mlir/lib/Conversion/ReconcileUnrealizedCasts/ReconcileUnrealizedCasts.cpp

   1 //===- ReconcileUnrealizedCasts.cpp - Eliminate noop unrealized casts -----===//
   2 //
   3 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
   4 // See https://llvm.org/LICENSE.txt for license information.
   5 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
   6 //
   7 //===----------------------------------------------------------------------===//
   8
   9 #include "mlir/Conversion/ReconcileUnrealizedCasts/ReconcileUnrealizedCasts.h"
  10
  11 #include "mlir/IR/BuiltinOps.h"
  12 #include "mlir/Pass/Pass.h"
  13 #include "mlir/Transforms/DialectConversion.h"
  14
  15 namespace mlir {
  16 #define GEN_PASS_DEF_RECONCILEUNREALIZEDCASTS
  17 #include "mlir/Conversion/Passes.h.inc"
  18 } // namespace mlir
  19
  20 using namespace mlir;
  21
  22 namespace {
  23
  24 /// Pass to simplify and eliminate unrealized conversion casts.
  25 ///
  26 /// This pass processes unrealized_conversion_cast ops in a worklist-driven
  27 /// fashion. For each matched cast op, if the chain of input casts eventually
  28 /// reaches a cast op where the input types match the output types of the
  29 /// matched op, replace the matched op with the inputs.
  30 ///
  31 /// Example:
  32 /// %1 = unrealized_conversion_cast %0 : !A to !B
  33 /// %2 = unrealized_conversion_cast %1 : !B to !C
  34 /// %3 = unrealized_conversion_cast %2 : !C to !A
  35 ///
  36 /// In the above example, %0 can be used instead of %3 and all cast ops are
  37 /// folded away.
  38 struct ReconcileUnrealizedCasts
  39     : public impl::ReconcileUnrealizedCastsBase<ReconcileUnrealizedCasts> {
  40   ReconcileUnrealizedCasts() = default;
  41
  42   void runOnOperation() override {
  43     SmallVector<UnrealizedConversionCastOp> ops;
  44     getOperation()->walk(
  45         [&](UnrealizedConversionCastOp castOp) { ops.push_back(castOp); });
  46     reconcileUnrealizedCasts(ops);
  47   }
  48 };
  49
  50 } // namespace
  51
  52 std::unique_ptr<Pass> mlir::createReconcileUnrealizedCastsPass() {
  53   return std::make_unique<ReconcileUnrealizedCasts>();
  54 }