The previous implementation decomposes tanh(x) into
`(exp(2x) - 1)/(exp(2x)+1), x < 0`
`(1 - exp(-2x))/(1 + exp(-2x)), x >= 0`
This is fine as it avoids overflow with the exponential, but the whole
decomposition is computed for both cases unconditionally, then the
result is chosen based off the sign of the input. This results in doing
two expensive exp computations.
The proposed change avoids doing the whole computation twice by
exploiting the reflection symmetry `tanh(-x) = -tanh(x)`. We can
"normalize" the input to be positive by setting `y = sign(x) * x`, where
the sign of `x` is computed as `sign(x) = (float)(x > 0) * (-2) + 1`.
Then compute `z = tanh(y) `with the decomposition above for `x >=0` and
"denormalize" the result `z * sign(x)` to retain the sign. The reason it
is done this way is that it is very amenable to vectorization.
This method trades the duplicate decomposition computations (which takes
5 instructions including an extra expensive exp and div) for 4 cheap
instructions to compute the signs value
`arith.cmpf `(which is a pre-existing instruction in the previous impl)
`arith.sitofp`
`arith.mulf`
`arith.addf`
and 1 more instruction to get the right sign in the result
5. `arith.mulf`.
Moreover, numerically, this implementation will yield the exact same
results as the previous implementation.
As part of the relanding, a casting issue from the original commit has
been fixed, i.e. casting bool to float with `uitofp`. Additionally a
correctness test with `mlir-cpu-runner` has been added.
…5025)"
This reverts commit 58ef9bec071383744fb703ff08df9806f25e4095.
There is a bool to float casting issue that needs to be sorted out to
make sure this is target independent
The previous implementation decomposes `tanh(x)` into
`(exp(2x) - 1)/(exp(2x)+1), x < 0`
`(1 - exp(-2x))/(1 + exp(-2x)), x >= 0`
This is fine as it avoids overflow with the exponential, but the whole
decomposition is computed for both cases unconditionally, then the
result is chosen based off the sign of the input. This results in doing
two expensive `exp` computations.
The proposed change avoids doing the whole computation twice by
exploiting the reflection symmetry `tanh(-x) = -tanh(x)`. We can
"normalize" the input to be positive by setting `y = sign(x) * x`, where
the sign of `x` is computed as `sign(x) = (float)(x > 0) * (-2) + 1`.
Then compute `z = tanh(y)` with the decomposition above for `x >=0` and
"denormalize" the result `z * sign(x)` to retain the sign. The reason it
is done this way is that it is very amenable to vectorization.
This method trades the duplicate decomposition computations (which takes
5 instructions including an extra expensive `exp` and `div`) for 4 cheap
instructions to compute the signs value
1. `arith.cmpf` (which is a pre-existing instruction in the previous
impl)
2. `arith.sitofp`
3. `arith.mulf`
4. `arith.addf`
and 1 more instruction to get the right sign in the result
5. `arith.mulf`. Moreover, numerically, this implementation will yield
the exact same results as the previous implementation.
The `GreedyPatternRewriteDriver` tries to iteratively fold ops and apply
rewrite patterns to ops. It has special handling for constants: they are
CSE'd and sometimes moved to parent regions to allow for additional
CSE'ing. This happens in `OperationFolder`.
To allow for efficient CSE'ing, `OperationFolder` maintains an internal
lookup data structure to find the existing constant ops with the same
value for each `IsolatedFromAbove` region:
```c++
/// A mapping between an insertion region and the constants that have been
/// created within it.
DenseMap<Region *, ConstantMap> foldScopes;
```
Rewrite patterns are allowed to modify operations. In particular, they
may move operations (including constants) from one region to another
one. Such an IR rewrite can make the above lookup data structure
inconsistent.
We encountered such a bug in a downstream project. This bug materialized
in the form of an op that uses the result of a constant op from a
different `IsolatedFromAbove` region (that is not accessible).
This commit changes the behavior of the `GreedyPatternRewriteDriver`
such that `OperationFolder` is used to CSE constants at the beginning of
each iteration (as the worklist is populated), but no longer during an
iteration. `OperationFolder` is no longer used after populating the
worklist, so we do not have to care about inconsistent state in the
`OperationFolder` due to IR rewrites. The `GreedyPatternRewriteDriver`
now performs the op folding by itself instead of calling
`OperationFolder::tryToFold`.
This change changes the order of constant ops in test cases, but not the
region in which they appear. All broken test cases were fixed by turning
`CHECK` into `CHECK-DAG`.
Alternatives considered: The state of `OperationFolder` could be
partially invalidated with every `notifyOperationModified` notification.
That is more fragile than the solution in this commit because incorrect
rewriter API usage can lead to missing notifications and hard-to-debug
`IsolatedFromAbove` violations. (It did not fix the above mention bug in
a downstream project, which could be due to incorrect rewriter API usage
or due to another conceptual problem that I missed.) Moreover, ops are
frequently getting modified during a greedy pattern rewrite, so we would
likely keep invalidating large parts of the state of `OperationFolder`
over and over.
Migration guide: Turn `CHECK` into `CHECK-DAG` in test cases. Constant
ops are no longer folded during a greedy pattern rewrite. If you rely on
folding (and rematerialization) of constant ops during a greedy pattern
rewrite, turn the folder into a pattern.
Powf expansion currently returns NaN when the base is negative.
This is because taking natural log of a negative number gives
NaN. This patch will square the base and half the exponent, thereby
getting around the negative base problem.
Reviewed By: rsuderman
Differential Revision: https://reviews.llvm.org/D158797
This reverts commit b96f6cf62902ca96ed5aa62d4e158292280284e1
since it has broken some Windows build bots
(see https://reviews.llvm.org/D157204).
Will recommit a fixed version later.
This reverts commit 87cef78fa1c7bf6efc544e990894a6062d56abec.
The issue in the original revert is that a lit test expecting a `-nan`
as an output was failing on M2. Since the IEEE 754-2008 standard does
not require the sign to be printed when displaying a `nan`, this
commit changes the `CHECK` for `-nan` to one that checks the result
value bitcasted to an `i32` to ensure that input is being left
unchanged. This check should now be independent of platform being used
to run test.
Reviewed By: jpienaar, mehdi_amini
Differential Revision: https://reviews.llvm.org/D148941
This commit adds a pattern that expands `math.roundeven` into
`math.round` + some ops from `arith`. This is needed to be able to run
`math.roundeven` in a vectorized manner.
Reviewed By: jpienaar
Differential Revision: https://reviews.llvm.org/D148285
The current expand pattern for `math.round` does not handle the
special values -0.0, +-inf, and +-nan correctly. It also does not
properly handle values with magnitude |x| >= 2^23. Lastly, the pattern
generates invalid IR when the input to `math.round` is a vector. This
patch fixes these issues.
Reviewed By: rsuderman
Differential Revision: https://reviews.llvm.org/D148398
Powf functions are pushed directly to libm. This is problematic for
situations where libm is not available. This patch will decompose the
powf function into log of exponent multiplied by log of base and raise
it to the exp.
Reviewed By: rsuderman
Differential Revision: https://reviews.llvm.org/D148164
Round functions are pushed directly to libm. This is problematic for
situations where libm is not available. This patch will decompose the
roundf function by adding 0.5 to positive number to input
(subtracting for negative) following by a truncate.
Reviewed By: rsuderman
Differential Revision: https://reviews.llvm.org/D148026
Exp2 functions are pushed directly to libm. This is problematic for
situations where libm is not available. This patch will expand the exp2
function to use exp2 with the input multiplied by ln2 (natural log).
Reviewed By: rsuderman
Differential Revision: https://reviews.llvm.org/D148064
Ceilf are pushed directly to libm. This is problematic for
situations where libm is not available. This patch will break down
a ceilf function to truncate followed by an increment if the
truncated value is smaller than the input value.
Reviewed By: rsuderman
Differential Revision: https://reviews.llvm.org/D147974
Floorf are pushed directly to libm. This is problematic for
situations where libm is not available. This patch will break down
a floorf function to truncate followed by an increment for negative
values, if necessary.
Reviewed By: rsuderman
Differential Revision: https://reviews.llvm.org/D147966
Fused multiply and add are being pushed directly to the libm. This is problematic
for situations where libm is not available. This patch will break down a fused multiply and
add into a multiply followed by an add.
Reviewed By: rsuderman
Differential Revision: https://reviews.llvm.org/D147811
The math arithmetic expansions do not support vectorized types.
Updated the lowerings so that they support vectorized types. This
includes a different implementation for `math.ctlz` to be a binary
search and not have variable termination time.
Reviewed By: jpienaar, NatashaKnk
Differential Revision: https://reviews.llvm.org/D147289
We can implement a polynomial approximation of math.tan by
decomposing to `math.sin` and `math.cos`. While it is not
technically a polynomial approximation it should be the most
straight forward approximation.
Reviewed By: jpienaar
Differential Revision: https://reviews.llvm.org/D144980
When adding an op to the worklist, also add its ancestors to the worklist. This allows for RewritePatterns to match an op `a` based on what is inside of the body of `a`.
This change fixes a problem that became apparent with `vector.warp_execute_on_lane_0`, but could probably be triggered with similar patterns. The pattern extracts an op `b` with `eligible = true` from the body of an op `a`:
```
test.a {
%0 = test.b() {eligible = true}
yield %0
}
```
Afterwards:
```
%0 = test.b() {eligible = true}
test.a {
yield %0
}
```
The pattern is an `OpRewritePattern<OpA>`. For some reason, `test.a` is not on the GreedyPatternRewriter's worklist. E.g., because no pattern could be applied and it was removed. Now, another pattern updates `test.b`, so that `eligible` is changed from `true` to `false`. The `OpRewritePattern<OpA>` could now be applied, but (without this revision) `test.a` is still not on the worklist.
Note: In the above example, an `OpRewritePattern<OpB>` could have been used instead of an `OpRewritePattern<OpA>`. With such a design, we can run into the same problem (when the `eligible` attr is on `test.a` and `test.b` is removed from the worklist because no patterns could be applied).
Note: This change uncovered an unrelated bug in TestSCFUtils.cpp that was triggered due to a change in the order in which ops are processed. A TODO is added to the broken code and test cases are adapted so that the bug is no longer triggered.
Differential Revision: https://reviews.llvm.org/D140304
Ctlz is an intrinsic in LLVM but does not have equivalent operations in SPIR-V.
Including a decomposition gives an alternative path for these platforms.
Reviewed By: NatashaKnk
Differential Revision: https://reviews.llvm.org/D126261
