[mlir][scf] Add no_inline attribute to scf.execute_region

More control over the IR.
Enabling users to explicitly specify which regions should be preserved, uncovers additional opportunities to utilize `scf.execute_region`.

Author: jungpark-mlir

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

@@ -119,6 +119,10 @@ def ExecuteRegionOp : SCF_Op<"execute_region", [
     ```
   }];
 
+  let arguments = (ins
+    UnitAttr:$no_inline
+  );
+
   let results = (outs Variadic<AnyType>);
 
   let regions = (region AnyRegion:$region);

mlir/lib/Dialect/SCF/IR/SCF.cpp

@@ -184,7 +184,7 @@ struct SingleBlockExecuteInliner : public OpRewritePattern<ExecuteRegionOp> {
 
   LogicalResult matchAndRewrite(ExecuteRegionOp op,
                                 PatternRewriter &rewriter) const override {
-    if (!op.getRegion().hasOneBlock())
+    if (!op.getRegion().hasOneBlock() || op.getNoInline())
       return failure();
     replaceOpWithRegion(rewriter, op, op.getRegion());
     return success();

mlir/test/Dialect/SCF/canonicalize.mlir

@@ -1461,6 +1461,28 @@ func.func @execute_region_elim() {
 
 // -----
 
+// CHECK-LABEL: func @execute_region_elim_noinline
+func.func @execute_region_elim_noinline() {
+  affine.for %i = 0 to 100 {
+    "test.foo"() : () -> ()
+    %v = scf.execute_region -> i64 {
+      %x = "test.val"() : () -> i64
+      scf.yield %x : i64
+    } {no_inline}
+    "test.bar"(%v) : (i64) -> ()
+  }
+  return
+}
+
+// CHECK-NEXT:     affine.for %arg0 = 0 to 100 {
+// CHECK-NEXT:       "test.foo"() : () -> ()
+// CHECK-NEXT:       scf.execute_region
+// CHECK-NEXT:       %[[VAL:.*]] = "test.val"() : () -> i64
+// CHECK-NEXT:       scf.yield %[[VAL]] : i64
+// CHECK-NEXT:     }
+
+// -----
+
 // CHECK-LABEL: func @func_execute_region_elim
 func.func @func_execute_region_elim() {
     "test.foo"() : () -> ()