This patch canonicalizes getelementptr instructions with constant
indices to use the `i8` source element type. This makes it easier for
optimizations to recognize that two GEPs are identical, because they
don't need to see past many different ways to express the same offset.
This is a first step towards
https://discourse.llvm.org/t/rfc-replacing-getelementptr-with-ptradd/68699.
This is limited to constant GEPs only for now, as they have a clear
canonical form, while we're not yet sure how exactly to deal with
variable indices.
The test llvm/test/Transforms/PhaseOrdering/switch_with_geps.ll gives
two representative examples of the kind of optimization improvement we
expect from this change. In the first test SimplifyCFG can now realize
that all switch branches are actually the same. In the second test it
can convert it into simple arithmetic. These are representative of
common optimization failures we see in Rust.
Fixes https://github.com/llvm/llvm-project/issues/69841.
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
