For some optimizations on comparisons it's necessary that the
union/intersect is exact and not a superset. Add methods that
return Optional<ConstantRange> only if the result is exact.
For the sake of simplicity this is implemented by comparing
the subset and superset approximations for now, but it should be
possible to do this more directly, as unionWith() and intersectWith()
already distinguish the cases where the result is imprecise for the
preferred range type functionality.
Add a variant of getEquivalentICmp() that produces an optional
offset. This allows us to create an equivalent icmp for all ranges.
Use this in the with.overflow folding code, which was doing this
adjustment separately -- this clarifies that the fold will indeed
always apply.
For certain combination of LHS and RHS constant ranges,
the signedness of the relational comparison predicate is irrelevant.
This implements complete and precise model for all predicates,
as confirmed by the brute-force tests. I'm not sure if there are
some more cases that we can handle here.
In a follow-up, CVP will make use of this.
Reviewed By: nikic
Differential Revision: https://reviews.llvm.org/D90924
The multiply() implementation is very slow -- it performs six
multiplications in double the bitwidth, which means that it will
typically work on allocated APInts and bypass fast-path
implementations. Add an additional implementation that doesn't
try to produce anything better than a full range if overflow is
possible. At least for the BasicAA use-case, we really don't care
about more precise modeling of overflow behavior. The current
use of multiply() is fine while the implementation is limited to
a single index, but extending it to the multiple-index case makes
the compile-time impact untenable.
For the common case where the shift amount is constant (a single
element range) we can easily compute a precise range (up to
unsigned envelope), so do that.
Stop using APInt constructors and methods that were soft-deprecated in
D109483. This fixes all the uses I found in llvm, except for the APInt
unit tests which should still test the deprecated methods.
Differential Revision: https://reviews.llvm.org/D110807
This renames the primary methods for creating a zero value to `getZero`
instead of `getNullValue` and renames predicates like `isAllOnesValue`
to simply `isAllOnes`. This achieves two things:
1) This starts standardizing predicates across the LLVM codebase,
following (in this case) ConstantInt. The word "Value" doesn't
convey anything of merit, and is missing in some of the other things.
2) Calling an integer "null" doesn't make any sense. The original sin
here is mine and I've regretted it for years. This moves us to calling
it "zero" instead, which is correct!
APInt is widely used and I don't think anyone is keen to take massive source
breakage on anything so core, at least not all in one go. As such, this
doesn't actually delete any entrypoints, it "soft deprecates" them with a
comment.
Included in this patch are changes to a bunch of the codebase, but there are
more. We should normalize SelectionDAG and other APIs as well, which would
make the API change more mechanical.
Differential Revision: https://reviews.llvm.org/D109483
Currently UREM & SREM on constant ranges produces overly pessimistic
results for single element constant ranges.
Delegate to APInt's implementation if both operands are single element
constant ranges. We already do something similar for other binary
operators, like binary AND.
Fixes PR49731.
Reviewed By: lebedev.ri
Differential Revision: https://reviews.llvm.org/D105115
"Does the predicate hold between two ranges?"
Not very surprisingly, some places were already doing this check,
without explicitly naming the algorithm, cleanup them all.
"Does the predicate hold between two ranges?"
Not very surprisingly, some places were already doing this check,
without explicitly naming the algorithm, cleanup them all.
When one of the inputs is a wrapping range, intersect with the
union of the two inputs. The union of the two inputs corresponds
to the result we would get if we treated the min/max as a simple
select.
This fixes PR48643.
We don't need any special handling for wrapping ranges (or empty
ranges for that matter). The sub() call will already compute a
correct and precise range.
We only need to adjust the test expectation: We're now computing
an optimal result, rather than an unsigned envelope.
Similar to the ConstantRange::getActiveBits(), and to similarly-named
methods in APInt, returns the bitwidth needed to represent
the given signed constant range
Much like APInt::getActiveBits(), computes how many bits are needed
to be able to represent every value in this constant range,
treating the values as unsigned.
Use the fact that `~X` is equivalent to `-1 - X`, which gives us
fully-precise answer, and we only need to special-handle the wrapped case.
This fires ~16k times for vanilla llvm test-suite + RawSpeed.
Pass the abs poison flag to the underlying ConstantRange
implementation, allowing CVP to simplify based on it.
Importantly, this recognizes that abs with poison flag is actually
non-negative...
This adds a common API for compute constant ranges of intrinsics.
The intention here is that
a) we can reuse the same code across different passes that handle
constant ranges, i.e. this can be reused in SCCP
b) we only have to add knowledge about supported intrinsics to
ConstantRange, not any consumers.
Differential Revision: https://reviews.llvm.org/D84587
Currently ConstantRange::binaryAnd/binaryOr results are too pessimistic
for single element constant ranges.
If both operands are single element ranges, we can use APInt's AND and
OR implementations directly.
Note that some other binary operations on constant ranges can cover the
single element cases naturally, but for OR and AND this unfortunately is
not the case.
Reviewers: nikic, spatel, lebedev.ri
Reviewed By: spatel
Differential Revision: https://reviews.llvm.org/D76446
The initial implementation just delegates to APInt's implementation of
XOR for single element ranges and conservatively returns the full set
otherwise.
Reviewers: nikic, spatel, lebedev.ri
Reviewed By: nikic
Differential Revision: https://reviews.llvm.org/D76453
We returning a full set, we should use ResultBitWidth. Otherwise we might
it assertions when the resulting constant ranges are used later on.
Reviewers: nikic, spatel, reames
Reviewed By: nikic
Differential Revision: https://reviews.llvm.org/D71937
As it can be seen from accompanying cleanup, it is not unheard of
to write `~Known.Zero` meaning "what maximal value can this KnownBits
produce". But i think `~Known.Zero` isn't *that* self-explanatory,
as compared to a method with a name.
Note that not all `~Known.Zero` places were cleaned up,
only those where this arguably improves things.
Summary:
To be used in `ConstantRange::mulWithNoOverflow()`,
may in future be useful for when saturating shift/mul ops are added.
These are precise as far as i can tell.
I initially though i will need `APInt::[us]mul_sat()` for these,
but it turned out much simpler to do what `ConstantRange::multiply()`
does - perform multiplication in twice the bitwidth, and then truncate.
Though here we want saturating signed truncation.
Reviewers: nikic, reames, spatel
Reviewed By: nikic
Subscribers: hiraditya, llvm-commits
Tags: #llvm
Differential Revision: https://reviews.llvm.org/D69994
Summary:
To be used in `ConstantRange::shlWithNoOverflow()`,
may in future be useful for when saturating shift/mul ops are added.
Unlike `ConstantRange::shl()`, these are precise.
Reviewers: nikic, spatel, reames
Reviewed By: nikic
Subscribers: hiraditya, llvm-commits
Tags: #llvm
Differential Revision: https://reviews.llvm.org/D69960
Summary:
Much like D67339, adds ConstantRange handling for
when we know no-wrap behavior of the `sub`.
Unlike addWithNoWrap(), we only get lucky re returning empty set
for signed wrap. For unsigned, we must perform overflow check manually.
A patch that makes use of this in LVI (CVP) to be posted later.
Reviewers: nikic, shchenz, efriedma
Reviewed By: nikic
Subscribers: hiraditya, llvm-commits
Tags: #llvm
Differential Revision: https://reviews.llvm.org/D69918
As discussed in https://reviews.llvm.org/D69918
that happens to work as intended, and returns empty set if
there is always an overflow because we get lucky with intersection.
Since there's now an explicit test for that, let's prefer cleaner code.
Summary:
If all the shifts amount are already poison-producing,
then we can add more poison-producing flags ontop:
https://rise4fun.com/Alive/Ocwi
Otherwise, we should only consider the possible range of shift amts that don't result in poison.
For unsigned range not not overflow, we must not shift out any set bits,
and the actual limit for `x` can be computed by backtransforming
the maximal value we could ever get out of the `shl` - `-1` through
`lshr`. If the `x` is any larger than that then it will overflow.
Likewise for signed range, but just in signed domain..
This is based on the general idea outlined by @nikic in https://reviews.llvm.org/D68672#1714990
Reviewers: nikic, sanjoy
Reviewed By: nikic
Subscribers: hiraditya, llvm-commits, nikic
Tags: #llvm
Differential Revision: https://reviews.llvm.org/D69217
llvm-svn: 375370
The implementation is conceptually simple: We separate the LHS and
RHS into positive and negative components and then also compute the
positive and negative components of the result, taking into account
that e.g. only pos/pos and neg/neg will give a positive result.
However, there's one significant complication: SignedMin / -1 is UB
for sdiv, and we can't just ignore it, because the APInt result of
SignedMin would break the sign segregation. Instead we drop SignedMin
or -1 from the corresponding ranges, taking into account some edge
cases with wrapped ranges.
Because of the sign segregation, the implementation ends up being
nearly fully precise even for wrapped ranges (the remaining
imprecision is due to ranges that are both signed and unsigned
wrapping and are divided by a trivial divisor like 1). This means
that the testing cannot just check the signed envelope as we
usually do. Instead we collect all possible results in a bitvector
and construct a better sign wrapped range (than the full envelope).
Differential Revision: https://reviews.llvm.org/D61238
llvm-svn: 362430
In order to fold an always overflowing signed saturating add/sub,
we need to know in which direction the always overflow occurs.
This patch splits up AlwaysOverflows into AlwaysOverflowsLow and
AlwaysOverflowsHigh to pass through this information (but it is
not used yet).
Differential Revision: https://reviews.llvm.org/D62463
llvm-svn: 361858
The guaranteed no-wrap region is never empty, it always contains at
least zero, so these optimizations don't ever apply.
To make this more obviously true, replace the conversative return
in makeGNWR with an assertion.
llvm-svn: 361698
Compute results in more direct ways, avoid subset intersect
operations. Extract the core code for computing mul nowrap ranges
into separate static functions, so they can be reused.
llvm-svn: 360189
Add support for srem() to ConstantRange so we can use it in LVI. For
srem the sign of the result matches the sign of the LHS. For the RHS
only the absolute value is important. Apart from that the logic is
like urem.
Just like for urem this is only an approximate implementation. The tests
check a few specific cases and run an exhaustive test for conservative
correctness (but not exactness).
Differential Revision: https://reviews.llvm.org/D61207
llvm-svn: 360055
I got confused on the terminology, and the change in D60598 was not
correct. I was thinking of "exact" in terms of the result being
non-approximate. However, the relevant distinction here is whether
the result is
* Largest range such that:
Forall Y in Other: Forall X in Result: X BinOp Y does not wrap.
(makeGuaranteedNoWrapRegion)
* Smallest range such that:
Forall Y in Other: Forall X not in Result: X BinOp Y wraps.
(A hypothetical makeAllowedNoWrapRegion)
* Both. (makeExactNoWrapRegion)
I'm adding a separate makeExactNoWrapRegion method accepting a
single APInt (same as makeExactICmpRegion) and using it in the
places where the guarantee is relevant.
Differential Revision: https://reviews.llvm.org/D60960
llvm-svn: 359402
Add support for abs() to ConstantRange. This will allow to handle
SPF_ABS select flavor in LVI and will also come in handy as a
primitive for the srem implementation.
The implementation is slightly tricky, because a) abs of signed min
is signed min and b) sign-wrapped ranges may have an abs() that is
smaller than a full range, so we need to explicitly handle them.
Differential Revision: https://reviews.llvm.org/D61084
llvm-svn: 359321
Add urem support to ConstantRange, so we can handle in in LVI. This
is an approximate implementation that tries to capture the most useful
conditions: If the LHS is always strictly smaller than the RHS, then
the urem is a no-op and the result is the same as the LHS range.
Otherwise the lower bound is zero and the upper bound is
min(LHSMax, RHSMax - 1).
Differential Revision: https://reviews.llvm.org/D60952
llvm-svn: 359019
This reverts commit 7bf4d7c07f2fac862ef34c82ad0fef6513452445.
After thinking about this more, this isn't right, the range is not exact
in the same sense as makeExactICmpRegion(). This needs a separate
function.
llvm-svn: 358876
Following D60632 makeGuaranteedNoWrapRegion() always returns an
exact nowrap region. Rename the function accordingly. This is in
line with the naming of makeExactICmpRegion().
llvm-svn: 358875
Add support for uadd_sat and friends to ConstantRange, so we can
handle uadd.sat and friends in LVI. The implementation is forwarding
to the corresponding APInt methods with appropriate bounds.
One thing worth pointing out here is that the handling of wrapping
ranges is not maximally accurate. A simple example is that adding 0
to a wrapped range will return a full range, rather than the original
wrapped range. The tests also only check that the non-wrapping
envelope is correct and minimal.
Differential Revision: https://reviews.llvm.org/D60946
llvm-svn: 358855
ConstantRanges have an annoying special case: If upper and lower are
the same, it can be either an empty or a full set. When constructing
constant ranges nearly always a full set is intended, but this still
requires an explicit check in many places.
This revision adds a getNonEmpty() constructor that disambiguates this
case: If upper and lower are the same, a full set is created.
Differential Revision: https://reviews.llvm.org/D60947
llvm-svn: 358854
Nikita Popov