With the introduction of the nusw flag in GEPNoWrapFlags, it should be
safe to weaken the check in LoopAccessAnalysis to just check the nusw
flag on the GEP, instead of inbounds.
isNoWrap has exactly one caller which handles Assume = true separately,
but too conservatively. Instead, pass Assume to isNoWrap, so it is
threaded into getPtrStride, which has the correct handling for the
Assume flag. Also note that the Stride == 1 check in isNoWrap is
incorrect: getPtrStride returns Strides == 1 or -1, except when
isNoWrapAddRec or Assume are true, assuming ShouldCheckWrap is true; we
can include the case of -1 Stride, and when isNoWrapAddRec is true. With
this change, passing Assume = true to getPtrStride could return a
non-unit stride, and we correctly handle that case as well.
After pr96656.ll were added to LAA and LoopVersioning, it was decided
that the bug is in a caller of LoopVersioning, not in LAA or
LoopVersioning itself. The new candidate was LoopLoadElim, but #96656
has since been marked invalid. Hence, re-organize the added tests to
avoid confusion, and the testcase from the investigation to
LoopLoadElim.
Update getDependenceDistanceStrideAndSize to reason about different
combinations of strides directly and explicitly.
Update getPtrStride to return 0 for invariant pointers.
Then proceed by checking the strides.
If either source or sink are not strided by a constant (i.e. not a
non-wrapping AddRec) or invariant, the accesses may overlap
with earlier or later iterations and we cannot generate runtime
checks to disambiguate them.
Otherwise they are either loop invariant or strided. In that case, we
can generate a runtime check to disambiguate them.
If both are strided by constants, we proceed as previously.
This is an alternative to
https://github.com/llvm/llvm-project/pull/99239 and also replaces
additional checks if the underlying object is loop-invariant.
Fixes https://github.com/llvm/llvm-project/issues/87189.
PR: https://github.com/llvm/llvm-project/pull/99577
Updated @B_indices_loaded_in_loop_A_stored to use a different offset
for one of the accesses we create runtime checks for; the original
version had a runtime check that was always true as the accesses always
overlapped.
The same pointer may be accessed with different types and the bound
includes the size of the accessed type to compute the end. Update the
cache to correctly disambiguate between different accessed types.
Add tests with accesses to the same pointer with different types. At the
moment, runtime checks for those accesses are incorrectly based on the
smaller type.
Add tests which are not safe to vectorize because %indices are loaded in
the loop and the same indices could be loaded in later iterations.
Tests for https://github.com/llvm/llvm-project/issues/87189.
This patch implements limited loop vectorization support for the 'all-in-one' histogram intrinsic. The feature is disabled by default, and when enabled will only vectorize if there are no other users of values in the gather-modify-scatter sequence.
The issue is in LoopAccessAnalysis, but the regression was seen in the
user LoopVersioning. Hence, add pre-commit tests for both, in
preparation to fix the issue in LoopAccessAnalysis.
Introduce a Loop::getLocStr stolen from LoopVectorize's static function
getDebugLocString in order to have uniform debug output headers across
LoopVectorize, LoopAccessAnalysis, and LoopDistribute. The motivation
for this change is to have UpdateTestChecks recognize the headers and
automatically generate CHECK lines for debug output, with minimal
special-casing.
733b8b2 ([LAA] Simplify identification of speculatable strides [nfc])
refactored getStrideFromPointer() to compute directly on SCEVs, and
return an SCEV expression instead of a Value. However, it left behind a
call to getUniqueCastUse(), which is completely unnecessary. Remove
this, showing a positive test update, and simplify the surrounding
program logic.
Update LAA to use PSE::getSymbolicMaxBackedgeTakenCount which returns
the minimum of the countable exits.
When analyzing dependences and computing runtime checks, we need the
smallest upper bound on the number of iterations. In terms of memory
safety, it shouldn't matter if any uncomputable exits leave the loop,
as long as we prove that there are no dependences given the minimum of
the countable exits. The same should apply also for generating runtime
checks.
Note that this shifts the responsiblity of checking whether all exit
counts are computable or handling early-exits to the users of LAA.
Depends on https://github.com/llvm/llvm-project/pull/93498
PR: https://github.com/llvm/llvm-project/pull/93499
The test select-dependence.ll can be eliminated completely by dce, as it
returns a constant, and doesn't write any arguments. Lift out the local
allocas into arguments, so that it is less nonsensical. While at it,
rename the variables for greater readability, and regenerate the test
with UpdateTestChecks.
The test symbolic-stride.ll does not exercise all codepaths in
getStrideFromPointer, particularly when the operand is an
SCEVIntegralCastExpr. Cover these codepaths as well. This patch serves
as pre-commit tests for #92119.
Use getStartAndEndForAccess to compute the start and end of both src
and sink (factored out to helper in bce3680f45b57f). If they do not
overlap (i.e. SrcEnd <= SinkStart || SinkEnd <= SrcStart), there is no
dependence, regardless of stride.
PR: https://github.com/llvm/llvm-project/pull/92307
Applying the loop guards to the distance may prevent
isSafeDependenceDistance from determining NoDep, unless loop guards are
also applied to the backedge-taken-count.
Instead of applying the guards to both Dist and the
backedge-taken-count, just apply them after handling
isSafeDependenceDistance and constant distances; there is no benefit to
applying the guards before then.
This fixes a regression flagged by @bjope due to
ecae3ed958481cba7d60868cf3504292f7f4fdf5.
Following up to 933f49248, also update the code reasoning about
backwards dependences to support non-constant distances.
Update the code to use the signed minimum distance instead of a constant
distance
This means e checked the lower bound of the dependence distance and the
distance may be larger at runtime (and safe for vectorization). Whether
to classify it as Unknown or Backwards depends on the vector width and
LAA was updated to take TTI to get the maximum vector register width.
If the minimum dependence distance is larger than the max vector width,
we consider it as backwards-vectorizable. Otherwise we classify them as
Unknown, so we re-try with runtime checks.
PR: https://github.com/llvm/llvm-project/pull/91525
As discussed in https://github.com/llvm/llvm-project/pull/88039, support
different strides with isSafeDependenceDistance by passing the maximum
of both strides.
isSafeDependenceDistance tries to prove that
|Dist| > BackedgeTakenCount * Step
holds. Chosing the maximum stride computes the maximum range accesed by
the loop for all strides.
PR: https://github.com/llvm/llvm-project/pull/90036
Extend LoopAccessAnalysis to support different strides and as a
consequence non-constant distances between dependences using SCEV to
reason about the direction of the dependence.
In multiple places, logic to rule out dependences using the stride has
been updated to only be used if StrideA == StrideB, i.e. there's a
common stride.
We now also may bail out at multiple places where we may have to set
FoundNonConstantDistanceDependence. This is done when we need to bail
out and the distance is not constant to preserve original behavior.
Fixes https://github.com/llvm/llvm-project/issues/87336
PR: https://github.com/llvm/llvm-project/pull/88039
Add a number of LAA test cases with both forward and backward
dependences with non-constant strides and dependence distances.
This includes test coverage for
https://github.com/llvm/llvm-project/issues/87336
Also includes a LoopLoadElimination test to make sure the pass does not
crash on non-constant dependence distances.
At the moment, getUnderlyingObjects simply continues for phis that do
not refer to the same underlying object in loops, without adding them to
the list of underlying objects, effectively ignoring those phis.
Instead of ignoring those phis, add them to the list of underlying
objects. This fixes a miscompile where LoopAccessAnalysis fails to
identify a memory dependence, because no underlying objects can be found
for a set of memory accesses.
Fixes https://github.com/llvm/llvm-project/issues/82665.
PR: https://github.com/llvm/llvm-project/pull/84339
Similar to d39b4ce3ce8a3c256e01bdec2b140777a332a633
Using "eabi" or "gnueabi" for aarch64 targets is a common mistake and
warned by Clang Driver. We want to avoid them elsewhere as well. Just
use the common "aarch64" without other triple components.
LAA currently adds memory locations with their original AATags to AST.
However, scoped alias AATags may be valid only within one loop
iteration, while LAA reasons across iterations.
Fix this by determining which alias scopes are defined inside the loop,
and drop AATags that reference these scopes.
Fixes https://github.com/llvm/llvm-project/issues/79137.
