[mlir][linalg] Implement RegionBranchOpInterface and fix memory effects

* Implement RegionBranchOpInterface: The op has a region, but it is conceptually not entered. The region just describes the semantics of the (monolithic) op.
* Linalg structured ops do not allocate memory.

Differential Revision: https://reviews.llvm.org/D121798

Author: matthias-springer

mlir/include/mlir/Dialect/Linalg/IR/LinalgStructuredOps.td

@@ -16,6 +16,7 @@
 
 include "mlir/Dialect/Linalg/IR/LinalgBase.td"
 include "mlir/Dialect/Linalg/IR/LinalgInterfaces.td"
+include "mlir/Interfaces/ControlFlowInterfaces.td"
 include "mlir/Interfaces/InferTypeOpInterface.td"
 include "mlir/Interfaces/SideEffectInterfaces.td"
 
@@ -28,6 +29,7 @@ class LinalgStructuredBase_Op<string mnemonic, list<Trait> props>
        SingleBlockImplicitTerminator<"YieldOp">,
        DeclareOpInterfaceMethods<MemoryEffectsOpInterface>,
        LinalgStructuredInterface,
+       RegionBranchOpInterface,
        ReifyRankedShapedTypeOpInterface], props)> {
   code structuredOpsBaseDecls = [{
     // Return whether the op accesses the iteration indices.
@@ -40,6 +42,13 @@ class LinalgStructuredBase_Op<string mnemonic, list<Trait> props>
       return llvm::cast<LinalgOp>(getOperation()).reifyResultShapes(b,
           reifiedReturnShapes);
     }
+
+    void getSuccessorRegions(
+        Optional<unsigned> index, ArrayRef<Attribute> operands,
+        SmallVectorImpl<RegionSuccessor> &regions) {
+      // Op has a region, but conceptually the control flow does not enter the
+      // region.
+    }
   }];
 }
 

mlir/lib/Dialect/Linalg/IR/LinalgOps.cpp

@@ -661,10 +661,6 @@ static void getGenericEffectsImpl(
     SmallVectorImpl<SideEffects::EffectInstance<MemoryEffects::Effect>>
         &effects,
     ValueRange results, ValueRange inputBuffers, ValueRange outputs) {
-  for (Value value : results) {
-    effects.emplace_back(MemoryEffects::Allocate::get(), value,
-                         SideEffects::DefaultResource::get());
-  }
   for (Value value : inputBuffers) {
     effects.emplace_back(MemoryEffects::Read::get(), value,
                          SideEffects::DefaultResource::get());