Check if costs for partial reductions are valid up-front in
getScaledReductions instead when transforming each link in the chain in
transformToPartialReduction. This ensures that we either transform all
entries in the chain together, or none via the existing invalidation
logic.
This fixes a crash when a link in the chain would have invalid cost, as
in the added test cases.
Fixes https://github.com/llvm/llvm-project/issues/180340.
PR: https://github.com/llvm/llvm-project/pull/180438
Sub-reductions can be implemented in two ways:
(1) negate the operand in the vector loop (the default way).
(2) subtract the reduced value from the init value in the middle block.
Note that both ways keep the reduction itself as an 'add' reduction,
which is necessary because only llvm.vector.partial.reduce.add exists.
The ISD nodes for partial reductions don't support folding the
sub/negation into its operands because the following is not a valid
transformation:
```
sub(0, mul(ext(a), ext(b)))
-> mul(ext(a), ext(sub(0, b)))
```
It can therefore be better to choose option (2) such that the partial
reduction is always positive (starting at '0') and to do a final
subtract in the middle block.
For AArch64 there are no dot-product instructions that can
do a `partial.reduce.sub(acc, mul(ext(a), ext(b)))` operation.
I'm not sure if such instructions exist for other targets.
(If so then we may want to make this decision a target option)
This PR also increases the AArch64 cost of a partial sub-reduction
when this exists in an 'add-sub' reduction chain.
Fixes https://github.com/llvm/llvm-project/issues/178703
If a phi has fast math flags, we can propagate it to the widened select.
To do this, this patch makes VPPhi and VPBlendRecipe subclasses of
VPRecipeWithIRFlags, and propagates it through PlainCFGBuilder and
VPPredicator.
Alive2 proofs for some of the FMFs (it looks like it can't reason about
the full "fast" set yet)
nnan: https://alive2.llvm.org/ce/z/f0bRd4
nsz: https://alive2.llvm.org/ce/z/u9P96T
The actual motivation for this to eventually be able to move the special
casing for tail folding in
LoopVectorizationPlanner::addReductionResultComputation into the CFG in
#176143, which requires passing through FMFs.
Add a new VPInstruction opcode to compute the exiting value of an
induction variable after vectorization. This replaces the pattern of
extracting the last lane from the last part of the induction backedge
value when applicable.
This allows us to always use the pre-computed IV end value. It will also
allow unifying end value creation for both induction resume and exit
values.
PR: https://github.com/llvm/llvm-project/pull/175651
This patch restructures Find(First|Last)IV handling. Instead of
differentiating between FindLast, FindFirstIV and FindLastIV up front,
this patch simplifies the logic in IVDescriptor to just identify the
FindLast pattern up-front.
It then adds a new VPlan transformation to optimize FindLast reductions
to FindIV reductions if there is a suitable sentinel value.
Find(Last|First)IV recurrence kinds to a single FindIV kind.
This is simpler and more accurate, given selecting the first/last
induction of the final IV reduction is directly controlled by the
corresponding recurrence kind of the ComputeReductionResult.
The new structure also allows further optimizations, like vectorizing
FindLastIV with another boolean reduction that tracks if the condition
in the loop was ever true, if there is no suitable sentinel value.
PR: https://github.com/llvm/llvm-project/pull/177870
Make sure we find the actual select for the exit users and only use it
for the final link in the chain. This fixes a miscompile after
90b3712d8a20efa2cbaadc177da576e485dce038.
Enforce that all VPInstructions set the correct OpType of the VPIRFlags.
Flag mis-matches (e.g. VPInstruction Add without `OverflowingBinOp`
being set) can cause crashes (e.g. in CSE) or potentially mis-compiles.
Add a few helpers in VPBuilder to create common instructions with
correct flags.
PR: https://github.com/llvm/llvm-project/pull/179138
When a recipe can be safely sunk and all of its users are outside the
vector loop region in the same dedicated exit block, the recipe does not
need to be executed on every iteration.
This patch extends the VPlan-based LICM (Loop Invariant Code Motion) to
also sink such recipes from the vector loop region into the exit block.
This reduces redundant computation and improves cost model accuracy.
TODO: Support nested loop sinking
TODO: Support sinking `VPReplicateRecipe` (requires `replicateByVF`
fixes)
TODO: Support recipes with multiple defined values (e.g., interleaved
loads)
TODO: Clone recipes without users to all exit blocks
TODO: Support PHI node users by checking incoming value blocks
TODO: Support sinking when users are in multiple blocks
TODO: Clone recipes when users are on multiple exit paths
Co-authored-by: Luke Lau <luke@igalia.com>
---------
Co-authored-by: Luke Lau <luke@igalia.com>
Co-authored-by: Luke Lau <luke_lau@icloud.com>
This is split out from #177114.
In order to make canonicalizeEVLLoops a generic "convert to variable
stepping" transform, move the code that changes the exit condition to a
separate transform since not all variable stepping loops will want to
transform the exit condition. Run it before canonicalizeEVLLoops before
VPEVLBasedIVPHIRecipe is expanded.
Also relax the assertion for VPInstruction::ExplicitVectorLength to just
bail instead, since eventually VPEVLBasedIVPHIRecipe will be used by
other loops that aren't EVL tail folded.
This reverts commit d1e477b00b49c63ff4dd513eeb14a5b18bc055d7.
Recommit with a extra checks making sure extends are VPWidenCastRecipes,
rejecting VPReplicateRecipes.
Original message:
As a first step, move the existing partial reduction detection logic to
VPlan, trying to preserve the existing code structure & behavior as
closely as possible.
With this, partial reductions are detected and created together in a
single step.
This allows forming partial reductions and bundling them up if
profitable together in a follow-up.
PR: https://github.com/llvm/llvm-project/pull/167851
This reverts commit f4e8cc1a2229dca76d21c8d37439c4c194b06b86.
This change wasn't NFC; it causes failed asserts when building
ffmpeg for i686 windows, see
https://github.com/llvm/llvm-project/pull/167851 for details.
As a first step, move the existing partial reduction detection logic to
VPlan, trying to preserve the existing code structure & behavior as
closely as possible.
With this, partial reductions are detected and created together in a
single step.
This allows forming partial reductions and bundling them up if
profitable together in a follow-up.
PR: https://github.com/llvm/llvm-project/pull/167851
Re-commit of https://github.com/llvm/llvm-project/pull/175839 after
fixing build without `LLVM_ENABLE_DUMP`.
This consists of the following changes:
* Merge several overloads of `VPlanTransforms::runPass` into a single
function to avoid code duplication.
* Add helper macro `RUN_VPLAN_PASS` to capture the transformation name
and pass it to the helper above for printing.
* Add new `-vplan-print-after-all` option (somewhat similar to existing
`-vplan-verify-each`).
* Add two empty passes `printAfterInitialConstruction`/`printFinalVPlan`
so that initial/final VPlans would be supported in `-vplan-print-after-all`
This follows the original future plans in
https://github.com/llvm/llvm-project/pull/123640.
This makes use of the llvm.vector.partial.reduce.fadd intrinsics added
in #163975 to handle the following with FDOT:
```
float32_t fdot(float16_t *src, int N) {
float32_t sum = 0.0f;
for (int i=0; i<N; ++i)
sum += src[i];
return sum;
}
```
This consists of the following changes:
* Merge several overloads of `VPlanTransforms::runPass` into a single
function
to avoid code duplication.
* Add helper macro `RUN_VPLAN_PASS` to capture the transformation name
and pass it to the helper above for printing.
* Add new `-vplan-print-after-all` option (somewhat similar to existing
`-vplan-verify-each`).
* Add two empty passes `printAfterInitialConstruction`/`printFinalVPlan`
so that initial/final
VPlans would be supported in `-vplan-print-after-all`
This follows the original future plans in
https://github.com/llvm/llvm-project/pull/123640.
In some cases, we identify patterns as reductions, even though they can
be simplified to a non-reduction.
Mark VPReductionPHIRecipe as not reading from memory & not having
side-effects, to clean them up.
We also need to remove ComputeReductionResult VPInstructions with
live-in arguments. This means there is actually no reduction, and we
need to fold it to the live in. Otherwise we would incorrectly reduce
the live-in.
PR: https://github.com/llvm/llvm-project/pull/176795
Move SubclassID to VPRecipeBase, and store VPRecipeBase directly in
VPRecipeValue, instead of VPDef. This allows for some additional
simplifications and VPDef now just holds various helpers to deal with
removing and adding VPValues.
This reverts commit 16395da0ff577750571b99fe28281ce6fb6a3ae8.
PR: https://github.com/llvm/llvm-project/pull/174282
Bail out on scalable vectors in helper. Currently this is not causing
issues, but fixes a potential crash that would be exposed by a follow-up
change.
Test would exposes the issue in the future has been added in
8c5352cf3e14ec0c56f592091899d229de8436a7.
When `extract-lane` only contains single vector operand. We can simplify
it to `extractelement`.
This patch makes `extract-lane` generate simple `extractelement` when it
only contains single vector operand to prevent unused IR generated.
This patch is mostly NFC, the unused IR should be removed in following
IR passes.
Fold select c, false, true -> not c. This allows for more accurate cost
estimation and fixes the underlying issue for the cost divergence
between legacy and VPlan-based cost model that caused the revert of
01d34eb38fa058 in ed004cf42bf57c.
https://alive2.llvm.org/ce/z/yVuSgW.
Addresses part of #153144 and splits off part of #166164
There are two parts to the EVL transform:
1) Convert the loop so the number of elements processed each iteration
is EVL, not VF. The IV and header mask are replaced with EVL-based
variants.
2) Optimize users of the EVL based header mask to VP intrinsic based
recipes.
(1) changes the semantics of the vector loop region, whereas (2) needs
to preserve them. This splits (2) out so we don't mix the two up, and
allows us to move (1) earlier in the pipeline in a future PR.
This patch improves the lowering for BranchOnTwoConds added in
https://github.com/llvm/llvm-project/pull/172750 by replacing the branch
on OR with a chain of 2 branches.
On Apple M cores, the new lowering is ~8-10% faster for std::find-like
loops. It also makes it easier to determine the early exits in VPlan. I
am also planning on extensions to support loops with multiple early
exits and early-exits at different positions, which should also be
slightly easier to do with the new representation.
PR: https://github.com/llvm/llvm-project/pull/174016
This patch simplifies extract-lane(%lane_num, %X) to %X when %X is a
scalar value. Extracting from a scalar is redundant since there is only
one value to extract.
This patch adds VPValue sub-classes for the different cases we currently
have:
* VPIRValue: A live-in VPValue that wraps an underlying IR value
* VPSymbolicValue: A symbolic VPValue not tied to an underlying value,
e.g. the vector trip count or VF VPValues
* VPRecipeValue: A VPValue defined by a VPDef/VPRecipeBase.
This has multiple benefits:
* clearer constructors for each kind of VPValue
* limited scope: for example allows moving VPDef member to VPRecipeValue,
reducing size of other VPValues.
* stricter type checking for member variables (e.g. using VPLiveIn in
the Value -> live-in map in VPlan, or using VPSymbolicValue for symbolic
member VPValues)
There probably are additional opportunities for cleanups as follow-ups.
PR: https://github.com/llvm/llvm-project/pull/172758
The original patch, landed as a2db31b0 ([VPlan] Simplify pow-of-2
(mul|udiv) -> (shl|lshr), #172477) had a critical commutative matcher
bug, which has now been fixed. An assert has also been strengthened,
following a post-commit review.
All extra state has been removed from VPWidenSelectRecipe at this point.
There's no benefit of having a separate recipe and Select can easily be
handled by the existing VPWidenRecipe.
PR: https://github.com/llvm/llvm-project/pull/174234
This fixes a crash after introducing BranchOnTwoConds (524b1788,
https://github.com/llvm/llvm-project/pull/172750) when trying to
replace BranchOnTwoConds with a VPBranchOnCond, without dissolving the
region.
In that case, we need to update the appropriate condition operand.
This PR introduces a new BranchOnTwoConds VPInstruction, that takes 2
boolean operands and must be placed in a block with 3 successors.
If condition I is true, branches to successor I, otherwise falls through
to check the next condition. If both conditions are false, branch to the
third successor.
This new branch recipe is used for early-exit loops, to simplify the
representation in VPlan initially, by avoid the need for splitting the
middle block early on, in a way that preserves the single-exit block
property of regions. All exits still go through the latch block, but
they can go to more than 2 successors.
This idea was part of one of the original proposals for how to model
early exits in VPlan, but at that point in time, there was no good way
to handle this during code-gen, and we went with the early split-middle
block approach initially.
Now that we dissolve regions before ::execute, the new recipe can be
lowered nicely after regions have been removed, to a set of VPBBs and
BranchOnCond recipes. The initial lowering preserves the original
structure with the split middle blocks. Follow-ups will improve the
lowering to avoid this splitting, providing performance gains.
PR: https://github.com/llvm/llvm-project/pull/172750
