A value from reachable block may come to a Phi node as its input from
unreachable block. This may confuse matchSimpleRecurrence which
has no access to DomTree and can falsely recognize something as a recurrency
because of this effect, as the attached test shows.
Patch `ae7b1e` deals with half of this problem, but it only accounts from
the case when an unreachable instruction comes to Phi as an input.
This patch provides a generalization by checking that no Phi block's
predecessor is unreachable (no matter what the input is).
Differential Revision: https://reviews.llvm.org/D99929
Reviewed By: reames
This fixes an issue introduced with my change d4648e, and reported in pr49768.
The root problem is that dominance collapses in unreachable code, and that LoopInfo explicitly only models reachable code. Since the recurrence matcher doesn't filter by reachability (and can't easily because not all consumers have domtree), we need to bailout before assuming that finding a recurrence implies we found a loop.
SCEV currently tries to prove implications of x pred y by also
trying to imply ~y pred ~x. This is expensive in terms of
compile-time (in fact, the majority of isImpliedCond compile-time
is spent here) and generally not fruitful. The issue is that this
also swaps the operands and thus breaks canonical ordering. If
originally we were trying to prove an implication like
X > C1 -> Y > C2, then we'll now try to prove X > C1 -> C3 > ~Y,
which will not work.
The only real case where we can get some use out of this transform
is if the original conditions were in the form X > C1 -> Y < C2, were
then swapped to X > C1 -> C2 > Y and are then swapped again here to
X > C1 -> ~Y > C3.
As such, handle this at a higher level, where we are doing the
swapping in the first place. There's four different ways that we
can line up a predicate and a swapped predicate, so we use some
heuristics to pick some profitable way.
Because we now try this transform at a higher level
(isImpliedCondOperands rather than isImpliedCondOperandsHelper),
we can also prove additional facts. Of the added tests, one was
proven previously while the other wasn't.
Differential Revision: https://reviews.llvm.org/D90926
This patch exploits the knowledge that we may be running many fewer than bitwidth iterations of the loop, and may be able to disallow the overflow case. This patch specifically implements only the shl case, but this can be generalized to ashr and lshr without difficulty.
Differential Revision: https://reviews.llvm.org/D98222
By definition of Implication operator, `false -> true` and `false -> false`. It means that
`false` implies any predicate, no matter true or false. We don't need to go any further
trying to prove the statement we need and just always say that `false` implies it in this case.
In practice it means that we are trying to prove something guarded by `false` condition,
which means that this code is unreachable, and we can safely prove any fact or perform any
transform in this code.
Differential Revision: https://reviews.llvm.org/D98706
Reviewed By: lebedev.ri
Provides API that allows to check predicate for being true or
false with one call. Current implementation is naive and just
calls isKnownPredicate twice, but further we can rework this
logic trying to use one check to prove both facts.
One of (and primary) callers of isBasicBlockEntryGuardedByCond is
isKnownPredicateAt, which makes isKnownPredicate check before it.
It already makes non-recursive check inside. So, on this execution
path this check is made twice. The only other caller is
isLoopEntryGuardedByCond. Moving the check there should save some
compile time.
This reverts commit 329aeb5db4,
and relands commit 61f006ac65.
This is a continuation of D89456.
As it was suggested there, now that SCEV models `PtrToInt`,
we can try to improve SCEV's pointer handling.
In particular, i believe, i will need this in the future
to further fix `SCEVAddExpr`operation type handling.
This removes special handling of `ConstantPointerNull`
from `ScalarEvolution::createSCEV()`, and add constant folding
into `ScalarEvolution::getPtrToIntExpr()`.
This way, `null` constants stay as such in SCEV's,
but gracefully become zero integers when asked.
Reviewed By: Meinersbur
Differential Revision: https://reviews.llvm.org/D98147
This is a continuation of D89456.
As it was suggested there, now that SCEV models `PtrToInt`,
we can try to improve SCEV's pointer handling.
In particular, i believe, i will need this in the future
to further fix `SCEVAddExpr`operation type handling.
This removes special handling of `ConstantPointerNull`
from `ScalarEvolution::createSCEV()`, and add constant folding
into `ScalarEvolution::getPtrToIntExpr()`.
This way, `null` constants stay as such in SCEV's,
but gracefully become zero integers when asked.
Reviewed By: Meinersbur
Differential Revision: https://reviews.llvm.org/D98147
This was suggested by lebedev.ri over on D96534. You'll note lack of tests. During review, we weren't actually able to find a case which exercises it, but both I and lebedev.ri feel it's a reasonable change, straight forward, and near free.
Differential Revision: https://reviews.llvm.org/D97064
When computing a range for a SCEVUnknown, today we use computeKnownBits for unsigned ranges, and computeNumSignBots for signed ranges. This means we miss opportunities to improve range results.
One common missed pattern is that we have a signed range of a value which CKB can determine is positive, but CNSB doesn't convey that information. The current range includes the negative part, and is thus double the size.
Per the removed comment, the original concern which delayed using both (after some code merging years back) was a compile time concern. CTMark results (provided by Nikita, thanks!) showed a geomean impact of about 0.1%. This doesn't seem large enough to avoid higher quality results.
Differential Revision: https://reviews.llvm.org/D96534
This reverts commit b7d870eae7 and the
subsequent fix "[Polly] Fix build after AssumptionCache change (D96168)"
(commit e6810cab09).
It caused indeterminism in the output, such that e.g. the
polly-x86_64-linux buildbot failed accasionally.
The AssumptionCache mechanism is used to feed assumes into known bits computations. Most places in SCEV passed it in, but one place appears to have been missed.
Spotted via inspection, don't have a test case which actually exercises this, but it seemed like an obvious fixit.
PR49043 exposed a problem when it comes to RAUW llvm.assumes. While
D96106 would fix it for GVNSink, it seems a more general concern. To
avoid future problems this patch moves away from the vector of weak
reference model used in the assumption cache. Instead, we track the
llvm.assume calls with a callback handle which will remove itself from
the cache if the call is deleted.
Fixes PR49043.
Reviewed By: nikic
Differential Revision: https://reviews.llvm.org/D96168
Extend applyLoopGuards() to take into account conditions/assumes proving some
value %v to be divisible by D by rewriting %v to (%v / D) * D. This lets the
loop unroller and the loop vectorizer identify more loops as not requiring
remainder loops.
Differential Revision: https://reviews.llvm.org/D95521
We use `EquivalenceClasses` to cache the notion that two SCEVs are equivalent,
so save time in situation when `A` is equivalent to `B` and `B` is equivalent to `C`,
making check "if `A` is equivalent to `C`?" cheaper.
We also return `0` in the comparator when we reach max analysis depth to save
compile time. After doing this, we also cache them as being equivalent.
Now, imagine the following situation:
- `A` is proved equivalent to `B`;
- `C` is proved equivalent to `D`;
- Comparison of `A` against `D` is proved non-zero;
- Comparison of `B` against `C` reaches max depth (and gets cached as equivalence).
Now, before the invocation of compare(`B`, `C`), `A` and `D` belonged
to different equivalence classes, and their comparison returned non-zero.
After the the invocation of compare(`B`, `C`), equivalence classes get merged
and `A`, `B`, `C` and `D` all fall into the same equivalence class. So the comparator
will change its behavior for couple `A` and `D`, with weird consequences following it.
This comparator is finally used in `std::stable_sort`, and this behavior change
makes it crash (looks like it's causing a memory corruption).
Solution: this patch changes `CompareSCEVComplexity` to return `None`
when the max depth is reached. So in this case, we do not cache these SCEVs
(and their parents in the tree) as being equivalent.
Differential Revision: https://reviews.llvm.org/D94654
Reviewed By: lebedev.ri
In computeLoadConstantCompareExitLimit, the addrec used to compute the
exit count should be from the loop which the exiting block belongs to.
Reviewed by: mkazantsev
Differential Revision: https://reviews.llvm.org/D92367
Let getTruncateExpr() short-circuit to zero when the value being truncated is
known to have at least as many trailing zeros as the target type.
Differential Revision: https://reviews.llvm.org/D93973
This patch makes SCEV recognize 'select A, B, false' and 'select A, true, B'.
This is a performance improvement that will be helpful after unsound select -> and/or transformation is removed, as discussed in D93065.
SCEV's answers for the select form should be a bit more conservative than the equivalent `and A, B` / `or A, B`.
Take this example: https://alive2.llvm.org/ce/z/NsP9ue .
To check whether it is valid for SCEV's computeExitLimit to return min(n, m) as ExactNotTaken value, I put llvm.assume at tgt.
It fails because the exit limit becomes poison if n is zero and m is poison. This is problematic if e.g. the exit value of i is replaced with min(n, m).
If either n or m is constant, we can revive the analysis again. I added relevant tests and put alive2 links there.
If and is used instead, this is okay: https://alive2.llvm.org/ce/z/K9rbJk . Hence the existing analysis is sound.
Reviewed By: nikic
Differential Revision: https://reviews.llvm.org/D93882
Reverted because the compile time impact is still too high.
isKnownViaNonRecursiveReasoning is used twice, we can do it just once.
Differential Revision: https://reviews.llvm.org/D92152
Previously we tried to using isKnownPredicateAt, but it makes an
extra query to isKnownPredicate, which has negative impact on compile
time. Let's try to use more lightweight isBasicBlockEntryGuardedByCond.
Differential Revision: https://reviews.llvm.org/D92152
A piece of code in `isLoopBackedgeGuardedByCond` basically duplicates
the dominators traversal from `isBlockEntryGuardedByCond` called from
`isKnownPredicateAt`, but it's less powerful because it does not give context
to `isImpliedCond`. This patch reuses the `isKnownPredicateAt `function there,
reducing the amount of code duplication and making it more powerful.
Differential Revision: https://reviews.llvm.org/D92152
Reviewed By: skatkov
Use more context to prove contextual facts about the last iteration. It is
only executed when the backedge is taken, so we can use `isLoopBackedgeGuardedByCond`
to make this check.
Differential Revision: https://reviews.llvm.org/D91535
Reviewed By: skatkov
The TypeSize warning would occur because RuntimePointerChecking::insert
was not scalable vector aware. The fix is to use
ScalarEvolution::getSizeOfExpr to grab the size of types.
Differential Revision: https://reviews.llvm.org/D90171
This reverts commit 7dcc889917.
This patch introduced a logical error that breaks whole logic of this analysis.
All checks we are making are supposed to be loop-independent, so that we could
safely remove the range check. The 'nw' fact is loop-dependent, so we can remove
the check basing on facts from this very check.
Motivating examples will follow-up.
This reverts commit 2734a9ebf4.
This patch appeared to not be a NFC. It introduced an execution path where
monotonicity check on limited space started relying in existing nsw/nuw
flags, which is illegal. The motivating test will follow-up.
SCEV makes a logical mistake when handling EitherMayExit in
case when both conditions must be met to exit the loop. The
mistake looks like follows: "if condition `A` fails within at most `X` first
iterations, and `B` fails within at most `Y` first iterations, then `A & B`
fails at most within `min (X, Y)` first iterations". This is wrong, because
both of them must fail at the same time.
Simple example illustrating this is following: we have an IV with step 1,
condition `A` = "IV is even", condition `B` = "IV is odd". Both `A` and `B`
will fail within first two iterations. But it doesn't mean that both of them
will fail within first two first iterations at the same time, which would mean
that IV is neither even nor odd at the same time within first 2 iterations.
We can only do so for known exact BE counts, but not for max.
Differential Revision: https://reviews.llvm.org/D91942
Reviewed By: nikic
Handling of `and` and `or` vastly uses copy-paste. Factored out into
a helper function as preparation step for further fix (see PR48225).
Differential Revision: https://reviews.llvm.org/D91864
Reviewed By: nikic
This is a cut down version of 1ec6e1 which was reverted due to a compile time issue. The key changes made from that patch: 1) only infer the flags needed along each path, 2) be careful to preserve order of checks, and 3) avoid computing NW flags at all since we need to prove the stronger property (does not cross 0) in the caller anyways.
Assuming this doesn't trip regressions, I'm going to try weakening (1). My end objective is to move flag inference into addrec construction. If I can't weaken (1) without compile time impact, I'll have a problem.
In an effort to make code around flag determination more readable, and (possibly) prepare for a follow up change, factor out some of the flag detection logic. In the process, reduce the number of locations we mutate wrap flags by a couple.
Note that this isn't NFC. The old code tried for NSW xor (NUW || NW). This is, two different paths computed different sets of wrap flags. The new code will try for all three. The result is that some expressions end up with a few extra flags set.
The SCEV code for constructing GEP expressions currently assumes
that the addition of the base and all the offsets is nsw if the GEP
is inbounds. While the addition of the offsets is indeed nsw, the
addition to the base address is not, as the base address is
interpreted as an unsigned value.
Fix the GEP expression code to not assume nsw for the base+offset
calculation. However, do assume nuw if we know that the offset is
non-negative. With this, we use the same behavior as the
construction of GEP addrecs does. (Modulo the fact that we
disregard SCEV unification, as the pre-existing FIXME points out).
Differential Revision: https://reviews.llvm.org/D90648
A piece of logic of `isLoopInvariantExitCondDuringFirstIterations` is actually
a generalized predicate monotonicity check. This patch moves it into the
corresponding method and generalizes it a bit.
Differential Revision: https://reviews.llvm.org/D90395
Reviewed By: apilipenko
Lift limitation on step being `+/- 1`. In fact, the only thing it is needed for
is proving no-self-wrap. We can instead check this flag directly.
Theoretically it can increase the scope of the transform, but I could not
construct such test easily.
Differential Revision: https://reviews.llvm.org/D91126
Reviewed By: apilipenko
This changes the definition of t2DoLoopStart from
t2DoLoopStart rGPR
to
GPRlr = t2DoLoopStart rGPR
This will hopefully mean that low overhead loops are more tied together,
and we can more reliably generate loops without reverting or being at
the whims of the register allocator.
This is a fairly simple change in itself, but leads to a number of other
required alterations.
- The hardware loop pass, if UsePhi is set, now generates loops of the
form:
%start = llvm.start.loop.iterations(%N)
loop:
%p = phi [%start], [%dec]
%dec = llvm.loop.decrement.reg(%p, 1)
%c = icmp ne %dec, 0
br %c, loop, exit
- For this a new llvm.start.loop.iterations intrinsic was added, identical
to llvm.set.loop.iterations but produces a value as seen above, gluing
the loop together more through def-use chains.
- This new instrinsic conceptually produces the same output as input,
which is taught to SCEV so that the checks in MVETailPredication are not
affected.
- Some minor changes are needed to the ARMLowOverheadLoop pass, but it has
been left mostly as before. We should now more reliably be able to tell
that the t2DoLoopStart is correct without having to prove it, but
t2WhileLoopStart and tail-predicated loops will remain the same.
- And all the tests have been updated. There are a lot of them!
This patch on it's own might cause more trouble that it helps, with more
tail-predicated loops being reverted, but some additional patches can
hopefully improve upon that to get to something that is better overall.
Differential Revision: https://reviews.llvm.org/D89881
Our range computation methods benefit from no-wrap flags. But if the ranges
were first computed before the flags were set, the cached range will be too
pessimistic.
We need to drop cached ranges whenever we sharpen AddRec's no wrap flags.
Differential Revision: https://reviews.llvm.org/D89847
Reviewed By: fhahn
Strengthening nowrap flags is relatively expensive. Make sure we
only do it if we're actually going to use the flags -- we don't
use them for many recursive invocations. Additionally, if we're
reusing an existing SCEV node, there's no point in trying to
strengthen the flags if we don't have any new baseline facts.
This change falls slightly short of being NFC, because the way
flags during add+addrec / mul+addrec folding are handled may be
more precise (as less operands are included in the calculation).
Instead of performing a sequence of pairwise additions, directly
construct a multi-operand add expression.
This should be NFC modulo any SCEV canonicalization deficiencies.
This is functionally-identical to the previous implementation,
just using a generic interface to do that instead of hand-rolled one,
with caching as a bonus. Thought the sinking is still recursive..
Note that SCEVRewriteVisitor<>'s default implementations
don't preserve NoWrap flags on Add/Mul (but does on AddRec!),
but here we know we can preserve them,
so `visitAddExpr()`/`visitMulExpr()` are specialized.
If we've got an SCEVPtrToIntExpr(op), where op is not an SCEVUnknown,
we want to sink the SCEVPtrToIntExpr into an operand,
so that the operation is performed on integers,
and eventually we end up with just an `SCEVPtrToIntExpr(SCEVUnknown)`.
Reviewed By: mkazantsev
Differential Revision: https://reviews.llvm.org/D89692
And use it to model LLVM IR's `ptrtoint` cast.
This is essentially an alternative to D88806, but with no chance for
all the problems it caused due to having the cast as implicit there.
(see rG7ee6c402474a2f5fd21c403e7529f97f6362fdb3)
As we've established by now, there are at least two reasons why we want this:
* It will allow SCEV to actually model the `ptrtoint` casts
and their operands, instead of treating them as `SCEVUnknown`
* It should help with initial problem of PR46786 - this should eventually allow us
to not loose pointer-ness of an expression in more cases
As discussed in [[ https://bugs.llvm.org/show_bug.cgi?id=46786 | PR46786 ]], in principle,
we could just extend `SCEVUnknown` with a `is ptrtoint` cast, because `ScalarEvolution::getPtrToIntExpr()`
should sink the cast as far down into the expression as possible,
so in the end we should always end up with `SCEVPtrToIntExpr` of `SCEVUnknown`.
But i think that it isn't the best solution, because it doesn't really matter
from memory consumption side - there probably won't be *that* many `SCEVPtrToIntExpr`s
for it to matter, and it allows for much better discoverability.
Reviewed By: mkazantsev
Differential Revision: https://reviews.llvm.org/D89456
URem operations with constant power-of-2 second operands are modeled as
such. This patch on its own has very little impact (e.g. no changes in
CodeGen for MultiSource/SPEC2000/SPEC2006 on X86 -O3 -flto), but I'll
soon post follow-up patches that make use of it to more accurately
determine the trip multiple.
Reviewed By: mkazantsev
Differential Revision: https://reviews.llvm.org/D89821
This reverts commit e038b60d91.
This reverts commit a0d84d8031.
This revert was a mistake. The reason of the failures was
"Use uint64_t for branch weights instead of uint32_t"
Differential Revision: https://reviews.llvm.org/D87832
When we need to prove implication of expressions of different type width,
the default strategy is to widen everything to wider type and prove in this
type. This does not interact well with AddRecs with negative steps and
unsigned predicates: such AddRec will likely not have a `nuw` flag, and its
`zext` to wider type will not be an AddRec. In contraty, `trunc` of an AddRec
in some cases can easily be proved to be an `AddRec` too.
This patch introduces an alternative way to handling implications of different
type widths. If we can prove that wider type values actually fit in the narrow type,
we truncate them and prove the implication in narrow type.
The return was due to revert of underlying patch that this one depends on.
Unit test temporarily disabled because the required logic in SCEV is switched
off due to compile time reasons.
Differential Revision: https://reviews.llvm.org/D89548
We can sharpen the range of a AddRec if we know that it does not
self-wrap and know the symbolic iteration count in the loop. If we can
evaluate the value of AddRec on the last iteration and prove that at least
one its intermediate value lies between start and end, then no-wrap flag
allows us to conclude that all of them also lie between start and end. So
the estimate of range can be improved to union of ranges of start and end.
Switched off by default, can be turned on by flag.
Differential Revision: https://reviews.llvm.org/D89381
Reviewed By: lebedev.ri, nikic
This reverts commit c6ca26c0bf.
This breaks stage2 builds due to hitting this assert:
```
Assertion failed: (WeightSum <= UINT32_MAX && "Expected weights to scale down to 32 bits"), function calcMetadataWeights
```
when compiling AArch64RegisterBankInfo.cpp in LLVM.
Even if the exact exit count is unknown, we can still prove that this
exit will not be taken. If we can prove that the predicate is monotonic,
fulfilled on first & last iteration, and no overflow happened in between,
then the check can be removed.
Differential Revision: https://reviews.llvm.org/D87832
Reviewed By: apilipenko
Same change as 0dda633317, but for
mul expressions. We want to first fold any constant operans and
then strengthen the nowrap flags, as we can compute more precise
flags at that point.
Establish parity with the handling of add expressions, by always
constant folding mul expression operands before checking the depth
limit (this is a non-recursive simplification). The code was already
unconditionally constant folding the case where all operands were
constants, but was not folding multiple constant operands together
if there were also non-constant operands.
This requires picking out a different demonstration for depth-based
folding differences in the limit-depth.ll test.
Separate out the code handling constant folding into a separate
block, that is independent of other folds that need a constant
first operand. Also make some minor adjustments to make the
constant folding look nearly identical to the same code in
getAddExpr().
The only reason this change is not strictly NFC is that the
C1*(C2+V) fold is moved below the constant folding, which means
that it now also applies to C1*C2*(C3+V), as it should.
We should first try to constant fold the add expression and only
strengthen nowrap flags afterwards. This allows us to determine
stronger flags if e.g. only two operands are left after constant
folding (and thus "guaranteed no wrap region" code applies) or the
resulting operands are non-negative and thus nsw->nuw strengthening
applies.
We want to have a caching version of symbolic BE exit count
rather than recompute it every time we need it.
Differential Revision: https://reviews.llvm.org/D89954
Reviewed By: nikic, efriedma
When we need to prove implication of expressions of different type width,
the default strategy is to widen everything to wider type and prove in this
type. This does not interact well with AddRecs with negative steps and
unsigned predicates: such AddRec will likely not have a `nuw` flag, and its
`zext` to wider type will not be an AddRec. In contraty, `trunc` of an AddRec
in some cases can easily be proved to be an `AddRec` too.
This patch introduces an alternative way to handling implications of different
type widths. If we can prove that wider type values actually fit in the narrow type,
we truncate them and prove the implication in narrow type.
Differential Revision: https://reviews.llvm.org/D89548
Reviewed By: fhahn
This reverts commit a10a64e7e3.
It broke polly/test/ScopInfo/NonAffine/non-affine-loop-condition-dependent-access_3.ll
The difference suggests that this may be a serious issue.
Fixed wrapping range case & proof methods reduced to constant range
checks to save compile time.
Differential Revision: https://reviews.llvm.org/D89381
The main tricky thing here is forward-declaring the enum:
we have to specify it's underlying data type.
In particular, this avoids the danger of switching over the SCEVTypes,
but actually switching over an integer, and not being notified
when some case is not handled.
I have updated most of such switches to be exaustive and not have
a default case, where it's pretty obvious to be the intent,
however not all of them.
All existing SCEV cast types operate on integers.
D89456 will add SCEVPtrToIntExpr cast expression type.
I believe this is best for consistency.
Reviewed By: mkazantsev
Differential Revision: https://reviews.llvm.org/D89455
It's not pretty, but probably better than modelling it
as an opaque SCEVUnknown, i guess.
It is relevant e.g. for the loop that was brought up in
https://bugs.llvm.org/show_bug.cgi?id=46786#c26
as an example of what we'd be able to better analyze
once SCEV handles `ptrtoint` (D89456).
But as it is evident, even if we deal with `ptrtoint` there,
we also fail to model such an `ashr`.
Also, modeling of mul-of-exact-shr/div could use improvement.
As per alive2:
https://alive2.llvm.org/ce/z/tnfZKd
```
define i8 @src(i8 %0) {
%2 = ashr exact i8 %0, 4
ret i8 %2
}
declare i8 @llvm.abs(i8, i1)
declare i8 @llvm.smin(i8, i8)
declare i8 @llvm.smax(i8, i8)
define i8 @tgt(i8 %x) {
%abs_x = call i8 @llvm.abs(i8 %x, i1 false)
%div = udiv exact i8 %abs_x, 16
%t0 = call i8 @llvm.smax(i8 %x, i8 -1)
%t1 = call i8 @llvm.smin(i8 %t0, i8 1)
%r = mul nsw i8 %div, %t1
ret i8 %r
}
```
Transformation seems to be correct!
It was reverted because of negative compile time impact. In this version,
less powerful proof methods are used (non-recursive reasoning only), and
scope limited to constant End values to avoid explision of complex proofs.
Differential Revision: https://reviews.llvm.org/D89381
We can sharpen the range of a AddRec if we know that it does not
self-wrap and know the symbolic iteration count in the loop. If we can
evaluate the value of AddRec on the last iteration and prove that at least
one its intermediate value lies between start and end, then no-wrap flag
allows us to conclude that all of them also lie between start and end. So
the estimate of range can be improved to union of ranges of start and end.
Differential Revision: https://reviews.llvm.org/D89381
Reviewed By: efriedma
While we haven't encountered an earth-shattering problem with this yet,
by now it is pretty evident that trying to model the ptr->int cast
implicitly leads to having to update every single place that assumed
no such cast could be needed. That is of course the wrong approach.
Let's back this out, and re-attempt with some another approach,
possibly one originally suggested by Eli Friedman in
https://bugs.llvm.org/show_bug.cgi?id=46786#c20
which should hopefully spare us this pain and more.
This reverts commits 1fb6104293,
7324616660,
aaafe350bb,
e92a8e0c74.
I've kept&improved the tests though.
As being pointed out by @efriedma in
https://reviews.llvm.org/rGaaafe350bb65#inline-4883
of course we can't just call ptrtoint in sign-extending case
and be done with it, because it will zero-extend.
I'm not sure what i was thinking there.
This is very much not an NFC, however looking at the user of
BuildConstantFromSCEV() i'm not sure how to actually show that
it results in a different constant expression.
Much similar to the ZExt/Trunc handling.
Thanks goes to Alexander Richardson for nudging towards noticing this one proactively.
The appropriate (currently crashing) test coverage added.
Max Kazantsev