Coverage Report

Created: 2018-02-20 23:11

/Users/buildslave/jenkins/workspace/clang-stage2-coverage-R/llvm/tools/polly/lib/Transform/FlattenAlgo.cpp
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//===------ FlattenAlgo.cpp ------------------------------------*- C++ -*-===//
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//
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//                     The LLVM Compiler Infrastructure
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//
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// This file is distributed under the University of Illinois Open Source
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// License. See LICENSE.TXT for details.
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//
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//===----------------------------------------------------------------------===//
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//
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// Main algorithm of the FlattenSchedulePass. This is a separate file to avoid
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// the unittest for this requiring linking against LLVM.
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//
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//===----------------------------------------------------------------------===//
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#include "polly/FlattenAlgo.h"
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#include "polly/Support/ISLOStream.h"
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#include "polly/Support/ISLTools.h"
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#include "llvm/Support/Debug.h"
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#define DEBUG_TYPE "polly-flatten-algo"
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using namespace polly;
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using namespace llvm;
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namespace {
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/// Whether a dimension of a set is bounded (lower and upper) by a constant,
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/// i.e. there are two constants Min and Max, such that every value x of the
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/// chosen dimensions is Min <= x <= Max.
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bool isDimBoundedByConstant(isl::set Set, unsigned dim) {
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  auto ParamDims = Set.dim(isl::dim::param);
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  Set = Set.project_out(isl::dim::param, 0, ParamDims);
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  Set = Set.project_out(isl::dim::set, 0, dim);
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  auto SetDims = Set.dim(isl::dim::set);
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  Set = Set.project_out(isl::dim::set, 1, SetDims - 1);
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  return bool(Set.is_bounded());
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}
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/// Whether a dimension of a set is (lower and upper) bounded by a constant or
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/// parameters, i.e. there are two expressions Min_p and Max_p of the parameters
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/// p, such that every value x of the chosen dimensions is
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/// Min_p <= x <= Max_p.
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bool isDimBoundedByParameter(isl::set Set, unsigned dim) {
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  Set = Set.project_out(isl::dim::set, 0, dim);
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  auto SetDims = Set.dim(isl::dim::set);
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  Set = Set.project_out(isl::dim::set, 1, SetDims - 1);
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  return bool(Set.is_bounded());
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}
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/// Whether BMap's first out-dimension is not a constant.
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bool isVariableDim(const isl::basic_map &BMap) {
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  auto FixedVal = BMap.plain_get_val_if_fixed(isl::dim::out, 0);
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  return !FixedVal || FixedVal.is_nan();
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}
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/// Whether Map's first out dimension is no constant nor piecewise constant.
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bool isVariableDim(const isl::map &Map) {
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  return Map.foreach_basic_map([](isl::basic_map BMap) -> isl::stat {
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    if (isVariableDim(BMap))
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      return isl::stat::error;
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    return isl::stat::ok;
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  }) == isl::stat::ok;
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}
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/// Whether UMap's first out dimension is no (piecewise) constant.
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bool isVariableDim(const isl::union_map &UMap) {
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  return UMap.foreach_map([](isl::map Map) -> isl::stat {
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    if (isVariableDim(Map))
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      return isl::stat::error;
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    return isl::stat::ok;
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  }) == isl::stat::ok;
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}
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/// Compute @p UPwAff - @p Val.
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isl::union_pw_aff subtract(isl::union_pw_aff UPwAff, isl::val Val) {
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  if (Val.is_zero())
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    return UPwAff;
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  auto Result = isl::union_pw_aff::empty(UPwAff.get_space());
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  UPwAff.foreach_pw_aff([=, &Result](isl::pw_aff PwAff) -> isl::stat {
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    auto ValAff =
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        isl::pw_aff(isl::set::universe(PwAff.get_space().domain()), Val);
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    auto Subtracted = PwAff.sub(ValAff);
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    Result = Result.union_add(isl::union_pw_aff(Subtracted));
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    return isl::stat::ok;
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  });
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  return Result;
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}
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/// Compute @UPwAff * @p Val.
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isl::union_pw_aff multiply(isl::union_pw_aff UPwAff, isl::val Val) {
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  if (Val.is_one())
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    return UPwAff;
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  auto Result = isl::union_pw_aff::empty(UPwAff.get_space());
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  UPwAff.foreach_pw_aff([=, &Result](isl::pw_aff PwAff) -> isl::stat {
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    auto ValAff =
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        isl::pw_aff(isl::set::universe(PwAff.get_space().domain()), Val);
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    auto Multiplied = PwAff.mul(ValAff);
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    Result = Result.union_add(Multiplied);
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    return isl::stat::ok;
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  });
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  return Result;
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}
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/// Remove @p n dimensions from @p UMap's range, starting at @p first.
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///
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/// It is assumed that all maps in the maps have at least the necessary number
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/// of out dimensions.
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isl::union_map scheduleProjectOut(const isl::union_map &UMap, unsigned first,
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                                  unsigned n) {
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  if (n == 0)
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    return UMap; /* isl_map_project_out would also reset the tuple, which should
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                    have no effect on schedule ranges */
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  auto Result = isl::union_map::empty(UMap.get_space());
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  UMap.foreach_map([=, &Result](isl::map Map) -> isl::stat {
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    auto Outprojected = Map.project_out(isl::dim::out, first, n);
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    Result = Result.add_map(Outprojected);
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    return isl::stat::ok;
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  });
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  return Result;
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}
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/// Return the number of dimensions in the input map's range.
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///
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/// Because this function takes an isl_union_map, the out dimensions could be
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/// different. We return the maximum number in this case. However, a different
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/// number of dimensions is not supported by the other code in this file.
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size_t scheduleScatterDims(const isl::union_map &Schedule) {
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  unsigned Dims = 0;
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  Schedule.foreach_map([&Dims](isl::map Map) -> isl::stat {
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    Dims = std::max(Dims, Map.dim(isl::dim::out));
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    return isl::stat::ok;
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  });
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  return Dims;
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}
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/// Return the @p pos' range dimension, converted to an isl_union_pw_aff.
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isl::union_pw_aff scheduleExtractDimAff(isl::union_map UMap, unsigned pos) {
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  auto SingleUMap = isl::union_map::empty(UMap.get_space());
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  UMap.foreach_map([=, &SingleUMap](isl::map Map) -> isl::stat {
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    auto MapDims = Map.dim(isl::dim::out);
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    auto SingleMap = Map.project_out(isl::dim::out, 0, pos);
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    SingleMap = SingleMap.project_out(isl::dim::out, 1, MapDims - pos - 1);
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    SingleUMap = SingleUMap.add_map(SingleMap);
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    return isl::stat::ok;
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  });
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  auto UAff = isl::union_pw_multi_aff(SingleUMap);
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  auto FirstMAff = isl::multi_union_pw_aff(UAff);
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  return FirstMAff.get_union_pw_aff(0);
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}
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/// Flatten a sequence-like first dimension.
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///
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/// A sequence-like scatter dimension is constant, or at least only small
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/// variation, typically the result of ordering a sequence of different
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/// statements. An example would be:
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///   { Stmt_A[] -> [0, X, ...]; Stmt_B[] -> [1, Y, ...] }
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/// to schedule all instances of Stmt_A before any instance of Stmt_B.
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///
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/// To flatten, first begin with an offset of zero. Then determine the lowest
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/// possible value of the dimension, call it "i" [In the example we start at 0].
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/// Considering only schedules with that value, consider only instances with
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/// that value and determine the extent of the next dimension. Let l_X(i) and
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/// u_X(i) its minimum (lower bound) and maximum (upper bound) value. Add them
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/// as "Offset + X - l_X(i)" to the new schedule, then add "u_X(i) - l_X(i) + 1"
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/// to Offset and remove all i-instances from the old schedule. Repeat with the
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/// remaining lowest value i' until there are no instances in the old schedule
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/// left.
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/// The example schedule would be transformed to:
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///   { Stmt_X[] -> [X - l_X, ...]; Stmt_B -> [l_X - u_X + 1 + Y - l_Y, ...] }
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isl::union_map tryFlattenSequence(isl::union_map Schedule) {
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  auto IslCtx = Schedule.get_ctx();
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  auto ScatterSet = isl::set(Schedule.range());
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  auto ParamSpace = Schedule.get_space().params();
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  auto Dims = ScatterSet.dim(isl::dim::set);
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  assert(Dims >= 2);
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  // Would cause an infinite loop.
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  if (!isDimBoundedByConstant(ScatterSet, 0)) {
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    DEBUG(dbgs() << "Abort; dimension is not of fixed size\n");
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    return nullptr;
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  }
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  auto AllDomains = Schedule.domain();
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  auto AllDomainsToNull = isl::union_pw_multi_aff(AllDomains);
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  auto NewSchedule = isl::union_map::empty(ParamSpace);
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  auto Counter = isl::pw_aff(isl::local_space(ParamSpace.set_from_params()));
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  while (!ScatterSet.is_empty()) {
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    DEBUG(dbgs() << "Next counter:\n  " << Counter << "\n");
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    DEBUG(dbgs() << "Remaining scatter set:\n  " << ScatterSet << "\n");
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    auto ThisSet = ScatterSet.project_out(isl::dim::set, 1, Dims - 1);
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    auto ThisFirst = ThisSet.lexmin();
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    auto ScatterFirst = ThisFirst.add_dims(isl::dim::set, Dims - 1);
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    auto SubSchedule = Schedule.intersect_range(ScatterFirst);
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    SubSchedule = scheduleProjectOut(SubSchedule, 0, 1);
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    SubSchedule = flattenSchedule(SubSchedule);
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    auto SubDims = scheduleScatterDims(SubSchedule);
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    auto FirstSubSchedule = scheduleProjectOut(SubSchedule, 1, SubDims - 1);
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    auto FirstScheduleAff = scheduleExtractDimAff(FirstSubSchedule, 0);
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    auto RemainingSubSchedule = scheduleProjectOut(SubSchedule, 0, 1);
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    auto FirstSubScatter = isl::set(FirstSubSchedule.range());
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    DEBUG(dbgs() << "Next step in sequence is:\n  " << FirstSubScatter << "\n");
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    if (!isDimBoundedByParameter(FirstSubScatter, 0)) {
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      DEBUG(dbgs() << "Abort; sequence step is not bounded\n");
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      return nullptr;
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    }
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    auto FirstSubScatterMap = isl::map::from_range(FirstSubScatter);
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    // isl_set_dim_max returns a strange isl_pw_aff with domain tuple_id of
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    // 'none'. It doesn't match with any space including a 0-dimensional
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    // anonymous tuple.
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    // Interesting, one can create such a set using
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    // isl_set_universe(ParamSpace). Bug?
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    auto PartMin = FirstSubScatterMap.dim_min(0);
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    auto PartMax = FirstSubScatterMap.dim_max(0);
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    auto One = isl::pw_aff(isl::set::universe(ParamSpace.set_from_params()),
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                           isl::val::one(IslCtx));
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    auto PartLen = PartMax.add(PartMin.neg()).add(One);
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    auto AllPartMin = isl::union_pw_aff(PartMin).pullback(AllDomainsToNull);
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    auto FirstScheduleAffNormalized = FirstScheduleAff.sub(AllPartMin);
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    auto AllCounter = isl::union_pw_aff(Counter).pullback(AllDomainsToNull);
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    auto FirstScheduleAffWithOffset =
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        FirstScheduleAffNormalized.add(AllCounter);
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    auto ScheduleWithOffset = isl::union_map(FirstScheduleAffWithOffset)
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                                  .flat_range_product(RemainingSubSchedule);
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    NewSchedule = NewSchedule.unite(ScheduleWithOffset);
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    ScatterSet = ScatterSet.subtract(ScatterFirst);
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    Counter = Counter.add(PartLen);
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  }
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  DEBUG(dbgs() << "Sequence-flatten result is:\n  " << NewSchedule << "\n");
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  return NewSchedule;
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}
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/// Flatten a loop-like first dimension.
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///
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/// A loop-like dimension is one that depends on a variable (usually a loop's
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/// induction variable). Let the input schedule look like this:
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///   { Stmt[i] -> [i, X, ...] }
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///
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/// To flatten, we determine the largest extent of X which may not depend on the
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/// actual value of i. Let l_X() the smallest possible value of X and u_X() its
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/// largest value. Then, construct a new schedule
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///   { Stmt[i] -> [i * (u_X() - l_X() + 1), ...] }
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isl::union_map tryFlattenLoop(isl::union_map Schedule) {
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  assert(scheduleScatterDims(Schedule) >= 2);
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  auto Remaining = scheduleProjectOut(Schedule, 0, 1);
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  auto SubSchedule = flattenSchedule(Remaining);
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  auto SubDims = scheduleScatterDims(SubSchedule);
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  auto SubExtent = isl::set(SubSchedule.range());
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  auto SubExtentDims = SubExtent.dim(isl::dim::param);
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  SubExtent = SubExtent.project_out(isl::dim::param, 0, SubExtentDims);
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  SubExtent = SubExtent.project_out(isl::dim::set, 1, SubDims - 1);
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  if (!isDimBoundedByConstant(SubExtent, 0)) {
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    DEBUG(dbgs() << "Abort; dimension not bounded by constant\n");
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    return nullptr;
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  }
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  auto Min = SubExtent.dim_min(0);
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  DEBUG(dbgs() << "Min bound:\n  " << Min << "\n");
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  auto MinVal = getConstant(Min, false, true);
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  auto Max = SubExtent.dim_max(0);
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  DEBUG(dbgs() << "Max bound:\n  " << Max << "\n");
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  auto MaxVal = getConstant(Max, true, false);
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  if (!MinVal || !MaxVal || MinVal.is_nan() || MaxVal.is_nan()) {
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    DEBUG(dbgs() << "Abort; dimension bounds could not be determined\n");
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    return nullptr;
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  }
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  auto FirstSubScheduleAff = scheduleExtractDimAff(SubSchedule, 0);
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  auto RemainingSubSchedule = scheduleProjectOut(std::move(SubSchedule), 0, 1);
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  auto LenVal = MaxVal.sub(MinVal).add_ui(1);
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  auto FirstSubScheduleNormalized = subtract(FirstSubScheduleAff, MinVal);
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  // TODO: Normalize FirstAff to zero (convert to isl_map, determine minimum,
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  // subtract it)
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  auto FirstAff = scheduleExtractDimAff(Schedule, 0);
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  auto Offset = multiply(FirstAff, LenVal);
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  auto Index = FirstSubScheduleNormalized.add(Offset);
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  auto IndexMap = isl::union_map(Index);
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  auto Result = IndexMap.flat_range_product(RemainingSubSchedule);
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  DEBUG(dbgs() << "Loop-flatten result is:\n  " << Result << "\n");
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  return Result;
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}
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} // anonymous namespace
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isl::union_map polly::flattenSchedule(isl::union_map Schedule) {
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  auto Dims = scheduleScatterDims(Schedule);
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  DEBUG(dbgs() << "Recursive schedule to process:\n  " << Schedule << "\n");
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  // Base case; no dimensions left
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  if (Dims == 0) {
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    // TODO: Add one dimension?
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    return Schedule;
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  }
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  // Base case; already one-dimensional
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  if (Dims == 1)
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    return Schedule;
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  // Fixed dimension; no need to preserve variabledness.
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  if (!isVariableDim(Schedule)) {
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    DEBUG(dbgs() << "Fixed dimension; try sequence flattening\n");
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    auto NewScheduleSequence = tryFlattenSequence(Schedule);
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    if (NewScheduleSequence)
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      return NewScheduleSequence;
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  }
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  // Constant stride
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  DEBUG(dbgs() << "Try loop flattening\n");
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  auto NewScheduleLoop = tryFlattenLoop(Schedule);
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  if (NewScheduleLoop)
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    return NewScheduleLoop;
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  // Try again without loop condition (may blow up the number of pieces!!)
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  DEBUG(dbgs() << "Try sequence flattening again\n");
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  auto NewScheduleSequence = tryFlattenSequence(Schedule);
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  if (NewScheduleSequence)
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    return NewScheduleSequence;
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  // Cannot flatten
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  return Schedule;
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}