[mlir][linalg][bufferize] Support std.select bufferization

This op is an example for how to deal with ops who's OpResult may aliasing with one of multiple OpOperands.

Differential Revision: https://reviews.llvm.org/D116868

mlir/include/mlir/Dialect/Linalg/ComprehensiveBufferize/AffineInterfaceImpl.h

@@ -1,4 +1,4 @@
-//===- LinalgInterfaceImpl.h - Linalg Impl. of BufferizableOpInterface ----===//
+//===- AffineInterfaceImpl.h - Affine Impl. of BufferizableOpInterface ----===//
 //
 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
 // See https://llvm.org/LICENSE.txt for license information.

mlir/include/mlir/Dialect/Linalg/ComprehensiveBufferize/BufferizableOpInterface.h

@@ -346,18 +346,18 @@ class BufferizationState {
   /// In the above example, Values with a star satisfy the condition. When
   /// starting the traversal from Value 1, the resulting SetVector is:
   /// { 2, 7, 8, 5 }
-  llvm::SetVector<Value> findValueInReverseUseDefChain(
+  SetVector<Value> findValueInReverseUseDefChain(
       Value value, llvm::function_ref<bool(Value)> condition) const;
 
-  /// Find the Value of the last preceding write of a given Value.
+  /// Find the Values of the last preceding write of a given Value.
   ///
   /// Note: Unknown ops are handled conservatively and assumed to be writes.
   /// Furthermore, BlockArguments are also assumed to be writes. There is no
   /// analysis across block boundaries.
   ///
   /// Note: When reaching an end of the reverse SSA use-def chain, that value
   /// is returned regardless of whether it is a memory write or not.
-  Value findLastPrecedingWrite(Value value) const;
+  SetVector<Value> findLastPrecedingWrite(Value value) const;
 
   /// Creates a memref allocation.
   FailureOr<Value> createAlloc(OpBuilder &b, Location loc, MemRefType type,

mlir/include/mlir/Dialect/Linalg/ComprehensiveBufferize/ModuleBufferization.h

@@ -31,7 +31,7 @@ runComprehensiveBufferize(ModuleOp moduleOp,
 
 namespace std_ext {
 
-void registerBufferizableOpInterfaceExternalModels(DialectRegistry &registry);
+void registerModuleBufferizationExternalModels(DialectRegistry &registry);
 
 } // namespace std_ext
 } // namespace comprehensive_bufferize

mlir/include/mlir/Dialect/Linalg/ComprehensiveBufferize/StdInterfaceImpl.h

@@ -0,0 +1,27 @@
+//===- StdInterfaceImpl.h - Standard Impl. of BufferizableOpInterface- ----===//
+//
+// 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_DIALECT_LINALG_COMPREHENSIVEBUFFERIZE_STD_INTERFACE_IMPL_H
+#define MLIR_DIALECT_LINALG_COMPREHENSIVEBUFFERIZE_STD_INTERFACE_IMPL_H
+
+namespace mlir {
+
+class DialectRegistry;
+
+namespace linalg {
+namespace comprehensive_bufferize {
+namespace std_ext {
+
+void registerBufferizableOpInterfaceExternalModels(DialectRegistry &registry);
+
+} // namespace std_ext
+} // namespace comprehensive_bufferize
+} // namespace linalg
+} // namespace mlir
+
+#endif // MLIR_DIALECT_LINALG_COMPREHENSIVEBUFFERIZE_STD_INTERFACE_IMPL_H

mlir/lib/Dialect/Linalg/ComprehensiveBufferize/BufferizableOpInterface.cpp

@@ -305,26 +305,18 @@ llvm::SetVector<Value> mlir::linalg::comprehensive_bufferize::
   return result;
 }
 
-// Find the Value of the last preceding write of a given Value.
-Value mlir::linalg::comprehensive_bufferize::BufferizationState::
-    findLastPrecedingWrite(Value value) const {
-  SetVector<Value> result =
-      findValueInReverseUseDefChain(value, [&](Value value) {
-        Operation *op = value.getDefiningOp();
-        if (!op)
-          return true;
-        auto bufferizableOp = options.dynCastBufferizableOp(op);
-        if (!bufferizableOp)
-          return true;
-        return bufferizableOp.isMemoryWrite(value.cast<OpResult>(), *this);
-      });
-
-  // To simplify the analysis, `scf.if` ops are considered memory writes. There
-  // are currently no other ops where one OpResult may alias with multiple
-  // OpOperands. Therefore, this function should return exactly one result at
-  // the moment.
-  assert(result.size() == 1 && "expected exactly one result");
-  return result.front();
+// Find the Values of the last preceding write of a given Value.
+llvm::SetVector<Value> mlir::linalg::comprehensive_bufferize::
+    BufferizationState::findLastPrecedingWrite(Value value) const {
+  return findValueInReverseUseDefChain(value, [&](Value value) {
+    Operation *op = value.getDefiningOp();
+    if (!op)
+      return true;
+    auto bufferizableOp = options.dynCastBufferizableOp(op);
+    if (!bufferizableOp)
+      return true;
+    return bufferizableOp.isMemoryWrite(value.cast<OpResult>(), *this);
+  });
 }
 
 mlir::linalg::comprehensive_bufferize::BufferizationState::BufferizationState(
@@ -404,15 +396,19 @@ mlir::linalg::comprehensive_bufferize::BufferizationState::getBuffer(
       createAlloc(rewriter, loc, operandBuffer, options.createDeallocs);
   if (failed(resultBuffer))
     return failure();
-  // Do not copy if the last preceding write of `operand` is an op that does
+  // Do not copy if the last preceding writes of `operand` are ops that do
   // not write (skipping ops that merely create aliases). E.g., InitTensorOp.
   // Note: If `findLastPrecedingWrite` reaches the end of the reverse SSA
   // use-def chain, it returns that value, regardless of whether it is a
   // memory write or not.
-  Value lastWrite = findLastPrecedingWrite(operand);
-  if (auto bufferizableOp = options.dynCastBufferizableOp(lastWrite))
-    if (!bufferizableOp.isMemoryWrite(lastWrite.cast<OpResult>(), *this))
-      return resultBuffer;
+  SetVector<Value> lastWrites = findLastPrecedingWrite(operand);
+  if (llvm::none_of(lastWrites, [&](Value lastWrite) {
+        if (auto bufferizableOp = options.dynCastBufferizableOp(lastWrite))
+          return bufferizableOp.isMemoryWrite(lastWrite.cast<OpResult>(),
+                                              *this);
+        return true;
+      }))
+    return resultBuffer;
   // Do not copy if the copied data is never read.
   OpResult aliasingOpResult = getAliasingOpResult(opOperand);
   if (aliasingOpResult && !bufferizesToMemoryRead(opOperand) &&

mlir/lib/Dialect/Linalg/ComprehensiveBufferize/CMakeLists.txt

@@ -7,6 +7,7 @@ set(LLVM_OPTIONAL_SOURCES
   LinalgInterfaceImpl.cpp
   ModuleBufferization.cpp
   SCFInterfaceImpl.cpp
+  StdInterfaceImpl.cpp
   TensorInterfaceImpl.cpp
   VectorInterfaceImpl.cpp
 )
@@ -61,6 +62,14 @@ add_mlir_dialect_library(MLIRSCFBufferizableOpInterfaceImpl
   MLIRSCF
 )
 
+add_mlir_dialect_library(MLIRStdBufferizableOpInterfaceImpl
+  StdInterfaceImpl.cpp
+
+  LINK_LIBS PUBLIC
+  MLIRBufferizableOpInterface
+  MLIRStandard
+)
+
 add_mlir_dialect_library(MLIRTensorBufferizableOpInterfaceImpl
   TensorInterfaceImpl.cpp
 

mlir/lib/Dialect/Linalg/ComprehensiveBufferize/ComprehensiveBufferize.cpp

@@ -219,7 +219,8 @@ static bool hasReadAfterWriteInterference(
   for (OpOperand *uRead : usesRead) {
     Operation *readingOp = uRead->getOwner();
 
-    // Find most recent write of uRead by following the SSA use-def chain. E.g.:
+    // Find most recent writes of uRead by following the SSA use-def chain.
+    // E.g.:
     //
     // %0 = "writing_op"(%t) : tensor<?x32> -> tensor<?xf32>
     // %1 = "aliasing_op"(%0) : tensor<?x32> -> tensor<?xf32>
@@ -228,7 +229,7 @@ static bool hasReadAfterWriteInterference(
     // In the above example, if uRead is the OpOperand of reading_op, lastWrite
     // is %0. Note that operations that create an alias but do not write (such
     // as ExtractSliceOp) are skipped.
-    Value lastWrite = state.findLastPrecedingWrite(uRead->get());
+    SetVector<Value> lastWrites = state.findLastPrecedingWrite(uRead->get());
 
     // Look for conflicting memory writes. Potential conflicts are writes to an
     // alias that have been decided to bufferize inplace.
@@ -265,35 +266,38 @@ static bool hasReadAfterWriteInterference(
       if (insideMutuallyExclusiveRegions(readingOp, conflictingWritingOp))
         continue;
 
-      // No conflict if the conflicting write happens before the last
-      // write.
-      if (Operation *writingOp = lastWrite.getDefiningOp()) {
-        if (happensBefore(conflictingWritingOp, writingOp, domInfo))
-          // conflictingWritingOp happens before writingOp. No conflict.
-          continue;
-        // No conflict if conflictingWritingOp is contained in writingOp.
-        if (writingOp->isProperAncestor(conflictingWritingOp))
-          continue;
-      } else {
-        auto bbArg = lastWrite.cast<BlockArgument>();
-        Block *block = bbArg.getOwner();
-        if (!block->findAncestorOpInBlock(*conflictingWritingOp))
-          // conflictingWritingOp happens outside of the block. No
-          // conflict.
-          continue;
-      }
+      // Check all possible last writes.
+      for (Value lastWrite : lastWrites) {
+        // No conflict if the conflicting write happens before the last
+        // write.
+        if (Operation *writingOp = lastWrite.getDefiningOp()) {
+          if (happensBefore(conflictingWritingOp, writingOp, domInfo))
+            // conflictingWritingOp happens before writingOp. No conflict.
+            continue;
+          // No conflict if conflictingWritingOp is contained in writingOp.
+          if (writingOp->isProperAncestor(conflictingWritingOp))
+            continue;
+        } else {
+          auto bbArg = lastWrite.cast<BlockArgument>();
+          Block *block = bbArg.getOwner();
+          if (!block->findAncestorOpInBlock(*conflictingWritingOp))
+            // conflictingWritingOp happens outside of the block. No
+            // conflict.
+            continue;
+        }
 
-      // No conflict if the conflicting write and the last write are the same
-      // use.
-      if (state.getAliasingOpResult(*uConflictingWrite) == lastWrite)
-        continue;
+        // No conflict if the conflicting write and the last write are the same
+        // use.
+        if (state.getAliasingOpResult(*uConflictingWrite) == lastWrite)
+          continue;
 
-      // All requirements are met. Conflict found!
+        // All requirements are met. Conflict found!
 
-      if (options.printConflicts)
-        annotateConflict(uRead, uConflictingWrite, lastWrite);
+        if (options.printConflicts)
+          annotateConflict(uRead, uConflictingWrite, lastWrite);
 
-      return true;
+        return true;
+      }
     }
   }
 

mlir/lib/Dialect/Linalg/ComprehensiveBufferize/ModuleBufferization.cpp

@@ -938,7 +938,7 @@ struct FuncOpInterface
 } // namespace mlir
 
 void mlir::linalg::comprehensive_bufferize::std_ext::
-    registerBufferizableOpInterfaceExternalModels(DialectRegistry &registry) {
+    registerModuleBufferizationExternalModels(DialectRegistry &registry) {
   registry.addOpInterface<CallOp, std_ext::CallOpInterface>();
   registry.addOpInterface<ReturnOp, std_ext::ReturnOpInterface>();
   registry.addOpInterface<FuncOp, std_ext::FuncOpInterface>();

mlir/lib/Dialect/Linalg/ComprehensiveBufferize/StdInterfaceImpl.cpp

@@ -0,0 +1,79 @@
+//===- StdInterfaceImpl.cpp - Standard Impl. of BufferizableOpInterface ---===//
+//
+// 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/Dialect/Linalg/ComprehensiveBufferize/StdInterfaceImpl.h"
+
+#include "mlir/Dialect/Linalg/ComprehensiveBufferize/BufferizableOpInterface.h"
+#include "mlir/Dialect/StandardOps/IR/Ops.h"
+#include "mlir/IR/Dialect.h"
+#include "mlir/IR/Operation.h"
+
+namespace mlir {
+namespace linalg {
+namespace comprehensive_bufferize {
+namespace std_ext {
+
+/// Bufferization of std.select. Just replace the operands.
+struct SelectOpInterface
+    : public BufferizableOpInterface::ExternalModel<SelectOpInterface,
+                                                    SelectOp> {
+  bool bufferizesToMemoryRead(Operation *op, OpOperand &opOperand,
+                              const BufferizationState &state) const {
+    return false;
+  }
+
+  bool bufferizesToMemoryWrite(Operation *op, OpOperand &opOperand,
+                               const BufferizationState &state) const {
+    return false;
+  }
+
+  OpResult getAliasingOpResult(Operation *op, OpOperand &opOperand,
+                               const BufferizationState &state) const {
+    return op->getOpResult(0) /*result*/;
+  }
+
+  SmallVector<OpOperand *>
+  getAliasingOpOperand(Operation *op, OpResult opResult,
+                       const BufferizationState &state) const {
+    return {&op->getOpOperand(1) /*true_value*/,
+            &op->getOpOperand(2) /*false_value*/};
+  }
+
+  LogicalResult bufferize(Operation *op, RewriterBase &rewriter,
+                          const BufferizationState &state) const {
+    auto selectOp = cast<SelectOp>(op);
+    // `getBuffer` introduces copies if an OpOperand bufferizes out-of-place.
+    // TODO: It would be more efficient to copy the result of the `select` op
+    // instead of its OpOperands. In the worst case, 2 copies are inserted at
+    // the moment (one for each tensor). When copying the op result, only one
+    // copy would be needed.
+    Value trueBuffer =
+        *state.getBuffer(rewriter, selectOp->getOpOperand(1) /*true_value*/);
+    Value falseBuffer =
+        *state.getBuffer(rewriter, selectOp->getOpOperand(2) /*false_value*/);
+    replaceOpWithNewBufferizedOp<SelectOp>(
+        rewriter, op, selectOp.getCondition(), trueBuffer, falseBuffer);
+    return success();
+  }
+
+  BufferRelation bufferRelation(Operation *op, OpResult opResult,
+                                const BufferizationAliasInfo &aliasInfo,
+                                const BufferizationState &state) const {
+    return BufferRelation::None;
+  }
+};
+
+} // namespace std_ext
+} // namespace comprehensive_bufferize
+} // namespace linalg
+} // namespace mlir
+
+void mlir::linalg::comprehensive_bufferize::std_ext::
+    registerBufferizableOpInterfaceExternalModels(DialectRegistry &registry) {
+  registry.addOpInterface<SelectOp, std_ext::SelectOpInterface>();
+}

mlir/lib/Dialect/Linalg/Transforms/CMakeLists.txt

@@ -49,6 +49,7 @@ add_mlir_dialect_library(MLIRLinalgTransforms
   MLIRSCF
   MLIRSCFBufferizableOpInterfaceImpl
   MLIRSCFTransforms
+  MLIRStdBufferizableOpInterfaceImpl
   MLIRPass
   MLIRStandard
   MLIRStandardOpsTransforms

mlir/lib/Dialect/Linalg/Transforms/ComprehensiveBufferizePass.cpp

@@ -17,6 +17,7 @@
 #include "mlir/Dialect/Linalg/ComprehensiveBufferize/LinalgInterfaceImpl.h"
 #include "mlir/Dialect/Linalg/ComprehensiveBufferize/ModuleBufferization.h"
 #include "mlir/Dialect/Linalg/ComprehensiveBufferize/SCFInterfaceImpl.h"
+#include "mlir/Dialect/Linalg/ComprehensiveBufferize/StdInterfaceImpl.h"
 #include "mlir/Dialect/Linalg/ComprehensiveBufferize/TensorInterfaceImpl.h"
 #include "mlir/Dialect/Linalg/ComprehensiveBufferize/VectorInterfaceImpl.h"
 #include "mlir/Dialect/Linalg/Passes.h"
@@ -51,6 +52,7 @@ struct LinalgComprehensiveModuleBufferize
     bufferization_ext::registerBufferizableOpInterfaceExternalModels(registry);
     linalg_ext::registerBufferizableOpInterfaceExternalModels(registry);
     scf_ext::registerBufferizableOpInterfaceExternalModels(registry);
+    std_ext::registerModuleBufferizationExternalModels(registry);
     std_ext::registerBufferizableOpInterfaceExternalModels(registry);
     tensor_ext::registerBufferizableOpInterfaceExternalModels(registry);
     vector_ext::registerBufferizableOpInterfaceExternalModels(registry);