We currently preserve the nsw flag when negating scales, which is
incorrect for INT_MIN.
However, just dropping the NSW flag in this case makes BasicAA
behavior unreliable and asymmetric, because we may or may not
drop the NSW flag depending on which side gets subtracted.
Instead, leave the Scale alone and add an additional IsNegated flag,
which indicates that the whole VarIndex should be interpreted as a
subtraction. This allows us to retain the NSW flag.
When accumulating the offset range, we need to use subtraction
instead of adding for IsNegated indices. Everything else works on
the absolute value of the scale, so the negation does not matter
there.
Fixes https://github.com/llvm/llvm-project/issues/63266.
Differential Revision: https://reviews.llvm.org/D153270
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.
Make the range check more precise by calculating the range of
potentially accessed bytes for both accesses and checking whether
their intersection is empty. In that case there can be no overlap
between the accesses and the result is NoAlias.
This is more powerful than the previous approach, because it can
deal with sign-wrapped ranges. In the test case the original range
is [-1, INT_MAX] but becomes [0, INT_MIN] after applying the offset.
This is a wrapping range, so getSignedMin/getSignedMax will treat
it as a full range. However, the range excludes the elements
[INT_MIN+1, -1], which is enough to prove NoAlias with an access
at offset -1.
Differential Revision: https://reviews.llvm.org/D112486
D109746 made BasicAA use range information to determine the
minimum/maximum GEP offset. However, it was limited to the case of
a single variable index. This patch extends support to multiple
indices by adding all the ranges together.
Differential Revision: https://reviews.llvm.org/D112378
The information can be implicit (from `ValueTracking`) or explicit.
This implements the backend part of the following RFC
https://groups.google.com/g/llvm-dev/c/T9o51zB1JY.
We still need to settle on how to best represent the information in the
IR, but this is a separate discussion.
Differential Revision: https://reviews.llvm.org/D109746
