[mlir][affine] Add pass --affine-raise-from-memref

mlir/include/mlir/Dialect/Affine/Passes.h

@@ -22,6 +22,9 @@ namespace mlir {
 namespace func {
 class FuncOp;
 } // namespace func
+namespace memref {
+class MemRefDialect;
+} // namespace memref
 
 namespace affine {
 class AffineForOp;
@@ -48,6 +51,9 @@ createAffineLoopInvariantCodeMotionPass();
 /// ops.
 std::unique_ptr<OperationPass<func::FuncOp>> createAffineParallelizePass();
 
+/// Creates a pass that converts some memref operators to affine operators.
+std::unique_ptr<OperationPass<func::FuncOp>> createRaiseMemrefToAffine();
+
 /// Apply normalization transformations to affine loop-like ops. If
 /// `promoteSingleIter` is true, single iteration loops are promoted (i.e., the
 /// loop is replaced by its loop body).

mlir/include/mlir/Dialect/Affine/Passes.td

@@ -397,6 +397,18 @@ def LoopCoalescing : Pass<"affine-loop-coalescing", "func::FuncOp"> {
   let dependentDialects = ["affine::AffineDialect","arith::ArithDialect"];
 }
 
+def RaiseMemrefDialect : Pass<"affine-raise-from-memref", "func::FuncOp"> {
+  let summary = "Turn some memref operators to affine operators where supported";
+  let description = [{
+    Raise memref.load and memref.store to affine.store and affine.load, inferring
+    the affine map of those operators if needed. This allows passes like --affine-scalrep
+    to optimize those loads and stores (forwarding them or eliminating them).
+    They can be turned back to memref dialect ops with --lower-affine.
+  }];
+  let constructor = "mlir::affine::createRaiseMemrefToAffine()";
+  let dependentDialects = ["affine::AffineDialect"];
+}
+
 def SimplifyAffineStructures : Pass<"affine-simplify-structures", "func::FuncOp"> {
   let summary = "Simplify affine expressions in maps/sets and normalize "
                 "memrefs";

mlir/lib/Dialect/Affine/IR/AffineOps.cpp

@@ -284,10 +284,12 @@ bool mlir::affine::isValidDim(Value value) {
     return isValidDim(value, getAffineScope(defOp));
 
   // This value has to be a block argument for an op that has the
-  // `AffineScope` trait or for an affine.for or affine.parallel.
+  // `AffineScope` trait or an induction var of an affine.for or
+  // affine.parallel.
+  if (isAffineInductionVar(value))
+    return true;
   auto *parentOp = llvm::cast<BlockArgument>(value).getOwner()->getParentOp();
-  return parentOp && (parentOp->hasTrait<OpTrait::AffineScope>() ||
-                      isa<AffineForOp, AffineParallelOp>(parentOp));
+  return parentOp && parentOp->hasTrait<OpTrait::AffineScope>();
 }
 
 // Value can be used as a dimension id iff it meets one of the following
@@ -306,10 +308,9 @@ bool mlir::affine::isValidDim(Value value, Region *region) {
 
   auto *op = value.getDefiningOp();
   if (!op) {
-    // This value has to be a block argument for an affine.for or an
+    // This value has to be an induction var for an affine.for or an
     // affine.parallel.
-    auto *parentOp = llvm::cast<BlockArgument>(value).getOwner()->getParentOp();
-    return isa<AffineForOp, AffineParallelOp>(parentOp);
+    return isAffineInductionVar(value);
   }
 
   // Affine apply operation is ok if all of its operands are ok.

mlir/lib/Dialect/Affine/Transforms/CMakeLists.txt

@@ -13,6 +13,7 @@ add_mlir_dialect_library(MLIRAffineTransforms
   LoopUnroll.cpp
   LoopUnrollAndJam.cpp
   PipelineDataTransfer.cpp
+  RaiseMemrefDialect.cpp
   ReifyValueBounds.cpp
   SuperVectorize.cpp
   SimplifyAffineStructures.cpp

mlir/lib/Dialect/Affine/Transforms/RaiseMemrefDialect.cpp

@@ -0,0 +1,187 @@
+//===- RaiseMemrefDialect.cpp - raise memref.store and load to affine ops -===//
+//
+// 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
+//
+//===----------------------------------------------------------------------===//
+//
+// This file implements functionality to convert memref load and store ops to
+// the corresponding affine ops, inferring the affine map as needed.
+//
+//===----------------------------------------------------------------------===//
+
+#include "mlir/Dialect/Affine/Analysis/Utils.h"
+#include "mlir/Dialect/Affine/Passes.h"
+#include "mlir/Dialect/Affine/Transforms/Transforms.h"
+#include "mlir/Dialect/Affine/Utils.h"
+#include "mlir/Dialect/Func/IR/FuncOps.h"
+#include "mlir/Dialect/MemRef/IR/MemRef.h"
+#include "mlir/IR/AffineExpr.h"
+#include "mlir/IR/Matchers.h"
+#include "mlir/IR/Operation.h"
+#include "mlir/Pass/Pass.h"
+#include "llvm/Support/Casting.h"
+#include "llvm/Support/Debug.h"
+
+namespace mlir {
+namespace affine {
+#define GEN_PASS_DEF_RAISEMEMREFDIALECT
+#include "mlir/Dialect/Affine/Passes.h.inc"
+} // namespace affine
+} // namespace mlir
+
+#define DEBUG_TYPE "raise-memref-to-affine"
+
+using namespace mlir;
+using namespace mlir::affine;
+
+namespace {
+
+/// Find the index of the given value in the `dims` list,
+/// and append it if it was not already in the list. The
+/// dims list is a list of symbols or dimensions of the
+/// affine map. Within the results of an affine map, they
+/// are identified by their index, which is why we need
+/// this function.
+static std::optional<size_t>
+findInListOrAdd(Value value, llvm::SmallVectorImpl<Value> &dims,
+                function_ref<bool(Value)> isValidElement) {
+
+  Value *loopIV = std::find(dims.begin(), dims.end(), value);
+  if (loopIV != dims.end()) {
+    // We found an IV that already has an index, return that index.
+    return {std::distance(dims.begin(), loopIV)};
+  }
+  if (isValidElement(value)) {
+    // This is a valid element for the dim/symbol list, push this as a
+    // parameter.
+    size_t idx = dims.size();
+    dims.push_back(value);
+    return idx;
+  }
+  return std::nullopt;
+}
+
+/// Convert a value to an affine expr if possible. Adds dims and symbols
+/// if needed.
+static AffineExpr toAffineExpr(Value value,
+                               llvm::SmallVectorImpl<Value> &affineDims,
+                               llvm::SmallVectorImpl<Value> &affineSymbols) {
+  using namespace matchers;
+  IntegerAttr::ValueType cst;
+  if (matchPattern(value, m_ConstantInt(&cst))) {
+    return getAffineConstantExpr(cst.getSExtValue(), value.getContext());
+  }
+
+  Operation *definingOp = value.getDefiningOp();
+  if (llvm::isa_and_nonnull<arith::AddIOp>(definingOp) ||
+      llvm::isa_and_nonnull<arith::MulIOp>(definingOp)) {
+    // TODO: replace recursion with explicit stack.
+    // For the moment this can be tolerated as we only recurse on
+    // arith.addi and arith.muli, so there cannot be any infinite
+    // recursion. The depth of these expressions should be in most
+    // cases very manageable, as affine expressions should be as
+    // simple as `a + b * c`.
+    AffineExpr lhsE =
+        toAffineExpr(definingOp->getOperand(0), affineDims, affineSymbols);
+    AffineExpr rhsE =
+        toAffineExpr(definingOp->getOperand(1), affineDims, affineSymbols);
+
+    if (lhsE && rhsE) {
+      AffineExprKind kind;
+      if (isa<arith::AddIOp>(definingOp)) {
+        kind = mlir::AffineExprKind::Add;
+      } else {
+        kind = mlir::AffineExprKind::Mul;
+
+        if (!lhsE.isSymbolicOrConstant() && !rhsE.isSymbolicOrConstant()) {
+          // This is not an affine expression, give up.
+          return {};
+        }
+      }
+      return getAffineBinaryOpExpr(kind, lhsE, rhsE);
+    }
+    return {};
+  }
+
+  if (auto dimIx = findInListOrAdd(value, affineSymbols, [](Value v) {
+        return affine::isValidSymbol(v);
+      })) {
+    return getAffineSymbolExpr(*dimIx, value.getContext());
+  }
+
+  if (auto dimIx = findInListOrAdd(
+          value, affineDims, [](Value v) { return affine::isValidDim(v); })) {
+
+    return getAffineDimExpr(*dimIx, value.getContext());
+  }
+
+  return {};
+}
+
+static LogicalResult
+computeAffineMapAndArgs(MLIRContext *ctx, ValueRange indices, AffineMap &map,
+                        llvm::SmallVectorImpl<Value> &mapArgs) {
+  SmallVector<AffineExpr> results;
+  SmallVector<Value> symbols;
+  SmallVector<Value> dims;
+
+  for (Value indexExpr : indices) {
+    AffineExpr res = toAffineExpr(indexExpr, dims, symbols);
+    if (!res) {
+      return failure();
+    }
+    results.push_back(res);
+  }
+
+  map = AffineMap::get(dims.size(), symbols.size(), results, ctx);
+
+  dims.append(symbols);
+  mapArgs.swap(dims);
+  return success();
+}
+
+struct RaiseMemrefDialect
+    : public affine::impl::RaiseMemrefDialectBase<RaiseMemrefDialect> {
+
+  void runOnOperation() override {
+    auto *ctx = &getContext();
+    Operation *op = getOperation();
+    IRRewriter rewriter(ctx);
+    AffineMap map;
+    SmallVector<Value> mapArgs;
+    op->walk([&](Operation *op) {
+      rewriter.setInsertionPoint(op);
+      if (auto store = llvm::dyn_cast_or_null<memref::StoreOp>(op)) {
+
+        if (succeeded(computeAffineMapAndArgs(ctx, store.getIndices(), map,
+                                              mapArgs))) {
+          rewriter.replaceOpWithNewOp<AffineStoreOp>(
+              op, store.getValueToStore(), store.getMemRef(), map, mapArgs);
+          return;
+        }
+
+        LLVM_DEBUG(llvm::dbgs()
+                   << "[affine] Cannot raise memref op: " << op << "\n");
+
+      } else if (auto load = llvm::dyn_cast_or_null<memref::LoadOp>(op)) {
+        if (succeeded(computeAffineMapAndArgs(ctx, load.getIndices(), map,
+                                              mapArgs))) {
+          rewriter.replaceOpWithNewOp<AffineLoadOp>(op, load.getMemRef(), map,
+                                                    mapArgs);
+          return;
+        }
+        LLVM_DEBUG(llvm::dbgs()
+                   << "[affine] Cannot raise memref op: " << op << "\n");
+      }
+    });
+  }
+};
+
+} // namespace
+
+std::unique_ptr<OperationPass<func::FuncOp>>
+mlir::affine::createRaiseMemrefToAffine() {
+  return std::make_unique<RaiseMemrefDialect>();
+}