In some cases, we can negate instruction if only one of it's operands
negates. Previously, we assumed that constants would have been
canonicalized to RHS already, but that isn't guaranteed to happen,
because of InstCombine worklist visitation order,
as the added test (previously-hanging) shows.
So if we only need to negate a single operand,
we should ensure ourselves that we try constant operand first.
Do that by re-doing the complexity sorting ourselves,
when we actually care about it.
Fixes https://bugs.llvm.org/show_bug.cgi?id=47752
We know V is a IntToPtrInst or PtrToIntInst type so we know its a CastInst - so use cast<> directly.
Prevents clang static analyzer warning that we could deference a null pointer.
This still only gets used for scalar types but now always uses ConstantExpr in preparation for vector support - it was using APInt methods in some places.
(it was introduced in https://lists.llvm.org/pipermail/llvm-dev/2015-January/080956.html)
This canonicalization seems dubious.
Most importantly, while it does not create `inttoptr` casts by itself,
it may cause them to appear later, see e.g. D88788.
I think it's pretty obvious that it is an undesirable outcome,
by now we've established that seemingly no-op `inttoptr`/`ptrtoint` casts
are not no-op, and are no longer eager to look past them.
Which e.g. means that given
```
%a = load i32
%b = inttoptr %a
%c = inttoptr %a
```
we likely won't be able to tell that `%b` and `%c` is the same thing.
As we can see in D88789 / D88788 / D88806 / D75505,
we can't really teach SCEV about this (not without the https://bugs.llvm.org/show_bug.cgi?id=47592 at least)
And we can't recover the situation post-inlining in instcombine.
So it really does look like this fold is actively breaking
otherwise-good IR, in a way that is not recoverable.
And that means, this fold isn't helpful in exposing the passes
that are otherwise unaware of these patterns it produces.
Thusly, i propose to simply not perform such a canonicalization.
The original motivational RFC does not state what larger problem
that canonicalization was trying to solve, so i'm not sure
how this plays out in the larger picture.
On vanilla llvm test-suite + RawSpeed, this results in
increase of asm instructions and final object size by ~+0.05%
decreases final count of bitcasts by -4.79% (-28990),
ptrtoint casts by -15.41% (-3423),
and of inttoptr casts by -25.59% (-6919, *sic*).
Overall, there's -0.04% less IR blocks, -0.39% instructions.
See https://bugs.llvm.org/show_bug.cgi?id=47592
Differential Revision: https://reviews.llvm.org/D88789
When retrying the "simplify with operand replaced" select
optimization without poison flags, also handle inbounds on GEPs.
Of course, this particular example would also be safe to transform
while keeping inbounds, but the underlying machinery does not
know this (yet).
Use m_Specific instead of m_Value followed by an equality check - we already do this for the similar folds above, it looks like an oversight in rG2b459fe7e1e where the original pattern match code looked a little different.
If we're bswap'ing some bytes and zero'ing the remainder we can perform this as a bswap+mask which helps us match 'partial' bswaps as a first step towards folding into a more complex bswap pattern.
Reapplied with early-out if recognizeBSwapOrBitReverseIdiom collects a source wider than the result type.
Differential Revision: https://reviews.llvm.org/D88578
If we're bswap'ing some bytes and zero'ing the remainder we can perform this as a bswap+mask which helps us match 'partial' bswaps as a first step towards folding into a more complex bswap pattern.
Differential Revision: https://reviews.llvm.org/D88578
When replacing X == Y ? f(X) : Z with X == Y ? f(Y) : Z, make sure
that Y cannot be undef. If it may be undef, we might end up picking
a different value for undef in the comparison and the select
operand.
I think we initially made this fold conservative to be safer, but we do not
need the alignment attribute/metadata limitation because the masked load
intrinsic itself specifies the alignment. A normal vector load is better for
IR transforms and should be no worse in codegen than the masked alternative.
If it is worse for some target, the backend can reverse this transform.
Differential Revision: https://reviews.llvm.org/D88505
Attempt to fold trunc (*shr (trunc A), C) --> trunc(*shr A, C) iff the shift amount if small enough that all zero/sign bits created by the shift are removed by the last trunc.
Helps fix the regressions encountered in D88316.
I've tweaked a couple of shift values as suggested by @lebedev.ri to ensure we have coverage of shift values close (above/below) to the max limit.
Differential Revision: https://reviews.llvm.org/D88429
This came from @lebedev.ri's suggestion to use m_SpecificInt_ICMP for D88429 - since I was going to change the m_APInt to m_Constant for that patch I thought I would do it for the only other user of the APInt first.
I've added a ConstantExpr::getUMin helper - its trivial to add UMAX/SMIN/SMAX but thought I'd wait until we have use cases.
Differential Revision: https://reviews.llvm.org/D88475
Fixes minor bug in D88402 where we were using the original shift constant (with undefs) instead of one with the splat values (re)splatted to all elements.
This patch adds handling of rotation patterns with constant shift amounts - the next bit will be how we want to support non-uniform constant vectors.
Differential Revision: https://reviews.llvm.org/D87452
In this patch I've fixed some warnings that arose from the implicit
cast of TypeSize -> uint64_t. I tried writing a variety of different
cases to show how this optimisation might work for scalable vectors
and found:
1. The optimisation does not work for cases where the cast type
is scalable and the allocated type is not. This because we need to
know how many times the cast type fits into the allocated type.
2. If we pass all the various checks for the case when the allocated
type is scalable and the cast type is not, then when creating the
new alloca we have to take vscale into account. This leads to
sub-optimal IR that is worse than the original IR.
3. For the remaining case when both the alloca and cast types are
scalable it is hard to find examples where the optimisation would
kick in, except for simple bitcasts, because we typically fail the
ABI alignment checks.
For now I've changed the code to bail out if only one of the alloca
and cast types is scalable. This means we continue to support the
existing cases where both types are fixed, and also the specific case
when both types are scalable with the same size and alignment, for
example a simple bitcast of an alloca to another type.
I've added tests that show we don't attempt to promote the alloca,
except for simple bitcasts:
Transforms/InstCombine/AArch64/sve-cast-of-alloc.ll
Differential revision: https://reviews.llvm.org/D87378
We do similar factorization folds in SimplifyUsingDistributiveLaws,
but that drops no-wrap properties. Propagating those optimally may
help solve:
https://llvm.org/PR47430
The propagation is all-or-nothing for these patterns: when all
3 incoming ops have nsw or nuw, the 2 new ops should have the
same no-wrap property:
https://alive2.llvm.org/ce/z/Dv8wsU
This also solves:
https://llvm.org/PR47584
The test (currently crashing) is reduced from the example provided
in the post-commit discussion in D87149.
Differential Revision: https://reviews.llvm.org/D87965
We cannot iterate on scalable vector, the number of elements is unknown at compile-time.
Reviewed By: efriedma
Differential Revision: https://reviews.llvm.org/D87918
Enable canonicalization of SPF_ABS and SPF_NABS to the abs intrinsic.
To be conservative, the one-use check on the comparison is retained,
this may be relaxed if all goes well.
It's pretty likely that this will uncover places that missing
handling for the abs() intrinsic. Please report any seen performance
regressions.
Differential Revision: https://reviews.llvm.org/D87188
Reapply after fixing SimplifyWithOpReplaced() to never return
the original value, which would lead to an infinite loop in this
transform.
-----
For selects of the type X == Y ? A : B, check if we can simplify A
by using the X == Y equality and replace the operand if that's
possible. We already try to do this in InstSimplify, but will only
fold if the result of the simplification is the same as B, in which
case the select can be dropped entirely. Here the select will be
retained, just one operand simplified.
As we are performing an actual replacement here, we don't have
problems with refinement / poison values.
Differential Revision: https://reviews.llvm.org/D87480
For selects of the type X == Y ? A : B, check if we can simplify A
by using the X == Y equality and replace the operand if that's
possible. We already try to do this in InstSimplify, but will only
fold if the result of the simplification is the same as B, in which
case the select can be dropped entirely. Here the select will be
retained, just one operand simplified.
As we are performing an actual replacement here, we don't have
problems with refinement / poison values.
Differential Revision: https://reviews.llvm.org/D87480
NOTE: There is a mailing list discussion on this: http://lists.llvm.org/pipermail/llvm-dev/2019-December/137632.html
Complemantary to the assumption outliner prototype in D71692, this patch
shows how we could simplify the code emitted for an alignemnt
assumption. The generated code is smaller, less fragile, and it makes it
easier to recognize the additional use as a "assumption use".
As mentioned in D71692 and on the mailing list, we could adopt this
scheme, and similar schemes for other patterns, without adopting the
assumption outlining.
This is a followup to D86834, which partially fixed this issue in
InstSimplify. However, InstCombine repeats the same transform while
dropping poison flags -- which does not cover cases where poison is
introduced in some other way.
The fix here is a bit more comprehensive, because things are quite
entangled, and it's hard to only partially address it without
regressing optimization. There are really two changes here:
* Export the SimplifyWithOpReplaced API from InstSimplify, with an
added AllowRefinement flag. For replacements inside the TrueVal
we don't actually care whether refinement occurs or not, the
replacement is always legal. This part of the transform is now
done in InstSimplify only. (It should be noted that the current
AllowRefinement check is not sufficient -- that's an issue we
need to address separately.)
* Change the InstCombine fold to work by temporarily dropping
poison generating flags, running the fold and then restoring the
flags if it didn't work out. This will ensure that the InstCombine
fold is correct as long as the InstSimplify fold is correct.
Differential Revision: https://reviews.llvm.org/D87445
Bail from maskIsAllZeroOrUndef and maskIsAllOneOrUndef prior to iterating over the number of
elements for scalable vectors.
Assert that the mask type is not scalable in possiblyDemandedEltsInMask .
Assert that the types are correct in all three functions.
Reviewed By: efriedma
Differential Revision: https://reviews.llvm.org/D87424
See discussion in D87149. Dropping volatile stores here is legal
per LLVM semantics, but causes issues for real code and may result
in a change to LLVM volatile semantics. Temporarily treat volatile
stores as "not guaranteed to transfer execution" in just this place,
until this issue has been resolved.
If we know that the abs operand is known negative, we can replace
it with a neg.
To avoid computing known bits twice, I've removed the fold for the
non-negative case from InstSimplify. Both the non-negative and the
negative case are handled by InstCombine now, with one known bits call.
Differential Revision: https://reviews.llvm.org/D87196
This was supposed to be an NFC cleanup, but there's
a real logic difference (did not drop 'nsw') visible
in some tests in addition to an efficiency improvement.
This is because in the case where we have 2 GEPs,
the code was *always* swapping the operands and
negating the result. But if we have 2 GEPs, we
should *never* need swapping/negation AFAICT.
This is part of improving flags propagation noticed
with PR47430.
Normal dead code elimination ignores assume intrinsics, so we fail to
delete assumes that are not meaningful (and potentially worse if they
cause conflicts with other assumptions).
The motivating example in https://llvm.org/PR47416 suggests that we
might have problems upstream from here (difference between C and C++),
but this should be a cheap way to make sure we remove more dead code.
Differential Revision: https://reviews.llvm.org/D87149
Amara Emerson