/llvm-project/issues/63126 by
ConstraintElimination. It is also simplified by IndVarSimplify now; note
the changes in llvm/test/Transforms/PhaseOrdering/loop-access-checks.ll,
due to this now being simplified earlier.
D152730 may add trivial pre-conditions of the form (ICMP_ULE, 0, B),
which won't be handled automatically by the constraint system, because
we don't add Var >= 0 for all variables in the unsigned system.
Handling the trivial condition explicitly here avoids having the
increase the number of rows in the system per variable.
https://alive2.llvm.org/ce/z/QC92ur
Depends on D152730.
Fixes#63125.
Reviewed By: nikic
Differential Revision: https://reviews.llvm.org/D158776
This patch adds additional logic to add additional facts for A != B, if
A is a monotonically increasing induction phi. The motivating use case
for this is removing checks when using iterators with hardened libc++,
e.g. https://godbolt.org/z/zhKEP37vG.
The patch pulls in SCEV to detect AddRecs. If possible, the patch adds
the following facts for a AddRec phi PN with StartValue as incoming
value from the loo preheader and B being an upper bound for PN from a
condition in the loop header.
* (ICMP_UGE, PN, StartValue)
* (ICMP_ULT, PN, B) [if (ICMP_ULE, StartValue, B)]
The patch also adds an optional precondition to FactOrCheck (the new
DoesHold field) , which can be used to only add a fact if the
precondition holds at the point the fact is added to the constraint
system.
Depends on D151799.
Reviewed By: nikic
Differential Revision: https://reviews.llvm.org/D152730
