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

[springerm]

Summary

• 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.

[nicolasvasilache]

Thanks for the fix!

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

 //
 //===----------------------------------------------------------------------===//
 
 #ifndef LINALG_STRUCTURED_OPS
 #define LINALG_STRUCTURED_OPS
 
 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"
 
 // Base Tablegen class for Linalg ops.
 // Linalg ops that correspond to library calls operate on ShapedType as their
 // first operands. These may be optionally followed by non-view operands
 // depending on the specific Linalg op.
 class LinalgStructuredBase_Op<string mnemonic, list<Trait> props>
   : Op<Linalg_Dialect, mnemonic, !listconcat([
        SingleBlockImplicitTerminator<"YieldOp">,
        DeclareOpInterfaceMethods<MemoryEffectsOpInterface>,
        LinalgStructuredInterface,
+       RegionBranchOpInterface,
        ReifyRankedShapedTypeOpInterface], props)> {
   code structuredOpsBaseDecls = [{
     // Return whether the op accesses the iteration indices.
     bool hasIndexSemantics() {
       return !this->getBody()->getOps<IndexOp>().empty();
     }
 
     LogicalResult reifyResultShapes(OpBuilder &b,
         ReifiedRankedShapedTypeDims &reifiedReturnShapes) {
       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.
+    }
   }];
 }
 
 //===----------------------------------------------------------------------===//
 // Generic Linalg ops.
 //===----------------------------------------------------------------------===//
 
 def GenericOp : LinalgStructuredBase_Op<"generic", [AttrSizedOperandSegments]> {

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

ParseResult GenericOp::parse(OpAsmParser &parser, OperationState &result) {
 
   return success();
 }
 
 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());
   }
   for (Value value : outputs) {
     effects.emplace_back(MemoryEffects::Read::get(), value,
                          SideEffects::DefaultResource::get());
     effects.emplace_back(MemoryEffects::Write::get(), value,