SLP/TTI do not know about the cost estimation for addsub pattern,
supported by X86. Previously the support for pattern detection was added
(seeTTI::isLegalAltInstr), but the cost still did not estimated
properly.
If decided to resize the instruction, need to drop wrapping flags from
the resulting vector instructions to avoid incorrect
optimizations/assumptions later.
Fixes PR75995.
Issue is covered by existing test
llvm/test/Transforms/SLPVectorizer/RISCV/phi-const.ll
See issue #75632 for ideas for how we could catch these more easily in
the future.
SLP Vectorizer can discard vector entries at unknown positions. This
example shows the behaviour:
https://godbolt.org/z/or43EM594
The following instruction inserts an element at an unknown position:
```
%2 = insertelement <3 x i64> poison, i64 %value, i64 %position
```
The position depends on an argument that is unknown at compile time.
After running SLP, one can see there is no more instruction present
referencing `%position`.
This happens as SLP parallelizes the two adds in the example. It then
needs to merge the original vector with the new vector.
Within `isUndefVector`, the SLP vectorizer constructs a bitmap
indicating which elements of the original vector are poison values. It
does this by walking the insertElement instructions.
If it encounters an insert with a non-constant position, it is ignored.
This will result in poison values to be used for all entries, where
there are no inserts with constant positions.
However, as the position is unknown, the element could be anywhere.
Therefore, I think it is only safe to assume none of the entries are
poison values and to simply take them all over when constructing the
shuffleVector instruction.
This fixes#75437
nodes, having same last instruction.
If the user nodes has the same last-instruction, used as insert points
for the buildvector nodes, finding the proper dependency is crucial.
Before, it depended on the indices of the buildvectors themselves but
looks like it should depend on indices of the user nodes, because it
identifies the vectorization order and, thus, properly aligns
buildvector nodes in terms of def-use chain.
Minor simplification applied to VFShape::getScalarShape,
VFShape::get, and VFABI::tryDemangleForVFABI methods.
Also, remove unnecessary `static_cast` in `SLPVectorizer.cpp`
Currently we emit gathers for scalars being vectorized in the tree as
a pair of extractelement/insertelement instructions. Instead we can try
to find all required vectors and emit shuffle vector instructions
directly, improving the code and reducing compile time.
Part of non-power-of-2 vectorization.
Differential Revision: https://reviews.llvm.org/D110978
Currently, MinBWs map uses Value* as a key and stores mapping for each
value to be demoted. It make is it hard to get the actual MinBWs value
for the buildvector scalars(constants), since same constant might be
used in different nodes with the different MinBWs values/decisions.
Also, it consumes extra memory for the vectorized values/instructions
from the same nodes.
Better to map actual nodes. It fixes the bitwidth data fetching for
buildvector scalars and improves memory consumption/analysis time for
other instructions.
No need to store optional boolean in the map, enough to store boolean
directly. Also, we can do preliminary check for instruction and if they
are not simple, mark as aliased without storing this result in the map.
If the gather node includes ordered loads only partially (not the whole
node consists of loads) and the other gathered scalar are not loads, and
no other dependency from other nodes is found, we still can improve the
cost of gather, if take into account the fact that these loads still can
be vectorized.
operand.
Need to copy the submask not to the very first part of the common
extractelements vector mask, but to the proper one to avoid wrong code
emission.
If the buildvector node contains extractelement, which vector operand
depends on vector node, need to check if the node is ready and use
vectorized value instead of the original vector operation.
SLP includes analysis for the minimum bitwidth, the actual integer
operations can be emitted. It allows to reduce register pressure and
improve perf. Currently, it includes only cost model and the next
transformation relies on InstructionCombiner. Better to do it directly
in SLP, it allows to reduce compile time and fix cost model issues.
SLP includes analysis for the minimum bitwidth, the actual integer
operations can be emitted. It allows to reduce register pressure and
improve perf. Currently, it includes only cost model and the next
transformation relies on InstructionCombiner. Better to do it directly
in SLP, it allows to reduce compile time and fix cost model issues.
Currently tryToGatherExtractElements function analyzes the whole vector,
regrdless number of actual registers, used in this vector. It may
prevent some optimizations, because per-register analysis may allow to
simplify the final code by reusing more already emitted vectors and
better shuffles.
Differential Revision: https://reviews.llvm.org/D148855
This causes asserts:
llvm-project/llvm/lib/Transforms/Vectorize/SLPVectorizer.cpp:10082:
Value *llvm::slpvectorizer::BoUpSLP::ShuffleInstructionBuilder::adjustExtracts(
const TreeEntry *, MutableArrayRef<int>, unsigned int, bool &):
Assertion `Part == 0 && "Expected firs part."' failed.
See comment on the code review.
> Currently tryToGatherExtractElements function analyzes the whole vector,
> regrdless number of actual registers, used in this vector. It may
> prevent some optimizations, because per-register analysis may allow to
> simplify the final code by reusing more already emitted vectors and
> better shuffles.
>
> Differential Revision: https://reviews.llvm.org/D148855
This reverts commit 9dfdbd7887.
Currently tryToGatherExtractElements function analyzes the whole vector,
regrdless number of actual registers, used in this vector. It may
prevent some optimizations, because per-register analysis may allow to
simplify the final code by reusing more already emitted vectors and
better shuffles.
Differential Revision: https://reviews.llvm.org/D148855
This reverts commit 3e6d7c6d98.
That commit caused miscompilation of ffmpeg's libavcodec/vp9dsp_8bpp.o
on aarch64; the file still compiles correctly, but no longer produces
the right result - see https://reviews.llvm.org/D148855#4655968
for details.
Alexey Bataev
Kazu Hirata
Alexey Bataev
Arthur Eubanks
Reid Kleckner
Maurice Heumann
Paschalis Mpeis
Alexander Kornienko
Valery Dmitriev
Hans Wennborg
Martin Storsjö