[Mlir-commits] [mlir] [MLIR][SCF] Define `-scf-rotate-while` pass (PR #99850)

[Mehdi Amini]

================
@@ -0,0 +1,82 @@
+//===- RotateWhileLoop.cpp - scf.while loop rotation ----------------------===//
+//
+// 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
+//
+//===----------------------------------------------------------------------===//
+//
+// Rotates `scf.while` loops.
+//
+//===----------------------------------------------------------------------===//
+
+#include "mlir/Dialect/SCF/Transforms/Passes.h"
+
+#include "mlir/Dialect/SCF/IR/SCF.h"
+#include "mlir/Dialect/SCF/Transforms/Passes.h"
+#include "mlir/Dialect/SCF/Transforms/Patterns.h"
+#include "mlir/Dialect/SCF/Transforms/Transforms.h"
+#include "mlir/IR/Diagnostics.h"
+#include "mlir/Transforms/GreedyPatternRewriteDriver.h"
+
+#include "llvm/Support/Debug.h"
+
+#define DEBUG_TYPE "scf-rotate-while"
+
+namespace mlir {
+#define GEN_PASS_DEF_SCFROTATEWHILELOOPPASS
+#include "mlir/Dialect/SCF/Transforms/Passes.h.inc"
+} // namespace mlir
+
+using namespace mlir;
+
+namespace {
+struct RotateWhileLoopPattern : OpRewritePattern<scf::WhileOp> {
+  RotateWhileLoopPattern(bool rotateLoop, MLIRContext *context,
+                         PatternBenefit benefit = 1,
+                         ArrayRef<StringRef> generatedNames = {})
+      : OpRewritePattern<scf::WhileOp>(context, benefit, generatedNames),
+        forceCreateCheck(rotateLoop) {}
+
+  LogicalResult matchAndRewrite(scf::WhileOp whileOp,
+                                PatternRewriter &rewriter) const final {
+    FailureOr<scf::WhileOp> result =
+        scf::wrapWhileLoopInZeroTripCheck(whileOp, rewriter, forceCreateCheck);
+    if (failed(result) || *result == whileOp) {
+      LLVM_DEBUG(whileOp->emitRemark("Failed to rotate loop"));
+      return failure();
+    };
+    return success();
+  }
+
+  bool forceCreateCheck;
+};
+
+struct SCFRotateWhileLoopPass
+    : impl::SCFRotateWhileLoopPassBase<SCFRotateWhileLoopPass> {
+  using Base::Base;
+
+  void runOnOperation() final {
+    Operation *parentOp = getOperation();
+    MLIRContext *context = &getContext();
+    RewritePatternSet patterns(context);
+    SCFRotateWhileLoopPassOptions options{forceCreateCheck};
+    scf::populateSCFRotateWhileLoopPatterns(patterns, options);
+    // Avoid applying the pattern to a loop more than once.
+    GreedyRewriteConfig config;
+    config.strictMode = GreedyRewriteStrictness::ExistingOps;
+    [[maybe_unused]] LogicalResult success =
+        applyPatternsAndFoldGreedily(parentOp, std::move(patterns), config);
----------------
joker-eph wrote:

My comments stand though, I still don't understand why the pass is using the pattern and greedy rewriter in the first place?

for my other comment: `wrapWhileLoopInZeroTripCheck` does not document when it is returning a failure, which means I can't really understand the pattern behavior (when is it returning success/failure), can you document this?

https://github.com/llvm/llvm-project/pull/99850