[Mlir-commits] [mlir] [MLIR][Transforms] add eliminate-explicit-rounding pass (PR #93443)

[Jakub Kuderski]

================
@@ -0,0 +1,86 @@
+//===- EliminateExplicitRounding.cpp - Remove intermediate extf/truncf pairs
+//-===//
+//
+// 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 removing intermediate extf/truncf pairs inserted from
+// type conversion.
+//
+//===----------------------------------------------------------------------===//
+#include "mlir/Dialect/Arith/Transforms/Passes.h"
+
+#include "mlir/Dialect/Arith/IR/Arith.h"
+#include "mlir/IR/PatternMatch.h"
+#include "mlir/IR/TypeUtilities.h"
+#include "mlir/Transforms/GreedyPatternRewriteDriver.h"
+
+namespace mlir {
+namespace arith {
+#define GEN_PASS_DEF_ELIMINATEEXPLICITROUNDING
+#include "mlir/Dialect/Arith/Transforms/Passes.h.inc"
+} // namespace arith
+} // namespace mlir
+
+using namespace mlir;
+
+namespace {
+
+struct EliminateExplicitRoundingRewritePattern final
+    : OpRewritePattern<arith::ExtFOp> {
+  using OpRewritePattern::OpRewritePattern;
+  using FilterFunction = std::function<bool(Operation *)>;
+
+  EliminateExplicitRoundingRewritePattern(MLIRContext *context,
+                                          FilterFunction filterFunc = nullptr)
+      : OpRewritePattern(context), filterFunc(filterFunc) {}
+
+  LogicalResult matchAndRewrite(arith::ExtFOp extFOp,
+                                PatternRewriter &rewriter) const final {
+    // Check whether match `truncF->extF` pair.
+    auto truncFOp = extFOp.getOperand().getDefiningOp<arith::TruncFOp>();
+    if (!truncFOp)
+      return failure();
+
+    // Check whether need to filter out.
+    if (filterFunc && filterFunc(extFOp))
+      return failure();
+
+    // Check whether the rounding pair's input and output data type are the
+    // same. Currently only consider to eliminate rounding pairs for (bf16 / f16
+    // <-> f32).
+    auto input = truncFOp.getOperand();
+    auto inTy = input.getType();
+    auto outTy = extFOp.getType();
+    auto shortTy = getElementTypeOrSelf(truncFOp.getType());
+    if (inTy == outTy && getElementTypeOrSelf(inTy).isF32() &&
+        (shortTy.isF16() || shortTy.isBF16())) {
+      rewriter.replaceOp(extFOp, {input});
+      return success();
+    }
+
+    return failure();
+  }
+
+private:
+  FilterFunction filterFunc;
+};
+
+struct EliminateExplicitRounding final
+    : arith::impl::EliminateExplicitRoundingBase<EliminateExplicitRounding> {
+  using EliminateExplicitRoundingBase::EliminateExplicitRoundingBase;
+  void runOnOperation() override {
+    RewritePatternSet patterns(&getContext());
+    patterns.insert<EliminateExplicitRoundingRewritePattern>(&getContext());
+    FrozenRewritePatternSet patternSet(std::move(patterns));
+    SmallVector<Operation *> ops;
+    getOperation()->walk([&](arith::ExtFOp op) { ops.push_back(op); });
+    if (failed(applyOpPatternsAndFold(ops, patternSet)))
+      signalPassFailure();
----------------
kuhar wrote:

> However, in the current design, this pass is executed only after all f32 promotions are completed, so nested cases do not occur

This pass is not a part of a single pipeline; I don think we can assume this is the only context when it can be invoked. In fact, it's not part of any pass pipeline right now.

https://github.com/llvm/llvm-project/pull/93443