[Mlir-commits] [mlir] [mlir][scf] Uplift `scf.while` to `scf.for` (PR #76108)

[Matthias Springer]

================
@@ -0,0 +1,250 @@
+//===- UpliftWhileToFor.cpp - scf.while to scf.for loop uplifting ---------===//
+//
+// 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
+//
+//===----------------------------------------------------------------------===//
+//
+// Transforms SCF.WhileOp's into SCF.ForOp's.
+//
+//===----------------------------------------------------------------------===//
+
+#include "mlir/Dialect/SCF/Transforms/Passes.h"
+
+#include "mlir/Dialect/Arith/IR/Arith.h"
+#include "mlir/Dialect/SCF/IR/SCF.h"
+#include "mlir/Dialect/SCF/Transforms/Patterns.h"
+#include "mlir/IR/Dominance.h"
+#include "mlir/IR/PatternMatch.h"
+#include "mlir/Transforms/GreedyPatternRewriteDriver.h"
+
+namespace mlir {
+#define GEN_PASS_DEF_SCFUPLIFTWHILETOFOR
+#include "mlir/Dialect/SCF/Transforms/Passes.h.inc"
+} // namespace mlir
+
+using namespace mlir;
+
+static bool checkIndexType(arith::CmpIOp op, unsigned indexBitWidth) {
+  auto type = op.getLhs().getType();
+  if (isa<mlir::IndexType>(type))
+    return true;
+
+  if (type.isSignlessInteger(indexBitWidth))
+    return true;
+
+  return false;
+}
+
+namespace {
+struct UpliftWhileOp : public OpRewritePattern<scf::WhileOp> {
+  UpliftWhileOp(MLIRContext *context, unsigned indexBitWidth_)
+      : OpRewritePattern<scf::WhileOp>(context), indexBitWidth(indexBitWidth_) {
+  }
+
+  LogicalResult matchAndRewrite(scf::WhileOp loop,
+                                PatternRewriter &rewriter) const override {
+    Block *beforeBody = loop.getBeforeBody();
+    if (!llvm::hasSingleElement(beforeBody->without_terminator()))
+      return rewriter.notifyMatchFailure(loop, "Loop body must have single op");
+
+    auto cmp = dyn_cast<arith::CmpIOp>(beforeBody->front());
+    if (!cmp)
+      return rewriter.notifyMatchFailure(loop,
+                                         "Loop body must have single cmp op");
+
+    auto beforeTerm = cast<scf::ConditionOp>(beforeBody->getTerminator());
+    if (!llvm::hasSingleElement(cmp->getUses()) &&
+        beforeTerm.getCondition() == cmp.getResult())
+      return rewriter.notifyMatchFailure(loop, [&](Diagnostic &diag) {
+        diag << "Expected single condiditon use: " << *cmp;
+      });
+
+    if (ValueRange(beforeBody->getArguments()) != beforeTerm.getArgs())
+      return rewriter.notifyMatchFailure(loop, "Invalid args order");
+
+    using Pred = arith::CmpIPredicate;
+    auto predicate = cmp.getPredicate();
+    if (predicate != Pred::slt && predicate != Pred::sgt)
+      return rewriter.notifyMatchFailure(loop, [&](Diagnostic &diag) {
+        diag << "Expected 'slt' or 'sgt' predicate: " << *cmp;
+      });
+
+    if (!checkIndexType(cmp, indexBitWidth))
+      return rewriter.notifyMatchFailure(loop, [&](Diagnostic &diag) {
+        diag << "Expected index-like type: " << *cmp;
+      });
+
+    BlockArgument iterVar;
+    Value end;
+    DominanceInfo dom;
+    for (bool reverse : {false, true}) {
+      auto expectedPred = reverse ? Pred::sgt : Pred::slt;
+      if (cmp.getPredicate() != expectedPred)
+        continue;
+
+      auto arg1 = reverse ? cmp.getRhs() : cmp.getLhs();
+      auto arg2 = reverse ? cmp.getLhs() : cmp.getRhs();
+
+      auto blockArg = dyn_cast<BlockArgument>(arg1);
+      if (!blockArg || blockArg.getOwner() != beforeBody)
+        continue;
+
+      if (!dom.properlyDominates(arg2, loop))
+        continue;
+
+      iterVar = blockArg;
+      end = arg2;
+      break;
+    }
+
+    if (!iterVar)
+      return rewriter.notifyMatchFailure(loop, [&](Diagnostic &diag) {
+        diag << "Unrecognized cmp form: " << *cmp;
+      });
+
+    if (!llvm::hasNItems(iterVar.getUses(), 2))
+      return rewriter.notifyMatchFailure(loop, [&](Diagnostic &diag) {
+        diag << "Unrecognized iter var: " << iterVar;
+      });
+
+    Block *afterBody = loop.getAfterBody();
+    auto afterTerm = cast<scf::YieldOp>(afterBody->getTerminator());
+    auto argNumber = iterVar.getArgNumber();
+    auto afterTermIterArg = afterTerm.getResults()[argNumber];
+
+    auto iterVarAfter = afterBody->getArgument(argNumber);
+
+    Value step;
+    for (auto &use : iterVarAfter.getUses()) {
+      auto owner = dyn_cast<arith::AddIOp>(use.getOwner());
----------------
matthias-springer wrote:

Maybe add TODO that `SubIOp` are not supported yet.

https://github.com/llvm/llvm-project/pull/76108