This patch adds a generic DAGCombine for vector-predicated (VP) nodes.
Those for which we can determine that no vector element is active can be
replaced by either undef or, for reductions, the start value.
This is tested rather trivially at the IR level, where it's possible
that we want to teach instcombine to perform this optimization.
However, we can also see the zero-evl case arise during SelectionDAG
legalization, when wide VP operations can be split into two and the
upper operation emerges as trivially false.
It's possible that we could perform this optimization "proactively"
(both on legal vectors and before splitting) and reduce the width of an
operation and insert it into a larger undef vector:
```
v8i32 vp_add x, y, mask, 4
->
v8i32 insert_subvector (v8i32 undef), (v4i32 vp_add xsub, ysub, mask, 4), i32 0
```
This is somewhat analogous to similar vector narrow/widening
optimizations, but it's unclear at this point whether that's beneficial
to do this for VP ops for any/all targets.
Reviewed By: craig.topper
Differential Revision: https://reviews.llvm.org/D109148
One of the cases identified in PR45116 - we don't need to limit store narrowing to ABI alignment, we can use allowsMemoryAccess - which tests using getABITypeAlign, but also checks if a target permits (fast) misaligned memory access by checking allowsMisalignedMemoryAccesses as a fallback.
The fmul is a canonicalizing operation, and fneg is not so this would
break denormals that need flushing and also would not quiet signaling
nans. Fold to fsub instead, which is also canonicalizing.
This extends the custom lowering for extending loads on
fixed length vectors in SVE to support masked extending loads.
The existing tests for correct behaviour of masked extending loads
exhibit bad code generation due to the legalistaion of i1 vectors.
They have been left as-is and new tests have been added that do not
exhibit this behaviour.
Differential Revision: https://reviews.llvm.org/D108200
Soft deprecrate isNullValue/isAllOnesValue and update in tree
callers. This matches the changes to the APInt interface from
D109483.
Reviewed By: lattner
Differential Revision: https://reviews.llvm.org/D109535
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
Given a select_cc producing a constant and a invertion of the constant
for a comparison more than zero, we can produce an xor with ashr
instead, which produces smaller code. The ashr either sets all bits or
clear all bits depending on if the value is negative. This is then xor'd
with the constant to optionally negate the value.
https://alive2.llvm.org/ce/z/DTFaBZ
This includes a OneUseCheck on the Cmp, which seems to make thinks a
little worse and will be removed in a followup.
Differential Revision: https://reviews.llvm.org/D109149
The check for whether a rotate is possible occurs before the
memory legality checks for the integer type. So it's possible we
decide we can use a rotate, but then fail the legality checks. If
that happens we should not fall back to a vector type. This triggers
an assertion in the rotate handling when it finds a vector type
instead of an integer type.
In theory we could use a shufflevector in place of the rotate, but
right now I'd just like to fix the crash.
Reviewed By: RKSimon
Differential Revision: https://reviews.llvm.org/D108839
Without this change only the preferred fusion opcode is tested
when attempting to combine FMA operations.
If both FMA and FMAD are available then FMA ops formed prior to
legalization will not be merged post legalization as FMAD becomes
the preferred fusion opcode.
Reviewed By: foad
Differential Revision: https://reviews.llvm.org/D108619
This is another bug exposed by https://llvm.org/PR51612
(and the one that triggered the initial assertion) in the report.
That example was suppressed with:
985b48f183
...but these would still crash because we created nodes
like UADDO without the expected 2 output values.
There are 2 bugs here:
1. We were not checking uses of operand 2 (the false value of the select).
2. We were not checking for multiple uses of nodes that produce >1 result.
Correcting those is enough to avoid the crash in the reduced test based on:
https://llvm.org/PR51612
The additional use check on operand 0 (the condition value of the select)
should not strictly be necessary because we are only replacing one use
with another (whether it makes performance sense to do the transform with
that pattern is not clear). But as noted in the TODO, changing that
uncovers another bug.
Note: there's at least one more bug here - we aren't propagating EVTs
correctly, but I plan to fix that in another patch.
For ISD::EXTRACT_SUBVECTOR, its second operand must be a constant
multiple of the known-minimum vector length of the result type.
Reviewed By: dmgreen
Differential Revision: https://reviews.llvm.org/D107795
One of the cases identified in PR45116 - we don't need to limit load combines to ABI alignment, we can use allowsMemoryAccess - which tests using getABITypeAlign, but also checks if a target permits (fast) misaligned memory loads by checking allowsMisalignedMemoryAccesses as a fallback.
One of the cases identified in PR45116 - we don't need to limit load combines (in this case for fp->int load/store copies) to ABI alignment, we can use allowsMemoryAccess - which tests using getABITypeAlign, but also checks if a target permits (fast) misaligned memory loads by checking allowsMisalignedMemoryAccesses as a fallback.
Differential Revision: https://reviews.llvm.org/D108318
One of the cases identified in PR45116 - we don't need to limit load combines (in this case for ISD::BUILD_PAIR) to ABI alignment, we can use allowsMemoryAccess - which tests using getABITypeAlign, but also checks if a target permits (fast) misaligned memory loads by checking allowsMisalignedMemoryAccesses as a fallback.
This helps in particular for 32-bit X86 cases loading 64-bit size data, reducing codegen diffs vs x86_64.
Differential Revision: https://reviews.llvm.org/D108307
Follow-up to D107068, attempt to fold nested concat_vectors/undefs, as long as both the vector and inner subvector types are legal.
This exposed the same issue in ARM's MVE LowerCONCAT_VECTORS_i1 (raised as PR51365) and AArch64's performConcatVectorsCombine which both assumed concat_vectors only took 2 subvector operands.
Differential Revision: https://reviews.llvm.org/D107597
visitEXTRACT_SUBVECTOR can sometimes create illegal BITCASTs when
removing "redundant" INSERT_SUBVECTOR operations. This patch adds
an extra check to ensure such combines only occur after operation
legalisation if any resulting BITBAST is itself legal.
Differential Revision: https://reviews.llvm.org/D108086
We don't have real demanded bits support for MULHU, but we can
still use the known bits based constant folding support at the end
of SimplifyDemandedBits to simplify a MULHU. This helps with cases
where we know the LHS and RHS have enough leading zeros so that
the high multiply result is always 0.
Reviewed By: RKSimon
Differential Revision: https://reviews.llvm.org/D106471
IR typically creates INSERT_SUBVECTOR patterns as a widening of the subvector with undefs to pad to the destination size, followed by a shuffle for the actual insertion - SelectionDAGBuilder has to do something similar for shuffles when source/destination vectors are different sizes.
This combine attempts to recognize these patterns by looking for a shuffle of a subvector (from a CONCAT_VECTORS) that starts at a modulo of its size into an otherwise identity shuffle of the base vector.
This uncovered a couple of target-specific issues as we haven't often created INSERT_SUBVECTOR nodes in generic code - aarch64 could only handle insertions into the bottom of undefs (i.e. a vector widening), and x86-avx512 vXi1 insertion wasn't keeping track of undef elements in the base vector.
Fixes PR50053
Differential Revision: https://reviews.llvm.org/D107068
This allows special constants like to 0 to be recognized. It's also
expected by isel patterns if a target had a mulh with immediate instructions.
The commuting done by tablegen won't commute patterns with immediates since it
expects DAGCombine to have done it.
Reviewed By: foad
Differential Revision: https://reviews.llvm.org/D107486
We had some similar hasOneUse/isNON_EXTLoad early-outs spread out over different parts of the method - we should pull them all together.
Noticed while triaging PR45116
This transform was added with D58874, but there were no tests for overflow ops.
We need to change this one way or another because it can crash as shown in:
https://llvm.org/PR51238
Note that if there are no uses of an overflow op's bool overflow result, we
reduce it to a regular math op, so we continue to fold that case either way.
If we have uses of both the math and the overflow bool, then we are likely
not saving anything by creating an independent sub instruction as seen in
the test diffs here.
This patch makes the behavior in SDAG consistent with what we do in
instcombine AFAICT.
Differential Revision: https://reviews.llvm.org/D106983
This patch adds a peephole optimization `SETCC(FREEZE(x),const)` => `FREEZE(SETCC(x,const))`
if the SETCC is only used by BRCOND.
Combined with `BRCOND(FREEZE(X)) => BRCOND(X)`, this leads to a nice improvement in the generated assembly when x is a masked loaded value.
Reviewed By: efriedma
Differential Revision: https://reviews.llvm.org/D105344
This patch builds on top of D106575 in which scalable-vector splats were
supported in `ISD::matchBinaryPredicate`. It teaches the DAGCombiner how
to perform a variety of the pre-existing saturating add/sub combines on
scalable-vector types.
Reviewed By: craig.topper
Differential Revision: https://reviews.llvm.org/D106652
This patch extends support for (scalable-vector) splats in the
DAGCombiner via the `ISD::matchBinaryPredicate` function, which enable a
variety of simple combines of constants.
Users of this function may now have to distinguish between
`BUILD_VECTOR` and `SPLAT_VECTOR` vector operands. The way of dealing
with this in-tree follows the approach added for
`ISD::matchUnaryPredicate` implemented in D94501.
Reviewed By: craig.topper
Differential Revision: https://reviews.llvm.org/D106575
I've setup the basic framework for the isGuaranteedNotToBeUndefOrPoison call and updated DAGCombiner::visitFREEZE to use it, further Opcodes can be handled when we have test coverage.
I'm not aware of any vector test freeze coverage so the DemandedElts (and the Depth) args are not being used yet - but they are in place.
SelectionDAG::isGuaranteedNotToBePoison wrappers have also been added.
Differential Revision: https://reviews.llvm.org/D106668
This adds custom lowering for truncating stores when operating on
fixed length vectors in SVE. It also includes a DAG combine to
fold extends followed by truncating stores into non-truncating
stores in order to prevent this pattern appearing once truncating
stores are supported.
Currently truncating stores are not used in certain cases where
the size of the vector is larger than the target vector width.
Differential Revision: https://reviews.llvm.org/D104471
Reland of 31859f896.
This change implements new DAG notes GLOBAL_GET/GLOBAL_SET, and
lowering methods for load and stores of reference types from IR
globals. Once the lowering creates the new nodes, tablegen pattern
matches those and converts them to Wasm global.get/set.
Reviewed By: tlively
Differential Revision: https://reviews.llvm.org/D104797
The existing rule about the operand type is strange. Instead, just say
the operand is a TargetConstant with the right width. (Legalization
ignores TargetConstants, so it doesn't matter if that width is legal.)
Highlights:
1. I had to substantially rewrite the AArch64 isel patterns to expect a
TargetConstant. Nothing too exotic, but maybe a little hairy. Maybe
worth considering a target-specific node with some dagcombines instead
of this complicated nest of isel patterns.
2. Our behavior on RV32 for vectors of i64 has changed slightly. In
particular, we correctly preserve the width of the arithmetic through
legalization. This changes the DAG a bit. Maybe room for
improvement here.
3. I explicitly defined the behavior around overflow. This is necessary
to make the DAGCombine transforms legal, and I don't think it causes any
practical issues.
Differential Revision: https://reviews.llvm.org/D105673
I'm going to extend the functionality started in D106058 so move the folds into their own method to reduce the amount of code in DAGCombiner::visitSELECT
Similar to the folds performed in InstCombinerImpl::foldSelectOpOp, this attempts to push a select further up to help merge a pair of binops.
I'm primarily interested in select(cond,add(x,y),add(x,z)) folds to help expose pointer math (see https://bugs.llvm.org/show_bug.cgi?id=51069 etc.) but I've tried to use the more generic isBinOp().
Differential Revision: https://reviews.llvm.org/D106058
This adds custom lowering for truncating stores when operating on
fixed length vectors in SVE. It also includes a DAG combine to
fold extends followed by truncating stores into non-truncating
stores in order to prevent this pattern appearing once truncating
stores are supported.
Currently truncating stores are not used in certain cases where
the size of the vector is larger than the target vector width.
Differential Revision: https://reviews.llvm.org/D104471
We already have reassociation code for Adds and Ors separately in DAG
combiner, this adds it for the combination of the two where Ors act like
Adds. It reassociates (add (or (x, c), y) -> (add (add (x, y), c)) where
we know that the Ors operands have no common bits set, and the Or has
one use.
Differential Revision: https://reviews.llvm.org/D104765
Fraser Cormack