diff --git a/mlir/lib/Dialect/StandardOps/IR/Ops.cpp b/mlir/lib/Dialect/StandardOps/IR/Ops.cpp
--- a/mlir/lib/Dialect/StandardOps/IR/Ops.cpp
+++ b/mlir/lib/Dialect/StandardOps/IR/Ops.cpp
@@ -1520,6 +1520,29 @@
 }
 
 namespace {
+struct DimOf1DAllocaFromRank : public OpRewritePattern<DimOp> {
+  using OpRewritePattern<DimOp>::OpRewritePattern;
+
+  LogicalResult matchAndRewrite(DimOp dim,
+                                PatternRewriter &rewriter) const override {
+    auto alloca = dim.memrefOrTensor().getDefiningOp<AllocaOp>();
+
+    if (!alloca)
+      return failure();
+
+    auto type = alloca.getType().dyn_cast<ShapedType>();
+    if (!type || type.getRank() != 1)
+      return failure();
+
+    auto rank = alloca.getOperand(0).getDefiningOp<RankOp>();
+    if (!rank)
+      return failure();
+
+    rewriter.replaceOp(dim, {rank});
+    return success();
+  }
+};
+
 /// Fold dim of a memref reshape operation to a load into the reshape's shape
 /// operand.
 struct DimOfMemRefReshape : public OpRewritePattern<DimOp> {
@@ -1560,8 +1583,9 @@
 
 void DimOp::getCanonicalizationPatterns(OwningRewritePatternList &results,
                                         MLIRContext *context) {
-  results.insert<DimOfMemRefReshape, DimOfCastOp<TensorToMemrefOp>,
-                 DimOfCastOp<tensor::CastOp>>(context);
+  results.insert<DimOf1DAllocaFromRank, DimOfMemRefReshape,
+                 DimOfCastOp<TensorToMemrefOp>, DimOfCastOp<tensor::CastOp>>(
+      context);
 }
 
 // ---------------------------------------------------------------------------
diff --git a/mlir/test/Dialect/Standard/canonicalize.mlir b/mlir/test/Dialect/Standard/canonicalize.mlir
--- a/mlir/test/Dialect/Standard/canonicalize.mlir
+++ b/mlir/test/Dialect/Standard/canonicalize.mlir
@@ -134,6 +134,22 @@
 
 // -----
 
+// Test case: Folding of dim((alloca(rank(%v)), %idx) -> rank(%v)
+// CHECK-LABEL: func @dim_of_1d_alloca_from_rank(
+//  CHECK-SAME:     %[[MEM:[0-9a-z]+]]: memref<*xf32>
+//  CHECK-NEXT:   %[[RANK:.*]] = rank %[[MEM]] : memref<*xf32>
+//  CHECK-NEXT:   return %[[RANK]] : index
+func @dim_of_1d_alloca_from_rank(%arg0: memref<*xf32>)
+    -> index {
+  %0 = rank %arg0 : memref<*xf32>
+  %1 = alloca(%0) : memref<?xindex>
+  %c0 = constant 0 : index
+  %2 = dim %1, %c0 : memref<?xindex>
+  return %2 : index
+}
+
+// -----
+
 // Test case: Folding of dim(memref_reshape %v %shp, %idx) -> load %shp[%idx]
 // CHECK-LABEL: func @dim_of_memref_reshape(
 //  CHECK-SAME:     %[[MEM:[0-9a-z]+]]: memref<*xf32>,