[mlir][SCF] Implement RegionBranchOpInterface on ExecuteRegionOp

[springerm]

Summary

This is needed for the BufferDeallocation pass.

Depends On D121522

[bondhugula]

mlir/lib/Dialect/SCF/SCF.cpp

253

Stale comment? This will never branch back to itself.

[springerm]

mlir/lib/Dialect/SCF/SCF.cpp

253

ahh yes, copy pasta

[springerm]

update

mlir/include/mlir/Dialect/SCF/SCFOps.td

]> {
   let assemblyFormat =
       [{ `(` $condition `)` attr-dict ($args^ `:` type($args))? }];
 }
 
 //===----------------------------------------------------------------------===//
 // ExecuteRegionOp
 //===----------------------------------------------------------------------===//
 
-def ExecuteRegionOp : SCF_Op<"execute_region"> {
+def ExecuteRegionOp : SCF_Op<"execute_region", [
+    DeclareOpInterfaceMethods<RegionBranchOpInterface>]> {
   let summary = "operation that executes its region exactly once";
   let description = [{
     The `execute_region` operation is used to allow multiple blocks within SCF
     and other operations which can hold only one block.  The `execute_region`
     operation executes the region held exactly once and cannot have any operands.
     As such, its region has no arguments. All SSA values that dominate the op can
     be accessed inside the op. The op's region can have multiple blocks and the
     blocks can have multiple distinct terminators. Values returned from this op's

mlir/lib/Dialect/SCF/SCF.cpp

struct MultiBlockExecuteInliner : public OpRewritePattern<ExecuteRegionOp> {
   }
 };
 
 void ExecuteRegionOp::getCanonicalizationPatterns(RewritePatternSet &results,
                                                   MLIRContext *context) {
   results.add<SingleBlockExecuteInliner, MultiBlockExecuteInliner>(context);
 }
 
+/// Given the region at `index`, or the parent operation if `index` is None,
+/// return the successor regions. These are the regions that may be selected
+/// during the flow of control. `operands` is a set of optional attributes that
+/// correspond to a constant value for each operand, or null if that operand is
+/// not a constant.
+void ExecuteRegionOp::getSuccessorRegions(
+    Optional<unsigned> index, ArrayRef<Attribute> operands,
+    SmallVectorImpl<RegionSuccessor> &regions) {
+  // If the predecessor is the ExecuteRegionOp, branch into the body.
+  if (!index.hasValue()) {
+    regions.push_back(RegionSuccessor(&getRegion()));
+    return;
+  }
+
+  // Otherwise, the region branches back to the parent operation.
+  regions.push_back(RegionSuccessor(getResults()));
+}
+
 //===----------------------------------------------------------------------===//
 // ConditionOp
 //===----------------------------------------------------------------------===//
 
 MutableOperandRange
 ConditionOp::getMutableSuccessorOperands(Optional<unsigned> index) {
   // Pass all operands except the condition to the successor region.
   return getArgsMutable();