The IR may contain multiple llvm.vscale intrinsics that have not been CSEd.
This patch ensures that multiple vscales can be treated the same, either in the
decomposition of geps and when we subtract one decomposition from another.
This extends #80818 when IsNSW is lost (possibly due to looking through
multiple GEPs), to check the vscale_range for an access that will not
overflow even with the maximum range.
This patch adds a simple alias analysis check for accesses that are scalable
with a offset between them that is also trivially scalable (there are no other
constant/variable offsets). We essentially divide each side by vscale and are
left needing to check that the offset >= typesize.
This is a separate, but related issue to #69152 that was attempting to improve
AA with scalable dependency distances. This patch attempts to improve when
there are scalable accesses with a constant offset between them. We happen to
get a report of such a thing recently, where so long as the vscale_range is
known, the maximum size of the access can be assessed and better aliasing
results can be returned.
The Upper range of the vscale_range, along with known part of the typesize are
used to prove that Off >= CR.upper * LSize. It does not try to produce
PartialAlias results at the moment from the lower vscale_range. It also enables
the added benefit of allowing better alias analysis when the RHS of the two
values is scalable, but the LHS is normal and can be treated like any other
aliasing query.
With opaque pointers, we cannot use the pointer element type to
determine the LocationSize for the AA query. Instead, -aa-eval
tests are now required to have an explicit load or store for any
pointer they want to compute alias results for, and the load/store
types are used to determine the location size.
This may affect ordering of results, and sorting within one result,
as the type is not considered part of the sorted string anymore.
To somewhat minimize the churn, printing still uses faux typed
pointer notation.
Currently, DecomposeGEP() bails out on the whole decomposition if
it encounters a scalable GEP type anywhere. However, it is fine to
still analyze other GEPs that we look through before hitting the
scalable GEP. This does mean that the decomposed GEP base is no
longer required to be the same as the underlying object. However,
I don't believe this property is necessary for correctness anymore.
This allows us to compute slightly more precise aliasing results
for GEP chains containing scalable vectors, though my primary
interest here is simplifying the code.
Differential Revision: https://reviews.llvm.org/D110511
Summary:
Don't attempt to analyze the decomposed GEP for scalable type.
GEP index scale is not compile-time constant for scalable type.
Be conservative, return MayAlias.
Explicitly call TypeSize::getFixedSize() to assert on places where
scalable type doesn't make sense.
Add unit tests to check functionality of -basicaa for scalable type.
This patch is needed for D76944.
Reviewers: sdesmalen, efriedma, spatel, bjope, ctetreau
Reviewed By: efriedma
Subscribers: tschuett, hiraditya, rkruppe, psnobl, llvm-commits
Tags: #llvm
Differential Revision: https://reviews.llvm.org/D77828
