[mlir][SCF] Make the scf.take_assumed_branch transform only read its target handle

[nicolasvasilache]

Summary

Handles are tracked properly and usage composes better if we don't artificially lose handles.

mlir/lib/Dialect/SCF/TransformOps/SCFTransformOps.cpp

return emitDefiniteFailure()
            << ((getTakeElseBranch()) ? "`else`" : "`then`") << " region";
   }
   replaceOpWithRegion(rewriter, ifOp, region);
   return DiagnosedSilenceableFailure::success();
 }
 
 void transform::TakeAssumedBranchOp::getEffects(
     SmallVectorImpl<MemoryEffects::EffectInstance> &effects) {
-  consumesHandle(getTarget(), effects);
+  onlyReadsHandle(getTarget(), effects);
   modifiesPayload(effects);
 }
 
 //===----------------------------------------------------------------------===//
 // Transform op registration
 //===----------------------------------------------------------------------===//
 
 namespace {

mlir/test/Dialect/SCF/transform-op-take-assumed-branch.mlir

 // RUN: mlir-opt %s -test-transform-dialect-interpreter -split-input-file -verify-diagnostics --allow-unregistered-dialect | FileCheck %s
 
 func.func @if_no_else(%cond: i1, %a: index, %b: memref<?xf32>, %c: i8) {
   scf.if %cond {
     "some_op"(%cond, %b) : (i1, memref<?xf32>) -> ()
     scf.yield
   }
   return
 }
 
 transform.sequence failures(propagate) {
 ^bb0(%arg1: !transform.any_op):
   %if = transform.structured.match ops{["scf.if"]} in %arg1 
     : (!transform.any_op) -> !transform.any_op
-
   // expected-error @+1 {{requires an scf.if op with a single-block `else` region}}
   transform.scf.take_assumed_branch %if take_else_branch 
     : (!transform.any_op) -> ()
 }
 
 // -----
 
+// CHECK-LABEL: if_no_else
+func.func @if_no_else(%cond: i1, %a: index, %b: memref<?xf32>, %c: i8) {
+  scf.if %cond {
+    "some_op"(%cond, %b) : (i1, memref<?xf32>) -> ()
+    scf.yield
+  }
+  return
+}
+
+transform.sequence failures(propagate) {
+^bb0(%arg1: !transform.any_op):
+  %if = transform.structured.match ops{["scf.if"]} in %arg1 
+    : (!transform.any_op) -> !transform.any_op
+  %some_op = transform.structured.match ops{["some_op"]} in %arg1 
+    : (!transform.any_op) -> !transform.any_op
+
+  transform.scf.take_assumed_branch %if : (!transform.any_op) -> ()
+  
+  // Handle to formerly nested `some_op` is still valid after the transform.
+  transform.print %some_op: !transform.any_op
+}
+
+// -----
+
 // CHECK-LABEL: tile_tensor_pad
 func.func @tile_tensor_pad(
   %arg0 : tensor<?x?xf32>, %cst : f32, %low: index, %high: index) 
     -> tensor<20x40xf32>
 {
   //     CHECK: scf.forall
   // CHECK-NOT:   scf.if
   // CHECK-NOT:     tensor.generate