LAA: refactor dependence class to prep for scaled strides (NFC) #122113
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Rearrange the DepDistanceAndSizeInfo struct in preparation to scale strides. getDependenceDistanceStrideAndSize now returns the data of CommonStride, MaxStride, and clarifies when to rety with runtime checks, in place of (unscaled) strides.
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@llvm/pr-subscribers-llvm-analysis Author: Ramkumar Ramachandra (artagnon) ChangesRearrange the DepDistanceAndSizeInfo struct in preparation to scale strides. getDependenceDistanceStrideAndSize now returns the data of CommonStride, MaxStride, and clarifies when to rety with runtime checks, in place of (unscaled) strides. Full diff: https://github.com/llvm/llvm-project/pull/122113.diff 2 Files Affected:
diff --git a/llvm/include/llvm/Analysis/LoopAccessAnalysis.h b/llvm/include/llvm/Analysis/LoopAccessAnalysis.h
index a35bc7402d1a89..7bc8c4deae1a36 100644
--- a/llvm/include/llvm/Analysis/LoopAccessAnalysis.h
+++ b/llvm/include/llvm/Analysis/LoopAccessAnalysis.h
@@ -366,16 +366,20 @@ class MemoryDepChecker {
struct DepDistanceStrideAndSizeInfo {
const SCEV *Dist;
- uint64_t StrideA;
- uint64_t StrideB;
+ uint64_t MaxStride;
+ std::optional<uint64_t> CommonStride;
+ bool ShouldRetryWithRuntimeCheck;
uint64_t TypeByteSize;
bool AIsWrite;
bool BIsWrite;
- DepDistanceStrideAndSizeInfo(const SCEV *Dist, uint64_t StrideA,
- uint64_t StrideB, uint64_t TypeByteSize,
- bool AIsWrite, bool BIsWrite)
- : Dist(Dist), StrideA(StrideA), StrideB(StrideB),
+ DepDistanceStrideAndSizeInfo(const SCEV *Dist, uint64_t MaxStride,
+ std::optional<uint64_t> CommonStride,
+ bool ShouldRetryWithRuntimeCheck,
+ uint64_t TypeByteSize, bool AIsWrite,
+ bool BIsWrite)
+ : Dist(Dist), MaxStride(MaxStride), CommonStride(CommonStride),
+ ShouldRetryWithRuntimeCheck(ShouldRetryWithRuntimeCheck),
TypeByteSize(TypeByteSize), AIsWrite(AIsWrite), BIsWrite(BIsWrite) {}
};
diff --git a/llvm/lib/Analysis/LoopAccessAnalysis.cpp b/llvm/lib/Analysis/LoopAccessAnalysis.cpp
index 2c75d5625cb66d..38e9145826c08e 100644
--- a/llvm/lib/Analysis/LoopAccessAnalysis.cpp
+++ b/llvm/lib/Analysis/LoopAccessAnalysis.cpp
@@ -1994,8 +1994,23 @@ MemoryDepChecker::getDependenceDistanceStrideAndSize(
DL.getTypeStoreSizeInBits(ATy) == DL.getTypeStoreSizeInBits(BTy);
if (!HasSameSize)
TypeByteSize = 0;
- return DepDistanceStrideAndSizeInfo(Dist, std::abs(StrideAPtrInt),
- std::abs(StrideBPtrInt), TypeByteSize,
+
+ StrideAPtrInt = std::abs(StrideAPtrInt);
+ StrideBPtrInt = std::abs(StrideBPtrInt);
+
+ uint64_t MaxStride = std::max(StrideAPtrInt, StrideBPtrInt);
+
+ std::optional<uint64_t> CommonStride;
+ if (StrideAPtrInt == StrideBPtrInt)
+ CommonStride = StrideAPtrInt;
+
+ // TODO: Historically, we don't retry with runtime checks unless the
+ // (unscaled) strides are the same. Fix this once the condition for runtime
+ // checks in isDependent is fixed.
+ bool ShouldRetryWithRuntimeCheck = CommonStride.has_value();
+
+ return DepDistanceStrideAndSizeInfo(Dist, MaxStride, CommonStride,
+ ShouldRetryWithRuntimeCheck, TypeByteSize,
AIsWrite, BIsWrite);
}
@@ -2011,23 +2026,21 @@ MemoryDepChecker::isDependent(const MemAccessInfo &A, unsigned AIdx,
if (std::holds_alternative<Dependence::DepType>(Res))
return std::get<Dependence::DepType>(Res);
- auto &[Dist, StrideA, StrideB, TypeByteSize, AIsWrite, BIsWrite] =
+ auto &[Dist, MaxStride, CommonStride, ShouldRetryWithRuntimeCheck,
+ TypeByteSize, AIsWrite, BIsWrite] =
std::get<DepDistanceStrideAndSizeInfo>(Res);
bool HasSameSize = TypeByteSize > 0;
- std::optional<uint64_t> CommonStride =
- StrideA == StrideB ? std::make_optional(StrideA) : std::nullopt;
if (isa<SCEVCouldNotCompute>(Dist)) {
- // TODO: Relax requirement that there is a common stride to retry with
- // non-constant distance dependencies.
- FoundNonConstantDistanceDependence |= CommonStride.has_value();
+ // TODO: Relax requirement that there is a common unscaled stride to retry
+ // with non-constant distance dependencies.
+ FoundNonConstantDistanceDependence |= ShouldRetryWithRuntimeCheck;
LLVM_DEBUG(dbgs() << "LAA: Dependence because of uncomputable distance.\n");
return Dependence::Unknown;
}
ScalarEvolution &SE = *PSE.getSE();
auto &DL = InnermostLoop->getHeader()->getDataLayout();
- uint64_t MaxStride = std::max(StrideA, StrideB);
// If the distance between the acecsses is larger than their maximum absolute
// stride multiplied by the symbolic maximum backedge taken count (which is an
@@ -2086,7 +2099,7 @@ MemoryDepChecker::isDependent(const MemAccessInfo &A, unsigned AIdx,
// condition to consider retrying with runtime checks. Historically, we
// did not set it when strides were different but there is no inherent
// reason to.
- FoundNonConstantDistanceDependence |= CommonStride.has_value();
+ FoundNonConstantDistanceDependence |= ShouldRetryWithRuntimeCheck;
return Dependence::Unknown;
}
if (!HasSameSize ||
@@ -2105,7 +2118,7 @@ MemoryDepChecker::isDependent(const MemAccessInfo &A, unsigned AIdx,
int64_t MinDistance = SE.getSignedRangeMin(Dist).getSExtValue();
// Below we only handle strictly positive distances.
if (MinDistance <= 0) {
- FoundNonConstantDistanceDependence |= CommonStride.has_value();
+ FoundNonConstantDistanceDependence |= ShouldRetryWithRuntimeCheck;
return Dependence::Unknown;
}
@@ -2118,7 +2131,7 @@ MemoryDepChecker::isDependent(const MemAccessInfo &A, unsigned AIdx,
// condition to consider retrying with runtime checks. Historically, we
// did not set it when strides were different but there is no inherent
// reason to.
- FoundNonConstantDistanceDependence |= CommonStride.has_value();
+ FoundNonConstantDistanceDependence |= ShouldRetryWithRuntimeCheck;
}
if (!HasSameSize) {
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david-arm
approved these changes
Jan 8, 2025
fhahn
reviewed
Jan 8, 2025
artagnon
changed the title
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LLVM Buildbot has detected a new failure on builder Full details are available at: https://lab.llvm.org/buildbot/#/builders/30/builds/13455 Here is the relevant piece of the build log for the reference |
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Rearrange the DepDistanceAndSizeInfo struct in preparation to scale strides. getDependenceDistanceStrideAndSize now returns the data of CommonStride, MaxStride, and clarifies when to retry with runtime checks, in place of (unscaled) strides.