[mlir][linalg][bufferize] Allow returning arbitrary memrefs

[springerm]

Summary

If allowReturnMemref is set to true, arbitrary memrefs may be returned from FuncOps. Also remove allocation hoisting code, which is only partly implemented at the moment.

The purpose of this commit is to untangle bufferize from aliasInfo. (Even with this change, they are not fully untangled yet.)

Depends On D114226

[nicolasvasilache]

Thanks for the cleanup!

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

 namespace {
 /// A specialization of BufferizationState that keeps track of additional
 /// state required for bufferization of function boundaries.
 struct ModuleBufferizationState : public BufferizationState {
   using BufferizationState::BufferizationState;
 
   /// A map for looking up bufferized function types.
   DenseMap<FuncOp, FunctionType> bufferizedFunctionTypes;
+
+  /// A mapping of return values to equivalent BlockArguments.
+  DenseMap<Value, BlockArgument> equivalentReturnValToBBArg;
 };
 } // namespace
 
 static bool isaTensor(Type t) { return t.isa<TensorType>(); }
 
+/// If `value` is a memref::CastOp, return its source. Otherwise, return
+/// `value` directly.
+static Value getNonCastedValue(Value value) {
+  while (auto castOp = value.getDefiningOp<memref::CastOp>())
+    value = castOp.source();
+  return value;
+}
+
 /// Remove the attribute that triggers inplace bufferization on a FuncOp
 /// argument `bbArg`.
 static void removeBufferizationFuncArguments(BlockArgument bbArg) {
   auto funcOp = cast<FuncOp>(bbArg.getOwner()->getParentOp());
   funcOp.removeArgAttr(bbArg.getArgNumber(),
                        BufferizableOpInterface::kBufferLayoutAttrName);
   funcOp.removeArgAttr(bbArg.getArgNumber(),
                        BufferizableOpInterface::kInplaceableAttrName);
static FunctionType getOrCreateBufferizedFunctionType(
 
   auto it2 = bufferizedFunctionTypes.try_emplace(
       funcOp, getBufferizedFunctionType(funcOp.getContext(), argumentTypes,
                                         resultTypes));
   LDBG("FT: " << funcOp.getType() << " -> " << it2.first->second << "\n");
   return it2.first->second;
 }
 
-/// Return the op with Allocate MemoryEffect if `v` is equivalent to such an
-/// an op. Return null otherwise.
-static Operation *getEquivalentAlloc(Value value,
-                                     const BufferizationAliasInfo &aliasInfo) {
-  Operation *res = nullptr;
-  aliasInfo.applyOnEquivalenceClass(value, [&](Value v) {
-    if (!res)
-      if (auto interface =
-              dyn_cast_or_null<MemoryEffectOpInterface>(v.getDefiningOp()))
-        if (auto effect =
-                interface.getEffectOnValue<MemoryEffects::Allocate>(v))
-          res = v.getDefiningOp();
-  });
-  return res;
-}
+/// Store function BlockArguments that are equivalent to a returned value in
+/// the given ModuleBufferizationState.
+static void populateEquivalentFuncOpBBArgs(FuncOp funcOp,
+                                           ModuleBufferizationState &state) {
+  // Support only single return-terminated block in the function.
+  ReturnOp returnOp = getAssumedUniqueReturnOp(funcOp);
+  assert(returnOp && "expected func with single return op");
 
-/// Return the first argument of the enclosing FuncOp that is equivalent to `v`.
-/// Return null if no such bbArg can be found.
-static BlockArgument
-getEquivalentEnclosingFuncBBArg(Value v,
-                                const BufferizationAliasInfo &aliasInfo) {
-  if (!v.getType().isa<RankedTensorType>())
-    return nullptr;
-  Operation *op = v.getParentBlock()->getParentOp();
-  FuncOp funcOp = dyn_cast<FuncOp>(op);
-  if (!funcOp)
-    funcOp = op->getParentOfType<FuncOp>();
-  assert(funcOp && "expected non-null FuncOp");
-  for (BlockArgument bbArg : funcOp.getArguments()) {
-    if (!bbArg.getType().isa<RankedTensorType>())
-      continue;
-    if (aliasInfo.areEquivalentBufferizedValues(v, bbArg))
-      return bbArg;
-  }
-  return nullptr;
+  for (Value returnVal : returnOp.operands())
+    if (returnVal.getType().isa<RankedTensorType>())
+      for (BlockArgument bbArg : funcOp.getArguments())
+        if (bbArg.getType().isa<RankedTensorType>())
+          if (state.aliasInfo.areEquivalentBufferizedValues(returnVal, bbArg))
+            state.equivalentReturnValToBBArg[returnVal] = bbArg;
 }
 
 /// Rewrite the `funcOp` arguments analysis return values and terminator into
 /// buffer form (using the canonical memref layout for now), according to the
 /// inPlace-bufferizable information of the function arguments.
+///
 /// This relies on a buffer equivalence analysis of each return operand. When a
-/// result buffer is equivalent to:
-///   1. a BlockArgument of `funcOp`, it can be dropped from the return values
-///      and becomes inplaceable at all callers. This assumes all CallOp perform
-///      the necessary work to clone operands so as to make them inplaceable.
-//       Reliance on this logic will need to be relaxed in thefuture.
-///   2. an op with an Alloc effect, this currently fails bufferization but is a
-///      candidate for hoisting and creating a new inplace operand at all caller
-///      sites.
-///   3. if such a hoisting for 2. is not possible (e.g. data-dependent that
-///      prevents hoisting), this is currently unsupported and will require a
-///      refcounted buffer type.
-static LogicalResult bufferizeFuncOpBoundary(
-    FuncOp funcOp, BufferizationAliasInfo &aliasInfo,
-    DenseMap<FuncOp, FunctionType> &bufferizedFunctionTypes) {
+/// result buffer is equivalent to a BlockArgument of `funcOp`, it can be
+/// dropped from the return values and becomes inplaceable at all callers. This
+/// assumes all CallOp perform the necessary work to clone operands so as to
+/// make them inplaceable. Reliance on this logic will need to be relaxed in the
+/// future.
+///
+/// Note: Returning a memref currently fails bufferization. If such memrefs
+/// originate from an op with an Alloc effect, they could be hoisted in the
+/// future.
+static LogicalResult bufferizeFuncOpBoundary(FuncOp funcOp,
+                                             ModuleBufferizationState &state) {
   LLVM_DEBUG(DBGS() << "Begin bufferizeFuncOpBoundary:\n" << funcOp << "\n");
+  BufferizationAliasInfo &aliasInfo = state.aliasInfo;
 
   // If nothing to do then we are done.
   if (!llvm::any_of(funcOp.getType().getInputs(), isaTensor) &&
       !llvm::any_of(funcOp.getType().getResults(), isaTensor))
     return success();
 
   // Get the bufferized FunctionType for funcOp or construct it if not yet
   // available.
static LogicalResult bufferizeFuncOpBoundary(FuncOp funcOp,
   // ============================
   // The body of such functions is assumed opaque and we can't know the
   // bufferization contract they want to enforce atm.
   // As a consequence, only support functions that don't return any tensor atm.
   if (funcOp.getBody().empty()) {
     if (llvm::any_of(funcOp.getType().getResults(), isaTensor))
       return funcOp->emitError() << "cannot bufferize bodiless function that "
                                  << "returns a tensor";
-    FunctionType bufferizedFuncType =
-        getOrCreateBufferizedFunctionType(funcOp, funcOp.getType().getInputs(),
-                                          TypeRange{}, bufferizedFunctionTypes);
+    FunctionType bufferizedFuncType = getOrCreateBufferizedFunctionType(
+        funcOp, funcOp.getType().getInputs(), TypeRange{},
+        state.bufferizedFunctionTypes);
     funcOp.setType(bufferizedFuncType);
     LLVM_DEBUG(DBGS() << "End bufferizeFuncOpBoundary no fun body: " << funcOp);
     return success();
   }
 
   // Support only single return-terminated block in the function.
   ReturnOp returnOp = getAssumedUniqueReturnOp(funcOp);
   assert(returnOp && "expected func with single return op");
 
   // 1. For each FuncOp result, keep track of which inplace argument it reuses.
   SmallVector<Value> returnValues;
   for (OpOperand &returnOperand : returnOp->getOpOperands()) {
+    Value returnVal = returnOperand.get();
+
     // If not a renturn tensor type just forward it.
-    if (!returnOperand.get().getType().isa<RankedTensorType>()) {
-      returnValues.push_back(returnOperand.get());
+    if (!returnVal.getType().isa<RankedTensorType>()) {
+      returnValues.push_back(returnVal);
       continue;
     }
 
     // If return operand is equivalent to some bbArg, no need to return it.
-    Value returnVal = returnOperand.get();
-    if (getEquivalentEnclosingFuncBBArg(returnVal, aliasInfo))
-      continue;
-
-    // TODO: Need to hoist above function boundary.
-    if (Operation *allocOp = getEquivalentAlloc(returnVal, aliasInfo)) {
-      returnValues.push_back(allocOp->getResult(0));
+    if (state.equivalentReturnValToBBArg.count(returnVal))
       continue;
-    }
 
-    // Other cases legitimately need to return a tensor, this is currently not
-    // supported. For instance, if hoisting across function boundary has
-    // failed, it may be due to e.g. data-dependent sizes. In such a case, we
-    // would need a better type than memref.
-    int64_t returnIdx = returnOperand.getOperandNumber();
-    return returnOp->emitError()
-           << "buffer result #" << returnIdx << " not produced by an alloc\n";
+    // Cast values at the call site if necessary.
+    returnValues.push_back(getNonCastedValue(state.lookupBuffer(returnVal)));
   }
 
   // 2. Rewrite the terminator without the inPlace bufferizable values.
   ValueRange retValues{returnValues};
   FunctionType bufferizedFuncType = getOrCreateBufferizedFunctionType(
       funcOp, funcOp.getType().getInputs(), retValues.getTypes(),
-      bufferizedFunctionTypes);
+      state.bufferizedFunctionTypes);
   OpBuilder b(returnOp);
   b.create<ReturnOp>(returnOp.getLoc(), returnValues);
   returnOp->erase();
 
   // 3. Rewrite the bbArgs.
   // Iterate on the original `numArgs` and replace them in order.
   // This guarantees the argument order still matches after the rewrite.
   Block &frontBlock = funcOp.body().front();
struct CallOpInterface
   /// marked inplaceable. For now, it is the responsibility of the `callOp`
   /// bufferization to allow FuncOp that are inplaceable to write inPlace.
   LogicalResult bufferize(Operation *op, OpBuilder &b,
                           BufferizationState &state) const {
     CallOp callOp = cast<CallOp>(op);
     FuncOp funcOp = getCalledFunction(callOp);
     assert(isa<CallOp>(callOp.getOperation()) && funcOp &&
            "expected Callop to a FuncOp");
+    auto &moduleState = static_cast<ModuleBufferizationState &>(state);
 
     // Take a guard before anything else.
     OpBuilder::InsertionGuard g(b);
     b.setInsertionPoint(callOp);
 
     // 1. Filter return types:
     //    - if the callee is bodiless / external, we cannot inspect it and we
     //      cannot assume anything. We can just assert that it does not return a
     //      tensor as this would have to bufferize to "return a memref", whose
     //      semantics is ill-defined.
     //    - if the callee has a body, we perform inter-procedural equivalence
     //      analysis. When successful, a result folds onto an operand. When
-    //      unsuccessful, additional work is needed to either:
+    //      unsuccessful, additional work is needed (TODO) to either:
     //        * hoist a result into an inplaceable operand or
     //        * devise a better representation to truly return a buffer.
     SmallVector<Type> resultTypes;
-    SmallVector<Value> hoistedArguments;
     if (funcOp.body().empty()) {
       if (llvm::any_of(funcOp.getType().getResults(), isaTensor))
         return callOp->emitError()
                << "cannot bufferize bodiless function that returns a tensor";
     } else {
       ReturnOp returnOp = getAssumedUniqueReturnOp(funcOp);
       assert(returnOp && "expected func with single return op");
 
       // For each FuncOp result, keep track of which inplace argument it reuses.
       for (OpOperand &returnOperand : returnOp->getOpOperands()) {
         Type returnType = returnOperand.get().getType();
         if (!isaTensor(returnType)) {
           resultTypes.push_back(returnType);
           continue;
         }
 
         // If return operand is equivalent to some bbArg, no need to return it.
         Value returnVal = returnOperand.get();
-        if (BlockArgument bbArg =
-                getEquivalentEnclosingFuncBBArg(returnVal, state.aliasInfo)) {
+        if (moduleState.equivalentReturnValToBBArg.count(returnVal)) {
+          BlockArgument bbArg =
+              moduleState.equivalentReturnValToBBArg[returnVal];
           Value oldRes = callOp->getResult(returnOperand.getOperandNumber());
           int64_t idx = bbArg.getArgNumber();
           Value buffer = state.lookupBuffer(callOp->getOperand(idx));
           // Add CallOp operand/result equivalence: this is interprocedural
           // info.
           state.aliasInfo.insertNewBufferEquivalence(oldRes, buffer);
           state.mapBuffer(oldRes, buffer);
           // Add a ToTensorOp to kill all uses of the CallOp return.
           // Replace all uses of the CallOp results so we can erase the CallOp.
           // This ToTensorOp must fold/DCE away or bufferization should be
           // considered failed.
           Value toTensorOp =
               b.create<bufferization::ToTensorOp>(callOp.getLoc(), buffer);
           oldRes.replaceAllUsesWith(toTensorOp);
           // Add new op equivalence info.
           state.aliasInfo.insertNewBufferEquivalence(toTensorOp, buffer);
           state.mapBuffer(toTensorOp, buffer);
           continue;
         }
 
-        // TODO: Need to hoist above function boundary.
-        if (Operation *allocOp =
-                getEquivalentAlloc(returnVal, state.aliasInfo)) {
-          hoistedArguments.push_back(allocOp->getResult(0));
-          continue;
-        }
-
-        // Other cases legitimately need to return a tensor, this is currently
-        // not supported. For instance, if hoisting across function boundary has
-        // failed, it may be due to e.g. data-dependent sizes. In such a case,
-        // we would we need a better type than memref.
         resultTypes.push_back(returnType);
-
-        int64_t returnIdx = returnOperand.getOperandNumber();
-        return returnOp->emitError() << "buffer result #" << returnIdx
-                                     << " not produced by an alloc\n";
       }
     }
 
     // 2. Compute bufferized FunctionType.
     SmallVector<Type> argumentTypes{callOp->getOperandTypes()};
-    ValueRange hoistedArgs{hoistedArguments};
-    llvm::append_range(argumentTypes, hoistedArgs.getTypes());
     // Get the bufferized FunctionType for funcOp or construct it if not yet
     // available.
-    // TODO: Assert that `state` is a ModuleBufferizationState.
-    FunctionType bufferizedFuncType = getOrCreateBufferizedFunctionType(
-        funcOp, argumentTypes, resultTypes,
-        static_cast<ModuleBufferizationState &>(state).bufferizedFunctionTypes);
+    FunctionType bufferizedFuncType =
+        getOrCreateBufferizedFunctionType(funcOp, argumentTypes, resultTypes,
+                                          moduleState.bufferizedFunctionTypes);
 
     // 3. Rewrite tensor operands as memrefs based on `bufferizedFuncType`.
     SmallVector<Value> newOperands;
     newOperands.reserve(callOp->getNumOperands());
     for (OpOperand &opOperand : callOp->getOpOperands()) {
       Value tensorOperand = opOperand.get();
       // Non-tensor operands are just copied.
       if (!tensorOperand.getType().isa<TensorType>()) {
for (FuncOp funcOp : orderedFuncOps) {
     if (callerMap.find(funcOp) != callerMap.end())
       for (BlockArgument bbArg : funcOp.getArguments())
         if (bbArg.getType().isa<TensorType>())
           aliasInfo.setBufferizesToWritableMemory(bbArg);
 
     // Analyze and bufferize funcOp.
     if (failed(runComprehensiveBufferize(funcOp, options, state)))
       return failure();
+
+    populateEquivalentFuncOpBBArgs(funcOp, state);
   }
 
   if (options.testAnalysisOnly)
     return success();
 
   for (FuncOp funcOp : orderedFuncOps) {
     // Note: It would be good to apply cleanups here but we cannot as aliasInfo
     // would be invalidated.
-    if (failed(bufferizeFuncOpBoundary(funcOp, aliasInfo,
-                                       state.bufferizedFunctionTypes)))
+    if (failed(bufferizeFuncOpBoundary(funcOp, state)))
       return failure();
 
     if (!options.allowReturnMemref &&
         llvm::any_of(funcOp.getType().getResults(), [](Type t) {
           return t.isa<MemRefType, UnrankedMemRefType>();
         })) {
       funcOp->emitError("memref return type is unsupported");
       return failure();

mlir/test/Dialect/Linalg/comprehensive-module-bufferize-invalid.mlir

%res = scf.for %arg0 = %c0 to %iters step %c1 iter_args(%bbarg = %A) -> (tensor<?xf32>) {
     scf.yield %r : tensor<?xf32>
   }
   call @fun_with_side_effects(%res) : (tensor<?xf32>) -> ()
   return
 }
 
 // -----
 
+// expected-error @+1 {{memref return type is unsupported}}
 func @extract_slice_fun(%A : tensor<?xf32> {linalg.inplaceable = true})
   ->  tensor<4xf32>
 {
   // This bufferizes to a pattern that the cross-function boundary pass needs to
   // convert into a new memref argument at all call site; this may be either:
   //   - an externally created aliasing subview (if we want to allow aliasing
   //     function arguments).
   //   - a new alloc + copy (more expensive but does not create new function
   //     argument aliasing).
   %r0 = tensor.extract_slice %A[0][4][1] : tensor<?xf32> to tensor<4xf32>
 
-  // expected-error @+1 {{buffer result #0 not produced by an alloc}}
   return %r0: tensor<4xf32>
 }
 
 // -----
 
 func @scf_yield(%b : i1, %A : tensor<4xf32>, %B : tensor<4xf32>) -> tensor<4xf32>
 {
   // expected-error @+1 {{result buffer is ambiguous}}