chromium/v8/src/compiler/turboshaft/structural-optimization-reducer.h

// Copyright 2022 the V8 project authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

#ifndef V8_COMPILER_TURBOSHAFT_STRUCTURAL_OPTIMIZATION_REDUCER_H_
#define V8_COMPILER_TURBOSHAFT_STRUCTURAL_OPTIMIZATION_REDUCER_H_

#include <cstdio>

#include "src/compiler/turboshaft/assembler.h"
#include "src/compiler/turboshaft/index.h"
#include "src/compiler/turboshaft/opmasks.h"
#include "src/zone/zone.h"

// The StructuralOptimizationReducer reducer is suitable for changing the
// graph in a way that doesn't reduce individual operations, rather changes
// the structure of the graph.
//
// We currently support a reduction which transforms if-else cascades
// that check if a given value is equal to a 32-bit constant from a given set
// into a switch with cases corresponding to the constants in the set.
//
// So for example code like:
//    [only pure ops 1]
//    if (x == 3) {
//      B1;
//    } else {
//      [only pure ops 2]
//      if (x == 5) {
//        B2;
//      } else {
//        B3;
//      }
//    }
//
// will be transformed to:
//    [only pure ops 1]
//    [only pure ops 2]
//    switch (x) {
//      case 3:
//        B1;
//      case 5:
//        B2;
//      default:
//        B3;
//    }
//
// Or represented graphically:
//                                                 [only pure ops 1]
//       [only pure ops 1]                         [only pure ops 2]
//           x == 3                                    Switch(x)
//           Branch                                    |    |   |
//           |    |                                -----    |   ------
//       -----    ------                    case 3 |        |        | default
//       |             |                           |        |        |
//     T |             | F                         v        |        |
//       v             v                           B1       |        v
//       B1      [only pure ops 2]    becomes               |        B3
//                   x == 5           ======>        case 5 |
//                   Branch                                 v
//                   |    |                                 B2
//               -----    ------
//               |             |
//             T |             | F
//               v             v
//              B2            B3
//

// TODO(mslekova): Introduce a flag and move to a common graph place.
// #define TRACE_REDUCTIONS
#ifdef TRACE_REDUCTIONS
#define TRACE …
#else  // TRACE_REDUCTIONS
#define TRACE …

#endif  // TRACE_REDUCTIONS

namespace v8::internal::compiler::turboshaft {

template <class Next>
class StructuralOptimizationReducer : public Next { … };

}  // namespace v8::internal::compiler::turboshaft

#undef TRACE

#endif  // V8_COMPILER_TURBOSHAFT_STRUCTURAL_OPTIMIZATION_REDUCER_H_