[mlir][memref] Introduce memref.distinct_objects op

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

@@ -153,7 +153,7 @@ def AssumeAlignmentOp : MemRef_Op<"assume_alignment", [
       The `assume_alignment` operation takes a memref and an integer alignment
       value. It returns a new SSA value of the same memref type, but associated
       with the assumption that the underlying buffer is aligned to the given
-      alignment. 
+      alignment.
 
       If the buffer isn't aligned to the given alignment, its result is poison.
       This operation doesn't affect the semantics of a program where the
@@ -168,14 +168,49 @@ def AssumeAlignmentOp : MemRef_Op<"assume_alignment", [
   let assemblyFormat = "$memref `,` $alignment attr-dict `:` type($memref)";
   let extraClassDeclaration = [{
     MemRefType getType() { return ::llvm::cast<MemRefType>(getResult().getType()); }
-    
+
     Value getViewSource() { return getMemref(); }
   }];
 
   let hasVerifier = 1;
   let hasFolder = 1;
 }
 
+//===----------------------------------------------------------------------===//
+// DistinctObjectsOp
+//===----------------------------------------------------------------------===//
+
+def DistinctObjectsOp : MemRef_Op<"distinct_objects", [
+      Pure,
+      DeclareOpInterfaceMethods<InferTypeOpInterface>
+      // ViewLikeOpInterface TODO: ViewLikeOpInterface only supports a single argument
+    ]> {
+  let summary = "assumption that acesses to specific memrefs will never alias";
+  let description = [{
+      The `distinct_objects` operation takes a list of memrefs and returns the same
+      memrefs, with the additional assumption that accesses to them will never
+      alias with each other. This means that loads and stores to different
+      memrefs in the list can be safely reordered.
+
+      If the memrefs do alias, the load/store behavior is undefined. This
+      operation doesn't affect the semantics of a valid program. It is
+      intended for optimization purposes, allowing the compiler to generate more
+      efficient code based on the non-aliasing assumption. The optimization is
+      best-effort.
+
+      Example:
+
+      ```mlir
+      %1, %2 = memref.distinct_objects %a, %b : memref<?xf32>, memref<?xf32>
+      ```
+  }];
+  let arguments = (ins Variadic<AnyMemRef>:$operands);
+  let results = (outs Variadic<AnyMemRef>:$results);
+
+  let assemblyFormat = "$operands attr-dict `:` type($operands)";
+  let hasVerifier = 1;
+}
+
 //===----------------------------------------------------------------------===//
 // AllocOp
 //===----------------------------------------------------------------------===//

mlir/lib/Conversion/MemRefToLLVM/MemRefToLLVM.cpp

@@ -465,6 +465,50 @@ struct AssumeAlignmentOpLowering
   }
 };
 
+struct DistinctObjectsOpLowering
+    : public ConvertOpToLLVMPattern<memref::DistinctObjectsOp> {
+  using ConvertOpToLLVMPattern<
+      memref::DistinctObjectsOp>::ConvertOpToLLVMPattern;
+  explicit DistinctObjectsOpLowering(const LLVMTypeConverter &converter)
+      : ConvertOpToLLVMPattern<memref::DistinctObjectsOp>(converter) {}
+
+  LogicalResult
+  matchAndRewrite(memref::DistinctObjectsOp op, OpAdaptor adaptor,
+                  ConversionPatternRewriter &rewriter) const override {
+    ValueRange operands = adaptor.getOperands();
+    if (operands.size() <= 1) {
+      // Fast path.
+      rewriter.replaceOp(op, operands);
+      return success();
+    }
+
+    Location loc = op.getLoc();
+    SmallVector<Value> ptrs;
+    for (auto [origOperand, newOperand] :
+         llvm::zip_equal(op.getOperands(), operands)) {
+      auto memrefType = cast<MemRefType>(origOperand.getType());
+      Value ptr = getStridedElementPtr(rewriter, loc, memrefType, newOperand,
+                                       /*indices=*/{});
+      ptrs.push_back(ptr);
+    }
+
+    auto cond =
+        LLVM::ConstantOp::create(rewriter, loc, rewriter.getI1Type(), 1);
+    // Generate separate_storage assumptions for each pair of pointers.
+    for (auto i : llvm::seq<size_t>(ptrs.size() - 1)) {
+      for (auto j : llvm::seq<size_t>(i + 1, ptrs.size())) {
+        Value ptr1 = ptrs[i];
+        Value ptr2 = ptrs[j];
+        LLVM::AssumeOp::create(rewriter, loc, cond,
+                               LLVM::AssumeSeparateStorageTag{}, ptr1, ptr2);
+      }
+    }
+
+    rewriter.replaceOp(op, operands);
+    return success();
+  }
+};
+
 // A `dealloc` is converted into a call to `free` on the underlying data buffer.
 // The memref descriptor being an SSA value, there is no need to clean it up
 // in any way.
@@ -1997,22 +2041,23 @@ void mlir::populateFinalizeMemRefToLLVMConversionPatterns(
   patterns.add<
       AllocaOpLowering,
       AllocaScopeOpLowering,
-      AtomicRMWOpLowering,
       AssumeAlignmentOpLowering,
+      AtomicRMWOpLowering,
       ConvertExtractAlignedPointerAsIndex,
       DimOpLowering,
+      DistinctObjectsOpLowering,
       ExtractStridedMetadataOpLowering,
       GenericAtomicRMWOpLowering,
       GetGlobalMemrefOpLowering,
       LoadOpLowering,
       MemRefCastOpLowering,
-      MemorySpaceCastOpLowering,
       MemRefReinterpretCastOpLowering,
       MemRefReshapeOpLowering,
+      MemorySpaceCastOpLowering,
       PrefetchOpLowering,
       RankOpLowering,
-      ReassociatingReshapeOpConversion<memref::ExpandShapeOp>,
       ReassociatingReshapeOpConversion<memref::CollapseShapeOp>,
+      ReassociatingReshapeOpConversion<memref::ExpandShapeOp>,
       StoreOpLowering,
       SubViewOpLowering,
       TransposeOpLowering,

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

@@ -542,6 +542,29 @@ OpFoldResult AssumeAlignmentOp::fold(FoldAdaptor adaptor) {
   return getMemref();
 }
 
+//===----------------------------------------------------------------------===//
+// DistinctObjectsOp
+//===----------------------------------------------------------------------===//
+
+LogicalResult DistinctObjectsOp::verify() {
+  if (getOperandTypes() != getResultTypes())
+    return emitOpError("operand types and result types must match");
+
+  if (getOperandTypes().empty())
+    return emitOpError("expected at least one operand");
+
+  return success();
+}
+
+LogicalResult DistinctObjectsOp::inferReturnTypes(
+    MLIRContext * /*context*/, std::optional<Location> /*location*/,
+    ValueRange operands, DictionaryAttr /*attributes*/,
+    OpaqueProperties /*properties*/, RegionRange /*regions*/,
+    SmallVectorImpl<Type> &inferredReturnTypes) {
+  llvm::copy(operands.getTypes(), std::back_inserter(inferredReturnTypes));
+  return success();
+}
+
 //===----------------------------------------------------------------------===//
 // CastOp
 //===----------------------------------------------------------------------===//

mlir/test/Conversion/MemRefToLLVM/memref-to-llvm.mlir

@@ -195,6 +195,36 @@ func.func @assume_alignment(%0 : memref<4x4xf16>) {
 
 // -----
 
+// ALL-LABEL: func @distinct_objects
+//  ALL-SAME:   (%[[ARG0:.*]]: memref<?xf16>, %[[ARG1:.*]]: memref<?xf32>, %[[ARG2:.*]]: memref<?xf64>)
+func.func @distinct_objects(%arg0: memref<?xf16>, %arg1: memref<?xf32>, %arg2: memref<?xf64>) -> (memref<?xf16>, memref<?xf32>, memref<?xf64>) {
+//   ALL-DAG:   %[[CAST_0:.*]] = builtin.unrealized_conversion_cast %[[ARG0]] : memref<?xf16> to !llvm.struct<(ptr, ptr, i64, array<1 x i64>, array<1 x i64>)>
+//   ALL-DAG:   %[[CAST_1:.*]] = builtin.unrealized_conversion_cast %[[ARG1]] : memref<?xf32> to !llvm.struct<(ptr, ptr, i64, array<1 x i64>, array<1 x i64>)>
+//   ALL-DAG:   %[[CAST_2:.*]] = builtin.unrealized_conversion_cast %[[ARG2]] : memref<?xf64> to !llvm.struct<(ptr, ptr, i64, array<1 x i64>, array<1 x i64>)>
+//       ALL:   %[[PTR_0:.*]] = llvm.extractvalue %[[CAST_0]][1] : !llvm.struct<(ptr, ptr, i64, array<1 x i64>, array<1 x i64>)>
+//       ALL:   %[[PTR_1:.*]] = llvm.extractvalue %[[CAST_1]][1] : !llvm.struct<(ptr, ptr, i64, array<1 x i64>, array<1 x i64>)>
+//       ALL:   %[[PTR_2:.*]] = llvm.extractvalue %[[CAST_2]][1] : !llvm.struct<(ptr, ptr, i64, array<1 x i64>, array<1 x i64>)>
+//       ALL:   %[[TRUE:.*]] = llvm.mlir.constant(true) : i1
+//       ALL:   llvm.intr.assume %[[TRUE]] ["separate_storage"(%[[PTR_0]], %[[PTR_1]] : !llvm.ptr, !llvm.ptr)] : i1
+//       ALL:   llvm.intr.assume %[[TRUE]] ["separate_storage"(%[[PTR_0]], %[[PTR_2]] : !llvm.ptr, !llvm.ptr)] : i1
+//       ALL:   llvm.intr.assume %[[TRUE]] ["separate_storage"(%[[PTR_1]], %[[PTR_2]] : !llvm.ptr, !llvm.ptr)] : i1
+  %1, %2, %3 = memref.distinct_objects %arg0, %arg1, %arg2 : memref<?xf16>, memref<?xf32>, memref<?xf64>
+  return %1, %2, %3 : memref<?xf16>, memref<?xf32>, memref<?xf64>
+}
+
+// -----
+
+// ALL-LABEL: func @distinct_objects_noop
+//  ALL-SAME:   (%[[ARG0:.*]]: memref<?xf16>)
+func.func @distinct_objects_noop(%arg0: memref<?xf16>) -> memref<?xf16> {
+// 1-operand version is noop
+//  ALL-NEXT:   return %[[ARG0]]
+  %1 = memref.distinct_objects %arg0 : memref<?xf16>
+  return %1 : memref<?xf16>
+}
+
+// -----
+
 // CHECK-LABEL: func @assume_alignment_w_offset
 // CHECK-INTERFACE-LABEL: func @assume_alignment_w_offset
 func.func @assume_alignment_w_offset(%0 : memref<4x4xf16, strided<[?, ?], offset: ?>>) {

mlir/test/Dialect/MemRef/invalid.mlir

@@ -1169,3 +1169,19 @@ func.func @expand_shape_invalid_output_shape(
       into memref<2x15x20xf32, strided<[60000, 4000, 2], offset: 100>>
   return
 }
+
+// -----
+
+func.func @distinct_objects_types_mismatch(%arg0: memref<?xf32>, %arg1: memref<?xi32>) -> (memref<?xi32>, memref<?xf32>) {
+  // expected-error @+1 {{operand types and result types must match}}
+  %0, %1 = "memref.distinct_objects"(%arg0, %arg1) : (memref<?xf32>, memref<?xi32>) -> (memref<?xi32>, memref<?xf32>)
+  return %0, %1 : memref<?xi32>, memref<?xf32>
+}
+
+// -----
+
+func.func @distinct_objects_0_operands() {
+  // expected-error @+1 {{expected at least one operand}}
+  "memref.distinct_objects"() : () -> ()
+  return
+}

mlir/test/Dialect/MemRef/ops.mlir

@@ -302,6 +302,15 @@ func.func @assume_alignment(%0: memref<4x4xf16>) {
   return
 }
 
+// CHECK-LABEL: func @distinct_objects
+// CHECK-SAME: (%[[ARG0:.*]]: memref<?xf16>, %[[ARG1:.*]]: memref<?xf32>, %[[ARG2:.*]]: memref<?xf64>)
+func.func @distinct_objects(%arg0: memref<?xf16>, %arg1: memref<?xf32>, %arg2: memref<?xf64>) -> (memref<?xf16>, memref<?xf32>, memref<?xf64>) {
+  // CHECK:  %[[RES:.*]]:3 = memref.distinct_objects %[[ARG0]], %[[ARG1]], %[[ARG2]] : memref<?xf16>, memref<?xf32>, memref<?xf64>
+  %1, %2, %3 = memref.distinct_objects %arg0, %arg1, %arg2 : memref<?xf16>, memref<?xf32>, memref<?xf64>
+  // CHECK:  return %[[RES]]#0, %[[RES]]#1, %[[RES]]#2 : memref<?xf16>, memref<?xf32>, memref<?xf64>
+  return %1, %2, %3 : memref<?xf16>, memref<?xf32>, memref<?xf64>
+}
+
 // CHECK-LABEL: func @expand_collapse_shape_static
 func.func @expand_collapse_shape_static(
     %arg0: memref<3x4x5xf32>,