"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.
When the optimality check fails, print the inputs, the computed
range and the better range that was found. This makes it much
simpler to identify the cause of the failure.
Make sure that full ranges (which, unlikely all the other cases,
have multiple ways to construct them that all result in the same
range) only print one message by handling them separately.
The current infrastructure for exhaustive ConstantRange testing is
somewhat confusing in what exactly it tests and currently cannot even
be used for operations that produce smallest-size results, rather than
signed/unsigned envelopes.
This patch makes the testing more principled by collecting the exact
set of results of an operation into a bit set and then comparing it
against the range approximation by:
* Checking conservative correctness: All elements in the set must be
in the range.
* Checking optimality under a given preference function: None of the
(slack-free) ranges that can be constructed from the set are
preferred over the computed range.
Implemented preference functions are:
* PreferSmallest: Smallest range regardless of signed/unsigned wrapping
behavior. Probably what we would call "optimal" without further
qualification.
* PreferSmallestUnsigned/Signed: Smallest range that has no
unsigned/signed wrapping. We use this if our calculation is precise
only up to signed/unsigned envelope.
* PreferSmallestNonFullUnsigned/Signed: Smallest range that has no
unsigned/signed wrapping -- but preferring a smaller wrapping range
over a (non-wrapping) full range. We use this if we have a fully
precise calculation but apply a sign preference to the result
(union/intersection). Even with a sign preference, returning a
wrapping range is still "strictly better" than returning a full one.
This also addresses PR49273 by replacing the fragile manual range
construction logic in testBinarySetOperationExhaustive() with generic
code that isn't specialized to the particular form of ranges that set
operations can produces.
Differential Revision: https://reviews.llvm.org/D88356
I have long complained that while we have exhaustive tests
for ConstantRange, they are, uh, not good.
The approach of groking our own constant range
via exhaustive enumeration is, mysterious.
It neither tells us without doubt that the result is
conservatively correct, nor the precise match to the ConstantRange
result tells us that the result is precise.
But yeah, it's fast, i give it that.
In short, there are three things that we need to check:
1. That ConstantRange result is conservatively correct
2. That ConstantRange range is reasonable
3. That ConstantRange result is reasonably precise
So let's not just check the middle one, but all three.
This provides precision test coverage for D88178.
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.
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
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
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
Enumerate one less constant range in TestNoWrapRegionExhaustive,
which was unnecessary. This allows us to bump the bit count from
3 to 5 while keeping reasonable timing.
Drop four tests for multiply nowrap regions, as these cover subsets
of the exhaustive test. They do use a wider bitwidth, but I don't
think it's worthwhile to have them additionally now.
llvm-svn: 375369
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
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
As motivated in D60598, this drops support for specifying both NUW and
NSW in makeGuaranteedNoWrapRegion(). None of the users of this function
currently make use of this.
When both NUW and NSW are specified, the exact nowrap region has two
disjoint parts and makeGNWR() returns one of them. This result doesn't
seem to be useful for anything, but makes the semantics of the function
fuzzier.
Differential Revision: https://reviews.llvm.org/D60632
llvm-svn: 358340
makeGuaranteedNoWrapRegion() is actually makeExactNoWrapRegion() as
long as only one of NUW or NSW is specified. This is not obvious from
the current documentation, and some code seems to think that it is
only exact for single-element ranges. Clarify docs and add tests to
be more confident this really holds.
There are currently no users of makeGuaranteedNoWrapRegion() that
pass both NUW and NSW. I think it would be best to drop support for
this entirely and then rename the function to makeExactNoWrapRegion().
Knowing that the no-wrap region is exact is useful, because we can
backwards-constrain values. What I have in mind in particular is
that LVI should be able to constrain values on edges where the
with.overflow overflow flag is false.
Differential Revision: https://reviews.llvm.org/D60598
llvm-svn: 358305
Same as the other ConstantRange overflow checking methods, but for
unsigned mul. In this case there is no cheap overflow criterion, so
using umul_ov for the implementation.
Differential Revision: https://reviews.llvm.org/D60574
llvm-svn: 358228
This extends D59959 to unionWith(), allowing to specify that a
non-wrapping unsigned/signed range is preferred. This is somewhat
less useful than the intersect case, because union operations are
rarer. An example use would the the phi union computed in SCEV.
The implementation is mostly a straightforward use of getPreferredRange(),
but I also had to adjust some <=/< checks to make sure that no ranges with
lower==upper get constructed before they're passed to getPreferredRange(),
as these have additional constraints.
Differential Revision: https://reviews.llvm.org/D60377
llvm-svn: 357876
The intersection of two ConstantRanges may consist of two disjoint
ranges. As we can only return one range as the result, we need to
return one of the two possible ranges that cover both. Currently the
result is picked based on set size. However, this is not always
optimal: If we're in an unsigned context, we'd prefer to get a large
unsigned range over a small signed range -- the latter effectively
becomes a full set in the unsigned domain.
This revision adds a PreferredRangeType, which can be either Smallest,
Unsigned or Signed. Smallest is the current behavior and Unsigned and
Signed are new variants that prefer not to wrap the unsigned/signed
domain. The new type isn't used anywhere yet (but SCEV will be a good
first user, see D60035).
I've also added some comments to illustrate the various cases in
intersectWith(), which should hopefully make it more obvious what is
going on.
Differential Revision: https://reviews.llvm.org/D59959
llvm-svn: 357873
Add isAllNegative() and isAllNonNegative() methods to ConstantRange,
which determine whether all values in the constant range are
negative/non-negative.
This is useful for replacing KnownBits isNegative() and isNonNegative()
calls when changing code to use constant ranges.
Differential Revision: https://reviews.llvm.org/D60264
llvm-svn: 357871
if we do SHL of two 16-bit ranges like [0, 30000) with [1,2) we get
"full-set" instead of what I would have expected [0, 60000) which is
still in the 16-bit unsigned range.
This patch changes the SHL algorithm to allow getting a usable range
even in this case.
Differential Revision: https://reviews.llvm.org/D57983
llvm-svn: 357854
Guillaume Chatelet