1//===- ScheduleOrderedAssignments.h --- Assignment scheduling ---*- C++ -*-===//
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// This file defines a utility to analyze and schedule the evaluation of
9// of hlfir::OrderedAssignmentTreeOpInterface trees that represent Fortran
10// Forall, Where, user defined assignments and assignments to vector
11// subscripted entities.
12//===----------------------------------------------------------------------===//
13
14#ifndef OPTIMIZER_HLFIR_TRANSFORM_SCHEDULEORDEREDASSIGNMENTS_H
15#define OPTIMIZER_HLFIR_TRANSFORM_SCHEDULEORDEREDASSIGNMENTS_H
16
17#include "flang/Optimizer/HLFIR/HLFIROps.h"
18
19namespace hlfir {
20
21/// Structure to represent that the value yielded by some region
22/// must be fully evaluated and saved for all index values at
23/// a given point of the ordered assignment tree evaluation.
24/// All subsequent evaluation depending on the value yielded
25/// by this region will use the value that was saved.
26struct SaveEntity {
27 mlir::Region *yieldRegion;
28 /// Returns the hlfir.yield op argument.
29 mlir::Value getSavedValue();
30};
31
32/// A run is a list of actions required to evaluate an ordered assignment tree
33/// that can be done in the same loop nest.
34/// The actions can evaluate and saves element values into temporary or evaluate
35/// assignments.
36/// The evaluation of an action in a run will cause the evaluation of all the
37/// regions that yield entities required to implement the action, except if the
38/// region was saved in a previous run, in which case it will use the previously
39/// saved value.
40struct Run {
41 /// An action is either saving the values yielded by a region, or evaluating
42 /// the assignment part of an hlfir::RegionAssignOp.
43 using Action = std::variant<hlfir::RegionAssignOp, SaveEntity>;
44 llvm::SmallVector<Action> actions;
45 llvm::SmallVector<mlir::MemoryEffects::EffectInstance> memoryEffects;
46};
47
48/// List of runs to be executed in order to evaluate an order assignment tree.
49using Schedule = llvm::SmallVector<Run>;
50
51/// Example of schedules and run, and what they mean:
52/// Fortran: forall (i=i:10) x(i) = y(i)
53///
54/// hlfir.forall lb { hlfir.yield %c1} ub { hlfir.yield %c10} do {
55/// ^bb1(%i: index)
56/// hlfir.region_assign {
57/// %yi_addr = hlfir.designate %y(%i)
58/// %yi = fir.load %yi_addr
59/// hlfir.yield %yi
60/// } to {
61/// %xi = hlfir.designate %x(%i)
62/// hlfir.yield %xi
63/// }
64/// }
65///
66/// If the scheduling analysis cannot prove that %x and %y do not overlap, it
67/// will generate 2 runs for the schdule. The first containing
68/// SaveEntity{rhs_region}, and the second one containing the
69/// hlfir.region_assign.
70///
71/// The lowering of that schedule will have to:
72/// For the first run:
73/// 1. create a temporary to contain all the %yi for all %i
74/// 2. create a loop nest for the forall, evaluate the %yi and save them
75/// inside the loop, but do not evaluate the LHS or assignment.
76/// For the second run:
77/// 3. create a loop nest again for the forall, evaluate the LHS, get the
78/// saved %yi, and evaluate %yi to %xi. After all runs:
79/// 4. clean the temporary for the %yi.
80///
81/// If the scheduling analysis can prove %x and %y do not overlap, it will
82/// generate only one run with the hlfir.region_assign, which will be
83/// implemented as a single loop that evaluate %xi, %yi and does %xi = %yi in
84/// the loop body.
85
86/// Core function that analyzes an ordered assignment tree and builds a
87/// schedule for its evaluation.
88/// The main goal of the scheduler is to avoid creating temporary storage
89/// (required for SaveEntity). But it can optionally be asked to fuse Forall
90/// and Where assignments in the same loop nests when possible since it has the
91/// memory effects analysis at hand.
92Schedule buildEvaluationSchedule(hlfir::OrderedAssignmentTreeOpInterface root,
93 bool tryFusingAssignments);
94
95} // namespace hlfir
96#endif // OPTIMIZER_HLFIR_TRANSFORM_SCHEDULEORDERASSIGNMENTS_H
97

source code of flang/lib/Optimizer/HLFIR/Transforms/ScheduleOrderedAssignments.h