diff --git a/mlir/include/mlir/Dialect/Arithmetic/Utils/Utils.h b/mlir/include/mlir/Dialect/Arithmetic/Utils/Utils.h
index a4dcf9622098..1d4353f176b1 100644
--- a/mlir/include/mlir/Dialect/Arithmetic/Utils/Utils.h
+++ b/mlir/include/mlir/Dialect/Arithmetic/Utils/Utils.h
@@ -31,8 +31,8 @@ detail::op_matcher<arith::ConstantIndexOp> matchConstantIndex();
 void canonicalizeSubViewPart(SmallVectorImpl<OpFoldResult> &values,
                              function_ref<bool(int64_t)> isDynamic);
 
-void getPositionsOfShapeOne(unsigned rank, ArrayRef<int64_t> shape,
-                            llvm::SmallDenseSet<unsigned> &dimsToProject);
+llvm::SmallBitVector getPositionsOfShapeOne(unsigned rank,
+                                            ArrayRef<int64_t> shape);
 
 /// Pattern to rewrite a subview op with constant arguments.
 template <typename OpType, typename ResultTypeFunc, typename CastOpFunc>
diff --git a/mlir/include/mlir/Dialect/MemRef/IR/MemRefOps.td b/mlir/include/mlir/Dialect/MemRef/IR/MemRefOps.td
index 6438e707f7c2..81839dfde9c5 100644
--- a/mlir/include/mlir/Dialect/MemRef/IR/MemRefOps.td
+++ b/mlir/include/mlir/Dialect/MemRef/IR/MemRefOps.td
@@ -1639,7 +1639,7 @@ def SubViewOp : MemRef_OpWithOffsetSizesAndStrides<"subview", [
 
     /// Return the dimensions of the source type that are dropped when
     /// the result is rank-reduced.
-    llvm::SmallDenseSet<unsigned> getDroppedDims();
+    llvm::SmallBitVector getDroppedDims();
   }];
 
   let hasCanonicalizer = 1;
diff --git a/mlir/include/mlir/Dialect/Tensor/IR/TensorOps.td b/mlir/include/mlir/Dialect/Tensor/IR/TensorOps.td
index ec597e9f650a..a4dc2953b201 100644
--- a/mlir/include/mlir/Dialect/Tensor/IR/TensorOps.td
+++ b/mlir/include/mlir/Dialect/Tensor/IR/TensorOps.td
@@ -316,8 +316,7 @@ def Tensor_ExtractSliceOp : Tensor_OpWithOffsetSizesAndStrides<"extract_slice",
 
     /// Return the dimensions of the source that are dropped in the
     /// result when the result is rank-reduced.
-    llvm::SmallDenseSet<unsigned> getDroppedDims();
-
+    llvm::SmallBitVector getDroppedDims();
   }];
 
   let hasCanonicalizer = 1;
diff --git a/mlir/include/mlir/IR/AffineMap.h b/mlir/include/mlir/IR/AffineMap.h
index cd6fce22b614..82a33b065440 100644
--- a/mlir/include/mlir/IR/AffineMap.h
+++ b/mlir/include/mlir/IR/AffineMap.h
@@ -18,7 +18,10 @@
 #include "mlir/Support/LLVM.h"
 #include "llvm/ADT/ArrayRef.h"
 #include "llvm/ADT/DenseMapInfo.h"
-#include "llvm/ADT/DenseSet.h"
+
+namespace llvm {
+class SmallBitVector;
+} // namespace llvm
 
 namespace mlir {
 
@@ -372,8 +375,7 @@ AffineMap compressUnusedDims(AffineMap map);
 SmallVector<AffineMap> compressUnusedDims(ArrayRef<AffineMap> maps);
 
 /// Drop the dims that are not listed in `unusedDims`.
-AffineMap compressDims(AffineMap map,
-                       const llvm::SmallDenseSet<unsigned> &unusedDims);
+AffineMap compressDims(AffineMap map, const llvm::SmallBitVector &unusedDims);
 
 /// Drop the symbols that are not used.
 AffineMap compressUnusedSymbols(AffineMap map);
@@ -385,7 +387,7 @@ SmallVector<AffineMap> compressUnusedSymbols(ArrayRef<AffineMap> maps);
 
 /// Drop the symbols that are not listed in `unusedSymbols`.
 AffineMap compressSymbols(AffineMap map,
-                          const llvm::SmallDenseSet<unsigned> &unusedSymbols);
+                          const llvm::SmallBitVector &unusedSymbols);
 
 /// Returns a map with the same dimension and symbol count as `map`, but whose
 /// results are the unique affine expressions of `map`.
@@ -521,9 +523,8 @@ AffineMap concatAffineMaps(ArrayRef<AffineMap> maps);
 ///    result               : affine_map<(d0, d1) -> (d0, 0)>
 ///
 /// This function also compresses unused symbols away.
-AffineMap
-getProjectedMap(AffineMap map,
-                const llvm::SmallDenseSet<unsigned> &projectedDimensions);
+AffineMap getProjectedMap(AffineMap map,
+                          const llvm::SmallBitVector &projectedDimensions);
 
 /// Apply a permutation from `map` to `source` and return the result.
 template <typename T>
diff --git a/mlir/lib/Conversion/MemRefToLLVM/MemRefToLLVM.cpp b/mlir/lib/Conversion/MemRefToLLVM/MemRefToLLVM.cpp
index a4a82d66b0cb..d21d21e045fb 100644
--- a/mlir/lib/Conversion/MemRefToLLVM/MemRefToLLVM.cpp
+++ b/mlir/lib/Conversion/MemRefToLLVM/MemRefToLLVM.cpp
@@ -18,6 +18,7 @@
 #include "mlir/Dialect/MemRef/IR/MemRef.h"
 #include "mlir/IR/AffineMap.h"
 #include "mlir/IR/BlockAndValueMapping.h"
+#include "llvm/ADT/SmallBitVector.h"
 
 using namespace mlir;
 
@@ -1503,10 +1504,10 @@ struct SubViewOpLowering : public ConvertOpToLLVMPattern<memref::SubViewOp> {
     SmallVector<OpFoldResult> mixedStrides = subViewOp.getMixedStrides();
     assert(mixedSizes.size() == mixedStrides.size() &&
            "expected sizes and strides of equal length");
-    llvm::SmallDenseSet<unsigned> unusedDims = subViewOp.getDroppedDims();
+    llvm::SmallBitVector unusedDims = subViewOp.getDroppedDims();
     for (int i = inferredShapeRank - 1, j = resultShapeRank - 1;
          i >= 0 && j >= 0; --i) {
-      if (unusedDims.contains(i))
+      if (unusedDims.test(i))
         continue;
 
       // `i` may overflow subViewOp.getMixedSizes because of trailing semantics.
diff --git a/mlir/lib/Dialect/Arithmetic/Utils/Utils.cpp b/mlir/lib/Dialect/Arithmetic/Utils/Utils.cpp
index 74dd373f17cd..4e35c5b31924 100644
--- a/mlir/lib/Dialect/Arithmetic/Utils/Utils.cpp
+++ b/mlir/lib/Dialect/Arithmetic/Utils/Utils.cpp
@@ -12,6 +12,7 @@
 
 #include "mlir/Dialect/Arithmetic/Utils/Utils.h"
 #include "mlir/Dialect/Arithmetic/IR/Arithmetic.h"
+#include "llvm/ADT/SmallBitVector.h"
 
 using namespace mlir;
 
@@ -37,16 +38,16 @@ void mlir::canonicalizeSubViewPart(
   }
 }
 
-void mlir::getPositionsOfShapeOne(
-    unsigned rank, ArrayRef<int64_t> shape,
-    llvm::SmallDenseSet<unsigned> &dimsToProject) {
-  dimsToProject.reserve(rank);
+llvm::SmallBitVector mlir::getPositionsOfShapeOne(unsigned rank,
+                                                  ArrayRef<int64_t> shape) {
+  llvm::SmallBitVector dimsToProject(shape.size());
   for (unsigned pos = 0, e = shape.size(); pos < e && rank > 0; ++pos) {
     if (shape[pos] == 1) {
-      dimsToProject.insert(pos);
+      dimsToProject.set(pos);
       --rank;
     }
   }
+  return dimsToProject;
 }
 
 Value mlir::getValueOrCreateConstantIndexOp(OpBuilder &b, Location loc,
diff --git a/mlir/lib/Dialect/Linalg/Transforms/Fusion.cpp b/mlir/lib/Dialect/Linalg/Transforms/Fusion.cpp
index 9eda19ae3f4b..32d8ee098bce 100644
--- a/mlir/lib/Dialect/Linalg/Transforms/Fusion.cpp
+++ b/mlir/lib/Dialect/Linalg/Transforms/Fusion.cpp
@@ -520,10 +520,10 @@ mlir::linalg::fuseProducerOfTensor(OpBuilder &b, OpResult producerOpResult,
 /// Prune all dimensions that are of reduction iterator type from `map`.
 static AffineMap pruneReductionDimsFromMap(ArrayRef<Attribute> iteratorTypes,
                                            AffineMap map) {
-  llvm::SmallDenseSet<unsigned> projectedDims;
+  llvm::SmallBitVector projectedDims(iteratorTypes.size());
   for (const auto &attr : llvm::enumerate(iteratorTypes)) {
     if (!isParallelIterator(attr.value()))
-      projectedDims.insert(attr.index());
+      projectedDims.set(attr.index());
   }
   return getProjectedMap(map, projectedDims);
 }
diff --git a/mlir/lib/Dialect/Linalg/Transforms/Transforms.cpp b/mlir/lib/Dialect/Linalg/Transforms/Transforms.cpp
index d8e00ca5d4ed..65a0ed8ec68f 100644
--- a/mlir/lib/Dialect/Linalg/Transforms/Transforms.cpp
+++ b/mlir/lib/Dialect/Linalg/Transforms/Transforms.cpp
@@ -187,7 +187,7 @@ static LogicalResult padOperandToSmallestStaticBoundingBox(
     return failure(hasDynamicShape);
 
   // Compute the dropped dimensions if `sliceOp` is ranke-reducing.
-  llvm::SmallDenseSet<unsigned> droppedDims = sliceOp.getDroppedDims();
+  llvm::SmallBitVector droppedDims = sliceOp.getDroppedDims();
 
   // Upper bound the `sliceOp` sizes to obtain a static bounding box.
   SmallVector<int64_t> staticSizes;
@@ -195,7 +195,7 @@ static LogicalResult padOperandToSmallestStaticBoundingBox(
   auto shapedOp = cast<OffsetSizeAndStrideOpInterface>(sliceOp.getOperation());
   for (const auto &en : enumerate(shapedOp.getMixedSizes())) {
     // Skip dropped dimensions.
-    if (droppedDims.contains(en.index()))
+    if (droppedDims.test(en.index()))
       continue;
     // If the size is an attribute add it directly to `staticSizes`.
     if (en.value().is<Attribute>()) {
diff --git a/mlir/lib/Dialect/MemRef/IR/MemRefOps.cpp b/mlir/lib/Dialect/MemRef/IR/MemRefOps.cpp
index dad063ea30bc..21cb8d60f2d3 100644
--- a/mlir/lib/Dialect/MemRef/IR/MemRefOps.cpp
+++ b/mlir/lib/Dialect/MemRef/IR/MemRefOps.cpp
@@ -20,6 +20,7 @@
 #include "mlir/Interfaces/InferTypeOpInterface.h"
 #include "mlir/Interfaces/ViewLikeInterface.h"
 #include "llvm/ADT/STLExtras.h"
+#include "llvm/ADT/SmallBitVector.h"
 
 using namespace mlir;
 using namespace mlir::memref;
@@ -590,17 +591,17 @@ static std::map<int64_t, unsigned> getNumOccurences(ArrayRef<int64_t> vals) {
 /// This accounts for cases where there are multiple unit-dims, but only a
 /// subset of those are dropped. For MemRefTypes these can be disambiguated
 /// using the strides. If a dimension is dropped the stride must be dropped too.
-static llvm::Optional<llvm::SmallDenseSet<unsigned>>
+static llvm::Optional<llvm::SmallBitVector>
 computeMemRefRankReductionMask(MemRefType originalType, MemRefType reducedType,
                                ArrayRef<OpFoldResult> sizes) {
-  llvm::SmallDenseSet<unsigned> unusedDims;
+  llvm::SmallBitVector unusedDims(originalType.getRank());
   if (originalType.getRank() == reducedType.getRank())
     return unusedDims;
 
   for (const auto &dim : llvm::enumerate(sizes))
     if (auto attr = dim.value().dyn_cast<Attribute>())
       if (attr.cast<IntegerAttr>().getInt() == 1)
-        unusedDims.insert(dim.index());
+        unusedDims.set(dim.index());
 
   SmallVector<int64_t> originalStrides, candidateStrides;
   int64_t originalOffset, candidateOffset;
@@ -623,8 +624,9 @@ computeMemRefRankReductionMask(MemRefType originalType, MemRefType reducedType,
       getNumOccurences(originalStrides);
   std::map<int64_t, unsigned> candidateStridesNumOccurences =
       getNumOccurences(candidateStrides);
-  llvm::SmallDenseSet<unsigned> prunedUnusedDims;
-  for (unsigned dim : unusedDims) {
+  for (size_t dim = 0, e = unusedDims.size(); dim != e; ++dim) {
+    if (!unusedDims.test(dim))
+      continue;
     int64_t originalStride = originalStrides[dim];
     if (currUnaccountedStrides[originalStride] >
         candidateStridesNumOccurences[originalStride]) {
@@ -635,7 +637,7 @@ computeMemRefRankReductionMask(MemRefType originalType, MemRefType reducedType,
     if (currUnaccountedStrides[originalStride] ==
         candidateStridesNumOccurences[originalStride]) {
       // The stride for this is not dropped. Keep as is.
-      prunedUnusedDims.insert(dim);
+      unusedDims.reset(dim);
       continue;
     }
     if (currUnaccountedStrides[originalStride] <
@@ -646,17 +648,16 @@ computeMemRefRankReductionMask(MemRefType originalType, MemRefType reducedType,
     }
   }
 
-  for (auto prunedDim : prunedUnusedDims)
-    unusedDims.erase(prunedDim);
-  if (unusedDims.size() + reducedType.getRank() != originalType.getRank())
+  if ((int64_t)unusedDims.count() + reducedType.getRank() !=
+      originalType.getRank())
     return llvm::None;
   return unusedDims;
 }
 
-llvm::SmallDenseSet<unsigned> SubViewOp::getDroppedDims() {
+llvm::SmallBitVector SubViewOp::getDroppedDims() {
   MemRefType sourceType = getSourceType();
   MemRefType resultType = getType();
-  llvm::Optional<llvm::SmallDenseSet<unsigned>> unusedDims =
+  llvm::Optional<llvm::SmallBitVector> unusedDims =
       computeMemRefRankReductionMask(sourceType, resultType, getMixedSizes());
   assert(unusedDims && "unable to find unused dims of subview");
   return *unusedDims;
@@ -698,12 +699,12 @@ OpFoldResult DimOp::fold(ArrayRef<Attribute> operands) {
              memrefType.getDynamicDimIndex(unsignedIndex));
 
   if (auto subview = dyn_cast_or_null<SubViewOp>(definingOp)) {
-    llvm::SmallDenseSet<unsigned> unusedDims = subview.getDroppedDims();
+    llvm::SmallBitVector unusedDims = subview.getDroppedDims();
     unsigned resultIndex = 0;
     unsigned sourceRank = subview.getSourceType().getRank();
     unsigned sourceIndex = 0;
     for (auto i : llvm::seq<unsigned>(0, sourceRank)) {
-      if (unusedDims.count(i))
+      if (unusedDims.test(i))
         continue;
       if (resultIndex == unsignedIndex) {
         sourceIndex = i;
@@ -1734,11 +1735,11 @@ Type SubViewOp::inferRankReducedResultType(unsigned resultRank,
   int rankDiff = inferredType.getRank() - resultRank;
   if (rankDiff > 0) {
     auto shape = inferredType.getShape();
-    llvm::SmallDenseSet<unsigned> dimsToProject;
-    mlir::getPositionsOfShapeOne(rankDiff, shape, dimsToProject);
+    llvm::SmallBitVector dimsToProject =
+        getPositionsOfShapeOne(rankDiff, shape);
     SmallVector<int64_t> projectedShape;
     for (unsigned pos = 0, e = shape.size(); pos < e; ++pos)
-      if (!dimsToProject.contains(pos))
+      if (!dimsToProject.test(pos))
         projectedShape.push_back(shape[pos]);
 
     AffineMap map = inferredType.getLayout().getAffineMap();
@@ -2015,7 +2016,7 @@ static MemRefType getCanonicalSubViewResultType(
   auto nonRankReducedType = SubViewOp::inferResultType(sourceType, mixedOffsets,
                                                        mixedSizes, mixedStrides)
                                 .cast<MemRefType>();
-  llvm::Optional<llvm::SmallDenseSet<unsigned>> unusedDims =
+  llvm::Optional<llvm::SmallBitVector> unusedDims =
       computeMemRefRankReductionMask(currentSourceType, currentResultType,
                                      mixedSizes);
   // Return nullptr as failure mode.
@@ -2023,7 +2024,7 @@ static MemRefType getCanonicalSubViewResultType(
     return nullptr;
   SmallVector<int64_t> shape;
   for (const auto &sizes : llvm::enumerate(nonRankReducedType.getShape())) {
-    if (unusedDims->count(sizes.index()))
+    if (unusedDims->test(sizes.index()))
       continue;
     shape.push_back(sizes.value());
   }
diff --git a/mlir/lib/Dialect/MemRef/Transforms/FoldSubViewOps.cpp b/mlir/lib/Dialect/MemRef/Transforms/FoldSubViewOps.cpp
index 213b442998b0..5080a69688b9 100644
--- a/mlir/lib/Dialect/MemRef/Transforms/FoldSubViewOps.cpp
+++ b/mlir/lib/Dialect/MemRef/Transforms/FoldSubViewOps.cpp
@@ -18,6 +18,7 @@
 #include "mlir/Dialect/Vector/IR/VectorOps.h"
 #include "mlir/IR/BuiltinTypes.h"
 #include "mlir/Transforms/GreedyPatternRewriteDriver.h"
+#include "llvm/ADT/SmallBitVector.h"
 
 using namespace mlir;
 
@@ -50,9 +51,9 @@ resolveSourceIndices(Location loc, PatternRewriter &rewriter,
   // Check if this is rank-reducing case. Then for every unit-dim size add a
   // zero to the indices.
   unsigned resultDim = 0;
-  llvm::SmallDenseSet<unsigned> unusedDims = subViewOp.getDroppedDims();
+  llvm::SmallBitVector unusedDims = subViewOp.getDroppedDims();
   for (auto dim : llvm::seq<unsigned>(0, subViewOp.getSourceType().getRank())) {
-    if (unusedDims.count(dim))
+    if (unusedDims.test(dim))
       useIndices.push_back(rewriter.create<arith::ConstantIndexOp>(loc, 0));
     else
       useIndices.push_back(indices[resultDim++]);
@@ -106,11 +107,11 @@ static Value getMemRefOperand(vector::TransferWriteOp op) {
 static AffineMapAttr getPermutationMapAttr(MLIRContext *context,
                                            memref::SubViewOp subViewOp,
                                            AffineMap currPermutationMap) {
-  llvm::SmallDenseSet<unsigned> unusedDims = subViewOp.getDroppedDims();
+  llvm::SmallBitVector unusedDims = subViewOp.getDroppedDims();
   SmallVector<AffineExpr> exprs;
   int64_t sourceRank = subViewOp.getSourceType().getRank();
   for (auto dim : llvm::seq<int64_t>(0, sourceRank)) {
-    if (unusedDims.count(dim))
+    if (unusedDims.test(dim))
       continue;
     exprs.push_back(getAffineDimExpr(dim, context));
   }
diff --git a/mlir/lib/Dialect/Tensor/IR/TensorOps.cpp b/mlir/lib/Dialect/Tensor/IR/TensorOps.cpp
index 58233d6dd6ff..a26ad993b495 100644
--- a/mlir/lib/Dialect/Tensor/IR/TensorOps.cpp
+++ b/mlir/lib/Dialect/Tensor/IR/TensorOps.cpp
@@ -19,6 +19,7 @@
 #include "mlir/IR/PatternMatch.h"
 #include "mlir/IR/TypeUtilities.h"
 #include "llvm/ADT/STLExtras.h"
+#include "llvm/ADT/SmallBitVector.h"
 
 using namespace mlir;
 using namespace mlir::tensor;
@@ -935,11 +936,11 @@ RankedTensorType ExtractSliceOp::inferRankReducedResultType(
   int rankDiff = inferredType.getRank() - resultRank;
   if (rankDiff > 0) {
     auto shape = inferredType.getShape();
-    llvm::SmallDenseSet<unsigned> dimsToProject;
-    mlir::getPositionsOfShapeOne(rankDiff, shape, dimsToProject);
+    llvm::SmallBitVector dimsToProject =
+        getPositionsOfShapeOne(rankDiff, shape);
     SmallVector<int64_t> projectedShape;
     for (unsigned pos = 0, e = shape.size(); pos < e; ++pos)
-      if (!dimsToProject.contains(pos))
+      if (!dimsToProject.test(pos))
         projectedShape.push_back(shape[pos]);
     inferredType =
         RankedTensorType::get(projectedShape, inferredType.getElementType());
@@ -1076,10 +1077,10 @@ getCanonicalSliceResultType(unsigned resultRank, RankedTensorType sourceType,
   return resultType;
 }
 
-llvm::SmallDenseSet<unsigned> ExtractSliceOp::getDroppedDims() {
-  llvm::SmallDenseSet<unsigned> droppedDims;
+llvm::SmallBitVector ExtractSliceOp::getDroppedDims() {
   ArrayRef<int64_t> resultShape = getType().getShape();
   SmallVector<OpFoldResult> mixedSizes = getMixedSizes();
+  llvm::SmallBitVector droppedDims(mixedSizes.size());
   unsigned shapePos = 0;
   for (const auto &size : enumerate(mixedSizes)) {
     Optional<int64_t> sizeVal = getConstantIntValue(size.value());
@@ -1091,7 +1092,7 @@ llvm::SmallDenseSet<unsigned> ExtractSliceOp::getDroppedDims() {
       shapePos++;
       continue;
     }
-    droppedDims.insert(size.index());
+    droppedDims.set(size.index());
   }
   return droppedDims;
 }
@@ -1101,10 +1102,10 @@ LogicalResult ExtractSliceOp::reifyResultShapes(
   reifiedReturnShapes.resize(1);
   reifiedReturnShapes[0].reserve(getType().getRank());
   SmallVector<OpFoldResult> mixedSizes = getMixedSizes();
-  llvm::SmallDenseSet<unsigned> droppedDims = getDroppedDims();
+  llvm::SmallBitVector droppedDims = getDroppedDims();
   Location loc = getLoc();
   for (const auto &size : enumerate(mixedSizes)) {
-    if (droppedDims.count(size.index()))
+    if (droppedDims.test(size.index()))
       continue;
     if (auto attr = size.value().dyn_cast<Attribute>()) {
       reifiedReturnShapes[0].push_back(builder.create<arith::ConstantIndexOp>(
diff --git a/mlir/lib/IR/AffineMap.cpp b/mlir/lib/IR/AffineMap.cpp
index ecdf8376b5fc..7fbe7488b97e 100644
--- a/mlir/lib/IR/AffineMap.cpp
+++ b/mlir/lib/IR/AffineMap.cpp
@@ -547,13 +547,13 @@ AffineMap AffineMap::getMinorSubMap(unsigned numResults) const {
 }
 
 AffineMap mlir::compressDims(AffineMap map,
-                             const llvm::SmallDenseSet<unsigned> &unusedDims) {
+                             const llvm::SmallBitVector &unusedDims) {
   unsigned numDims = 0;
   SmallVector<AffineExpr> dimReplacements;
   dimReplacements.reserve(map.getNumDims());
   MLIRContext *context = map.getContext();
   for (unsigned dim = 0, e = map.getNumDims(); dim < e; ++dim) {
-    if (unusedDims.contains(dim))
+    if (unusedDims.test(dim))
       dimReplacements.push_back(getAffineConstantExpr(0, context));
     else
       dimReplacements.push_back(getAffineDimExpr(numDims++, context));
@@ -566,15 +566,11 @@ AffineMap mlir::compressDims(AffineMap map,
 }
 
 AffineMap mlir::compressUnusedDims(AffineMap map) {
-  llvm::SmallDenseSet<unsigned> usedDims;
+  llvm::SmallBitVector unusedDims(map.getNumDims(), true);
   map.walkExprs([&](AffineExpr expr) {
     if (auto dimExpr = expr.dyn_cast<AffineDimExpr>())
-      usedDims.insert(dimExpr.getPosition());
+      unusedDims.reset(dimExpr.getPosition());
   });
-  llvm::SmallDenseSet<unsigned> unusedDims;
-  for (unsigned d = 0, e = map.getNumDims(); d != e; ++d)
-    if (!usedDims.contains(d))
-      unusedDims.insert(d);
   return compressDims(map, unusedDims);
 }
 
@@ -613,15 +609,14 @@ SmallVector<AffineMap> mlir::compressUnusedDims(ArrayRef<AffineMap> maps) {
                             [](AffineMap m) { return compressUnusedDims(m); });
 }
 
-AffineMap
-mlir::compressSymbols(AffineMap map,
-                      const llvm::SmallDenseSet<unsigned> &unusedSymbols) {
+AffineMap mlir::compressSymbols(AffineMap map,
+                                const llvm::SmallBitVector &unusedSymbols) {
   unsigned numSymbols = 0;
   SmallVector<AffineExpr> symReplacements;
   symReplacements.reserve(map.getNumSymbols());
   MLIRContext *context = map.getContext();
   for (unsigned sym = 0, e = map.getNumSymbols(); sym < e; ++sym) {
-    if (unusedSymbols.contains(sym))
+    if (unusedSymbols.test(sym))
       symReplacements.push_back(getAffineConstantExpr(0, context));
     else
       symReplacements.push_back(getAffineSymbolExpr(numSymbols++, context));
@@ -634,15 +629,11 @@ mlir::compressSymbols(AffineMap map,
 }
 
 AffineMap mlir::compressUnusedSymbols(AffineMap map) {
-  llvm::SmallDenseSet<unsigned> usedSymbols;
+  llvm::SmallBitVector unusedSymbols(map.getNumSymbols(), true);
   map.walkExprs([&](AffineExpr expr) {
     if (auto symExpr = expr.dyn_cast<AffineSymbolExpr>())
-      usedSymbols.insert(symExpr.getPosition());
+      unusedSymbols.reset(symExpr.getPosition());
   });
-  llvm::SmallDenseSet<unsigned> unusedSymbols;
-  for (unsigned d = 0, e = map.getNumSymbols(); d != e; ++d)
-    if (!usedSymbols.contains(d))
-      unusedSymbols.insert(d);
   return compressSymbols(map, unusedSymbols);
 }
 
@@ -732,9 +723,8 @@ AffineMap mlir::concatAffineMaps(ArrayRef<AffineMap> maps) {
                         maps.front().getContext());
 }
 
-AffineMap
-mlir::getProjectedMap(AffineMap map,
-                      const llvm::SmallDenseSet<unsigned> &unusedDims) {
+AffineMap mlir::getProjectedMap(AffineMap map,
+                                const llvm::SmallBitVector &unusedDims) {
   return compressUnusedSymbols(compressDims(map, unusedDims));
 }
 
diff --git a/mlir/test/Dialect/MemRef/fold-subview-ops.mlir b/mlir/test/Dialect/MemRef/fold-subview-ops.mlir
index fc06cd35cc8c..6f8e46fab444 100644
--- a/mlir/test/Dialect/MemRef/fold-subview-ops.mlir
+++ b/mlir/test/Dialect/MemRef/fold-subview-ops.mlir
@@ -154,8 +154,8 @@ func @fold_rank_reducing_subview_with_load
 // CHECK-SAME:   %[[ARG16:[a-zA-Z0-9_]+]]: index
 //  CHECK-DAG:   %[[C0:.+]] = arith.constant 0 : index
 //  CHECK-DAG:   %[[I1:.+]] = affine.apply #[[MAP]](%[[ARG13]])[%[[ARG7]], %[[ARG1]]]
-//  CHECK-DAG:   %[[I2:.+]] = affine.apply #[[MAP]](%[[ARG14]])[%[[ARG8]], %[[ARG2]]]
-//  CHECK-DAG:   %[[I3:.+]] = affine.apply #[[MAP]](%[[C0]])[%[[ARG9]], %[[ARG3]]]
+//  CHECK-DAG:   %[[I2:.+]] = affine.apply #[[MAP]](%[[C0]])[%[[ARG8]], %[[ARG2]]]
+//  CHECK-DAG:   %[[I3:.+]] = affine.apply #[[MAP]](%[[ARG14]])[%[[ARG9]], %[[ARG3]]]
 //  CHECK-DAG:   %[[I4:.+]] = affine.apply #[[MAP]](%[[ARG15]])[%[[ARG10]], %[[ARG4]]]
 //  CHECK-DAG:   %[[I5:.+]] = affine.apply #[[MAP]](%[[ARG16]])[%[[ARG11]], %[[ARG5]]]
 //  CHECK-DAG:   %[[I6:.+]] = affine.apply #[[MAP]](%[[C0]])[%[[ARG12]], %[[ARG6]]]