Move LCSSA fixup from ::expandCodeForImpl to ::expand(). This has
the advantage that we directly preserve LCSSA nodes here instead of
relying on doing so in rememberInstruction. It also ensures that we
don't add the non-LCSSA-safe value to InsertedExpressions.
Alternative to D132704.
Fixes#57000.
Reviewed By: efriedma
Differential Revision: https://reviews.llvm.org/D134739
Simplify the code by using CastInst::CreateBitOrPointerCast directly. By
not going through the builder, the temporary instruction also won't get
registered in InsertedValues & co, which means less work overall and
simplifies the clean-up.
Instruction being hoisted could have nuw/nsw flags inferred from the old
context, and we cannot simply move it to the new location keeping them
because we are going to introduce new uses to them that didn't exist before.
Example in https://github.com/llvm/llvm-project/issues/57187 shows how
this can produce branch by poison from initially well-defined program.
This patch forcefully recomputes poison-generating flag in the new context.
Differential Revision: https://reviews.llvm.org/D132022
Reviewed By: fhahn, nikic
Replacing the following instances of UndefValue with PoisonValue, where the UndefValue is used as an arbitrary value:
- llvm/lib/CodeGen/WinEHPrepare.cpp
`demotePHIsOnFunclets`: RAUW arbitrary value for lingering uses of removed PHI nodes
- llvm/lib/Transforms/Utils/BasicBlockUtils.cpp
`FoldSingleEntryPHINodes`: Removes a self-referential single entry phi node.
- llvm/lib/Transforms/Utils/CallGraphUpdater.cpp
`finalize`: Remove all references to removed functions.
- llvm/lib/Transforms/Utils/ScalarEvolutionExpander.cpp
`cleanup`: the result is not used then the inserted instructions are removed.
- llvm/tools/bugpoint/CrashDebugger.cpp
`TestInts`: the program is cloned and instructions are removed to narrow down source of crash.
Differential Revision: https://reviews.llvm.org/D133640
This is a followup to D129630, which switches LSR to the member
isSafeToExpand() variant, and removes the freestanding function.
This is done by creating the SCEVExpander early (already during the
analysis phase). Because the SCEVExpander is now available for the
whole lifetime of LSRInstance, I've also made it into a member
variable, rather than passing it around in even more places.
Differential Revision: https://reviews.llvm.org/D129769
Motivation here is to unblock LSRs ability to use ICmpZero uses - the major effect of which is to enable count down IVs. The test changes reflect this goal, but the potential impact is much broader since this isn't a change in LSR at all.
SCEVExpander needs(*) to prove that expanding the expression is safe anywhere the SCEV expression is valid. In general, we can't expand any node which might fault (or exhibit UB) unless we can either a) prove it won't fault, or b) guard the faulting case. We'd been allowing non-zero constants here; this change extends it to non-zero values.
vscale is never zero. This is already implemented in ValueTracking, and this change just adds the same logic in SCEV's range computation (which in turn drives isKnownNonZero). We should common up some logic here, but let's do that in separate changes.
(*) As an aside, "needs" is such an interesting word here. First, we don't actually need to guard this at all; we could choose to emit a select for the RHS of ever udiv and remove this code entirely. Secondly, the property being checked here is way too strong. What the client actually needs is to expand the SCEV at some particular point in some particular loop. In the examples, the original urem dominates that loop and yet we completely ignore that information when analyzing legality. I don't plan to actively pursue either direction, just noting it for future reference.
Differential Revision: https://reviews.llvm.org/D129710
As a followup to D129630, this switches a usage of the freestanding
function in LoopPredication to use the member variant instead. This
was the last use of the freestanding function, so drop it entirely.
isSafeToExpand() for addrecs depends on whether the SCEVExpander
will be used in CanonicalMode. At least one caller currently gets
this wrong, resulting in PR50506.
Fix this by a) making the CanonicalMode argument on the freestanding
functions required and b) adding member functions on SCEVExpander
that automatically take the SCEVExpander mode into account. We can
use the latter variant nearly everywhere, and thus make sure that
there is no chance of CanonicalMode mismatch.
Fixes https://github.com/llvm/llvm-project/issues/50506.
Differential Revision: https://reviews.llvm.org/D129630
Migrate all binops to use FoldXYZ rather than CreateXYZ APIs,
which are compatible with InstSimplifyFolder and fallible constant
folding.
Rather than continuing to add one method for every single operator,
add a generic FoldBinOp (plus variants for nowrap, exact and fmf
operators), which we would need anyway for CreateBinaryOp.
This change is not NFC because IRBuilder with InstSimplifyFolder
may perform more folding. However, this patch changes SCEVExpander
to not use the folder in InsertBinOp to minimize practical impact
and keep this change as close to NFC as possible.
Clang-format InstructionSimplify and convert all "FunctionName"s to
"functionName". This patch does touch a lot of files but gets done with
the cleanup of InstructionSimplify in one commit.
This is the alternative to the less invasive clang-format only patch: D126783
Reviewed By: spatel, rengolin
Differential Revision: https://reviews.llvm.org/D126889
%x umin_seq %y is currently expanded to %x == 0 ? 0 : umin(%x, %y).
This patch changes the expansion to umin(%x, freeze %y) instead
(https://alive2.llvm.org/ce/z/wujUhp).
The motivation for this change are the test cases affected by
D124910, where the freeze expansion ultimately produces better
optimization results. This is largely because
`(%x umin_seq %y) == %x` is a common expansion pattern, which
reliably optimizes in freeze representation, but only sometimes
with the zero comparison (in particular, if %x == 0 can fold to
something else, we generally won't be able to cover reasonable
code from this.)
Differential Revision: https://reviews.llvm.org/D125372
SCEVs ExprValueMap currently tracks not only which IR Values
correspond to a given SCEV expression, but additionally stores that
it may be expanded in the form X+Offset. In theory, this allows
reusing existing IR Values in more cases.
In practice, this doesn't seem to be particularly useful (the test
changes are rather underwhelming) and adds a good bit of complexity.
Per https://github.com/llvm/llvm-project/issues/53905, we have an
invalidation issue with these offseted expressions.
Differential Revision: https://reviews.llvm.org/D120311
For those curious, the whole reason for tracking the predicate set seperately as opposed to just immediately registering the dependencies appears to be allowing the printing code to print a result without changing the PSE state. It's slightly questionable if this justifies the complexity, but since we can preserve it with local ugliness, I did so.
PredicatedScalarEvolution has a predicate type for representing A == B. This change generalizes it into something which can represent a A <pred> B.
This generality is currently unused, but is motivated by a couple of recent cases which have come up. In particular, I'm currently playing around with using this to simplify the runtime checking code in LoopVectorizer. Regardless of the outcome of that prototyping, generalizing the compare node seemed useful.
We could keep the non-i8 GEP code for non-opaque pointers, but
there's two reasons I'm dropping it: First, this actually appears
to be dead code, at least it isn't hit in any of our tests. I
expect that this is because we usually expand trip counts, and
those are never pointers (anymore). Second, the non-i8 GEP was
actually incorrect in multiple ways, because it used SCEV type
sizes, which don't match DL type sizes (for pointers) and certainly
don't match type alloc sizes (which is what GEPs actually use).
As such, I'm simplifying the code to always use the i8 GEP code
path if it does get hit.
Instead use either Type::getPointerElementType() or
Type::getNonOpaquePointerElementType().
This is part of D117885, in preparation for deprecating the API.
As discussed in https://github.com/llvm/llvm-project/issues/53020 / https://reviews.llvm.org/D116692,
SCEV is forbidden from reasoning about 'backedge taken count'
if the branch condition is a poison-safe logical operation,
which is conservatively correct, but is severely limiting.
Instead, we should have a way to express those
poison blocking properties in SCEV expressions.
The proposed semantics is:
```
Sequential/in-order min/max SCEV expressions are non-commutative variants
of commutative min/max SCEV expressions. If none of their operands
are poison, then they are functionally equivalent, otherwise,
if the operand that represents the saturation point* of given expression,
comes before the first poison operand, then the whole expression is not poison,
but is said saturation point.
```
* saturation point - the maximal/minimal possible integer value for the given type
The lowering is straight-forward:
```
compare each operand to the saturation point,
perform sequential in-order logical-or (poison-safe!) ordered reduction
over those checks, and if reduction returned true then return
saturation point else return the naive min/max reduction over the operands
```
https://alive2.llvm.org/ce/z/Q7jxvH (2 ops)
https://alive2.llvm.org/ce/z/QCRrhk (3 ops)
Note that we don't need to check the last operand: https://alive2.llvm.org/ce/z/abvHQS
Note that this is not commutative: https://alive2.llvm.org/ce/z/FK9e97
That allows us to handle the patterns in question.
Reviewed By: nikic, reames
Differential Revision: https://reviews.llvm.org/D116766
9345ab3a45 updated generateOverflowCheck to skip creating checks that
always evaluate to false. This in turn means that we only need to
create TruncTripCount if it is actually used.
Sink the TruncTripCount creating into ComputeEndCheck, so it is only
created when there's an actual check.
9345ab3a45 updated generateOverflowCheck to skip creating checks that
always evaluate to false. This in turn means that we only need to
compute |Step| * Trip count if the result of the multiplication is
actually used.
Sink the multiplication into ComputeEndCheck, so it is only created
when there's an actual check.
There is no need to sort inserted instructions by dominance, as the
deletion loop still requires RAUW with undef before deleting. Removing
instructions in reverse insertion order should still insure that the
number of uselist updates is kept to a minimum.
9345ab3a45 updated generateOverflowCheck to skip creating checks that
always evaluate to false. This in turn means that we only need to check
for overflows if the result of the multiplication is actually used.
Sink the Or for the overflow check into ComputeEndCheck, so it is only
created when there's an actual check.
Unsigned compares of the form <u 0 are always false. Do not create such
a redundant check in generateOverflowCheck.
The patch introduces a new lambda to create the check, so we can
exit early conveniently and skip creating some instructions feeding the
check.
I am planning to sink a few additional instructions as follow-ups, but I
would prefer to do this separately, to keep the changes and diff
smaller.
Reviewed By: reames
Differential Revision: https://reviews.llvm.org/D116811
Currently generateOverflowCheck always creates code for Step being
negative and positive, followed by a select at the end depending on
Step's sign.
This patch updates the code to only create either the checks for step
being positive or negative, if the sign is known.
Follow-up to D116696.
Reviewed By: reames
Differential Revision: https://reviews.llvm.org/D116747
This patch updates SCEVExpander::expandUnionPredicate to not create
redundant 'or false, x' instructions. While those are trivially
foldable, they can be easily avoided and hinder code that checks the
size/cost of the generated checks before further folds.
I am planning on look into a few other similar improvements to code
generated by SCEVExpander.
I remember a while ago @lebedev.ri working on doing some trivial folds
like that in IRBuilder itself, but there where concerns that such
changes may subtly break existing code.
Reviewed By: reames, lebedev.ri
Differential Revision: https://reviews.llvm.org/D116696
The basic problem we have is that we're trying to reuse an instruction which is mapped to some SCEV. Since we can have multiple such instructions (potentially with different flags), this is analogous to our need to drop flags when performing CSE. A trivial implementation would simply drop flags on any instruction we decided to reuse, and that would be correct.
This patch is almost that trivial patch except that we preserve flags on the reused instruction when existing users would imply UB on overflow already. Adding new users can, at most, refine this program to one which doesn't execute UB which is valid.
In practice, this fixes two conceptual problems with the previous code: 1) a binop could have been canonicalized into a form with different opcode or operands, or 2) the inbounds GEP case which was simply unhandled.
On the test changes, most are pretty straight forward. We loose some flags (in some cases, they'd have been dropped on the next CSE pass anyways). The one that took me the longest to understand was the ashr-expansion test. What's happening there is that we're considering reuse of the mul, previously we disallowed it entirely, now we allow it with no flags. The surrounding diffs are all effects of generating the same mul with a different operand order, and then doing simple DCE.
The loss of the inbounds is unfortunate, but even there, we can recover most of those once we actually treat branch-on-poison as immediate UB.
Differential Revision: https://reviews.llvm.org/D112734
This is a fix for test failures on expensive checks build caused by db289340c8.
With LLVM_ENABLE_EXPENSIVE_CHECKS enabled the llvm::sort shuffles the given container.
However, the sort is only called when the TTI is passed to replaceCongruentIVs.
In the mentioned patch we pass it TTI, so the sort happens. But due to shuffling
equivalent Phis may appear in different order from run to run.
With the stable_sort instead of sort this is impossible - the order of sorted Phis
is preserved.
It's a no-op, no overflow happens ever: https://alive2.llvm.org/ce/z/Zw89rZ
While generally i don't like such hacks,
we have a very good reason to do this: here we are expanding
a run-time correctness check for the vectorization,
and said `umul_with_overflow` will not be optimized out
before we query the cost of the checks we've generated.
Which means, the cost of run-time checks would be artificially inflated,
and after https://reviews.llvm.org/D109368 that will affect
the minimal trip count for which these checks are even evaluated.
And if they aren't even evaluated, then the vectorized code
certainly won't be run.
We could consider doing this in IRBuilder, but then we'd need to
also teach `CreateExtractValue()` to look into chain of `insertvalue`'s,
and i'm not sure there's precedent for that.
Refs. https://reviews.llvm.org/D109368#3089809
Always insert values into ExprValueMap, and instead skip using them
in SCEVExpander if poison-generating flags have been lost. This
ensures that all values that are in ValueExprMap are also in
ExprValueMap, so we can use the latter to invalidate the former.
This change is probably not entirely NFC for the case where
originally the SCEV had no nowrap flags but they were inferred
later, in which case that would now allow reusing the existing
value for expansion.
Differential Revision: https://reviews.llvm.org/D112389
Rather than checking for loop nest preheaders upfront in IVUsers,
move this requirement into isSafeToExpand() from SCEVExpander.
Historically, LSR did not check whether SCEVs are safe to expand
and fully relied on IVUsers to validate this. Later, support for
non-expandable SCEVs was added via rigid formulas.
Checking this in isSafeToExpand() makes it more obvious what
exactly this check is guarding against, and avoids the awkward
loop nest scan.
This is a followup to https://reviews.llvm.org/D111493#3055286.
Differential Revision: https://reviews.llvm.org/D111681
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
This is a followup to D104662 to generate slightly nicer code for
pointer overflow checks. Bypass expandAddToGEP and instead
explicitly generate i8 GEPs. This saves some bitcasts and negates
the value in a more obvious way. In particular, this prevents SCEV
from looking through the umul.with.overflow, same as in the integer
case.
The wrapping-pointer-ni.ll test deserves a comment: Previously,
this generated a typed GEP which used the umulo argument rather
than the multiplication result. This results in more compact IR in
that case, but effectively does the multiplication twice, the
second one is just hidden in the GEP. Reusing the umulo result
seems pretty reasonable to me.
Differential Revision: https://reviews.llvm.org/D109093
Florian Hahn