[mlir][memref] Add realloc op.

[bixia]

Summary

Add memref.realloc and canonicalization of the op. Add conversion patterns for
lowering the op to LLVM using unaligned alloc or aligned alloc based on the
conversion option.

Add filecheck tests for parsing and converting the op. Add an integration test.

[aartbik]

mlir/include/mlir/Dialect/MemRef/IR/MemRefOps.td

200

maybe add a comment that referencing memory through the "old" SSA value after the realloc is undefined behavior, perhaps with an example:

%new = memref.realloc(%old) ....
 
%0 = memref.load %new[%c]   // ok
%1 = memref.load %old[%c]   // UB

[Hardcode84]

mlir/lib/Conversion/MemRefToLLVM/MemRefToLLVM.cpp

2078

Please, do not add Dealloc here, it was specifically moved to these ifs, so it can be skipped completely

[bixia]

Add description about referencing memref via the old SSA value.
Revert the change that hoist the adding DeallocOpLowering.

[bixia]

mlir/include/mlir/Dialect/MemRef/IR/MemRefOps.td

200

Thanks for the suggestion! Add this to the end of the description.

mlir/lib/Conversion/MemRefToLLVM/MemRefToLLVM.cpp

2078

Thanks for catching this! I reverted this change.

[bixia]

Fix code format.

[bixia]

Avoid reallocation when new_size <= old_size.

[bixia]

Restore the description about referencing memref via the old SSA value.

[bixia]

Add a build method.

[ftynse]

High-level comment: since the lowering goes to alloc/memcpy/free, can't you have a pattern that rewrites realloc to memref.alloc/copy/dealloc instead of going directly to LLVM with a lot of code. The rewriter infrastructure should be able to handle that.

mlir/include/mlir/Dialect/MemRef/IR/MemRefOps.td

266

Could we please make the syntax of this op consistent with that of memref.alloc(a). Both take the dynamic size in parentheses.

mlir/lib/Conversion/MemRefToLLVM/AllocLikeConversion.cpp

53

Nit: this name confused me several times. I read it as emitting the IR that will produce a non-aligned allocation. But in fact the allocation is still aligned! It's just modified manually.

64

Nit: please expand auto unless the type is obvious from context (cast on the RHS) or difficult to spell (iterators).

65

Nit: I'd rather get the first parent with the SymbolTable trait. Allocations may well be in other module-like operations than the built-in module.

164

Please don't remove the newline.

mlir/lib/Conversion/MemRefToLLVM/MemRefToLLVM.cpp

103–257

///-document here what this does, specifically that it is not intended to be used directly + that derived classes must implement a method with a specific contract.

104

Nit: I'd rather suffix this with Base than with Impl.

141

Pass the callback by function_ref instead of std::function if it is not stored inside. The latter allocates on heap.

165

Use cast instead of dyn_cast if you never check the result for being null.

173

Direct IR modifications are not allowed in conversion patterns. This argument has to be passed to createBlock of the rewriter. Since the block is originally obtained by splitting, you can create a new block with the argument before the split-out pattern, and then merge that part into the newly created block with the argument.

mlir/lib/Dialect/MemRef/IR/MemRefOps.cpp

259

Please don't refer to layout map anymore, layouts have not been only maps for over a year. It's just a layout.

[bixia]

Address review comments.

[bixia]

mlir/lib/Conversion/MemRefToLLVM/AllocLikeConversion.cpp

53

Rename this to allocateBufferManuallyAlign.

64

Thanks! Fix here and other places.

65

Sorry, I don't quite understand what you said. Can you give an example for how the code may look like?
We are trying to create a forward declaration of the allocation function so that we can use the function in the module.
Here is the relevant part of the original code we are trying to rewrite in this PR.

mlir/lib/Conversion/MemRefToLLVM/MemRefToLLVM.cpp

103–257

Add document, please take another look.

173

Thanks!

[ftynse]

mlir/lib/Conversion/MemRefToLLVM/AllocLikeConversion.cpp

65

Instead of doing getParentOfType<ModuleOp>, it should be doing getParentWithTrait<SymbolTable>. MLIR offers no guarantees that functions are always contained in a ModuleOp. FWIW, in a GPU-targeting compilation, they will be contained in a GPUModuleOp.

[ftynse]

Have you seen my top-level comment in the original review? That one is a blocker, the rest are tidying up.

[bixia]

In D133424#3802619, @ftynse wrote:

Have you seen my top-level comment in the original review? That one is a blocker, the rest are tidying up.

Sorry I forgot to respond to that. I can't just use alloc/copy/dealloc because copy requires the two memref to have the same element type and same number of elements.
I may use "view", to create a "smaller view of the bigger memref" (if the realloc buffer is bigger, create a view of it. If the old buffer is bigger, create a view of it). However,
"view" requires the source memref to have i8 type, and memref.cast is not for this kind of cases. So I am kind of stuck here.

[bixia]

In D133424#3802795, @bixia wrote:

In D133424#3802619, @ftynse wrote:

Have you seen my top-level comment in the original review? That one is a blocker, the rest are tidying up.

Sorry I forgot to respond to that. I can't just use alloc/copy/dealloc because copy requires the two memref to have the same element type and same number of elements.
I may use "view", to create a "smaller view of the bigger memref" (if the realloc buffer is bigger, create a view of it. If the old buffer is bigger, create a view of it). However,
"view" requires the source memref to have i8 type, and memref.cast is not for this kind of cases. So I am kind of stuck here.

Also the direct lowering implementation avoids the alloc/copy/dealloc when the new size is smaller.

[ftynse]

mlir/lib/Conversion/MemRefToLLVM/MemRefToLLVM.cpp

177

Nit: cast here instead of dyn_cast.

mlir/test/Conversion/MemRefToLLVM/convert-dynamic-memref-ops.mlir

634–659

Overall suggestion for tests: drop the trailing types from operations except when they are meaningful for comprehension. For example, bitcast and the likes should keep the types because it's important to see what is being casted to what, but mul/add/extract value don't really need types. This will make the tests more robust to eventual syntactic changes that are in fact irrelevant to what is being tested.

[bixia]

Replace a dyn_cast with cast. Simplify FileCheck tests by removing unnecessary checking of trailing types.

[bixia]

mlir/lib/Conversion/MemRefToLLVM/AllocLikeConversion.cpp

65

Per offline conversation, add a TODO to fix these utility functions before we can use getParentWithTrait here.

mlir/test/Conversion/MemRefToLLVM/convert-dynamic-memref-ops.mlir

634–659

Thanks for the suggestion, it also help simplify the tests beside making them more robust.

[bixia]

Revert and unintentional change to a test.

mlir/include/mlir/Conversion/MemRefToLLVM/AllocLikeConversion.h

 //===- AllocLikeConversion.h - Convert allocation ops to LLVM ---*- C++ -*-===//
 //
 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
 // See https://llvm.org/LICENSE.txt for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
 //===----------------------------------------------------------------------===//
 
 #ifndef MLIR_CONVERSION_MEMREFTOLLVM_ALLOCLIKECONVERSION_H
 #define MLIR_CONVERSION_MEMREFTOLLVM_ALLOCLIKECONVERSION_H
 
 #include "mlir/Conversion/LLVMCommon/Pattern.h"
 
 namespace mlir {
 
-/// Lowering for AllocOp and AllocaOp.
-struct AllocLikeOpLLVMLowering : public ConvertToLLVMPattern {
+/// Lowering for memory allocation ops.
+struct AllocationOpLLVMLowering : public ConvertToLLVMPattern {
   using ConvertToLLVMPattern::createIndexConstant;
   using ConvertToLLVMPattern::getIndexType;
   using ConvertToLLVMPattern::getVoidPtrType;
 
-  explicit AllocLikeOpLLVMLowering(StringRef opName,
+  explicit AllocationOpLLVMLowering(StringRef opName,
                                     LLVMTypeConverter &converter)
       : ConvertToLLVMPattern(opName, &converter.getContext(), converter) {}
 
 protected:
-  // Returns 'input' aligned up to 'alignment'. Computes
-  // bumped = input + alignement - 1
-  // aligned = bumped - bumped % alignment
+  /// Computes the aligned value for 'input' as follows:
+  ///   bumped = input + alignement - 1
+  ///   aligned = bumped - bumped % alignment
   static Value createAligned(ConversionPatternRewriter &rewriter, Location loc,
                              Value input, Value alignment);
 
+  static MemRefType getMemRefResultType(Operation *op) {
+    return op->getResult(0).getType().cast<MemRefType>();
+  }
+
+  /// Computes the alignment for the given memory allocation op.
+  template <typename OpType>
+  Value getAlignment(ConversionPatternRewriter &rewriter, Location loc,
+                     OpType op) const {
+    MemRefType memRefType = op.getType();
+    Value alignment;
+    if (auto alignmentAttr = op.getAlignment()) {
+      alignment = createIndexConstant(rewriter, loc, *alignmentAttr);
+    } else if (!memRefType.getElementType().isSignlessIntOrIndexOrFloat()) {
+      // In the case where no alignment is specified, we may want to override
+      // `malloc's` behavior. `malloc` typically aligns at the size of the
+      // biggest scalar on a target HW. For non-scalars, use the natural
+      // alignment of the LLVM type given by the LLVM DataLayout.
+      alignment = getSizeInBytes(loc, memRefType.getElementType(), rewriter);
+    }
+    return alignment;
+  }
+
+  /// Computes the alignment for aligned_alloc used to allocate the buffer for
+  /// the memory allocation op.
+  ///
+  /// Aligned_alloc requires the allocation size to be a power of two, and the
+  /// allocation size to be a multiple of the alignment.
+  template <typename OpType>
+  int64_t alignedAllocationGetAlignment(ConversionPatternRewriter &rewriter,
+                                        Location loc, OpType op,
+                                        const DataLayout *defaultLayout) const {
+    if (Optional<uint64_t> alignment = op.getAlignment())
+      return *alignment;
+
+    // Whenever we don't have alignment set, we will use an alignment
+    // consistent with the element type; since the allocation size has to be a
+    // power of two, we will bump to the next power of two if it isn't.
+    unsigned eltSizeBytes =
+        getMemRefEltSizeInBytes(op.getType(), op, defaultLayout);
+    return std::max(kMinAlignedAllocAlignment,
+                    llvm::PowerOf2Ceil(eltSizeBytes));
+  }
+
+  /// Allocates a memory buffer using an allocation method that doesn't
+  /// guarantee alignment. Returns the pointer and its aligned value.
+  std::tuple<Value, Value>
+  allocateBufferManuallyAlign(ConversionPatternRewriter &rewriter, Location loc,
+                              Value sizeBytes, Operation *op,
+                              Value alignment) const;
+
+  /// Allocates a memory buffer using an aligned allocation method.
+  Value allocateBufferAutoAlign(ConversionPatternRewriter &rewriter,
+                                Location loc, Value sizeBytes, Operation *op,
+                                const DataLayout *defaultLayout,
+                                int64_t alignment) const;
+
+private:
+  /// Computes the byte size for the MemRef element type.
+  unsigned getMemRefEltSizeInBytes(MemRefType memRefType, Operation *op,
+                                   const DataLayout *defaultLayout) const;
+
+  /// Returns true if the memref size in bytes is known to be a multiple of
+  /// factor.
+  bool isMemRefSizeMultipleOf(MemRefType type, uint64_t factor, Operation *op,
+                              const DataLayout *defaultLayout) const;
+
+  /// The minimum alignment to use with aligned_alloc (has to be a power of 2).
+  static constexpr uint64_t kMinAlignedAllocAlignment = 16UL;
+};
+
+/// Lowering for AllocOp and AllocaOp.
+struct AllocLikeOpLLVMLowering : public AllocationOpLLVMLowering {
+  explicit AllocLikeOpLLVMLowering(StringRef opName,
+                                   LLVMTypeConverter &converter)
+      : AllocationOpLLVMLowering(opName, converter) {}
+
+protected:
   /// Allocates the underlying buffer. Returns the allocated pointer and the
   /// aligned pointer.
   virtual std::tuple<Value, Value>
   allocateBuffer(ConversionPatternRewriter &rewriter, Location loc,
                  Value sizeBytes, Operation *op) const = 0;
 
 private:
-  static MemRefType getMemRefResultType(Operation *op) {
-    return op->getResult(0).getType().cast<MemRefType>();
-  }
-
   // An `alloc` is converted into a definition of a memref descriptor value and
   // a call to `malloc` to allocate the underlying data buffer.  The memref
   // descriptor is of the LLVM structure type where:
   //   1. the first element is a pointer to the allocated (typed) data buffer,
   //   2. the second element is a pointer to the (typed) payload, aligned to the
   //      specified alignment,
   //   3. the remaining elements serve to store all the sizes and strides of the
   //      memref using LLVM-converted `index` type.

mlir/include/mlir/Dialect/MemRef/IR/MemRefOps.td

let description = [{
     %0 = memref.alloc()[%s] {alignment = 8} :
       memref<8x64xf32, affine_map<(d0, d1)[s0] -> ((d0 + s0), d1)>, 1>
     ```
   }];
   let hasVerifier = 1;
 }
 
 //===----------------------------------------------------------------------===//
+// ReallocOp
+//===----------------------------------------------------------------------===//
+
+
+def MemRef_ReallocOp : MemRef_Op<"realloc"> {
+  let summary = "memory reallocation operation";
+  let description = [{
+    The `realloc` operation changes the size of a memory region. The memory
+    region is specified by a 1D source memref and the size of the new memory
+    region is specified by a 1D result memref type and an optional dynamic Value
+    of `Index` type. The source and the result memref must be in the same memory
+    space and have the same element type.
+
+    The operation may move the memory region to a new location. In this case,
+    the content of the memory block is preserved up to the lesser of the new
+    and old sizes. If the new size if larger, the value of the extended memory
+    is undefined. This is consistent with the ISO C realloc.
+
+    The operation returns an SSA value for the memref.
+
+    Example:
+
+    ```mlir
+    %0 = memref.realloc %src : memref<64xf32> to memref<124xf32>
+    ```
+
+    The source memref may have a dynamic shape, in which case, the compiler will
+    generate code to extract its size from the runtime data structure for the
+    memref.
+
+    ```mlir
+    %1 = memref.realloc %src : memref<?xf32> to memref<124xf32>
+    ```
+
+    If the result memref has a dynamic shape, a result dimension operand is
+    needed to spefify its dynamic dimension. In the example below, the ssa value
+    '%d' specifies the unknown dimension of the result memref.
+
+    ```mlir
+    %2 = memref.realloc %src(%d) : memref<?xf32> to memref<?xf32>
+    ```
+
+    An optional `alignment` attribute may be specified to ensure that the
+    region of memory that will be indexed is aligned at the specified byte
+    boundary.  This is consistent with the fact that memref.alloc supports such
+    an optional alignment attribute. Note that in ISO C standard, neither alloc
+    nor realloc supports alignment, though there is aligned_alloc but not
+    aligned_realloc.
+
+    ```mlir
+    %3 = memref.ralloc %src {alignment = 8} : memref<64xf32> to memref<124xf32>
+    ```
+
+    Referencing the memref through the old SSA value after realloc is undefined
+    behavior.
+
+    ```mlir
+    %new = memref.realloc %old : memref<64xf32> to memref<124xf32>
+    %4 = memref.load %new[%index]   // ok
+    %5 = memref.load %old[%index]   // undefined behavior
+    ```
+  }];
+
+  let arguments = (ins MemRefRankOf<[AnyType], [1]>:$source,
+                   Optional<Index>:$dynamicResultSize,
+                   ConfinedAttr<OptionalAttr<I64Attr>,
+                                [IntMinValue<0>]>:$alignment);
+
+  let results = (outs MemRefRankOf<[AnyType], [1]>);
+
+  let builders = [
+    OpBuilder<(ins "MemRefType":$resultType,
+                  "Value":$source,
+                  CArg<"Value", "Value()">:$dynamicResultSize), [{
+      return build($_builder, $_state, resultType, source, dynamicResultSize,
+                   IntegerAttr());
+    }]>];
+
+    let extraClassDeclaration = [{
+    /// The result of a realloc is always a memref.
+    MemRefType getType() { return getResult().getType().cast<MemRefType>(); }
+  }];
+
+  let assemblyFormat = [{
+    $source (`(` $dynamicResultSize^ `)`)? attr-dict
+    `:` type($source) `to` type(results)
+  }];
+
+  let hasCanonicalizer = 1;
+  let hasVerifier = 1;
+}
+
+//===----------------------------------------------------------------------===//
 // AllocaOp
 //===----------------------------------------------------------------------===//
 
 def MemRef_AllocaOp : AllocLikeOp<"alloca", AutomaticAllocationScopeResource> {
   let summary = "stack memory allocation operation";
   let description = [{
     The `alloca` operation allocates memory on the stack, to be automatically
     released when control transfers back from the region of its closest

mlir/lib/Conversion/MemRefToLLVM/AllocLikeConversion.cpp

 //===- AllocLikeConversion.cpp - LLVM conversion for alloc operations -----===//
 //
 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
 // See https://llvm.org/LICENSE.txt for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
 //===----------------------------------------------------------------------===//
 
 #include "mlir/Conversion/MemRefToLLVM/AllocLikeConversion.h"
+#include "mlir/Analysis/DataLayoutAnalysis.h"
+#include "mlir/Dialect/LLVMIR/FunctionCallUtils.h"
 #include "mlir/Dialect/LLVMIR/LLVMDialect.h"
 
 using namespace mlir;
 
-Value AllocLikeOpLLVMLowering::createAligned(
+namespace {
+// TODO: Fix the LLVM utilities for looking up functions to take Operation*
+// with SymbolTable trait instead of ModuleOp and make similar change here. This
+// allows call sites to use getParentWithTrait<OpTrait::SymbolTable> instead
+// of getParentOfType<ModuleOp> to pass down the operation.
+LLVM::LLVMFuncOp getNotalignedAllocFn(LLVMTypeConverter *typeConverter,
+                                      ModuleOp module, Type indexType) {
+  bool useGenericFn = typeConverter->getOptions().useGenericFunctions;
+
+  if (useGenericFn)
+    return LLVM::lookupOrCreateGenericAllocFn(module, indexType);
+
+  return LLVM::lookupOrCreateMallocFn(module, indexType);
+}
+
+LLVM::LLVMFuncOp getAlignedAllocFn(LLVMTypeConverter *typeConverter,
+                                   ModuleOp module, Type indexType) {
+  bool useGenericFn = typeConverter->getOptions().useGenericFunctions;
+
+  if (useGenericFn)
+    return LLVM::lookupOrCreateGenericAlignedAllocFn(module, indexType);
+
+  return LLVM::lookupOrCreateAlignedAllocFn(module, indexType);
+}
+
+} // end namespace
+
+Value AllocationOpLLVMLowering::createAligned(
     ConversionPatternRewriter &rewriter, Location loc, Value input,
     Value alignment) {
   Value one = createIndexAttrConstant(rewriter, loc, alignment.getType(), 1);
   Value bump = rewriter.create<LLVM::SubOp>(loc, alignment, one);
   Value bumped = rewriter.create<LLVM::AddOp>(loc, input, bump);
   Value mod = rewriter.create<LLVM::URemOp>(loc, bumped, alignment);
   return rewriter.create<LLVM::SubOp>(loc, bumped, mod);
 }
 
+std::tuple<Value, Value> AllocationOpLLVMLowering::allocateBufferManuallyAlign(
+    ConversionPatternRewriter &rewriter, Location loc, Value sizeBytes,
+    Operation *op, Value alignment) const {
+  if (alignment) {
+    // Adjust the allocation size to consider alignment.
+    sizeBytes = rewriter.create<LLVM::AddOp>(loc, sizeBytes, alignment);
+  }
+
+  MemRefType memRefType = getMemRefResultType(op);
+  // Allocate the underlying buffer.
+  Type elementPtrType = this->getElementPtrType(memRefType);
+  LLVM::LLVMFuncOp allocFuncOp = getNotalignedAllocFn(
+      getTypeConverter(), op->getParentOfType<ModuleOp>(), getIndexType());
+  auto results = rewriter.create<LLVM::CallOp>(loc, allocFuncOp, sizeBytes);
+  Value allocatedPtr = rewriter.create<LLVM::BitcastOp>(loc, elementPtrType,
+                                                        results.getResult());
+
+  Value alignedPtr = allocatedPtr;
+  if (alignment) {
+    // Compute the aligned pointer.
+    Value allocatedInt =
+        rewriter.create<LLVM::PtrToIntOp>(loc, getIndexType(), allocatedPtr);
+    Value alignmentInt = createAligned(rewriter, loc, allocatedInt, alignment);
+    alignedPtr =
+        rewriter.create<LLVM::IntToPtrOp>(loc, elementPtrType, alignmentInt);
+  }
+
+  return std::make_tuple(allocatedPtr, alignedPtr);
+}
+
+unsigned AllocationOpLLVMLowering::getMemRefEltSizeInBytes(
+    MemRefType memRefType, Operation *op,
+    const DataLayout *defaultLayout) const {
+  const DataLayout *layout = defaultLayout;
+  if (const DataLayoutAnalysis *analysis =
+          getTypeConverter()->getDataLayoutAnalysis()) {
+    layout = &analysis->getAbove(op);
+  }
+  Type elementType = memRefType.getElementType();
+  if (auto memRefElementType = elementType.dyn_cast<MemRefType>())
+    return getTypeConverter()->getMemRefDescriptorSize(memRefElementType,
+                                                       *layout);
+  if (auto memRefElementType = elementType.dyn_cast<UnrankedMemRefType>())
+    return getTypeConverter()->getUnrankedMemRefDescriptorSize(
+        memRefElementType, *layout);
+  return layout->getTypeSize(elementType);
+}
+
+bool AllocationOpLLVMLowering::isMemRefSizeMultipleOf(
+    MemRefType type, uint64_t factor, Operation *op,
+    const DataLayout *defaultLayout) const {
+  uint64_t sizeDivisor = getMemRefEltSizeInBytes(type, op, defaultLayout);
+  for (unsigned i = 0, e = type.getRank(); i < e; i++) {
+    if (ShapedType::isDynamic(type.getDimSize(i)))
+      continue;
+    sizeDivisor = sizeDivisor * type.getDimSize(i);
+  }
+  return sizeDivisor % factor == 0;
+}
+
+Value AllocationOpLLVMLowering::allocateBufferAutoAlign(
+    ConversionPatternRewriter &rewriter, Location loc, Value sizeBytes,
+    Operation *op, const DataLayout *defaultLayout, int64_t alignment) const {
+  Value allocAlignment = createIndexConstant(rewriter, loc, alignment);
+
+  MemRefType memRefType = getMemRefResultType(op);
+  // Function aligned_alloc requires size to be a multiple of alignment; we pad
+  // the size to the next multiple if necessary.
+  if (!isMemRefSizeMultipleOf(memRefType, alignment, op, defaultLayout))
+    sizeBytes = createAligned(rewriter, loc, sizeBytes, allocAlignment);
+
+  Type elementPtrType = this->getElementPtrType(memRefType);
+  LLVM::LLVMFuncOp allocFuncOp = getAlignedAllocFn(
+      getTypeConverter(), op->getParentOfType<ModuleOp>(), getIndexType());
+  auto results = rewriter.create<LLVM::CallOp>(
+      loc, allocFuncOp, ValueRange({allocAlignment, sizeBytes}));
+  Value allocatedPtr = rewriter.create<LLVM::BitcastOp>(loc, elementPtrType,
+                                                        results.getResult());
+
+  return allocatedPtr;
+}
+
 LogicalResult AllocLikeOpLLVMLowering::matchAndRewrite(
     Operation *op, ArrayRef<Value> operands,
     ConversionPatternRewriter &rewriter) const {
   MemRefType memRefType = getMemRefResultType(op);
   if (!isConvertibleAndHasIdentityMaps(memRefType))
     return rewriter.notifyMatchFailure(op, "incompatible memref type");
   auto loc = op->getLoc();
 
LogicalResult AllocLikeOpLLVMLowering::matchAndRewrite(
 
   // Create the MemRef descriptor.
   auto memRefDescriptor = this->createMemRefDescriptor(
       loc, memRefType, allocatedPtr, alignedPtr, sizes, strides, rewriter);
 
   // Return the final value of the descriptor.
   rewriter.replaceOp(op, {memRefDescriptor});
   return success();
 }

mlir/lib/Conversion/MemRefToLLVM/MemRefToLLVM.cpp

 using namespace mlir;
 
 namespace {
 
 bool isStaticStrideOrOffset(int64_t strideOrOffset) {
   return !ShapedType::isDynamicStrideOrOffset(strideOrOffset);
 }
 
-struct AllocOpLowering : public AllocLikeOpLLVMLowering {
-  AllocOpLowering(LLVMTypeConverter &converter)
-      : AllocLikeOpLLVMLowering(memref::AllocOp::getOperationName(),
-                                converter) {}
-
-  LLVM::LLVMFuncOp getAllocFn(ModuleOp module) const {
-    bool useGenericFn = getTypeConverter()->getOptions().useGenericFunctions;
+LLVM::LLVMFuncOp getFreeFn(LLVMTypeConverter *typeConverter, ModuleOp module) {
+  bool useGenericFn = typeConverter->getOptions().useGenericFunctions;
 
-    if (useGenericFn)
-      return LLVM::lookupOrCreateGenericAllocFn(module, getIndexType());
+    return LLVM::lookupOrCreateGenericFreeFn(module);
 
-    return LLVM::lookupOrCreateMallocFn(module, getIndexType());
-  }
+  return LLVM::lookupOrCreateFreeFn(module);
 
+struct AllocOpLowering : public AllocLikeOpLLVMLowering {
+  AllocOpLowering(LLVMTypeConverter &converter)
+      : AllocLikeOpLLVMLowering(memref::AllocOp::getOperationName(),
+                                converter) {}
   std::tuple<Value, Value> allocateBuffer(ConversionPatternRewriter &rewriter,
                                           Location loc, Value sizeBytes,
                                           Operation *op) const override {
-    // Heap allocations.
-    memref::AllocOp allocOp = cast<memref::AllocOp>(op);
-    MemRefType memRefType = allocOp.getType();
-
-    Value alignment;
-    if (auto alignmentAttr = allocOp.getAlignment()) {
-      alignment = createIndexConstant(rewriter, loc, *alignmentAttr);
-    } else if (!memRefType.getElementType().isSignlessIntOrIndexOrFloat()) {
-      // In the case where no alignment is specified, we may want to override
-      // `malloc's` behavior. `malloc` typically aligns at the size of the
-      // biggest scalar on a target HW. For non-scalars, use the natural
-      // alignment of the LLVM type given by the LLVM DataLayout.
-      alignment = getSizeInBytes(loc, memRefType.getElementType(), rewriter);
-    }
-
-    if (alignment) {
-      // Adjust the allocation size to consider alignment.
-      sizeBytes = rewriter.create<LLVM::AddOp>(loc, sizeBytes, alignment);
-    }
-
-    // Allocate the underlying buffer and store a pointer to it in the MemRef
-    // descriptor.
-    Type elementPtrType = this->getElementPtrType(memRefType);
-    auto allocFuncOp = getAllocFn(allocOp->getParentOfType<ModuleOp>());
-    auto results = rewriter.create<LLVM::CallOp>(loc, allocFuncOp, sizeBytes);
-    Value allocatedPtr = rewriter.create<LLVM::BitcastOp>(loc, elementPtrType,
-                                                          results.getResult());
-
-    Value alignedPtr = allocatedPtr;
-    if (alignment) {
-      // Compute the aligned type pointer.
-      Value allocatedInt =
-          rewriter.create<LLVM::PtrToIntOp>(loc, getIndexType(), allocatedPtr);
-      Value alignmentInt =
-          createAligned(rewriter, loc, allocatedInt, alignment);
-      alignedPtr =
-          rewriter.create<LLVM::IntToPtrOp>(loc, elementPtrType, alignmentInt);
-    }
-
-    return std::make_tuple(allocatedPtr, alignedPtr);
+    return allocateBufferManuallyAlign(
+        rewriter, loc, sizeBytes, op,
+        getAlignment(rewriter, loc, cast<memref::AllocOp>(op)));
   }
 };
 
 struct AlignedAllocOpLowering : public AllocLikeOpLLVMLowering {
   AlignedAllocOpLowering(LLVMTypeConverter &converter)
       : AllocLikeOpLLVMLowering(memref::AllocOp::getOperationName(),
                                 converter) {}
-
-  /// Returns the memref's element size in bytes using the data layout active at
-  /// `op`.
-  // TODO: there are other places where this is used. Expose publicly?
-  unsigned getMemRefEltSizeInBytes(MemRefType memRefType, Operation *op) const {
-    const DataLayout *layout = &defaultLayout;
-    if (const DataLayoutAnalysis *analysis =
-            getTypeConverter()->getDataLayoutAnalysis()) {
-      layout = &analysis->getAbove(op);
-    }
-    Type elementType = memRefType.getElementType();
-    if (auto memRefElementType = elementType.dyn_cast<MemRefType>())
-      return getTypeConverter()->getMemRefDescriptorSize(memRefElementType,
-                                                         *layout);
-    if (auto memRefElementType = elementType.dyn_cast<UnrankedMemRefType>())
-      return getTypeConverter()->getUnrankedMemRefDescriptorSize(
-          memRefElementType, *layout);
-    return layout->getTypeSize(elementType);
-  }
-
-  /// Returns true if the memref size in bytes is known to be a multiple of
-  /// factor assuming the data layout active at `op`.
-  bool isMemRefSizeMultipleOf(MemRefType type, uint64_t factor,
-                              Operation *op) const {
-    uint64_t sizeDivisor = getMemRefEltSizeInBytes(type, op);
-    for (unsigned i = 0, e = type.getRank(); i < e; i++) {
-      if (ShapedType::isDynamic(type.getDimSize(i)))
-        continue;
-      sizeDivisor = sizeDivisor * type.getDimSize(i);
-    }
-    return sizeDivisor % factor == 0;
-  }
-
-  /// Returns the alignment to be used for the allocation call itself.
-  /// aligned_alloc requires the allocation size to be a power of two, and the
-  /// allocation size to be a multiple of alignment,
-  int64_t getAllocationAlignment(memref::AllocOp allocOp) const {
-    if (Optional<uint64_t> alignment = allocOp.getAlignment())
-      return *alignment;
-
-    // Whenever we don't have alignment set, we will use an alignment
-    // consistent with the element type; since the allocation size has to be a
-    // power of two, we will bump to the next power of two if it already isn't.
-    auto eltSizeBytes = getMemRefEltSizeInBytes(allocOp.getType(), allocOp);
-    return std::max(kMinAlignedAllocAlignment,
-                    llvm::PowerOf2Ceil(eltSizeBytes));
-  }
-
-  LLVM::LLVMFuncOp getAllocFn(ModuleOp module) const {
-    bool useGenericFn = getTypeConverter()->getOptions().useGenericFunctions;
-
-    if (useGenericFn)
-      return LLVM::lookupOrCreateGenericAlignedAllocFn(module, getIndexType());
-
-    return LLVM::lookupOrCreateAlignedAllocFn(module, getIndexType());
-  }
-
   std::tuple<Value, Value> allocateBuffer(ConversionPatternRewriter &rewriter,
                                           Location loc, Value sizeBytes,
                                           Operation *op) const override {
-    // Heap allocations.
-    memref::AllocOp allocOp = cast<memref::AllocOp>(op);
-    MemRefType memRefType = allocOp.getType();
-    int64_t alignment = getAllocationAlignment(allocOp);
-    Value allocAlignment = createIndexConstant(rewriter, loc, alignment);
-
-    // aligned_alloc requires size to be a multiple of alignment; we will pad
-    // the size to the next multiple if necessary.
-    if (!isMemRefSizeMultipleOf(memRefType, alignment, op))
-      sizeBytes = createAligned(rewriter, loc, sizeBytes, allocAlignment);
-
-    Type elementPtrType = this->getElementPtrType(memRefType);
-    auto allocFuncOp = getAllocFn(allocOp->getParentOfType<ModuleOp>());
-    auto results = rewriter.create<LLVM::CallOp>(
-        loc, allocFuncOp, ValueRange({allocAlignment, sizeBytes}));
-    Value allocatedPtr = rewriter.create<LLVM::BitcastOp>(loc, elementPtrType,
-                                                          results.getResult());
-
-    return std::make_tuple(allocatedPtr, allocatedPtr);
+    Value ptr = allocateBufferAutoAlign(
+        rewriter, loc, sizeBytes, op, &defaultLayout,
+        alignedAllocationGetAlignment(rewriter, loc, cast<memref::AllocOp>(op),
+                                      &defaultLayout));
+    return std::make_tuple(ptr, ptr);
   }
 
-  /// The minimum alignment to use with aligned_alloc (has to be a power of 2).
-  static constexpr uint64_t kMinAlignedAllocAlignment = 16UL;
-
+private:
   /// Default layout to use in absence of the corresponding analysis.
   DataLayout defaultLayout;
 };
 
 struct AllocaOpLowering : public AllocLikeOpLLVMLowering {
   AllocaOpLowering(LLVMTypeConverter &converter)
       : AllocLikeOpLLVMLowering(memref::AllocaOp::getOperationName(),
                                 converter) {}
std::tuple<Value, Value> allocateBuffer(ConversionPatternRewriter &rewriter,
     auto elementPtrType = this->getElementPtrType(allocaOp.getType());
 
     auto allocatedElementPtr = rewriter.create<LLVM::AllocaOp>(
         loc, elementPtrType, sizeBytes, allocaOp.getAlignment().value_or(0));
 
     return std::make_tuple(allocatedElementPtr, allocatedElementPtr);
   }
 };
 
+/// The base class for lowering realloc op, to support the implementation of
+/// realloc via allocation methods that may or may not support alignment.
+/// A derived class should provide an implementation of allocateBuffer using
+/// the underline allocation methods.
+struct ReallocOpLoweringBase : public AllocationOpLLVMLowering {
+  using OpAdaptor = typename memref::ReallocOp::Adaptor;
+
+  ReallocOpLoweringBase(LLVMTypeConverter &converter)
+      : AllocationOpLLVMLowering(memref::ReallocOp::getOperationName(),
+                                 converter) {}
+
+  /// Allocates the new buffer. Returns the allocated pointer and the
+  /// aligned pointer.
+  virtual std::tuple<Value, Value>
+  allocateBuffer(ConversionPatternRewriter &rewriter, Location loc,
+                 Value sizeBytes, memref::ReallocOp op) const = 0;
+
+  LogicalResult
+  matchAndRewrite(Operation *op, ArrayRef<Value> operands,
+                  ConversionPatternRewriter &rewriter) const final {
+    return matchAndRewrite(cast<memref::ReallocOp>(op),
+                           OpAdaptor(operands, op->getAttrDictionary()),
+                           rewriter);
+  }
+
+  // A `realloc` is converted as follows:
+  //   If new_size > old_size
+  //     1. allocates a new buffer
+  //     2. copies the content of the old buffer to the new buffer
+  //     3. release the old buffer
+  //     3. updates the buffer pointers in the memref descriptor
+  //   Update the size in the memref descriptor
+  // Alignment request is handled by allocating `alignment` more bytes than
+  // requested and shifting the aligned pointer relative to the allocated
+  // memory.
+  LogicalResult matchAndRewrite(memref::ReallocOp op, OpAdaptor adaptor,
+                                ConversionPatternRewriter &rewriter) const {
+    OpBuilder::InsertionGuard guard(rewriter);
+    Location loc = op.getLoc();
+
+    auto computeNumElements =
+        [&](MemRefType type, function_ref<Value()> getDynamicSize) -> Value {
+      // Compute number of elements.
+      int64_t size = type.getShape()[0];
+      Value numElements = ((size == ShapedType::kDynamicSize)
+                               ? getDynamicSize()
+                               : createIndexConstant(rewriter, loc, size));
+      Type indexType = getIndexType();
+      if (numElements.getType() != indexType)
+        numElements = typeConverter->materializeTargetConversion(
+            rewriter, loc, indexType, numElements);
+      return numElements;
+    };
+
+    MemRefDescriptor desc(adaptor.getSource());
+    Value oldDesc = desc;
+
+    // Split the block right before the current op into two blocks.
+    Block *currentBlock = rewriter.getInsertionBlock();
+    Block *block =
+        rewriter.splitBlock(currentBlock, rewriter.getInsertionPoint());
+    // Add a block argument by creating an empty block with the argument type
+    // and then merging the block into the empty block.
+    Block *endBlock = rewriter.createBlock(
+        block->getParent(), Region::iterator(block), oldDesc.getType(), loc);
+    rewriter.mergeBlocks(block, endBlock, {});
+    // Add a new block for the true branch of the conditional statement we will
+    // add.
+    Block *trueBlock = rewriter.createBlock(
+        currentBlock->getParent(), std::next(Region::iterator(currentBlock)));
+
+    rewriter.setInsertionPointToEnd(currentBlock);
+    Value src = op.getSource();
+    auto srcType = src.getType().dyn_cast<MemRefType>();
+    Value srcNumElements = computeNumElements(
+        srcType, [&]() -> Value { return desc.size(rewriter, loc, 0); });
+    auto dstType = op.getType().cast<MemRefType>();
+    Value dstNumElements = computeNumElements(
+        dstType, [&]() -> Value { return op.getDynamicResultSize(); });
+    Value cond = rewriter.create<LLVM::ICmpOp>(
+        loc, IntegerType::get(rewriter.getContext(), 1),
+        LLVM::ICmpPredicate::ugt, dstNumElements, srcNumElements);
+    rewriter.create<LLVM::CondBrOp>(loc, cond, trueBlock, ArrayRef<Value>(),
+                                    endBlock, ValueRange{oldDesc});
+
+    rewriter.setInsertionPointToStart(trueBlock);
+    Value sizeInBytes = getSizeInBytes(loc, dstType.getElementType(), rewriter);
+    // Compute total byte size.
+    auto dstByteSize =
+        rewriter.create<LLVM::MulOp>(loc, dstNumElements, sizeInBytes);
+    // Allocate a new buffer.
+    auto [dstRawPtr, dstAlignedPtr] =
+        allocateBuffer(rewriter, loc, dstByteSize, op);
+    // Copy the data from the old buffer to the new buffer.
+    Value srcAlignedPtr = desc.alignedPtr(rewriter, loc);
+    Value isVolatile =
+        rewriter.create<LLVM::ConstantOp>(loc, rewriter.getBoolAttr(false));
+    auto toVoidPtr = [&](Value ptr) -> Value {
+      return rewriter.create<LLVM::BitcastOp>(loc, getVoidPtrType(), ptr);
+    };
+    rewriter.create<LLVM::MemcpyOp>(loc, toVoidPtr(dstAlignedPtr),
+                                    toVoidPtr(srcAlignedPtr), dstByteSize,
+                                    isVolatile);
+    // Deallocate the old buffer.
+    LLVM::LLVMFuncOp freeFunc =
+        getFreeFn(getTypeConverter(), op->getParentOfType<ModuleOp>());
+    rewriter.create<LLVM::CallOp>(loc, freeFunc,
+                                  toVoidPtr(desc.allocatedPtr(rewriter, loc)));
+    // Replace the old buffer addresses in the MemRefDescriptor with the new
+    // buffer addresses.
+    desc.setAllocatedPtr(rewriter, loc, dstRawPtr);
+    desc.setAlignedPtr(rewriter, loc, dstAlignedPtr);
+    rewriter.create<LLVM::BrOp>(loc, Value(desc), endBlock);
+
+    rewriter.setInsertionPoint(op);
+    // Update the memref size.
+    MemRefDescriptor newDesc(endBlock->getArgument(0));
+    newDesc.setSize(rewriter, loc, 0, dstNumElements);
+    rewriter.replaceOp(op, {newDesc});
+    return success();
+  }
+
+private:
+  using ConvertToLLVMPattern::matchAndRewrite;
+};
+
+struct ReallocOpLowering : public ReallocOpLoweringBase {
+  ReallocOpLowering(LLVMTypeConverter &converter)
+      : ReallocOpLoweringBase(converter) {}
+  std::tuple<Value, Value> allocateBuffer(ConversionPatternRewriter &rewriter,
+                                          Location loc, Value sizeBytes,
+                                          memref::ReallocOp op) const override {
+    return allocateBufferManuallyAlign(rewriter, loc, sizeBytes, op,
+                                       getAlignment(rewriter, loc, op));
+  }
+};
+
+struct AlignedReallocOpLowering : public ReallocOpLoweringBase {
+  AlignedReallocOpLowering(LLVMTypeConverter &converter)
+      : ReallocOpLoweringBase(converter) {}
+  std::tuple<Value, Value> allocateBuffer(ConversionPatternRewriter &rewriter,
+                                          Location loc, Value sizeBytes,
+                                          memref::ReallocOp op) const override {
+    Value ptr = allocateBufferAutoAlign(
+        rewriter, loc, sizeBytes, op, &defaultLayout,
+        alignedAllocationGetAlignment(rewriter, loc, op, &defaultLayout));
+    return std::make_tuple(ptr, ptr);
+  }
+
+private:
+  /// Default layout to use in absence of the corresponding analysis.
+  DataLayout defaultLayout;
+};
+
 struct AllocaScopeOpLowering
     : public ConvertOpToLLVMPattern<memref::AllocaScopeOp> {
   using ConvertOpToLLVMPattern<memref::AllocaScopeOp>::ConvertOpToLLVMPattern;
 
   LogicalResult
   matchAndRewrite(memref::AllocaScopeOp allocaScopeOp, OpAdaptor adaptor,
                   ConversionPatternRewriter &rewriter) const override {
     OpBuilder::InsertionGuard guard(rewriter);

 // The memref descriptor being an SSA value, there is no need to clean it up
 // in any way.
 struct DeallocOpLowering : public ConvertOpToLLVMPattern<memref::DeallocOp> {
   using ConvertOpToLLVMPattern<memref::DeallocOp>::ConvertOpToLLVMPattern;
 
   explicit DeallocOpLowering(LLVMTypeConverter &converter)
       : ConvertOpToLLVMPattern<memref::DeallocOp>(converter) {}
 
-  LLVM::LLVMFuncOp getFreeFn(ModuleOp module) const {
-    bool useGenericFn = getTypeConverter()->getOptions().useGenericFunctions;
-
-    if (useGenericFn)
-      return LLVM::lookupOrCreateGenericFreeFn(module);
-
-    return LLVM::lookupOrCreateFreeFn(module);
-  }
-
   LogicalResult
   matchAndRewrite(memref::DeallocOp op, OpAdaptor adaptor,
                   ConversionPatternRewriter &rewriter) const override {
     // Insert the `free` declaration if it is not already present.
-    auto freeFunc = getFreeFn(op->getParentOfType<ModuleOp>());
+    LLVM::LLVMFuncOp freeFunc =
+        getFreeFn(getTypeConverter(), op->getParentOfType<ModuleOp>());
     MemRefDescriptor memref(adaptor.getMemref());
     Value casted = rewriter.create<LLVM::BitcastOp>(
         op.getLoc(), getVoidPtrType(),
         memref.allocatedPtr(rewriter, op.getLoc()));
     rewriter.replaceOpWithNewOp<LLVM::CallOp>(op, freeFunc, casted);
     return success();
   }
 };

 void mlir::populateMemRefToLLVMConversionPatterns(LLVMTypeConverter &converter,
                                                   RewritePatternSet &patterns) {
   // clang-format off
   patterns.add<
       AllocaOpLowering,
       AllocaScopeOpLowering,
       AtomicRMWOpLowering,
       AssumeAlignmentOpLowering,
       DimOpLowering,
       GenericAtomicRMWOpLowering,
       GlobalMemrefOpLowering,
       GetGlobalMemrefOpLowering,
       LoadOpLowering,
       MemRefCastOpLowering,
       MemRefCopyOpLowering,
       MemRefReinterpretCastOpLowering,
       MemRefReshapeOpLowering,
       PrefetchOpLowering,
       RankOpLowering,
       ReassociatingReshapeOpConversion<memref::ExpandShapeOp>,
       ReassociatingReshapeOpConversion<memref::CollapseShapeOp>,
       StoreOpLowering,
       SubViewOpLowering,
       TransposeOpLowering,
       ViewOpLowering>(converter);
   // clang-format on
   auto allocLowering = converter.getOptions().allocLowering;
   if (allocLowering == LowerToLLVMOptions::AllocLowering::AlignedAlloc)
-    patterns.add<AlignedAllocOpLowering, DeallocOpLowering>(converter);
+    patterns.add<AlignedAllocOpLowering, AlignedReallocOpLowering,
+                 DeallocOpLowering>(converter);
   else if (allocLowering == LowerToLLVMOptions::AllocLowering::Malloc)
-    patterns.add<AllocOpLowering, DeallocOpLowering>(converter);
+    patterns.add<AllocOpLowering, ReallocOpLowering, DeallocOpLowering>(
+        converter);
 }
 
 namespace {
 struct MemRefToLLVMPass
     : public impl::ConvertMemRefToLLVMBase<MemRefToLLVMPass> {
   MemRefToLLVMPass() = default;
 
   void runOnOperation() override {

mlir/lib/Dialect/MemRef/IR/MemRefOps.cpp

 
 void AllocaOp::getCanonicalizationPatterns(RewritePatternSet &results,
                                            MLIRContext *context) {
   results.add<SimplifyAllocConst<AllocaOp>, SimplifyDeadAlloc<AllocaOp>>(
       context);
 }
 
 //===----------------------------------------------------------------------===//
+// ReallocOp
+//===----------------------------------------------------------------------===//
+
+LogicalResult ReallocOp::verify() {
+  auto sourceType = getOperand(0).getType().cast<MemRefType>();
+  MemRefType resultType = getType();
+
+  // The source memref should have identity layout (or none).
+  if (!sourceType.getLayout().isIdentity())
+    return emitError("unsupported layout for source memref type ")
+           << sourceType;
+
+  // The result memref should have identity layout (or none).
+  if (!resultType.getLayout().isIdentity())
+    return emitError("unsupported layout for result memref type ")
+           << resultType;
+
+  // The source memref and the result memref should be in the same memory space.
+  if (sourceType.getMemorySpace() != resultType.getMemorySpace())
+    return emitError("different memory spaces specified for source memref "
+                     "type ")
+           << sourceType << " and result memref type " << resultType;
+
+  // The source memref and the result memref should have the same element type.
+  if (sourceType.getElementType() != resultType.getElementType())
+    return emitError("different element types specified for source memref "
+                     "type ")
+           << sourceType << " and result memref type " << resultType;
+
+  // Verify that we have the dynamic dimension operand when it is needed.
+  if (resultType.getNumDynamicDims() && !getDynamicResultSize())
+    return emitError("missing dimension operand for result type ")
+           << resultType;
+  if (!resultType.getNumDynamicDims() && getDynamicResultSize())
+    return emitError("unnecessary dimension operand for result type ")
+           << resultType;
+
+  return success();
+}
+
+void ReallocOp::getCanonicalizationPatterns(RewritePatternSet &results,
+                                            MLIRContext *context) {
+  results.add<SimplifyDeadAlloc<ReallocOp>>(context);
+}
+
+//===----------------------------------------------------------------------===//
 // AllocaScopeOp
 //===----------------------------------------------------------------------===//
 
 void AllocaScopeOp::print(OpAsmPrinter &p) {
   bool printBlockTerminators = false;
 
   p << ' ';
   if (!getResults().empty()) {

mlir/test/Conversion/MemRefToLLVM/convert-dynamic-memref-ops.mlir

func.func @ranked_unranked() {
   // ALIGNED-ALLOC: llvm.call @aligned_alloc
   // ALIGNED-ALLOC: llvm.bitcast
   // ALIGNED-ALLOC-SAME: !llvm.ptr<i8> to !llvm.[[INNER]]
   %0 = memref.alloc() : memref<1 x memref<* x f32>>
   memref.cast %0 : memref<1 x memref<* x f32>> to memref<* x memref<* x f32>>
   return
 }
 
+// -----
+
+// CHECK-LABEL:     func.func @realloc_dynamic(
+// CHECK-SAME:      %[[arg0:.*]]: memref<?xf32>,
+// CHECK-SAME:      %[[arg1:.*]]: index) -> memref<?xf32> {
+func.func @realloc_dynamic(%in: memref<?xf32>, %d: index) -> memref<?xf32>{
+// CHECK:           %[[descriptor:.*]] = builtin.unrealized_conversion_cast %[[arg0]]
+// CHECK:           %[[drc_dim:.*]] = llvm.extractvalue %[[descriptor]][3, 0]
+// CHECK:           %[[dst_dim:.*]] = builtin.unrealized_conversion_cast %[[arg1]] : index to i64
+// CHECK:           %[[cond:.*]] = llvm.icmp "ugt" %[[dst_dim]], %[[drc_dim]] : i64
+// CHECK:           llvm.cond_br %[[cond]], ^bb1, ^bb2(%[[descriptor]]
+// CHECK:           ^bb1:
+// CHECK:           %[[dst_null:.*]] = llvm.mlir.null : !llvm.ptr<f32>
+// CHECK:           %[[dst_gep:.*]] = llvm.getelementptr %[[dst_null]][1]
+// CHECK:           %[[dst_es:.*]] = llvm.ptrtoint %[[dst_gep]] : !llvm.ptr<f32> to i64
+// CHECK:           %[[dst_size:.*]] = llvm.mul %[[dst_dim]], %[[dst_es]]
+// CHECK:           %[[new_buffer_raw:.*]] = llvm.call @malloc(%[[dst_size]])
+// CHECK:           %[[new_buffer:.*]] = llvm.bitcast %[[new_buffer_raw]] : !llvm.ptr<i8> to !llvm.ptr<f32>
+// CHECK:           %[[old_buffer_aligned:.*]] = llvm.extractvalue %[[descriptor]][1]
+// CHECK:           %[[volatile:.*]] = llvm.mlir.constant(false) : i1
+// CHECK-DAG:       %[[new_buffer_void:.*]] = llvm.bitcast %[[new_buffer]] : !llvm.ptr<f32> to !llvm.ptr<i8>
+// CHECK-DAG:       %[[old_buffer_void:.*]] = llvm.bitcast %[[old_buffer_aligned]] : !llvm.ptr<f32> to !llvm.ptr<i8>
+// CHECK:           "llvm.intr.memcpy"(%[[new_buffer_void]], %[[old_buffer_void]], %[[dst_size]], %[[volatile]])
+// CHECK:           %[[old_buffer_unaligned:.*]] = llvm.extractvalue %[[descriptor]][0]
+// CHECK:           %[[old_buffer_unaligned_void:.*]] = llvm.bitcast %[[old_buffer_unaligned]] : !llvm.ptr<f32> to !llvm.ptr<i8>
+// CHECK:           llvm.call @free(%[[old_buffer_unaligned_void]])
+// CHECK:           %[[descriptor_update1:.*]] = llvm.insertvalue %[[new_buffer]], %[[descriptor]][0]
+// CHECK:           %[[descriptor_update2:.*]] = llvm.insertvalue %[[new_buffer]], %[[descriptor_update1]][1]
+// CHECK:           llvm.br ^bb2(%[[descriptor_update2]]
+// CHECK:           ^bb2(%[[descriptor_update3:.*]]: !llvm.struct<(ptr<f32>, ptr<f32>, i64, array<1 x i64>, array<1 x i64>)>):
+// CHECK:           %[[descriptor_update4:.*]] = llvm.insertvalue %[[dst_dim]], %[[descriptor_update3]][3, 0]
+// CHECK:           %[[descriptor_update5:.*]] = builtin.unrealized_conversion_cast %[[descriptor_update4]]
+// CHECK:           return %[[descriptor_update5]] : memref<?xf32>
+
+  %out = memref.realloc %in(%d) : memref<?xf32> to memref<?xf32>
+  return %out : memref<?xf32>
+}
+
+// -----
+
+// CHECK-LABEL:     func.func @realloc_dynamic_alignment(
+// CHECK-SAME:      %[[arg0:.*]]: memref<?xf32>,
+// CHECK-SAME:      %[[arg1:.*]]: index) -> memref<?xf32> {
+// ALIGNED-ALLOC-LABEL:   func.func @realloc_dynamic_alignment(
+// ALIGNED-ALLOC-SAME:    %[[arg0:.*]]: memref<?xf32>,
+// ALIGNED-ALLOC-SAME:    %[[arg1:.*]]: index) -> memref<?xf32> {
+func.func @realloc_dynamic_alignment(%in: memref<?xf32>, %d: index) -> memref<?xf32>{
+// CHECK:           %[[descriptor:.*]] = builtin.unrealized_conversion_cast %[[arg0]]
+// CHECK:           %[[drc_dim:.*]] = llvm.extractvalue %[[descriptor]][3, 0]
+// CHECK:           %[[dst_dim:.*]] = builtin.unrealized_conversion_cast %[[arg1]] : index to i64
+// CHECK:           %[[cond:.*]] = llvm.icmp "ugt" %[[dst_dim]], %[[drc_dim]] : i64
+// CHECK:           llvm.cond_br %[[cond]], ^bb1, ^bb2(%[[descriptor]]
+// CHECK:           ^bb1:
+// CHECK:           %[[dst_null:.*]] = llvm.mlir.null : !llvm.ptr<f32>
+// CHECK:           %[[dst_gep:.*]] = llvm.getelementptr %[[dst_null]][1]
+// CHECK:           %[[dst_es:.*]] = llvm.ptrtoint %[[dst_gep]] : !llvm.ptr<f32> to i64
+// CHECK:           %[[dst_size:.*]] = llvm.mul %[[dst_dim]], %[[dst_es]]
+// CHECK:           %[[alignment:.*]] = llvm.mlir.constant(8 : index) : i64
+// CHECK:           %[[adjust_dst_size:.*]] = llvm.add %[[dst_size]], %[[alignment]]
+// CHECK:           %[[new_buffer_raw:.*]] = llvm.call @malloc(%[[adjust_dst_size]])
+// CHECK:           %[[new_buffer_unaligned:.*]] = llvm.bitcast %[[new_buffer_raw]] : !llvm.ptr<i8> to !llvm.ptr<f32>
+// CHECK:           %[[new_buffer_int:.*]] = llvm.ptrtoint %[[new_buffer_unaligned]] : !llvm.ptr<f32>
+// CHECK:           %[[const_1:.*]] = llvm.mlir.constant(1 : index) : i64
+// CHECK:           %[[alignment_m1:.*]] = llvm.sub %[[alignment]], %[[const_1]]
+// CHECK:           %[[ptr_alignment_m1:.*]] = llvm.add %[[new_buffer_int]], %[[alignment_m1]]
+// CHECK:           %[[padding:.*]] = llvm.urem %[[ptr_alignment_m1]], %[[alignment]]
+// CHECK:           %[[new_buffer_aligned_int:.*]] = llvm.sub %[[ptr_alignment_m1]], %[[padding]]
+// CHECK:           %[[new_buffer_aligned:.*]] = llvm.inttoptr %[[new_buffer_aligned_int]] : i64 to !llvm.ptr<f32>
+// CHECK:           %[[old_buffer_aligned:.*]] = llvm.extractvalue %[[descriptor]][1]
+// CHECK:           %[[volatile:.*]] = llvm.mlir.constant(false) : i1
+// CHECK-DAG:       %[[new_buffer_void:.*]] = llvm.bitcast %[[new_buffer_aligned]] : !llvm.ptr<f32> to !llvm.ptr<i8>
+// CHECK-DAG:       %[[old_buffer_void:.*]] = llvm.bitcast %[[old_buffer_aligned]] : !llvm.ptr<f32> to !llvm.ptr<i8>
+// CHECK:           "llvm.intr.memcpy"(%[[new_buffer_void]], %[[old_buffer_void]], %[[dst_size]], %[[volatile]])
+// CHECK:           %[[old_buffer_unaligned:.*]] = llvm.extractvalue %[[descriptor]][0]
+// CHECK:           %[[old_buffer_unaligned_void:.*]] = llvm.bitcast %[[old_buffer_unaligned]] : !llvm.ptr<f32> to !llvm.ptr<i8>
+// CHECK:           llvm.call @free(%[[old_buffer_unaligned_void]])
+// CHECK:           %[[descriptor_update1:.*]] = llvm.insertvalue %[[new_buffer_unaligned]], %[[descriptor]][0]
+// CHECK:           %[[descriptor_update2:.*]] = llvm.insertvalue %[[new_buffer_aligned]], %[[descriptor_update1]][1]
+// CHECK:           llvm.br ^bb2(%[[descriptor_update2]]
+// CHECK:           ^bb2(%[[descriptor_update3:.*]]: !llvm.struct<(ptr<f32>, ptr<f32>, i64, array<1 x i64>, array<1 x i64>)>):
+// CHECK:           %[[descriptor_update4:.*]] = llvm.insertvalue %[[dst_dim]], %[[descriptor_update3]][3, 0]
+// CHECK:           %[[descriptor_update5:.*]] = builtin.unrealized_conversion_cast %[[descriptor_update4]]
+// CHECK:           return %[[descriptor_update5]] : memref<?xf32>
+
+// ALIGNED-ALLOC:           %[[descriptor:.*]] = builtin.unrealized_conversion_cast %[[arg0]]
+// ALIGNED-ALLOC:           %[[drc_dim:.*]] = llvm.extractvalue %[[descriptor]][3, 0]
+// ALIGNED-ALLOC:           %[[dst_dim:.*]] = builtin.unrealized_conversion_cast %[[arg1]] : index to i64
+// ALIGNED-ALLOC:           %[[cond:.*]] = llvm.icmp "ugt" %[[dst_dim]], %[[drc_dim]] : i64
+// ALIGNED-ALLOC:           llvm.cond_br %[[cond]], ^bb1, ^bb2(%[[descriptor]]
+// ALIGNED-ALLOC:           ^bb1:
+// ALIGNED-ALLOC:           %[[dst_null:.*]] = llvm.mlir.null : !llvm.ptr<f32>
+// ALIGNED-ALLOC:           %[[dst_gep:.*]] = llvm.getelementptr %[[dst_null]][1]
+// ALIGNED-ALLOC:           %[[dst_es:.*]] = llvm.ptrtoint %[[dst_gep]] : !llvm.ptr<f32> to i64
+// ALIGNED-ALLOC:           %[[dst_size:.*]] = llvm.mul %[[dst_dim]], %[[dst_es]]
+// ALIGNED-ALLOC-DAG:       %[[alignment:.*]] = llvm.mlir.constant(8 : index) : i64
+// ALIGNED-ALLOC-DAG:       %[[const_1:.*]] = llvm.mlir.constant(1 : index) : i64
+// ALIGNED-ALLOC:           %[[alignment_m1:.*]] = llvm.sub %[[alignment]], %[[const_1]]
+// ALIGNED-ALLOC:           %[[size_alignment_m1:.*]] = llvm.add %[[dst_size]], %[[alignment_m1]]
+// ALIGNED-ALLOC:           %[[padding:.*]] = llvm.urem %[[size_alignment_m1]], %[[alignment]]
+// ALIGNED-ALLOC:           %[[adjust_dst_size:.*]] = llvm.sub %[[size_alignment_m1]], %[[padding]]
+// ALIGNED-ALLOC:           %[[new_buffer_raw:.*]] = llvm.call @aligned_alloc(%[[alignment]], %[[adjust_dst_size]])
+// ALIGNED-ALLOC:           %[[new_buffer_aligned:.*]] = llvm.bitcast %[[new_buffer_raw]] : !llvm.ptr<i8> to !llvm.ptr<f32>
+// ALIGNED-ALLOC:           %[[old_buffer_aligned:.*]] = llvm.extractvalue %[[descriptor]][1]
+// ALIGNED-ALLOC:           %[[volatile:.*]] = llvm.mlir.constant(false) : i1
+// ALIGNED-ALLOC-DAG:       %[[new_buffer_void:.*]] = llvm.bitcast %[[new_buffer_aligned]] : !llvm.ptr<f32> to !llvm.ptr<i8>
+// ALIGNED-ALLOC-DAG:       %[[old_buffer_void:.*]] = llvm.bitcast %[[old_buffer_aligned]] : !llvm.ptr<f32> to !llvm.ptr<i8>
+// ALIGNED-ALLOC:           "llvm.intr.memcpy"(%[[new_buffer_void]], %[[old_buffer_void]], %[[dst_size]], %[[volatile]])
+// ALIGNED-ALLOC:           %[[old_buffer_unaligned:.*]] = llvm.extractvalue %[[descriptor]][0]
+// ALIGNED-ALLOC:           %[[old_buffer_unaligned_void:.*]] = llvm.bitcast %[[old_buffer_unaligned]] : !llvm.ptr<f32> to !llvm.ptr<i8>
+// ALIGNED-ALLOC:           llvm.call @free(%[[old_buffer_unaligned_void]])
+// ALIGNED-ALLOC:           %[[descriptor_update1:.*]] = llvm.insertvalue %[[new_buffer_aligned]], %[[descriptor]][0]
+// ALIGNED-ALLOC:           %[[descriptor_update2:.*]] = llvm.insertvalue %[[new_buffer_aligned]], %[[descriptor_update1]][1]
+// ALIGNED-ALLOC:           llvm.br ^bb2(%[[descriptor_update2]] : !llvm.struct<(ptr<f32>, ptr<f32>, i64, array<1 x i64>, array<1 x i64>)>)
+// ALIGNED-ALLOC:           ^bb2(%[[descriptor_update3:.*]]: !llvm.struct<(ptr<f32>, ptr<f32>, i64, array<1 x i64>, array<1 x i64>)>):
+// ALIGNED-ALLOC:           %[[descriptor_update4:.*]] = llvm.insertvalue %[[dst_dim]], %[[descriptor_update3]][3, 0]
+// ALIGNED-ALLOC:           %[[descriptor_update5:.*]] = builtin.unrealized_conversion_cast %[[descriptor_update4]]
+// ALIGNED-ALLOC:           return %[[descriptor_update5]] : memref<?xf32>
+
+  %out = memref.realloc %in(%d)  {alignment = 8} : memref<?xf32> to memref<?xf32>
+  return %out : memref<?xf32>
+}
+

mlir/test/Conversion/MemRefToLLVM/convert-static-memref-ops.mlir

func.func @memref.reshape_index(%arg0: memref<?x?xi32>, %shape: memref<1xindex>) ->  memref<?xi32> {
   // CHECK: %[[insert4:.*]] = llvm.insertvalue %[[one0:.*]], %[[insert3:.*]][4, 0] : !llvm.struct<(ptr<i32>, ptr<i32>, i64, array<1 x i64>, array<1 x i64>)>
 
   // CHECK: %[[result_cast:.*]] = builtin.unrealized_conversion_cast %[[insert4:.*]] : !llvm.struct<(ptr<i32>, ptr<i32>, i64, array<1 x i64>, array<1 x i64>)> to memref<?xi32>
   // CHECK: return %[[result_cast:.*]] : memref<?xi32>
 
   %1 = memref.reshape %arg0(%shape) : (memref<?x?xi32>, memref<1xindex>) -> memref<?xi32>
   return %1 : memref<?xi32>
 }
+
+// -----
+
+// CHECK-LABEL:     func.func @realloc_static(
+// CHECK-SAME:      %[[arg0:.*]]: memref<2xi32>) -> memref<4xi32> {
+func.func @realloc_static(%in: memref<2xi32>) -> memref<4xi32>{
+// CHECK:           %[[descriptor:.*]] = builtin.unrealized_conversion_cast %[[arg0]] : memref<2xi32> to !llvm.struct<(ptr<i32>, ptr<i32>, i64, array<1 x i64>, array<1 x i64>)>
+// CHECK:           %[[src_dim:.*]] = llvm.mlir.constant(2 : index) : i64
+// CHECK:           %[[dst_dim:.*]] = llvm.mlir.constant(4 : index) : i64
+// CHECK:           %[[cond:.*]] = llvm.icmp "ugt" %[[dst_dim]], %[[src_dim]]
+// CHECK:           llvm.cond_br %[[cond]], ^bb1, ^bb2(%[[descriptor]]
+// CHECK:           ^bb1:
+// CHECK:           %[[dst_null:.*]] = llvm.mlir.null : !llvm.ptr<i32>
+// CHECK:           %[[dst_gep:.*]] = llvm.getelementptr %[[dst_null]][1]
+// CHECK:           %[[dst_es:.*]] = llvm.ptrtoint %[[dst_gep]] : !llvm.ptr<i32> to i64
+// CHECK:           %[[dst_size:.*]] = llvm.mul %[[dst_dim]], %[[dst_es]]
+// CHECK:           %[[new_buffer_raw:.*]] = llvm.call @malloc(%[[dst_size]])
+// CHECK:           %[[new_buffer:.*]] = llvm.bitcast %[[new_buffer_raw]] : !llvm.ptr<i8> to !llvm.ptr<i32>
+// CHECK:           %[[old_buffer_aligned:.*]] = llvm.extractvalue %[[descriptor]][1]
+// CHECK:           %[[volatile:.*]] = llvm.mlir.constant(false) : i1
+// CHECK-DAG:       %[[new_buffer_void:.*]] = llvm.bitcast %[[new_buffer]] : !llvm.ptr<i32> to !llvm.ptr<i8>
+// CHECK-DAG:       %[[old_buffer_void:.*]] = llvm.bitcast %[[old_buffer_aligned]] : !llvm.ptr<i32> to !llvm.ptr<i8>
+// CHECK:           "llvm.intr.memcpy"(%[[new_buffer_void]], %[[old_buffer_void]], %[[dst_size]], %[[volatile]])
+// CHECK:           %[[old_buffer_unaligned:.*]] = llvm.extractvalue %[[descriptor]][0]
+// CHECK:           %[[old_buffer_unaligned_void:.*]] = llvm.bitcast %[[old_buffer_unaligned]] : !llvm.ptr<i32> to !llvm.ptr<i8>
+// CHECK:           llvm.call @free(%[[old_buffer_unaligned_void]])
+// CHECK:           %[[descriptor_update1:.*]] = llvm.insertvalue %[[new_buffer]], %[[descriptor]][0]
+// CHECK:           %[[descriptor_update2:.*]] = llvm.insertvalue %[[new_buffer]], %[[descriptor_update1]][1]
+// CHECK:           llvm.br ^bb2(%[[descriptor_update2]] : !llvm.struct<(ptr<i32>, ptr<i32>, i64, array<1 x i64>, array<1 x i64>)>)
+// CHECK:           ^bb2(%[[descriptor_update3:.*]]: !llvm.struct<(ptr<i32>, ptr<i32>, i64, array<1 x i64>, array<1 x i64>)>):
+// CHECK:           %[[descriptor_update4:.*]] = llvm.insertvalue %[[dst_dim]], %[[descriptor_update3]][3, 0]
+// CHECK:           %[[descriptor_update5:.*]] = builtin.unrealized_conversion_cast %[[descriptor_update4]]
+// CHECK:           return %[[descriptor_update5]] : memref<4xi32>
+
+  %out = memref.realloc %in : memref<2xi32> to memref<4xi32>
+  return %out : memref<4xi32>
+}
+
+// -----
+
+// CHECK-LABEL:     func.func @realloc_static_alignment(
+// CHECK-SAME:      %[[arg0:.*]]: memref<2xf32>) -> memref<4xf32> {
+func.func @realloc_static_alignment(%in: memref<2xf32>) -> memref<4xf32>{
+// CHECK:           %[[descriptor:.*]] = builtin.unrealized_conversion_cast %[[arg0]] : memref<2xf32> to !llvm.struct<(ptr<f32>, ptr<f32>, i64, array<1 x i64>, array<1 x i64>)>
+// CHECK:           %[[src_dim:.*]] = llvm.mlir.constant(2 : index) : i64
+// CHECK:           %[[dst_dim:.*]] = llvm.mlir.constant(4 : index) : i64
+// CHECK:           %[[cond:.*]] = llvm.icmp "ugt" %[[dst_dim]], %[[src_dim]] : i64
+// CHECK:           llvm.cond_br %[[cond]], ^bb1, ^bb2(%[[descriptor]]
+// CHECK:           ^bb1:
+// CHECK:           %[[dst_null:.*]] = llvm.mlir.null : !llvm.ptr<f32>
+// CHECK:           %[[dst_gep:.*]] = llvm.getelementptr %[[dst_null]][1]
+// CHECK:           %[[dst_es:.*]] = llvm.ptrtoint %[[dst_gep]] : !llvm.ptr<f32> to i64
+// CHECK:           %[[dst_size:.*]] = llvm.mul %[[dst_dim]], %[[dst_es]]
+// CHECK:           %[[alignment:.*]] = llvm.mlir.constant(8 : index) : i64
+// CHECK:           %[[adjust_dst_size:.*]] = llvm.add %[[dst_size]], %[[alignment]]
+// CHECK:           %[[new_buffer_raw:.*]] = llvm.call @malloc(%[[adjust_dst_size]])
+// CHECK:           %[[new_buffer_unaligned:.*]] = llvm.bitcast %[[new_buffer_raw]] : !llvm.ptr<i8> to !llvm.ptr<f32>
+// CHECK:           %[[new_buffer_int:.*]] = llvm.ptrtoint %[[new_buffer_unaligned]] : !llvm.ptr<f32>
+// CHECK:           %[[const_1:.*]] = llvm.mlir.constant(1 : index) : i64
+// CHECK:           %[[alignment_m1:.*]] = llvm.sub %[[alignment]], %[[const_1]]
+// CHECK:           %[[ptr_alignment_m1:.*]] = llvm.add %[[new_buffer_int]], %[[alignment_m1]]
+// CHECK:           %[[padding:.*]] = llvm.urem %[[ptr_alignment_m1]], %[[alignment]]
+// CHECK:           %[[new_buffer_aligned_int:.*]] = llvm.sub %[[ptr_alignment_m1]], %[[padding]]
+// CHECK:           %[[new_buffer_aligned:.*]] = llvm.inttoptr %[[new_buffer_aligned_int]] : i64 to !llvm.ptr<f32>
+// CHECK:           %[[old_buffer_aligned:.*]] = llvm.extractvalue %[[descriptor]][1]
+// CHECK:           %[[volatile:.*]] = llvm.mlir.constant(false) : i1
+// CHECK-DAG:       %[[new_buffer_void:.*]] = llvm.bitcast %[[new_buffer_aligned]] : !llvm.ptr<f32> to !llvm.ptr<i8>
+// CHECK-DAG:       %[[old_buffer_void:.*]] = llvm.bitcast %[[old_buffer_aligned]] : !llvm.ptr<f32> to !llvm.ptr<i8>
+// CHECK:           "llvm.intr.memcpy"(%[[new_buffer_void]], %[[old_buffer_void]], %[[dst_size]], %[[volatile]])
+// CHECK:           %[[old_buffer_unaligned:.*]] = llvm.extractvalue %[[descriptor]][0]
+// CHECK:           %[[old_buffer_unaligned_void:.*]] = llvm.bitcast %[[old_buffer_unaligned]] : !llvm.ptr<f32> to !llvm.ptr<i8>
+// CHECK:           llvm.call @free(%[[old_buffer_unaligned_void]])
+// CHECK:           %[[descriptor_update1:.*]] = llvm.insertvalue %[[new_buffer_unaligned]], %[[descriptor]][0]
+// CHECK:           %[[descriptor_update2:.*]] = llvm.insertvalue %[[new_buffer_aligned]], %[[descriptor_update1]][1]
+// CHECK:           llvm.br ^bb2(%[[descriptor_update2]]
+// CHECK:           ^bb2(%[[descriptor_update3:.*]]: !llvm.struct<(ptr<f32>, ptr<f32>, i64, array<1 x i64>, array<1 x i64>)>):
+// CHECK:           %[[descriptor_update4:.*]] = llvm.insertvalue %[[dst_dim]], %[[descriptor_update3]][3, 0]
+// CHECK:           %[[descriptor_update5:.*]] = builtin.unrealized_conversion_cast %[[descriptor_update4]]
+// CHECK:           return %[[descriptor_update5]] : memref<4xf32>
+
+
+  %out = memref.realloc %in {alignment = 8} : memref<2xf32> to memref<4xf32>
+  return %out : memref<4xf32>
+}

mlir/test/Dialect/MemRef/canonicalize.mlir

func.func @canonicalize_rank_reduced_subview(%arg0 : memref<8x?xf32>,
   %0 = memref.subview %arg0[%c0, %c0] [1, %arg1] [%c1, %c1] : memref<8x?xf32> to memref<?xf32, strided<[?], offset: ?>>
   return %0 :  memref<?xf32, strided<[?], offset: ?>>
 }
 //      CHECK: func @canonicalize_rank_reduced_subview
 // CHECK-SAME:     %[[ARG0:.+]]: memref<8x?xf32>
 // CHECK-SAME:     %[[ARG1:.+]]: index
 //      CHECK:   %[[SUBVIEW:.+]] = memref.subview %[[ARG0]][0, 0] [1, %[[ARG1]]] [1, 1]
 // CHECK-SAME:       memref<8x?xf32> to memref<?xf32, strided<[1], offset: ?>>
+
+// ----
+
+// CHECK-LABEL: func @memref_realloc_dead
+// CHECK-SAME: %[[SRC:[0-9a-z]+]]: memref<2xf32>
+// CHECK-NOT: memref.realloc
+// CHECK: return %[[SRC]]
+func.func @memref_realloc_dead(%src : memref<2xf32>, %v : f32) -> memref<2xf32>{
+  %0 = memref.realloc %src : memref<2xf32> to memref<4xf32>
+  %i2 = arith.constant 2 : index
+  memref.store %v, %0[%i2] : memref<4xf32>
+  return %src : memref<2xf32>
+}

mlir/test/Dialect/MemRef/invalid.mlir

func.func @atomic_yield_type_mismatch(%I: memref<10xf32>, %i : index) {
   // expected-error@+4 {{op types mismatch between yield op: 'i32' and its parent: 'f32'}}
   %x = memref.generic_atomic_rmw %I[%i] : memref<10xf32> {
     ^bb0(%old_value : f32):
       %c1 = arith.constant 1 : i32
       memref.atomic_yield %c1 : i32
   }
   return
 }
+
+// -----
+
+#map0 = affine_map<(d0) -> (d0 floordiv 8, d0 mod 8)>
+func.func @memref_realloc_layout(%src : memref<256xf32, #map0>) -> memref<?xf32>{
+  // expected-error@+1 {{unsupported layout}}
+  %0 = memref.realloc %src : memref<256xf32, #map0> to memref<?xf32>
+  return %0 : memref<?xf32>
+}
+
+// -----
+
+func.func @memref_realloc_sizes_1(%src : memref<2xf32>) -> memref<?xf32>{
+  // expected-error@+1 {{missing dimension operand}}
+  %0 = memref.realloc %src : memref<2xf32> to memref<?xf32>
+  return %0 : memref<?xf32>
+}
+
+// -----
+
+func.func @memref_realloc_sizes_2(%src : memref<?xf32>, %d : index)
+  -> memref<4xf32>{
+  // expected-error@+1 {{unnecessary dimension operand}}
+  %0 = memref.realloc %src(%d) : memref<?xf32> to memref<4xf32>
+  return %0 : memref<4xf32>
+}
+
+// -----
+
+func.func @memref_realloc_type(%src : memref<256xf32>) -> memref<?xi32>{
+  // expected-error@+1 {{different element types}}
+  %0 = memref.realloc %src : memref<256xf32> to memref<?xi32>
+  return %0 : memref<?xi32>
+}

mlir/test/Dialect/MemRef/ops.mlir

func.func @extract_strided_metadata(%memref : memref<10x?xf32>)
   %m2 = memref.reinterpret_cast %base to
       offset: [%offset],
       sizes: [%sizes#0, %sizes#1],
       strides: [%strides#0, %strides#1]
     : memref<f32> to memref<?x?xf32, strided<[?, ?], offset: ?>>
 
   return %m2: memref<?x?xf32, strided<[?, ?], offset: ?>>
 }
+
+// -----
+
+// CHECK-LABEL: func @memref_realloc_ss
+func.func @memref_realloc_ss(%src : memref<2xf32>) -> memref<4xf32>{
+  %0 = memref.realloc %src : memref<2xf32> to memref<4xf32>
+  return %0 : memref<4xf32>
+}
+
+// CHECK-LABEL: func @memref_realloc_sd
+func.func @memref_realloc_sd(%src : memref<2xf32>, %d : index) -> memref<?xf32>{
+  %0 = memref.realloc %src(%d) : memref<2xf32> to memref<?xf32>
+  return %0 : memref<?xf32>
+}
+
+// CHECK-LABEL: func @memref_realloc_ds
+func.func @memref_realloc_ds(%src : memref<?xf32>) -> memref<4xf32>{
+  %0 = memref.realloc %src: memref<?xf32> to memref<4xf32>
+  return %0 : memref<4xf32>
+}
+
+// CHECK-LABEL: func @memref_realloc_dd
+func.func @memref_realloc_dd(%src : memref<?xf32>, %d: index)
+  -> memref<?xf32>{
+  %0 = memref.realloc %src(%d) : memref<?xf32> to memref<?xf32>
+  return %0 : memref<?xf32>
+}

mlir/test/Integration/Dialect/Vector/CPU/test-realloc.mlir

+// RUN: mlir-opt %s -convert-scf-to-cf -convert-vector-to-llvm -convert-memref-to-llvm -convert-func-to-llvm -reconcile-unrealized-casts |\
+// RUN: mlir-cpu-runner -e entry -entry-point-result=void \
+// RUN:   -shared-libs=%mlir_lib_dir/libmlir_c_runner_utils%shlibext
+// RUN: mlir-opt %s -convert-scf-to-cf -convert-vector-to-llvm -convert-memref-to-llvm='use-aligned-alloc=1' -convert-func-to-llvm -arith-expand -reconcile-unrealized-casts |\
+// RUN: mlir-cpu-runner -e entry -entry-point-result=void \
+// RUN:   -shared-libs=%mlir_lib_dir/libmlir_c_runner_utils%shlibext | FileCheck %s
+
+func.func @entry() {
+  // Set up memory.
+  %c0 = arith.constant 0: index
+  %c1 = arith.constant 1: index
+  %c8 = arith.constant 8: index
+  %A = memref.alloc() : memref<8xf32>
+  scf.for %i = %c0 to %c8 step %c1 {
+    %i32 = arith.index_cast %i : index to i32
+    %fi = arith.sitofp %i32 : i32 to f32
+    memref.store %fi, %A[%i] : memref<8xf32>
+  }
+
+  %d0 = arith.constant -1.0 : f32
+  %Av = vector.transfer_read %A[%c0], %d0: memref<8xf32>, vector<8xf32>
+  vector.print %Av : vector<8xf32>
+  // CHECK: ( 0, 1, 2, 3, 4, 5, 6, 7 )
+
+  // Realloc with static sizes.
+  %B = memref.realloc %A : memref<8xf32> to memref<10xf32>
+
+  %c10 = arith.constant 10: index
+  scf.for %i = %c8 to %c10 step %c1 {
+    %i32 = arith.index_cast %i : index to i32
+    %fi = arith.sitofp %i32 : i32 to f32
+    memref.store %fi, %B[%i] : memref<10xf32>
+  }
+
+  %Bv = vector.transfer_read %B[%c0], %d0: memref<10xf32>, vector<10xf32>
+  vector.print %Bv : vector<10xf32>
+  // CHECK: ( 0, 1, 2, 3, 4, 5, 6, 7, 8, 9 )
+
+  // Realloc with dynamic sizes.
+  %Bd = memref.cast %B : memref<10xf32> to memref<?xf32>
+  %c13 = arith.constant 13: index
+  %Cd = memref.realloc %Bd(%c13) : memref<?xf32> to memref<?xf32>
+  %C = memref.cast %Cd : memref<?xf32> to memref<13xf32>
+
+  scf.for %i = %c10 to %c13 step %c1 {
+    %i32 = arith.index_cast %i : index to i32
+    %fi = arith.sitofp %i32 : i32 to f32
+    memref.store %fi, %C[%i] : memref<13xf32>
+  }
+
+  %Cv = vector.transfer_read %C[%c0], %d0: memref<13xf32>, vector<13xf32>
+  vector.print %Cv : vector<13xf32>
+  // CHECK: ( 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12 )
+
+  memref.dealloc %C : memref<13xf32>
+  return
+}