[LAA] Delay applying loop guards until after isSafeDependenceDistance.

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.

1 files changed, 3 insertions, 5 deletions

diff --git a/llvm/lib/Analysis/LoopAccessAnalysis.cpp b/llvm/lib/Analysis/LoopAccessAnalysis.cpp
index e92aa02..4ba2e15 100644
--- a/llvm/lib/Analysis/LoopAccessAnalysis.cpp
+++ b/llvm/lib/Analysis/LoopAccessAnalysis.cpp
@@ -1991,9 +1991,6 @@ getDependenceDistanceStrideAndSize(
     return MemoryDepChecker::Dependence::Unknown;
   }
 
-  if (!isa<SCEVConstant, SCEVCouldNotCompute>(Dist))
-    Dist = SE.applyLoopGuards(Dist, InnermostLoop);
-
   uint64_t TypeByteSize = DL.getTypeAllocSize(ATy);
   bool HasSameSize =
       DL.getTypeStoreSizeInBits(ATy) == DL.getTypeStoreSizeInBits(BTy);
@@ -2019,7 +2016,7 @@ MemoryDepChecker::Dependence::DepType MemoryDepChecker::isDependent(
   if (std::holds_alternative<Dependence::DepType>(Res))
     return std::get<Dependence::DepType>(Res);
 
-  const auto &[Dist, StrideA, StrideB, TypeByteSize, AIsWrite, BIsWrite] =
+  auto &[Dist, StrideA, StrideB, TypeByteSize, AIsWrite, BIsWrite] =
       std::get<DepDistanceStrideAndSizeInfo>(Res);
   bool HasSameSize = TypeByteSize > 0;
 
@@ -2062,7 +2059,8 @@ MemoryDepChecker::Dependence::DepType MemoryDepChecker::isDependent(
       LLVM_DEBUG(dbgs() << "LAA: Strided accesses are independent\n");
       return Dependence::NoDep;
     }
-  }
+  } else
+    Dist = SE.applyLoopGuards(Dist, InnermostLoop);
 
   // Negative distances are not plausible dependencies.
   if (SE.isKnownNonPositive(Dist)) {