[Mlir-commits] [mlir] [MLIR, LLVM]: Add an IR utility to perform slice walking (PR #103053)

[Tobias Gysi]

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@@ -0,0 +1,99 @@
+//===- SliceSupport.h - Helpers for performing IR slicing -------*- C++ -*-===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef MLIR_IR_SLICESUPPORT_H
+#define MLIR_IR_SLICESUPPORT_H
+
+#include "mlir/IR/ValueRange.h"
+
+namespace mlir {
+
+/// A class to signal how to proceed with the walk of the backward slice:
+/// - Interrupt: Stops the walk.
+/// - AdvanceTo: Continues the walk to user-specified values.
+/// - Skip: Continues the walk, but skips the predecessors of the current value.
+class WalkContinuation {
+public:
+  enum class WalkAction {
+    /// Stops the walk.
+    Interrupt,
+    /// Continues the walk to user-specified values.
+    AdvanceTo,
+    /// Continues the walk, but skips the predecessors of the current value.
+    Skip
+  };
+
+  WalkContinuation(WalkAction action, mlir::ValueRange nextValues)
+      : action(action), nextValues(nextValues) {}
+
+  /// Allows diagnostics to interrupt the walk.
+  explicit WalkContinuation(mlir::Diagnostic &&)
+      : action(WalkAction::Interrupt) {}
+
+  /// Allows diagnostics to interrupt the walk.
+  explicit WalkContinuation(mlir::InFlightDiagnostic &&)
+      : action(WalkAction::Interrupt) {}
+
+  /// Creates a continuation that interrupts the walk.
+  static WalkContinuation interrupt() {
+    return WalkContinuation(WalkAction::Interrupt, {});
+  }
+
+  /// Creates a continuation that adds the user-specified `nextValues` to the
+  /// work list and advances the walk. Unlike advance, this function does not
+  /// add the control flow predecessor values to the work list.
+  static WalkContinuation advanceTo(mlir::ValueRange nextValues) {
+    return WalkContinuation(WalkAction::AdvanceTo, nextValues);
+  }
+
+  /// Creates a continuation that advances the walk without adding any
+  /// predecessor values to the work list.
+  static WalkContinuation skip() {
+    return WalkContinuation(WalkAction::Skip, {});
+  }
+
+  /// Returns true if the walk was interrupted.
+  bool wasInterrupted() const { return action == WalkAction::Interrupt; }
+
+  /// Returns true if the walk was skipped.
+  bool wasSkipped() const { return action == WalkAction::Skip; }
+
+  /// Returns true if the walk was advanced to user-specified values.
+  bool wasAdvancedTo() const { return action == WalkAction::AdvanceTo; }
+
+  /// Returns the next values to continue the walk with.
+  mlir::ArrayRef<mlir::Value> getNextValues() const { return nextValues; }
+
+private:
+  WalkAction action;
+  /// The next values to continue the walk with.
+  mlir::SmallVector<mlir::Value> nextValues;
+};
+
+/// A callback that is invoked for each value encountered during the walk of the
+/// slice. The callback takes the current value, and returns the walk
+/// continuation, which determines if the walk should proceed and if yes, with
+/// which values.
+using WalkCallback = mlir::function_ref<WalkContinuation(mlir::Value)>;
+
+/// Walks the slice starting from the `rootValues` using a depth-first
+/// traversal. The walk calls the provided `walkCallback` for each value
+/// encountered in the slice and uses the returned walk continuation to
+/// determine how to proceed.
+WalkContinuation walkSlice(mlir::ValueRange rootValues,
+                           WalkCallback walkCallback);
+
+/// Computes a vector of all control predecessors of `value`. Relies on
+/// RegionBranchOpInterface and BranchOpInterface to determine predecessors.
+/// Returns nullopt if value has no predecessors or when the relevant operations
----------------
gysit wrote:

```suggestion
/// Returns nullopt if `value` has no predecessors or when the relevant operations
```
nit: alternative if the value has...

https://github.com/llvm/llvm-project/pull/103053