Revision 5deee77b677da97c4dadc966f76d8bf01d855c57 authored by Steven Johnson on 01 April 2020, 00:47:39 UTC, committed by Steven Johnson on 01 April 2020, 00:47:39 UTC
1 parent cb6f4a9
Schedule.h
#ifndef HALIDE_SCHEDULE_H
#define HALIDE_SCHEDULE_H
/** \file
* Defines the internal representation of the schedule for a function
*/
#include <stddef.h>
#include <map>
#include <string>
#include <utility>
#include <vector>
#include "Expr.h"
#include "IntrusivePtr.h"
#include "Parameter.h"
namespace Halide {
class Func;
struct VarOrRVar;
namespace Internal {
class Function;
class IRVisitor;
struct FunctionPtr;
struct LoopLevelContents;
} // namespace Internal
/** Different ways to handle a tail case in a split when the
* factor does not provably divide the extent. */
enum class TailStrategy {
/** Round up the extent to be a multiple of the split
* factor. Not legal for RVars, as it would change the meaning
* of the algorithm. Pros: generates the simplest, fastest
* code. Cons: if used on a stage that reads from the input or
* writes to the output, constrains the input or output size
* to be a multiple of the split factor. */
RoundUp,
/** Guard the inner loop with an if statement that prevents
* evaluation beyond the original extent. Always legal. The if
* statement is treated like a boundary condition, and
* factored out into a loop epilogue if possible. Pros: no
* redundant re-evaluation; does not constrain input our
* output sizes. Cons: increases code size due to separate
* tail-case handling; vectorization will scalarize in the tail
* case to handle the if statement. */
GuardWithIf,
/** Prevent evaluation beyond the original extent by shifting
* the tail case inwards, re-evaluating some points near the
* end. Only legal for pure variables in pure definitions. If
* the inner loop is very simple, the tail case is treated
* like a boundary condition and factored out into an
* epilogue.
*
* This is a good trade-off between several factors. Like
* RoundUp, it supports vectorization well, because the inner
* loop is always a fixed size with no data-dependent
* branching. It increases code size slightly for inner loops
* due to the epilogue handling, but not for outer loops
* (e.g. loops over tiles). If used on a stage that reads from
* an input or writes to an output, this stategy only requires
* that the input/output extent be at least the split factor,
* instead of a multiple of the split factor as with RoundUp. */
ShiftInwards,
/** For pure definitions use ShiftInwards. For pure vars in
* update definitions use RoundUp. For RVars in update
* definitions use GuardWithIf. */
Auto
};
/** Different ways to handle the case when the start/end of the loops of stages
* computed with (fused) are not aligned. */
enum class LoopAlignStrategy {
/** Shift the start of the fused loops to align. */
AlignStart,
/** Shift the end of the fused loops to align. */
AlignEnd,
/** compute_with will make no attempt to align the start/end of the
* fused loops. */
NoAlign,
/** By default, LoopAlignStrategy is set to NoAlign. */
Auto
};
/** Different ways to handle accesses outside the original extents in a prefetch. */
enum class PrefetchBoundStrategy {
/** Clamp the prefetched exprs by intersecting the prefetched region with
* the original extents. This may make the exprs of the prefetched region
* more complicated. */
Clamp,
/** Guard the prefetch with if-guards that ignores the prefetch if
* any of the prefetched region ever goes beyond the original extents
* (i.e. all or nothing). */
GuardWithIf,
/** Leave the prefetched exprs as are (no if-guards around the prefetch
* and no intersecting with the original extents). This makes the prefetch
* exprs simpler but this may cause prefetching of region outside the original
* extents. This is good if prefetch won't fault when accessing region
* outside the original extents. */
NonFaulting
};
/** A reference to a site in a Halide statement at the top of the
* body of a particular for loop. Evaluating a region of a halide
* function is done by generating a loop nest that spans its
* dimensions. We schedule the inputs to that function by
* recursively injecting realizations for them at particular sites
* in this loop nest. A LoopLevel identifies such a site. The site
* can either be a loop nest within all stages of a function
* or it can refer to a loop nest within a particular function's
* stage (initial definition or updates).
*
* Note that a LoopLevel is essentially a pointer to an underlying value;
* all copies of a LoopLevel refer to the same site, so mutating one copy
* (via the set() method) will effectively mutate all copies:
\code
Func f;
Var x;
LoopLevel a(f, x);
// Both a and b refer to LoopLevel(f, x)
LoopLevel b = a;
// Now both a and b refer to LoopLevel::root()
a.set(LoopLevel::root());
\endcode
* This is quite useful when splitting Halide code into utility libraries, as it allows
* a library to schedule code according to a caller's specifications, even if the caller
* hasn't fully defined its pipeline yet:
\code
Func demosaic(Func input,
LoopLevel intermed_compute_at,
LoopLevel intermed_store_at,
LoopLevel output_compute_at) {
Func intermed = ...;
Func output = ...;
intermed.compute_at(intermed_compute_at).store_at(intermed_store_at);
output.compute_at(output_compute_at);
return output;
}
void process() {
// Note that these LoopLevels are all undefined when we pass them to demosaic()
LoopLevel intermed_compute_at, intermed_store_at, output_compute_at;
Func input = ...;
Func demosaiced = demosaic(input, intermed_compute_at, intermed_store_at, output_compute_at);
Func output = ...;
// We need to ensure all LoopLevels have a well-defined value prior to lowering:
intermed_compute_at.set(LoopLevel(output, y));
intermed_store_at.set(LoopLevel(output, y));
output_compute_at.set(LoopLevel(output, x));
}
\endcode
*/
class LoopLevel {
Internal::IntrusivePtr<Internal::LoopLevelContents> contents;
explicit LoopLevel(Internal::IntrusivePtr<Internal::LoopLevelContents> c)
: contents(std::move(c)) {
}
LoopLevel(const std::string &func_name, const std::string &var_name,
bool is_rvar, int stage_index, bool locked = false);
public:
/** Return the index of the function stage associated with this loop level.
* Asserts if undefined */
int stage_index() const;
/** Identify the loop nest corresponding to some dimension of some function */
// @{
LoopLevel(const Internal::Function &f, const VarOrRVar &v, int stage_index = -1);
LoopLevel(const Func &f, const VarOrRVar &v, int stage_index = -1);
// @}
/** Construct an undefined LoopLevel. Calling any method on an undefined
* LoopLevel (other than set()) will assert. */
LoopLevel();
/** Construct a special LoopLevel value that implies
* that a function should be inlined away. */
static LoopLevel inlined();
/** Construct a special LoopLevel value which represents the
* location outside of all for loops. */
static LoopLevel root();
/** Mutate our contents to match the contents of 'other'. */
void set(const LoopLevel &other);
// All the public methods below this point are meant only for internal
// use by Halide, rather than user code; hence, they are deliberately
// documented with plain comments (rather than Doxygen) to avoid being
// present in user documentation.
// Lock this LoopLevel.
LoopLevel &lock();
// Return the Func name. Asserts if the LoopLevel is_root() or is_inlined() or !defined().
std::string func() const;
// Return the VarOrRVar. Asserts if the LoopLevel is_root() or is_inlined() or !defined().
VarOrRVar var() const;
// Return true iff the LoopLevel is defined. (Only LoopLevels created
// with the default ctor are undefined.)
bool defined() const;
// Test if a loop level corresponds to inlining the function.
bool is_inlined() const;
// Test if a loop level is 'root', which describes the site
// outside of all for loops.
bool is_root() const;
// Return a string of the form func.var -- note that this is safe
// to call for root or inline LoopLevels, but asserts if !defined().
std::string to_string() const;
// Compare this loop level against the variable name of a for
// loop, to see if this loop level refers to the site
// immediately inside this loop. Asserts if !defined().
bool match(const std::string &loop) const;
bool match(const LoopLevel &other) const;
// Check if two loop levels are exactly the same.
bool operator==(const LoopLevel &other) const;
bool operator!=(const LoopLevel &other) const {
return !(*this == other);
}
private:
void check_defined() const;
void check_locked() const;
void check_defined_and_locked() const;
};
struct FuseLoopLevel {
LoopLevel level;
/** Contains alignment strategies for the fused dimensions (indexed by the
* dimension name). If not in the map, use the default alignment strategy
* to align the fused dimension (see \ref LoopAlignStrategy::Auto).
*/
std::map<std::string, LoopAlignStrategy> align;
FuseLoopLevel()
: level(LoopLevel::inlined().lock()) {
}
FuseLoopLevel(const LoopLevel &level, const std::map<std::string, LoopAlignStrategy> &align)
: level(level), align(align) {
}
};
namespace Internal {
class IRMutator;
struct ReductionVariable;
struct Split {
std::string old_var, outer, inner;
Expr factor;
bool exact; // Is it required that the factor divides the extent
// of the old var. True for splits of RVars. Forces
// tail strategy to be GuardWithIf.
TailStrategy tail;
enum SplitType { SplitVar = 0,
RenameVar,
FuseVars,
PurifyRVar };
// If split_type is Rename, then this is just a renaming of the
// old_var to the outer and not a split. The inner var should
// be ignored, and factor should be one. Renames are kept in
// the same list as splits so that ordering between them is
// respected.
// If split type is Purify, this replaces the old_var RVar to
// the outer Var. The inner var should be ignored, and factor
// should be one.
// If split_type is Fuse, then this does the opposite of a
// split, it joins the outer and inner into the old_var.
SplitType split_type;
bool is_rename() const {
return split_type == RenameVar;
}
bool is_split() const {
return split_type == SplitVar;
}
bool is_fuse() const {
return split_type == FuseVars;
}
bool is_purify() const {
return split_type == PurifyRVar;
}
};
struct Dim {
std::string var;
ForType for_type;
DeviceAPI device_api;
enum Type { PureVar = 0,
PureRVar,
ImpureRVar };
Type dim_type;
bool is_pure() const {
return (dim_type == PureVar) || (dim_type == PureRVar);
}
bool is_rvar() const {
return (dim_type == PureRVar) || (dim_type == ImpureRVar);
}
bool is_unordered_parallel() const {
return Halide::Internal::is_unordered_parallel(for_type);
}
bool is_parallel() const {
return Halide::Internal::is_parallel(for_type);
}
};
struct Bound {
std::string var;
Expr min, extent, modulus, remainder;
};
struct StorageDim {
std::string var;
Expr alignment;
Expr fold_factor;
bool fold_forward;
};
/** This represents two stages with fused loop nests from outermost to a specific
* loop level. The loops to compute func_1(stage_1) are fused with the loops to
* compute func_2(stage_2) from outermost to loop level var_name and the
* computation from stage_1 of func_1 occurs first.
*/
struct FusedPair {
std::string func_1;
std::string func_2;
size_t stage_1;
size_t stage_2;
std::string var_name;
FusedPair() = default;
FusedPair(const std::string &f1, size_t s1, const std::string &f2,
size_t s2, const std::string &var)
: func_1(f1), func_2(f2), stage_1(s1), stage_2(s2), var_name(var) {
}
bool operator==(const FusedPair &other) const {
return (func_1 == other.func_1) && (func_2 == other.func_2) &&
(stage_1 == other.stage_1) && (stage_2 == other.stage_2) &&
(var_name == other.var_name);
}
bool operator<(const FusedPair &other) const {
if (func_1 != other.func_1) {
return func_1 < other.func_1;
}
if (func_2 != other.func_2) {
return func_2 < other.func_2;
}
if (var_name != other.var_name) {
return var_name < other.var_name;
}
if (stage_1 != other.stage_1) {
return stage_1 < other.stage_1;
}
return stage_2 < other.stage_2;
}
};
struct PrefetchDirective {
std::string name;
std::string var;
Expr offset;
PrefetchBoundStrategy strategy;
// If it's a prefetch load from an image parameter, this points to that.
Parameter param;
};
struct FuncScheduleContents;
struct StageScheduleContents;
/** A schedule for a Function of a Halide pipeline. This schedule is
* applied to all stages of the Function. Right now this interface is
* basically a struct, offering mutable access to its innards.
* In the future it may become more encapsulated. */
class FuncSchedule {
IntrusivePtr<FuncScheduleContents> contents;
public:
FuncSchedule(IntrusivePtr<FuncScheduleContents> c)
: contents(std::move(c)) {
}
FuncSchedule(const FuncSchedule &other)
: contents(other.contents) {
}
FuncSchedule();
/** Return a deep copy of this FuncSchedule. It recursively deep copies all
* called functions, schedules, specializations, and reduction domains. This
* method takes a map of <old FunctionContents, deep-copied version> as input
* and would use the deep-copied FunctionContents from the map if exists
* instead of creating a new deep-copy to avoid creating deep-copies of the
* same FunctionContents multiple times.
*/
FuncSchedule deep_copy(
std::map<FunctionPtr, FunctionPtr> &copied_map) const;
/** This flag is set to true if the schedule is memoized. */
// @{
bool &memoized();
bool memoized() const;
// @}
/** Is the production of this Function done asynchronously */
bool &async();
bool async() const;
/** The list and order of dimensions used to store this
* function. The first dimension in the vector corresponds to the
* innermost dimension for storage (i.e. which dimension is
* tightly packed in memory) */
// @{
const std::vector<StorageDim> &storage_dims() const;
std::vector<StorageDim> &storage_dims();
// @}
/** The memory type (heap/stack/shared/etc) used to back this Func. */
// @{
MemoryType memory_type() const;
MemoryType &memory_type();
// @}
/** You may explicitly bound some of the dimensions of a function,
* or constrain them to lie on multiples of a given factor. See
* \ref Func::bound and \ref Func::align_bounds */
// @{
const std::vector<Bound> &bounds() const;
std::vector<Bound> &bounds();
// @}
/** You may explicitly specify an estimate of some of the function
* dimensions. See \ref Func::estimate */
// @{
const std::vector<Bound> &estimates() const;
std::vector<Bound> &estimates();
// @}
/** Mark calls of a function by 'f' to be replaced with its identity
* wrapper or clone during the lowering stage. If the string 'f' is empty,
* it means replace all calls to the function by all other functions
* (excluding itself) in the pipeline with the global identity wrapper.
* See \ref Func::in and \ref Func::clone_in for more details. */
// @{
const std::map<std::string, Internal::FunctionPtr> &wrappers() const;
std::map<std::string, Internal::FunctionPtr> &wrappers();
void add_wrapper(const std::string &f,
const Internal::FunctionPtr &wrapper);
// @}
/** At what sites should we inject the allocation and the
* computation of this function? The store_level must be outside
* of or equal to the compute_level. If the compute_level is
* inline, the store_level is meaningless. See \ref Func::store_at
* and \ref Func::compute_at */
// @{
const LoopLevel &store_level() const;
const LoopLevel &compute_level() const;
LoopLevel &store_level();
LoopLevel &compute_level();
// @}
/** Pass an IRVisitor through to all Exprs referenced in the
* Schedule. */
void accept(IRVisitor *) const;
/** Pass an IRMutator through to all Exprs referenced in the
* Schedule. */
void mutate(IRMutator *);
};
/** A schedule for a single stage of a Halide pipeline. Right now this
* interface is basically a struct, offering mutable access to its
* innards. In the future it may become more encapsulated. */
class StageSchedule {
IntrusivePtr<StageScheduleContents> contents;
public:
StageSchedule(IntrusivePtr<StageScheduleContents> c)
: contents(std::move(c)) {
}
StageSchedule(const StageSchedule &other)
: contents(other.contents) {
}
StageSchedule();
/** Return a copy of this StageSchedule. */
StageSchedule get_copy() const;
/** This flag is set to true if the dims list has been manipulated
* by the user (or if a ScheduleHandle was created that could have
* been used to manipulate it). It controls the warning that
* occurs if you schedule the vars of the pure step but not the
* update steps. */
// @{
bool &touched();
bool touched() const;
// @}
/** RVars of reduction domain associated with this schedule if there is any. */
// @{
const std::vector<ReductionVariable> &rvars() const;
std::vector<ReductionVariable> &rvars();
// @}
/** The traversal of the domain of a function can have some of its
* dimensions split into sub-dimensions. See \ref Func::split */
// @{
const std::vector<Split> &splits() const;
std::vector<Split> &splits();
// @}
/** The list and ordering of dimensions used to evaluate this
* function, after all splits have taken place. The first
* dimension in the vector corresponds to the innermost for loop,
* and the last is the outermost. Also specifies what type of for
* loop to use for each dimension. Does not specify the bounds on
* each dimension. These get inferred from how the function is
* used, what the splits are, and any optional bounds in the list below. */
// @{
const std::vector<Dim> &dims() const;
std::vector<Dim> &dims();
// @}
/** You may perform prefetching in some of the dimensions of a
* function. See \ref Func::prefetch */
// @{
const std::vector<PrefetchDirective> &prefetches() const;
std::vector<PrefetchDirective> &prefetches();
// @}
/** Innermost loop level of fused loop nest for this function stage.
* Fusion runs from outermost to this loop level. The stages being fused
* should not have producer/consumer relationship. See \ref Func::compute_with
* and \ref Stage::compute_with */
// @{
const FuseLoopLevel &fuse_level() const;
FuseLoopLevel &fuse_level();
// @}
/** List of function stages that are to be fused with this function stage
* from the outermost loop to a certain loop level. Those function stages
* are to be computed AFTER this function stage at the last fused loop level.
* This list is populated when realization_order() is called. See
* \ref Func::compute_with and \ref Stage::compute_with */
// @{
const std::vector<FusedPair> &fused_pairs() const;
std::vector<FusedPair> &fused_pairs();
/** Are race conditions permitted? */
// @{
bool allow_race_conditions() const;
bool &allow_race_conditions();
// @}
/** Use atomic update? */
// @{
bool atomic() const;
bool &atomic();
// @}
/** Atomic updates are only allowed on associative reductions.
* We try to prove the associativity, but the user can override
* the associativity test and suppress compiler error if the prover
* fails to recognize the associativity or the user does not care. */
// @{
bool override_atomic_associativity_test() const;
bool &override_atomic_associativity_test();
// @}
/** Pass an IRVisitor through to all Exprs referenced in the
* Schedule. */
void accept(IRVisitor *) const;
/** Pass an IRMutator through to all Exprs referenced in the
* Schedule. */
void mutate(IRMutator *);
};
} // namespace Internal
} // namespace Halide
#endif
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