Refactor getUsedValuesDefinedAbove to expose a variant taking a callback (NFC)

This will allow clients to implement a different collection strategy on these
values, including collecting each uses within the region for example.

PiperOrigin-RevId: 267803978

mlir/include/mlir/Transforms/RegionUtils.h

@@ -40,6 +40,16 @@ bool areValuesDefinedAbove(Range values, Region &limit) {
 void replaceAllUsesInRegionWith(Value *orig, Value *replacement,
                                 Region &region);
 
+/// Calls `callback` for each use of a value within `region` or its descendants
+/// that was defined at the ancestors of the `limit`.
+void visitUsedValuesDefinedAbove(Region &region, Region &limit,
+                                 function_ref<void(OpOperand *)> callback);
+
+/// Calls `callback` for each use of a value within any of the regions provided
+/// that was defined in one of the ancestors.
+void visitUsedValuesDefinedAbove(llvm::MutableArrayRef<Region> regions,
+                                 function_ref<void(OpOperand *)> callback);
+
 /// Fill `values` with a list of values defined at the ancestors of the `limit`
 /// region and used within `region` or its descendants.
 void getUsedValuesDefinedAbove(Region &region, Region &limit,

mlir/lib/Transforms/Utils/RegionUtils.cpp

@@ -32,8 +32,9 @@ void mlir::replaceAllUsesInRegionWith(Value *orig, Value *replacement,
   }
 }
 
-void mlir::getUsedValuesDefinedAbove(Region &region, Region &limit,
-                                     llvm::SetVector<Value *> &values) {
+void mlir::visitUsedValuesDefinedAbove(
+    Region &region, Region &limit,
+    llvm::function_ref<void(OpOperand *)> callback) {
   assert(limit.isAncestor(&region) &&
          "expected isolation limit to be an ancestor of the given region");
 
@@ -45,12 +46,25 @@ void mlir::getUsedValuesDefinedAbove(Region &region, Region &limit,
     properAncestors.insert(reg);
   }
 
-  region.walk([&values, &properAncestors](Operation *op) {
-    for (Value *operand : op->getOperands())
-      // Collect values that are used by an operation and defined in a proper
-      // ancestor of region.
-      if (properAncestors.count(operand->getParentRegion()))
-        values.insert(operand);
+  region.walk([callback, &properAncestors](Operation *op) {
+    for (OpOperand &operand : op->getOpOperands())
+      // Callback on values defined in a proper ancestor of region.
+      if (properAncestors.count(operand.get()->getParentRegion()))
+        callback(&operand);
+  });
+}
+
+void mlir::visitUsedValuesDefinedAbove(
+    llvm::MutableArrayRef<Region> regions,
+    llvm::function_ref<void(OpOperand *)> callback) {
+  for (Region &region : regions)
+    visitUsedValuesDefinedAbove(region, region, callback);
+}
+
+void mlir::getUsedValuesDefinedAbove(Region &region, Region &limit,
+                                     llvm::SetVector<Value *> &values) {
+  visitUsedValuesDefinedAbove(region, limit, [&](OpOperand *operand) {
+    values.insert(operand->get());
   });
 }