In order to explore different variants of reassociation current implementation uses "swap in a loop" approach. Unfortunately, the implementation is more complicated than it could be. This is an attempt to streamline the code. New approach is to extract core functionality into a helper function and call it explicitly as many times as required.
Reviewed By: nikic
Differential Revision: https://reviews.llvm.org/D112128
At the moment, rewriteLoopExitValue forgets the current phi node in the
loop that collects phis to rewrite. A few lines after the value is
forgotten, SCEV is used again to analyze incoming values and
potentially expand SCEV expression. This means that another SCEV is
created for PN, before the IR is actually updated in the next loop.
This leads to accessing invalid cached expression in combination with
D71539.
PN should only be changed once the actual incoming exit value is set in
the next loop. Moving invalidation there should ensure that PN is
invalidated in all relevant cases.
Reviewed By: mkazantsev
Differential Revision: https://reviews.llvm.org/D111495
bitcast (inselt (bitcast X), Y, 0) --> or (and X, MaskC), (zext Y)
https://alive2.llvm.org/ce/z/Ux-662
Similar to D111082 / db231ebdb07f :
We want to avoid relatively opaque vector ops on types that are
likely supported by the backend as scalar integers. The bitwise
logic ops are more likely to allow further combining.
We probably want to generalize this to allow a shift too, but
that would oppose instcombine's general rule of not creating
extra instructions, so that's left as a potential follow-up.
Alternatively, we could do that transform in VectorCombine
with the help of the TTI cost model.
This is part of solving:
https://llvm.org/PR52057
As discussed in:
* https://reviews.llvm.org/D94166
* https://lists.llvm.org/pipermail/llvm-dev/2020-September/145031.html
The GlobalIndirectSymbol class lost most of its meaning in
https://reviews.llvm.org/D109792, which disambiguated getBaseObject
(now getAliaseeObject) between GlobalIFunc and everything else.
In addition, as long as GlobalIFunc is not a GlobalObject and
getAliaseeObject returns GlobalObjects, a GlobalAlias whose aliasee
is a GlobalIFunc cannot currently be modeled properly. Creating
aliases for GlobalIFuncs does happen in the wild (e.g. glibc). In addition,
calling getAliaseeObject on a GlobalIFunc will currently return nullptr,
which is undesirable because it should return the object itself for
non-aliases.
This patch refactors the GlobalIFunc class to inherit directly from
GlobalObject, and removes GlobalIndirectSymbol (while inlining the
relevant parts into GlobalAlias and GlobalIFunc). This allows for
calling getAliaseeObject() on a GlobalIFunc to return the GlobalIFunc
itself, making getAliaseeObject() more consistent and enabling
alias-to-ifunc to be properly modeled in the IR.
I exercised some judgement in the API clients of GlobalIndirectSymbol:
some were 'monomorphized' for GlobalAlias and GlobalIFunc, and
some remained shared (with the type adapted to become GlobalValue).
Reviewed By: MaskRay
Differential Revision: https://reviews.llvm.org/D108872
To guarantee convergence of the algorithm each optimization step should decrease number of instructions when IR is modified. This property is not held in this test case. The problem is that SCEV Expander may do "unexpected" reassociation what results in creation of new min/max chains and introduction of extra instructions. As a result on each step we indefinitely optimize back and forth.
The solution is to restrict SCEV Expander to perform uncontrolled reassociations by means of "Unknown" expressions.
Reviewed By: nikic
Differential Revision: https://reviews.llvm.org/D112060
This is trivial. It was left out of the original review only because we had multiple copies of the same code in review at the same time, and keeping them in sync was easiest if the structure was kept in sync.
This patch duplicates a bit of logic we apply to comparisons encountered during the IV users walk to conditions which feed exit conditions. Why? simplifyAndExtend has a very limited list of users it walks. In particular, in the examples is stops at the zext and never visits the icmp. (Because we can't fold the zext to an addrec yet in SCEV.) Being willing to visit when we haven't simplified regresses multiple tests (seemingly because of less optimal results when computing trip counts).
Note that this can be trivially extended to multiple exiting blocks. I'm leaving that to a future patch (solely to cut down on the number of versions of the same code in review at once.)
Differential Revision: https://reviews.llvm.org/D111896
Using BPI within loop predication is non-trivial because BPI is only
preserved lossily in loop pass manager (one fix exposed by lossy
preservation is up for review at D111448). However, since loop
predication is only used in downstream pipelines, it is hard to keep BPI
from breaking for incomplete state with upstream changes in BPI.
Also, correctly preserving BPI for all loop passes is a non-trivial
undertaking (D110438 does this lossily), while the benefit of using it
in loop predication isn't clear.
In this patch, we rely on profile metadata to get almost similar benefit as
BPI, without actually using the complete heuristics provided by BPI.
This avoids the compile time explosion we tried to fix with D110438 and
also avoids fragile bugs because BPI can be lossy in loop passes
(D111448).
Reviewed-By: asbirlea, apilipenko
Differential Revision: https://reviews.llvm.org/D111668
Inspired by D111968, provide a isNegatedPowerOf2() wrapper instead of obfuscating code with (-Value).isPowerOf2() patterns, which I'm sure are likely avenues for typos.....
Differential Revision: https://reviews.llvm.org/D111998
Need to follow the order of the reused scalars from the
ReuseShuffleIndices mask rather than rely on the natural order.
Differential Revision: https://reviews.llvm.org/D111898
The goal is to allow grafting an inline tree from Clang or GCC into a new compilation without affecting other functions. For GCC, we're doing this by extracting the inline tree from dwarf information and generating the equivalent remarks.
This allows easier side-by-side asm analysis and a trial way to see if a particular inlining setup provides benefits by itself.
Testing:
ninja check-all
Reviewed By: wenlei, mtrofin
Differential Revision: https://reviews.llvm.org/D110658
This simplifies the return value of addRuntimeCheck from a pair of
instructions to a single `Value *`.
The existing users of addRuntimeChecks were ignoring the first element
of the pair, hence there is not reason to track FirstInst and return
it.
Additionally all users of addRuntimeChecks use the second returned
`Instruction *` just as `Value *`, so there is no need to return an
`Instruction *`. Therefore there is no need to create a redundant
dummy `and X, true` instruction any longer.
Effectively this change should not impact the generated code because the
redundant AND will be folded by later optimizations. But it is easy to
avoid creating it in the first place and it allows more accurately
estimating the cost of the runtime checks.
Record widening decisions for memory operations within the planned recipes and
use the recorded decisions in code-gen rather than querying the cost model.
Differential Revision: https://reviews.llvm.org/D110479
This is NFC-intended for the callers. Posting in case there are
other potential users that I missed.
I would also use this from VectorCombine in a patch for:
https://llvm.org/PR52178 ( D111901 )
Differential Revision: https://reviews.llvm.org/D111891
This reverts commit fa16329ae0721023376f24c7577b9020d438df1a.
See comments in discussion. Merged by mistake, not entirely getting what
the problem was.
When peeling a loop, we assume that the latch has a `br` terminator and
that all loop exits are either terminated with an `unreachable` or have
a terminating deoptimize call. So when we peel off the 1st iteration, we
change the IDom of all loop exits to the peeled copy of
`NCD(IDom(Exit), Latch)`. This works now, but if we add logic to support
loops with exits that are followed by a block with an `unreachable` or a
terminating deoptimize call, changing the exit's idom wouldn't be enough
and DT would be broken.
For example, let `Exit1` and `Exit2` are loop exits, and each of them
unconditionally branches to the same `unreachable` terminated block. So
neither of the exits dominates this unreachable block. If we change the
IDoms of the exits to some peeled loop block, we don't update the
dominators of the unreachable block. Currently we just don't get to the
peeling logic, saying that we can't peel such loops.
With this NFC we just insert edges from cloned exiting blocks to their
exits after peeling each iteration (we accumulate the insertion updates
and then after peeling apply the updates to DT).
This patch was a part of D110922.
Patch by Dmitry Makogon!
Differential Revision: https://reviews.llvm.org/D111611
Reviewed By: mkazantsev
This removes an over-specified fold. The more general transform
was added with:
727e642e970d
There's a difference on an existing test that shows a potentially
unnecessary use limit on an icmp fold.
That fold is in InstCombinerImpl::foldICmpSubConstant(), and IIRC
there was some back-and-forth on it and similar folds because they
could cause analysis/passes (SCEV, LSR?) to miss optimizations.
Differential Revision: https://reviews.llvm.org/D111410
(iN X s>> (N-1)) & Y --> (X < 0) ? Y : 0
https://alive2.llvm.org/ce/z/qeYhdz
I was looking at a missing abs() transform and found my way to this
generalization of an existing fold that was added with D67799.
As discussed in that review, we want to make sure codegen handles
this difference well, and for all of the targets/types that I
spot-checked, it looks good.
I am leaving the existing fold in place in this commit because
it covers a potentially missing icmp fold, but I plan to remove
that as a follow-up commit as suggested during review.
Differential Revision: https://reviews.llvm.org/D111410
This patch adds a pass option to only run transforms that scalarize
vector operations and do not create new vector instructions.
When running VectorCombine early in the pipeline introducing new vector
operations can have negative effects, like blocking loop or SLP
vectorization. To avoid regressions, restrict the early VectorCombine
run (when using -enable-matrix) to only perform scalarization and not
introduce new vector operations.
This is done as option to the pass directly, which is then set when
adding the pass to the pipeline. This is done for the new pass manager
only.
Reviewed By: spatel
Differential Revision: https://reviews.llvm.org/D111800
Fixes: https://bugs.llvm.org/show_bug.cgi?id=51841
This patch places an arbitrary limit on the size of DIExpressions that
we will produce via salvaging, for performance reasons. This helps to
fix a performance issue observed in the bug above, in which debug values
would be salvaged hundreds of times, producing expressions with over
1000 elements and causing the compiler to hang. Limiting the size of
debug values that we will produce to 128 largely fixes this issue.
Reviewed By: dblaikie, jmorse
Differential Revision: https://reviews.llvm.org/D110332
Add lshr (sext i1 X to iN), C --> select (X, -1 >> C, 0) case. This expands
C == N-1 case to arbitrary C.
Fixes PR52078.
Reviewed By: spatel, RKSimon, lebedev.ri
Differential Revision: https://reviews.llvm.org/D111330
Need to check that either Idx is UndefMaskElem and value is UndefValue
or Idx is valid and value is the same as the scalar value in the node.
Differential Revision: https://reviews.llvm.org/D111802
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
The initial MemoryAccess *Current assignment is never used, and all other uses are initialized/used within the worklist loop (and not across multiple iterations) - so move the variable internal to the loop.
Fixes scan-build unused assignment warning.
If the parameter had been annotated as nonnull because of the null
check, we want to remove the attribute, since it may no longer apply and
could result in miscompiles if left. Similarly, we also want to remove
undef-implying attributes, since they may not apply anymore either.
Fixes PR52110.
Reviewed By: nikic
Differential Revision: https://reviews.llvm.org/D111515
This extends the foldOpIntoPhi code used when visiting a freeze user of a phi to allow any non-undef/poison operand as opposed to only non-undef/poison constants. This lets us hoist a freeze in the increment of an IV into the preheader in many cases.
Differential Revision: https://reviews.llvm.org/D111744
Even if there are no interesting functions, the SCCP solver would still run
before bailing. Now bail earlier, avoid running the solver for nothing.
Differential Revision: https://reviews.llvm.org/D111645
This is NFC-intended for scalar code. There are still unnecessary
m_ConstantInt restrictions in surrounding code, so this is not a
complete fix.
This prevents regressions seen with a planned follow-on to D111410.
If we have an instruction which produces poison only when flags are specified on the instruction, then we know that freezing the operands and dropping flags is equivalent to freezing the result. If we know those flags don't result in any undefined behavior being executed, then there's no point in preserving the flags as we gain no knowledge by having them.
This patch extends the existing propagation logic which sinks freeze to single potential non-poison operands to allow dropping of flags when we know the freeze is the sole use of the instruction with poison flags.
The main value is that we tend to sink freezes towards the phi in IV cycles where the incoming value to the phi is the freeze of an IV increment. This will in turn (in a future patch), let us fold the freeze through the phi into the loop preheader. Motivated by eliminating need for CanonicalizeFreezeInLoops for the clearly profitable cases from onephi.ll test case in the test directory.
Differential Revision: https://reviews.llvm.org/D111675
This patch fixes another crash revealed by PR51614:
when *deciding* to vectorize with masked interleave groups, check if the access
is reverse (which is currently not supported).
Differential Revision: https://reviews.llvm.org/D108900
If another inlining session came after a ModuleInlinerWrapperPass, the
advisor alanysis would still be cached, but its Result would be cleared.
We need to clear both.
This addresses PR52118
Differential Revision: https://reviews.llvm.org/D111586
This may not be obvious, but Alive2 agrees:
https://alive2.llvm.org/ce/z/Ld9qNT
If the mul has "nsw", then -1 * INT_MIN is poison, so the
negate can also have "nsw" because 0 - INT_MIN is poison.
If the mul has "nuw", then that means the "OtherOp" can only
be 0 or 1 (anything else multiplied by 0xfff... would wrap).
So the replacement negate must be "nsw" because it is either
"0-0" or "0-1".
This is another regression noticed with a planned follow-up
to D111410.
This patch continues unblocking optimizations that are blocked by pseudo probe instrumentation.
Not exactly like DbgIntrinsics, PseudoProbe intrinsic has other attributes (such as mayread, maywrite, mayhaveSideEffect) that can block optimizations. The issues fixed are:
- Flipped default param of getFirstNonPHIOrDbg API to skip pseudo probes
- Unblocked CSE by avoiding pseudo probe from clobbering memory SSA
- Unblocked induction variable simpliciation
- Allow empty loop deletion by treating probe intrinsic isDroppable
- Some refactoring.
Reviewed By: wenlei
Differential Revision: https://reviews.llvm.org/D110847
collectLoopScalars collects pointer induction updates in ScalarPtrs, assuming
that the instruction will be scalar after vectorization. This may crash later
in VPReplicateRecipe::execute() if there there is another user of the instruction
other than the Phi node which needs to be widened.
This changes collectLoopScalars so that if there are any other users of
Update other than a Phi node, it is not added to ScalarPtrs.
Reviewed By: david-arm, fhahn
Differential Revision: https://reviews.llvm.org/D111294
This is a follow up of D110529 that disallowed constexprs. That change
introduced a regression as this also disallowed constexprs that are function
pointers, which is actually one of the motivating use cases that we do want to
support.
Differential Revision: https://reviews.llvm.org/D111567
This patch adds a new cost heuristic that allows peeling a single
iteration off read-only loops, if the loop contains a load that
1. is feeding an exit condition,
2. dominates the latch,
3. is not already known to be dereferenceable,
4. and has a loop invariant address.
If all non-latch exits are terminated with unreachable, such loads
in the loop are guaranteed to be dereferenceable after peeling,
enabling hoisting/CSE'ing them.
This enables vectorization of loops with certain runtime-checks, like
multiple calls to `std::vector::at` if the vector is passed as pointer.
Reviewed By: mkazantsev
Differential Revision: https://reviews.llvm.org/D108114
LoopSimplifyCFG does not need MSSA, but should preserve it if it's available.
This is a legacy PM change, aimed to denoise the test changes in D109958.
Differential Revision: https://reviews.llvm.org/D111578
There may be some other patterns like this or a generalization,
but this is an example that I noticed would definitely regress
with a planned follow-up to D111410.
https://alive2.llvm.org/ce/z/GVpQDb
At the moment, a VPValue is created for the backedge-taken count, which
is used by some recipes. To make it easier to identify the operands of
recipes using the backedge-taken count, print it at the beginning of the
VPlan if it is used.
Reviewed By: a.elovikov
Differential Revision: https://reviews.llvm.org/D111298
As a brief reminder, an "exit count" is the number of times the backedge executes before some event. It can be zero if we exit before the backedge is reached. A "trip count" is the number of times the loop header is entered if we branch into the loop. In general, TC = BTC + 1 and thus a zero trip count is ill defined
There is a cornercases which we don't handle well. Let's assume i8 for our examples to keep things simple. If BTC = 255, then the correct trip count is 256. However, 256 is not representable in i8.
In theory, code which needs to reason about trip counts is responsible for checking for this cornercase, and either bailing out, or handling it correctly. Historically, we don't have a great track record about actually doing so.
When reviewing D109676, I found myself asking a basic question. Was there any good reason to preserve the current wrap-to-zero behavior when converting from backedge taken counts to trip counts? After reviewing existing code, I could not find a single case which appears to correctly and precisely handle the overflow case.
This patch changes the default behavior to extend instead of wrap. That is, if the result might be 256, we return a value of i9 type to ensure we interpret the count correctly. I did leave the legacy behavior as an option since a) loop-flatten stops triggering if I extend due to weirdly specific pattern matching I didn't understand and b) we could reasonably use the mode if we'd externally established a lack of overflow.
I want to emphasize that this change is *not* NFC. There are two call sites (one in ScalarEvolution.cpp, one in LoopCacheAnalysis.cpp) which are switched to the extend semantics. The former appears imprecise (but correct) for a constant 255 BTC. The later appears incorrect, though I don't have a test case.
Differential Revision: https://reviews.llvm.org/D110587
https://bugs.llvm.org/show_bug.cgi?id=27506https://bugs.llvm.org/show_bug.cgi?id=31652https://bugs.llvm.org/show_bug.cgi?id=51043
Problems with SimpleLoopUnswitch cause the bug reports above.
```
while (...) {
if (C) { A }
else { B }
}
Into:
C' = freeze(C)
if (C') {
while (...) { A }
} else {
while (...) { B }
}
```
This problem can be solved by adding a freeze on hoisted branches(above transform) and has been solved by D29015.
However, D29015 is now reverted by performance regression(2b5a897651)
It is not the first time that an added freeze has caused performance regression.
SimplifyCFG also had a problem with UB caused by branching-on-undef, which was solved by adding freeze to the branching condition. (D104569)
Performance regression occurred in D104569, and patches such as D105344 and D105392 were written to minimize it.
This patch will correct the SimpleLoopUnswitch as D104569 handles the SimplyCFG while minimizing performance loss by introducing patches like D105344 and D105392(This patch was rebased with the author's permission)
Reviewed By: reames
Differential Revision: https://reviews.llvm.org/D106041
