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llvm / polly / refs/heads/svn-tags/RELEASE_502 / . / final / lib / Transform / DeLICM.cpp
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//===------ DeLICM.cpp -----------------------------------------*- C++ -*-===//
//
// The LLVM Compiler Infrastructure
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
//
// Undo the effect of Loop Invariant Code Motion (LICM) and
// GVN Partial Redundancy Elimination (PRE) on SCoP-level.
//
// Namely, remove register/scalar dependencies by mapping them back to array
// elements.
//
// The algorithms here work on the scatter space - the image space of the
// schedule returned by Scop::getSchedule(). We call an element in that space a
// "timepoint". Timepoints are lexicographically ordered such that we can
// defined ranges in the scatter space. We use two flavors of such ranges:
// Timepoint sets and zones. A timepoint set is simply a subset of the scatter
// space and is directly stored as isl_set.
//
// Zones are used to describe the space between timepoints as open sets, i.e.
// they do not contain the extrema. Using isl rational sets to express these
// would be overkill. We also cannot store them as the integer timepoints they
// contain; the (nonempty) zone between 1 and 2 would be empty and
// indistinguishable from e.g. the zone between 3 and 4. Also, we cannot store
// the integer set including the extrema; the set ]1,2[ + ]3,4[ could be
// coalesced to ]1,3[, although we defined the range [2,3] to be not in the set.
// Instead, we store the "half-open" integer extrema, including the lower bound,
// but excluding the upper bound. Examples:
//
// * The set { [i] : 1 <= i <= 3 } represents the zone ]0,3[ (which contains the
// integer points 1 and 2, but not 0 or 3)
//
// * { [1] } represents the zone ]0,1[
//
// * { [i] : i = 1 or i = 3 } represents the zone ]0,1[ + ]2,3[
//
// Therefore, an integer i in the set represents the zone ]i-1,i[, i.e. strictly
// speaking the integer points never belong to the zone. However, depending an
// the interpretation, one might want to include them. Part of the
// interpretation may not be known when the zone is constructed.
//
// Reads are assumed to always take place before writes, hence we can think of
// reads taking place at the beginning of a timepoint and writes at the end.
//
// Let's assume that the zone represents the lifetime of a variable. That is,
// the zone begins with a write that defines the value during its lifetime and
// ends with the last read of that value. In the following we consider whether a
// read/write at the beginning/ending of the lifetime zone should be within the
// zone or outside of it.
//
// * A read at the timepoint that starts the live-range loads the previous
// value. Hence, exclude the timepoint starting the zone.
//
// * A write at the timepoint that starts the live-range is not defined whether
// it occurs before or after the write that starts the lifetime. We do not
// allow this situation to occur. Hence, we include the timepoint starting the
// zone to determine whether they are conflicting.
//
// * A read at the timepoint that ends the live-range reads the same variable.
// We include the timepoint at the end of the zone to include that read into
// the live-range. Doing otherwise would mean that the two reads access
// different values, which would mean that the value they read are both alive
// at the same time but occupy the same variable.
//
// * A write at the timepoint that ends the live-range starts a new live-range.
// It must not be included in the live-range of the previous definition.
//
// All combinations of reads and writes at the endpoints are possible, but most
// of the time only the write->read (for instance, a live-range from definition
// to last use) and read->write (for instance, an unused range from last use to
// overwrite) and combinations are interesting (half-open ranges). write->write
// zones might be useful as well in some context to represent
// output-dependencies.
//
// @see convertZoneToTimepoints
//
//
// The code makes use of maps and sets in many different spaces. To not loose
// track in which space a set or map is expected to be in, variables holding an
// isl reference are usually annotated in the comments. They roughly follow isl
// syntax for spaces, but only the tuples, not the dimensions. The tuples have a
// meaning as follows:
//
// * Space[] - An unspecified tuple. Used for function parameters such that the
// function caller can use it for anything they like.
//
// * Domain[] - A statement instance as returned by ScopStmt::getDomain()
// isl_id_get_name: Stmt_<NameOfBasicBlock>
// isl_id_get_user: Pointer to ScopStmt
//
// * Element[] - An array element as in the range part of
// MemoryAccess::getAccessRelation()
// isl_id_get_name: MemRef_<NameOfArrayVariable>
// isl_id_get_user: Pointer to ScopArrayInfo
//
// * Scatter[] - Scatter space or space of timepoints
// Has no tuple id
//
// * Zone[] - Range between timepoints as described above
// Has no tuple id
//
// * ValInst[] - An llvm::Value as defined at a specific timepoint.
//
// A ValInst[] itself can be structured as one of:
//
// * [] - An unknown value.
// Always zero dimensions
// Has no tuple id
//
// * Value[] - An llvm::Value that is read-only in the SCoP, i.e. its
// runtime content does not depend on the timepoint.
// Always zero dimensions
// isl_id_get_name: Val_<NameOfValue>
// isl_id_get_user: A pointer to an llvm::Value
//
// * SCEV[...] - A synthesizable llvm::SCEV Expression.
// In contrast to a Value[] is has at least one dimension per
// SCEVAddRecExpr in the SCEV.
//
// * [Domain[] -> Value[]] - An llvm::Value that may change during the
// Scop's execution.
// The tuple itself has no id, but it wraps a map space holding a
// statement instance which defines the llvm::Value as the map's domain
// and llvm::Value itself as range.
//
// @see makeValInst()
//
// An annotation "{ Domain[] -> Scatter[] }" therefore means: A map from a
// statement instance to a timepoint, aka a schedule. There is only one scatter
// space, but most of the time multiple statements are processed in one set.
// This is why most of the time isl_union_map has to be used.
//
// The basic algorithm works as follows:
// At first we verify that the SCoP is compatible with this technique. For
// instance, two writes cannot write to the same location at the same statement
// instance because we cannot determine within the polyhedral model which one
// comes first. Once this was verified, we compute zones at which an array
// element is unused. This computation can fail if it takes too long. Then the
// main algorithm is executed. Because every store potentially trails an unused
// zone, we start at stores. We search for a scalar (MemoryKind::Value or
// MemoryKind::PHI) that we can map to the array element overwritten by the
// store, preferably one that is used by the store or at least the ScopStmt.
// When it does not conflict with the lifetime of the values in the array
// element, the map is applied and the unused zone updated as it is now used. We
// continue to try to map scalars to the array element until there are no more
// candidates to map. The algorithm is greedy in the sense that the first scalar
// not conflicting will be mapped. Other scalars processed later that could have
// fit the same unused zone will be rejected. As such the result depends on the
// processing order.
//
//===----------------------------------------------------------------------===//
#include "polly/DeLICM.h"
#include "polly/Options.h"
#include "polly/ScopInfo.h"
#include "polly/ScopPass.h"
#include "polly/Support/ISLOStream.h"
#include "polly/Support/ISLTools.h"
#include "polly/Support/VirtualInstruction.h"
#include "llvm/ADT/Statistic.h"
#define DEBUG_TYPE "polly-delicm"
using namespace polly;
using namespace llvm;
namespace {
cl::opt<int>
DelicmMaxOps("polly-delicm-max-ops",
cl::desc("Maximum number of isl operations to invest for "
"lifetime analysis; 0=no limit"),
cl::init(1000000), cl::cat(PollyCategory));
cl::opt<bool> DelicmOverapproximateWrites(
"polly-delicm-overapproximate-writes",
cl::desc(
"Do more PHI writes than necessary in order to avoid partial accesses"),
cl::init(false), cl::Hidden, cl::cat(PollyCategory));
cl::opt<bool> DelicmPartialWrites("polly-delicm-partial-writes",
cl::desc("Allow partial writes"),
cl::init(false), cl::Hidden,
cl::cat(PollyCategory));
cl::opt<bool>
DelicmComputeKnown("polly-delicm-compute-known",
cl::desc("Compute known content of array elements"),
cl::init(true), cl::Hidden, cl::cat(PollyCategory));
STATISTIC(DeLICMAnalyzed, "Number of successfully analyzed SCoPs");
STATISTIC(DeLICMOutOfQuota,
"Analyses aborted because max_operations was reached");
STATISTIC(DeLICMIncompatible, "Number of SCoPs incompatible for analysis");
STATISTIC(MappedValueScalars, "Number of mapped Value scalars");
STATISTIC(MappedPHIScalars, "Number of mapped PHI scalars");
STATISTIC(TargetsMapped, "Number of stores used for at least one mapping");
STATISTIC(DeLICMScopsModified, "Number of SCoPs optimized");
/// Class for keeping track of scalar def-use chains in the polyhedral
/// representation.
///
/// MemoryKind::Value:
/// There is one definition per llvm::Value or zero (read-only values defined
/// before the SCoP) and an arbitrary number of reads.
///
/// MemoryKind::PHI, MemoryKind::ExitPHI:
/// There is at least one write (the incoming blocks/stmts) and one
/// (MemoryKind::PHI) or zero (MemoryKind::ExitPHI) reads per llvm::PHINode.
class ScalarDefUseChains {
private:
/// The definitions (i.e. write MemoryAccess) of a MemoryKind::Value scalar.
DenseMap<const ScopArrayInfo *, MemoryAccess *> ValueDefAccs;
/// List of all uses (i.e. read MemoryAccesses) for a MemoryKind::Value
/// scalar.
DenseMap<const ScopArrayInfo *, SmallVector<MemoryAccess *, 4>> ValueUseAccs;
/// The receiving part (i.e. read MemoryAccess) of a MemoryKind::PHI scalar.
DenseMap<const ScopArrayInfo *, MemoryAccess *> PHIReadAccs;
/// List of all incoming values (write MemoryAccess) of a MemoryKind::PHI or
/// MemoryKind::ExitPHI scalar.
DenseMap<const ScopArrayInfo *, SmallVector<MemoryAccess *, 4>>
PHIIncomingAccs;
public:
/// Find the MemoryAccesses that access the ScopArrayInfo-represented memory.
///
/// @param S The SCoP to analyze.
void compute(Scop *S) {
// Purge any previous result.
reset();
for (auto &Stmt : *S) {
for (auto *MA : Stmt) {
if (MA->isOriginalValueKind() && MA->isWrite()) {
auto *SAI = MA->getScopArrayInfo();
assert(!ValueDefAccs.count(SAI) &&
"There can be at most one "
"definition per MemoryKind::Value scalar");
ValueDefAccs[SAI] = MA;
}
if (MA->isOriginalValueKind() && MA->isRead())
ValueUseAccs[MA->getScopArrayInfo()].push_back(MA);
if (MA->isOriginalAnyPHIKind() && MA->isRead()) {
auto *SAI = MA->getScopArrayInfo();
assert(!PHIReadAccs.count(SAI) &&
"There must be exactly one read "
"per PHI (that's where the PHINode is)");
PHIReadAccs[SAI] = MA;
}
if (MA->isOriginalAnyPHIKind() && MA->isWrite())
PHIIncomingAccs[MA->getScopArrayInfo()].push_back(MA);
}
}
}
/// Free all memory used by the analysis.
void reset() {
ValueDefAccs.clear();
ValueUseAccs.clear();
PHIReadAccs.clear();
PHIIncomingAccs.clear();
}
MemoryAccess *getValueDef(const ScopArrayInfo *SAI) const {
return ValueDefAccs.lookup(SAI);
}
ArrayRef<MemoryAccess *> getValueUses(const ScopArrayInfo *SAI) const {
auto It = ValueUseAccs.find(SAI);
if (It == ValueUseAccs.end())
return {};
return It->second;
}
MemoryAccess *getPHIRead(const ScopArrayInfo *SAI) const {
return PHIReadAccs.lookup(SAI);
}
ArrayRef<MemoryAccess *> getPHIIncomings(const ScopArrayInfo *SAI) const {
auto It = PHIIncomingAccs.find(SAI);
if (It == PHIIncomingAccs.end())
return {};
return It->second;
}
};
isl::union_map computeReachingDefinition(isl::union_map Schedule,
isl::union_map Writes, bool InclDef,
bool InclRedef) {
return computeReachingWrite(Schedule, Writes, false, InclDef, InclRedef);
}
isl::union_map computeReachingOverwrite(isl::union_map Schedule,
isl::union_map Writes,
bool InclPrevWrite,
bool InclOverwrite) {
return computeReachingWrite(Schedule, Writes, true, InclPrevWrite,
InclOverwrite);
}
/// Compute the next overwrite for a scalar.
///
/// @param Schedule { DomainWrite[] -> Scatter[] }
/// Schedule of (at least) all writes. Instances not in @p
/// Writes are ignored.
/// @param Writes { DomainWrite[] }
/// The element instances that write to the scalar.
/// @param InclPrevWrite Whether to extend the timepoints to include
/// the timepoint where the previous write happens.
/// @param InclOverwrite Whether the reaching overwrite includes the timepoint
/// of the overwrite itself.
///
/// @return { Scatter[] -> DomainDef[] }
isl::union_map computeScalarReachingOverwrite(isl::union_map Schedule,
isl::union_set Writes,
bool InclPrevWrite,
bool InclOverwrite) {
// { DomainWrite[] }
auto WritesMap = give(isl_union_map_from_domain(Writes.take()));
// { [Element[] -> Scatter[]] -> DomainWrite[] }
auto Result = computeReachingOverwrite(
std::move(Schedule), std::move(WritesMap), InclPrevWrite, InclOverwrite);
return give(isl_union_map_domain_factor_range(Result.take()));
}
/// Overload of computeScalarReachingOverwrite, with only one writing statement.
/// Consequently, the result consists of only one map space.
///
/// @param Schedule { DomainWrite[] -> Scatter[] }
/// @param Writes { DomainWrite[] }
/// @param InclPrevWrite Include the previous write to result.
/// @param InclOverwrite Include the overwrite to the result.
///
/// @return { Scatter[] -> DomainWrite[] }
isl::map computeScalarReachingOverwrite(isl::union_map Schedule,
isl::set Writes, bool InclPrevWrite,
bool InclOverwrite) {
auto ScatterSpace = getScatterSpace(Schedule);
auto DomSpace = give(isl_set_get_space(Writes.keep()));
auto ReachOverwrite = computeScalarReachingOverwrite(
Schedule, give(isl_union_set_from_set(Writes.take())), InclPrevWrite,
InclOverwrite);
auto ResultSpace = give(isl_space_map_from_domain_and_range(
ScatterSpace.take(), DomSpace.take()));
return singleton(std::move(ReachOverwrite), ResultSpace);
}
/// Compute the reaching definition of a scalar.
///
/// Compared to computeReachingDefinition, there is just one element which is
/// accessed and therefore only a set if instances that accesses that element is
/// required.
///
/// @param Schedule { DomainWrite[] -> Scatter[] }
/// @param Writes { DomainWrite[] }
/// @param InclDef Include the timepoint of the definition to the result.
/// @param InclRedef Include the timepoint of the overwrite into the result.
///
/// @return { Scatter[] -> DomainWrite[] }
isl::union_map computeScalarReachingDefinition(isl::union_map Schedule,
isl::union_set Writes,
bool InclDef, bool InclRedef) {
// { DomainWrite[] -> Element[] }
auto Defs = give(isl_union_map_from_domain(Writes.take()));
// { [Element[] -> Scatter[]] -> DomainWrite[] }
auto ReachDefs =
computeReachingDefinition(Schedule, Defs, InclDef, InclRedef);
// { Scatter[] -> DomainWrite[] }
return give(isl_union_set_unwrap(
isl_union_map_range(isl_union_map_curry(ReachDefs.take()))));
}
/// Compute the reaching definition of a scalar.
///
/// This overload accepts only a single writing statement as an isl_map,
/// consequently the result also is only a single isl_map.
///
/// @param Schedule { DomainWrite[] -> Scatter[] }
/// @param Writes { DomainWrite[] }
/// @param InclDef Include the timepoint of the definition to the result.
/// @param InclRedef Include the timepoint of the overwrite into the result.
///
/// @return { Scatter[] -> DomainWrite[] }
isl::map computeScalarReachingDefinition( // { Domain[] -> Zone[] }
isl::union_map Schedule, isl::set Writes, bool InclDef, bool InclRedef) {
auto DomainSpace = give(isl_set_get_space(Writes.keep()));
auto ScatterSpace = getScatterSpace(Schedule);
// { Scatter[] -> DomainWrite[] }
auto UMap = computeScalarReachingDefinition(
Schedule, give(isl_union_set_from_set(Writes.take())), InclDef,
InclRedef);
auto ResultSpace = give(isl_space_map_from_domain_and_range(
ScatterSpace.take(), DomainSpace.take()));
return singleton(UMap, ResultSpace);
}
/// Create a domain-to-unknown value mapping.
///
/// Value instances that do not represent a specific value are represented by an
/// unnamed tuple of 0 dimensions. Its meaning depends on the context. It can
/// either mean a specific but unknown value which cannot be represented by
/// other means. It conflicts with itself because those two unknown ValInsts may
/// have different concrete values at runtime.
///
/// The other meaning is an arbitrary or wildcard value that can be chosen
/// freely, like LLVM's undef. If matched with an unknown ValInst, there is no
/// conflict.
///
/// @param Domain { Domain[] }
///
/// @return { Domain[] -> ValInst[] }
isl::union_map makeUnknownForDomain(isl::union_set Domain) {
return give(isl_union_map_from_domain(Domain.take()));
}
/// Create a domain-to-unknown value mapping.
///
/// @see makeUnknownForDomain(isl::union_set)
///
/// @param Domain { Domain[] }
///
/// @return { Domain[] -> ValInst[] }
isl::map makeUnknownForDomain(isl::set Domain) {
return give(isl_map_from_domain(Domain.take()));
}
/// Return whether @p Map maps to an unknown value.
///
/// @param { [] -> ValInst[] }
bool isMapToUnknown(const isl::map &Map) {
auto Space = give(isl_space_range(isl_map_get_space(Map.keep())));
return !isl_map_has_tuple_id(Map.keep(), isl_dim_set) &&
!isl_space_is_wrapping(Space.keep()) &&
isl_map_dim(Map.keep(), isl_dim_out) == 0;
}
/// Return only the mappings that map to known values.
///
/// @param UMap { [] -> ValInst[] }
///
/// @return { [] -> ValInst[] }
isl::union_map filterKnownValInst(const isl::union_map &UMap) {
auto Result = give(isl_union_map_empty(isl_union_map_get_space(UMap.keep())));
UMap.foreach_map([=, &Result](isl::map Map) -> isl::stat {
if (!isMapToUnknown(Map))
Result = give(isl_union_map_add_map(Result.take(), Map.take()));
return isl::stat::ok;
});
return Result;
}
/// Try to find a 'natural' extension of a mapped to elements outside its
/// domain.
///
/// @param Relevant The map with mapping that may not be modified.
/// @param Universe The domain to which @p Relevant needs to be extended.
///
/// @return A map with that associates the domain elements of @p Relevant to the
/// same elements and in addition the elements of @p Universe to some
/// undefined elements. The function prefers to return simple maps.
isl::union_map expandMapping(isl::union_map Relevant, isl::union_set Universe) {
Relevant = give(isl_union_map_coalesce(Relevant.take()));
auto RelevantDomain = give(isl_union_map_domain(Relevant.copy()));
auto Simplified =
give(isl_union_map_gist_domain(Relevant.take(), RelevantDomain.take()));
Simplified = give(isl_union_map_coalesce(Simplified.take()));
return give(
isl_union_map_intersect_domain(Simplified.take(), Universe.take()));
}
/// Represent the knowledge of the contents of any array elements in any zone or
/// the knowledge we would add when mapping a scalar to an array element.
///
/// Every array element at every zone unit has one of two states:
///
/// - Unused: Not occupied by any value so a transformation can change it to
/// other values.
///
/// - Occupied: The element contains a value that is still needed.
///
/// The union of Unused and Unknown zones forms the universe, the set of all
/// elements at every timepoint. The universe can easily be derived from the
/// array elements that are accessed someway. Arrays that are never accessed
/// also never play a role in any computation and can hence be ignored. With a
/// given universe, only one of the sets needs to stored implicitly. Computing
/// the complement is also an expensive operation, hence this class has been
/// designed that only one of sets is needed while the other is assumed to be
/// implicit. It can still be given, but is mostly ignored.
///
/// There are two use cases for the Knowledge class:
///
/// 1) To represent the knowledge of the current state of ScopInfo. The unused
/// state means that an element is currently unused: there is no read of it
/// before the next overwrite. Also called 'Existing'.
///
/// 2) To represent the requirements for mapping a scalar to array elements. The
/// unused state means that there is no change/requirement. Also called
/// 'Proposed'.
///
/// In addition to these states at unit zones, Knowledge needs to know when
/// values are written. This is because written values may have no lifetime (one
/// reason is that the value is never read). Such writes would therefore never
/// conflict, but overwrite values that might still be required. Another source
/// of problems are multiple writes to the same element at the same timepoint,
/// because their order is undefined.
class Knowledge {
private:
/// { [Element[] -> Zone[]] }
/// Set of array elements and when they are alive.
/// Can contain a nullptr; in this case the set is implicitly defined as the
/// complement of #Unused.
///
/// The set of alive array elements is represented as zone, as the set of live
/// values can differ depending on how the elements are interpreted.
/// Assuming a value X is written at timestep [0] and read at timestep [1]
/// without being used at any later point, then the value is alive in the
/// interval ]0,1[. This interval cannot be represented by an integer set, as
/// it does not contain any integer point. Zones allow us to represent this
/// interval and can be converted to sets of timepoints when needed (e.g., in
/// isConflicting when comparing to the write sets).
/// @see convertZoneToTimepoints and this file's comment for more details.
isl::union_set Occupied;
/// { [Element[] -> Zone[]] }
/// Set of array elements when they are not alive, i.e. their memory can be
/// used for other purposed. Can contain a nullptr; in this case the set is
/// implicitly defined as the complement of #Occupied.
isl::union_set Unused;
/// { [Element[] -> Zone[]] -> ValInst[] }
/// Maps to the known content for each array element at any interval.
///
/// Any element/interval can map to multiple known elements. This is due to
/// multiple llvm::Value referring to the same content. Examples are
///
/// - A value stored and loaded again. The LoadInst represents the same value
/// as the StoreInst's value operand.
///
/// - A PHINode is equal to any one of the incoming values. In case of
/// LCSSA-form, it is always equal to its single incoming value.
///
/// Two Knowledges are considered not conflicting if at least one of the known
/// values match. Not known values are not stored as an unnamed tuple (as
/// #Written does), but maps to nothing.
///
/// Known values are usually just defined for #Occupied elements. Knowing
/// #Unused contents has no advantage as it can be overwritten.
isl::union_map Known;
/// { [Element[] -> Scatter[]] -> ValInst[] }
/// The write actions currently in the scop or that would be added when
/// mapping a scalar. Maps to the value that is written.
///
/// Written values that cannot be identified are represented by an unknown
/// ValInst[] (an unnamed tuple of 0 dimension). It conflicts with itself.
isl::union_map Written;
/// Check whether this Knowledge object is well-formed.
void checkConsistency() const {
#ifndef NDEBUG
// Default-initialized object
if (!Occupied && !Unused && !Known && !Written)
return;
assert(Occupied || Unused);
assert(Known);
assert(Written);
// If not all fields are defined, we cannot derived the universe.
if (!Occupied || !Unused)
return;
assert(isl_union_set_is_disjoint(Occupied.keep(), Unused.keep()) ==
isl_bool_true);
auto Universe = give(isl_union_set_union(Occupied.copy(), Unused.copy()));
assert(!Known.domain().is_subset(Universe).is_false());
assert(!Written.domain().is_subset(Universe).is_false());
#endif
}
public:
/// Initialize a nullptr-Knowledge. This is only provided for convenience; do
/// not use such an object.
Knowledge() {}
/// Create a new object with the given members.
Knowledge(isl::union_set Occupied, isl::union_set Unused,
isl::union_map Known, isl::union_map Written)
: Occupied(std::move(Occupied)), Unused(std::move(Unused)),
Known(std::move(Known)), Written(std::move(Written)) {
checkConsistency();
}
/// Return whether this object was not default-constructed.
bool isUsable() const { return (Occupied || Unused) && Known && Written; }
/// Print the content of this object to @p OS.
void print(llvm::raw_ostream &OS, unsigned Indent = 0) const {
if (isUsable()) {
if (Occupied)
OS.indent(Indent) << "Occupied: " << Occupied << "\n";
else
OS.indent(Indent) << "Occupied: <Everything else not in Unused>\n";
if (Unused)
OS.indent(Indent) << "Unused: " << Unused << "\n";
else
OS.indent(Indent) << "Unused: <Everything else not in Occupied>\n";
OS.indent(Indent) << "Known: " << Known << "\n";
OS.indent(Indent) << "Written : " << Written << '\n';
} else {
OS.indent(Indent) << "Invalid knowledge\n";
}
}
/// Combine two knowledges, this and @p That.
void learnFrom(Knowledge That) {
assert(!isConflicting(*this, That));
assert(Unused && That.Occupied);
assert(
!That.Unused &&
"This function is only prepared to learn occupied elements from That");
assert(!Occupied && "This function does not implement "
"`this->Occupied = "
"give(isl_union_set_union(this->Occupied.take(), "
"That.Occupied.copy()));`");
Unused = give(isl_union_set_subtract(Unused.take(), That.Occupied.copy()));
Known = give(isl_union_map_union(Known.take(), That.Known.copy()));
Written = give(isl_union_map_union(Written.take(), That.Written.take()));
checkConsistency();
}
/// Determine whether two Knowledges conflict with each other.
///
/// In theory @p Existing and @p Proposed are symmetric, but the
/// implementation is constrained by the implicit interpretation. That is, @p
/// Existing must have #Unused defined (use case 1) and @p Proposed must have
/// #Occupied defined (use case 1).
///
/// A conflict is defined as non-preserved semantics when they are merged. For
/// instance, when for the same array and zone they assume different
/// llvm::Values.
///
/// @param Existing One of the knowledges with #Unused defined.
/// @param Proposed One of the knowledges with #Occupied defined.
/// @param OS Dump the conflict reason to this output stream; use
/// nullptr to not output anything.
/// @param Indent Indention for the conflict reason.
///
/// @return True, iff the two knowledges are conflicting.
static bool isConflicting(const Knowledge &Existing,
const Knowledge &Proposed,
llvm::raw_ostream *OS = nullptr,
unsigned Indent = 0) {
assert(Existing.Unused);
assert(Proposed.Occupied);
#ifndef NDEBUG
if (Existing.Occupied && Proposed.Unused) {
auto ExistingUniverse = give(isl_union_set_union(Existing.Occupied.copy(),
Existing.Unused.copy()));
auto ProposedUniverse = give(isl_union_set_union(Proposed.Occupied.copy(),
Proposed.Unused.copy()));
assert(isl_union_set_is_equal(ExistingUniverse.keep(),
ProposedUniverse.keep()) == isl_bool_true &&
"Both inputs' Knowledges must be over the same universe");
}
#endif
// Do the Existing and Proposed lifetimes conflict?
//
// Lifetimes are described as the cross-product of array elements and zone
// intervals in which they are alive (the space { [Element[] -> Zone[]] }).
// In the following we call this "element/lifetime interval".
//
// In order to not conflict, one of the following conditions must apply for
// each element/lifetime interval:
//
// 1. If occupied in one of the knowledges, it is unused in the other.
//
// - or -
//
// 2. Both contain the same value.
//
// Instead of partitioning the element/lifetime intervals into a part that
// both Knowledges occupy (which requires an expensive subtraction) and for
// these to check whether they are known to be the same value, we check only
// the second condition and ensure that it also applies when then first
// condition is true. This is done by adding a wildcard value to
// Proposed.Known and Existing.Unused such that they match as a common known
// value. We use the "unknown ValInst" for this purpose. Every
// Existing.Unused may match with an unknown Proposed.Occupied because these
// never are in conflict with each other.
auto ProposedOccupiedAnyVal = makeUnknownForDomain(Proposed.Occupied);
auto ProposedValues = Proposed.Known.unite(ProposedOccupiedAnyVal);
auto ExistingUnusedAnyVal = makeUnknownForDomain(Existing.Unused);
auto ExistingValues = Existing.Known.unite(ExistingUnusedAnyVal);
auto MatchingVals = ExistingValues.intersect(ProposedValues);
auto Matches = MatchingVals.domain();
// Any Proposed.Occupied must either have a match between the known values
// of Existing and Occupied, or be in Existing.Unused. In the latter case,
// the previously added "AnyVal" will match each other.
if (!Proposed.Occupied.is_subset(Matches)) {
if (OS) {
auto Conflicting = Proposed.Occupied.subtract(Matches);
auto ExistingConflictingKnown =
Existing.Known.intersect_domain(Conflicting);
auto ProposedConflictingKnown =
Proposed.Known.intersect_domain(Conflicting);
OS->indent(Indent) << "Proposed lifetime conflicting with Existing's\n";
OS->indent(Indent) << "Conflicting occupied: " << Conflicting << "\n";
if (!ExistingConflictingKnown.is_empty())
OS->indent(Indent)
<< "Existing Known: " << ExistingConflictingKnown << "\n";
if (!ProposedConflictingKnown.is_empty())
OS->indent(Indent)
<< "Proposed Known: " << ProposedConflictingKnown << "\n";
}
return true;
}
// Do the writes in Existing conflict with occupied values in Proposed?
//
// In order to not conflict, it must either write to unused lifetime or
// write the same value. To check, we remove the writes that write into
// Proposed.Unused (they never conflict) and then see whether the written
// value is already in Proposed.Known. If there are multiple known values
// and a written value is known under different names, it is enough when one
// of the written values (assuming that they are the same value under
// different names, e.g. a PHINode and one of the incoming values) matches
// one of the known names.
//
// We convert here the set of lifetimes to actual timepoints. A lifetime is
// in conflict with a set of write timepoints, if either a live timepoint is
// clearly within the lifetime or if a write happens at the beginning of the
// lifetime (where it would conflict with the value that actually writes the
// value alive). There is no conflict at the end of a lifetime, as the alive
// value will always be read, before it is overwritten again. The last
// property holds in Polly for all scalar values and we expect all users of
// Knowledge to check this property also for accesses to MemoryKind::Array.
auto ProposedFixedDefs =
convertZoneToTimepoints(Proposed.Occupied, true, false);
auto ProposedFixedKnown =
convertZoneToTimepoints(Proposed.Known, isl::dim::in, true, false);
auto ExistingConflictingWrites =
Existing.Written.intersect_domain(ProposedFixedDefs);
auto ExistingConflictingWritesDomain = ExistingConflictingWrites.domain();
auto CommonWrittenVal =
ProposedFixedKnown.intersect(ExistingConflictingWrites);
auto CommonWrittenValDomain = CommonWrittenVal.domain();
if (!ExistingConflictingWritesDomain.is_subset(CommonWrittenValDomain)) {
if (OS) {
auto ExistingConflictingWritten =
ExistingConflictingWrites.subtract_domain(CommonWrittenValDomain);
auto ProposedConflictingKnown = ProposedFixedKnown.subtract_domain(
ExistingConflictingWritten.domain());
OS->indent(Indent)
<< "Proposed a lifetime where there is an Existing write into it\n";
OS->indent(Indent) << "Existing conflicting writes: "
<< ExistingConflictingWritten << "\n";
if (!ProposedConflictingKnown.is_empty())
OS->indent(Indent)
<< "Proposed conflicting known: " << ProposedConflictingKnown
<< "\n";
}
return true;
}
// Do the writes in Proposed conflict with occupied values in Existing?
auto ExistingAvailableDefs =
convertZoneToTimepoints(Existing.Unused, true, false);
auto ExistingKnownDefs =
convertZoneToTimepoints(Existing.Known, isl::dim::in, true, false);
auto ProposedWrittenDomain = Proposed.Written.domain();
auto KnownIdentical = ExistingKnownDefs.intersect(Proposed.Written);
auto IdenticalOrUnused =
ExistingAvailableDefs.unite(KnownIdentical.domain());
if (!ProposedWrittenDomain.is_subset(IdenticalOrUnused)) {
if (OS) {
auto Conflicting = ProposedWrittenDomain.subtract(IdenticalOrUnused);
auto ExistingConflictingKnown =
ExistingKnownDefs.intersect_domain(Conflicting);
auto ProposedConflictingWritten =
Proposed.Written.intersect_domain(Conflicting);
OS->indent(Indent) << "Proposed writes into range used by Existing\n";
OS->indent(Indent) << "Proposed conflicting writes: "
<< ProposedConflictingWritten << "\n";
if (!ExistingConflictingKnown.is_empty())
OS->indent(Indent)
<< "Existing conflicting known: " << ExistingConflictingKnown
<< "\n";
}
return true;
}
// Does Proposed write at the same time as Existing already does (order of
// writes is undefined)? Writing the same value is permitted.
auto ExistingWrittenDomain =
isl::manage(isl_union_map_domain(Existing.Written.copy()));
auto BothWritten =
Existing.Written.domain().intersect(Proposed.Written.domain());
auto ExistingKnownWritten = filterKnownValInst(Existing.Written);
auto ProposedKnownWritten = filterKnownValInst(Proposed.Written);
auto CommonWritten =
ExistingKnownWritten.intersect(ProposedKnownWritten).domain();
if (!BothWritten.is_subset(CommonWritten)) {
if (OS) {
auto Conflicting = BothWritten.subtract(CommonWritten);
auto ExistingConflictingWritten =
Existing.Written.intersect_domain(Conflicting);
auto ProposedConflictingWritten =
Proposed.Written.intersect_domain(Conflicting);
OS->indent(Indent) << "Proposed writes at the same time as an already "
"Existing write\n";
OS->indent(Indent) << "Conflicting writes: " << Conflicting << "\n";
if (!ExistingConflictingWritten.is_empty())
OS->indent(Indent)
<< "Exiting write: " << ExistingConflictingWritten << "\n";
if (!ProposedConflictingWritten.is_empty())
OS->indent(Indent)
<< "Proposed write: " << ProposedConflictingWritten << "\n";
}
return true;
}
return false;
}
};
std::string printIntruction(Instruction *Instr, bool IsForDebug = false) {
std::string Result;
raw_string_ostream OS(Result);
Instr->print(OS, IsForDebug);
OS.flush();
size_t i = 0;
while (i < Result.size() && Result[i] == ' ')
i += 1;
return Result.substr(i);
}
/// Base class for algorithms based on zones, like DeLICM.
class ZoneAlgorithm {
protected:
/// Hold a reference to the isl_ctx to avoid it being freed before we released
/// all of the isl objects.
///
/// This must be declared before any other member that holds an isl object.
/// This guarantees that the shared_ptr and its isl_ctx is destructed last,
/// after all other members free'd the isl objects they were holding.
std::shared_ptr<isl_ctx> IslCtx;
/// Cached reaching definitions for each ScopStmt.
///
/// Use getScalarReachingDefinition() to get its contents.
DenseMap<ScopStmt *, isl::map> ScalarReachDefZone;
/// The analyzed Scop.
Scop *S;
/// LoopInfo analysis used to determine whether values are synthesizable.
LoopInfo *LI;
/// Parameter space that does not need realignment.
isl::space ParamSpace;
/// Space the schedule maps to.
isl::space ScatterSpace;
/// Cached version of the schedule and domains.
isl::union_map Schedule;
/// Combined access relations of all MemoryKind::Array READ accesses.
/// { DomainRead[] -> Element[] }
isl::union_map AllReads;
/// Combined access relations of all MemoryKind::Array, MAY_WRITE accesses.
/// { DomainMayWrite[] -> Element[] }
isl::union_map AllMayWrites;
/// Combined access relations of all MemoryKind::Array, MUST_WRITE accesses.
/// { DomainMustWrite[] -> Element[] }
isl::union_map AllMustWrites;
/// The value instances written to array elements of all write accesses.
/// { [Element[] -> DomainWrite[]] -> ValInst[] }
isl::union_map AllWriteValInst;
/// All reaching definitions for MemoryKind::Array writes.
/// { [Element[] -> Zone[]] -> DomainWrite[] }
isl::union_map WriteReachDefZone;
/// Map llvm::Values to an isl identifier.
/// Used with -polly-use-llvm-names=false as an alternative method to get
/// unique ids that do not depend on pointer values.
DenseMap<Value *, isl::id> ValueIds;
/// Prepare the object before computing the zones of @p S.
ZoneAlgorithm(Scop *S, LoopInfo *LI)
: IslCtx(S->getSharedIslCtx()), S(S), LI(LI),
Schedule(give(S->getSchedule())) {
auto Domains = give(S->getDomains());
Schedule =
give(isl_union_map_intersect_domain(Schedule.take(), Domains.take()));
ParamSpace = give(isl_union_map_get_space(Schedule.keep()));
ScatterSpace = getScatterSpace(Schedule);
}
private:
/// Check whether @p Stmt can be accurately analyzed by zones.
///
/// What violates our assumptions:
/// - A load after a write of the same location; we assume that all reads
/// occur before the writes.
/// - Two writes to the same location; we cannot model the order in which
/// these occur.
///
/// Scalar reads implicitly always occur before other accesses therefore never
/// violate the first condition. There is also at most one write to a scalar,
/// satisfying the second condition.
bool isCompatibleStmt(ScopStmt *Stmt) {
auto Stores = makeEmptyUnionMap();
auto Loads = makeEmptyUnionMap();
// This assumes that the MemoryKind::Array MemoryAccesses are iterated in
// order.
for (auto *MA : *Stmt) {
if (!MA->isLatestArrayKind())
continue;
auto AccRel =
give(isl_union_map_from_map(getAccessRelationFor(MA).take()));
if (MA->isRead()) {
// Reject load after store to same location.
if (!isl_union_map_is_disjoint(Stores.keep(), AccRel.keep())) {
OptimizationRemarkMissed R(DEBUG_TYPE, "LoadAfterStore",
MA->getAccessInstruction());
R << "load after store of same element in same statement";
R << " (previous stores: " << Stores;
R << ", loading: " << AccRel << ")";
S->getFunction().getContext().diagnose(R);
return false;
}
Loads = give(isl_union_map_union(Loads.take(), AccRel.take()));
continue;
}
if (!isa<StoreInst>(MA->getAccessInstruction())) {
DEBUG(dbgs() << "WRITE that is not a StoreInst not supported\n");
OptimizationRemarkMissed R(DEBUG_TYPE, "UnusualStore",
MA->getAccessInstruction());
R << "encountered write that is not a StoreInst: "
<< printIntruction(MA->getAccessInstruction());
S->getFunction().getContext().diagnose(R);
return false;
}
// In region statements the order is less clear, eg. the load and store
// might be in a boxed loop.
if (Stmt->isRegionStmt() &&
!isl_union_map_is_disjoint(Loads.keep(), AccRel.keep())) {
OptimizationRemarkMissed R(DEBUG_TYPE, "StoreInSubregion",
MA->getAccessInstruction());
R << "store is in a non-affine subregion";
S->getFunction().getContext().diagnose(R);
return false;
}
// Do not allow more than one store to the same location.
if (!isl_union_map_is_disjoint(Stores.keep(), AccRel.keep())) {
OptimizationRemarkMissed R(DEBUG_TYPE, "StoreAfterStore",
MA->getAccessInstruction());
R << "store after store of same element in same statement";
R << " (previous stores: " << Stores;
R << ", storing: " << AccRel << ")";
S->getFunction().getContext().diagnose(R);
return false;
}
Stores = give(isl_union_map_union(Stores.take(), AccRel.take()));
}
return true;
}
void addArrayReadAccess(MemoryAccess *MA) {
assert(MA->isLatestArrayKind());
assert(MA->isRead());
// { DomainRead[] -> Element[] }
auto AccRel = getAccessRelationFor(MA);
AllReads = give(isl_union_map_add_map(AllReads.take(), AccRel.copy()));
}
void addArrayWriteAccess(MemoryAccess *MA) {
assert(MA->isLatestArrayKind());
assert(MA->isWrite());
auto *Stmt = MA->getStatement();
// { Domain[] -> Element[] }
auto AccRel = getAccessRelationFor(MA);
if (MA->isMustWrite())
AllMustWrites =
give(isl_union_map_add_map(AllMustWrites.take(), AccRel.copy()));
if (MA->isMayWrite())
AllMayWrites =
give(isl_union_map_add_map(AllMayWrites.take(), AccRel.copy()));
// { Domain[] -> ValInst[] }
auto WriteValInstance =
makeValInst(MA->getAccessValue(), Stmt,
LI->getLoopFor(MA->getAccessInstruction()->getParent()),
MA->isMustWrite());
// { Domain[] -> [Element[] -> Domain[]] }
auto IncludeElement =
give(isl_map_curry(isl_map_domain_map(AccRel.copy())));
// { [Element[] -> DomainWrite[]] -> ValInst[] }
auto EltWriteValInst = give(
isl_map_apply_domain(WriteValInstance.take(), IncludeElement.take()));
AllWriteValInst = give(
isl_union_map_add_map(AllWriteValInst.take(), EltWriteValInst.take()));
}
protected:
isl::union_set makeEmptyUnionSet() const {
return give(isl_union_set_empty(ParamSpace.copy()));
}
isl::union_map makeEmptyUnionMap() const {
return give(isl_union_map_empty(ParamSpace.copy()));
}
/// Check whether @p S can be accurately analyzed by zones.
bool isCompatibleScop() {
for (auto &Stmt : *S) {
if (!isCompatibleStmt(&Stmt))
return false;
}
return true;
}
/// Get the schedule for @p Stmt.
///
/// The domain of the result is as narrow as possible.
isl::map getScatterFor(ScopStmt *Stmt) const {
auto ResultSpace = give(isl_space_map_from_domain_and_range(
Stmt->getDomainSpace(), ScatterSpace.copy()));
return give(isl_union_map_extract_map(Schedule.keep(), ResultSpace.take()));
}
/// Get the schedule of @p MA's parent statement.
isl::map getScatterFor(MemoryAccess *MA) const {
return getScatterFor(MA->getStatement());
}
/// Get the schedule for the statement instances of @p Domain.
isl::union_map getScatterFor(isl::union_set Domain) const {
return give(isl_union_map_intersect_domain(Schedule.copy(), Domain.take()));
}
/// Get the schedule for the statement instances of @p Domain.
isl::map getScatterFor(isl::set Domain) const {
auto ResultSpace = give(isl_space_map_from_domain_and_range(
isl_set_get_space(Domain.keep()), ScatterSpace.copy()));
auto UDomain = give(isl_union_set_from_set(Domain.copy()));
auto UResult = getScatterFor(std::move(UDomain));
auto Result = singleton(std::move(UResult), std::move(ResultSpace));
assert(!Result ||
isl_set_is_equal(give(isl_map_domain(Result.copy())).keep(),
Domain.keep()) == isl_bool_true);
return Result;
}
/// Get the domain of @p Stmt.
isl::set getDomainFor(ScopStmt *Stmt) const {
return give(isl_set_remove_redundancies(Stmt->getDomain()));
}
/// Get the domain @p MA's parent statement.
isl::set getDomainFor(MemoryAccess *MA) const {
return getDomainFor(MA->getStatement());
}
/// Get the access relation of @p MA.
///
/// The domain of the result is as narrow as possible.
isl::map getAccessRelationFor(MemoryAccess *MA) const {
auto Domain = getDomainFor(MA);
auto AccRel = give(MA->getLatestAccessRelation());
return give(isl_map_intersect_domain(AccRel.take(), Domain.take()));
}
/// Get the reaching definition of a scalar defined in @p Stmt.
///
/// Note that this does not depend on the llvm::Instruction, only on the
/// statement it is defined in. Therefore the same computation can be reused.
///
/// @param Stmt The statement in which a scalar is defined.
///
/// @return { Scatter[] -> DomainDef[] }
isl::map getScalarReachingDefinition(ScopStmt *Stmt) {
auto &Result = ScalarReachDefZone[Stmt];
if (Result)
return Result;
auto Domain = getDomainFor(Stmt);
Result = computeScalarReachingDefinition(Schedule, Domain, false, true);
simplify(Result);
return Result;
}
/// Get the reaching definition of a scalar defined in @p DefDomain.
///
/// @param DomainDef { DomainDef[] }
/// The write statements to get the reaching definition for.
///
/// @return { Scatter[] -> DomainDef[] }
isl::map getScalarReachingDefinition(isl::set DomainDef) {
auto DomId = give(isl_set_get_tuple_id(DomainDef.keep()));
auto *Stmt = static_cast<ScopStmt *>(isl_id_get_user(DomId.keep()));
auto StmtResult = getScalarReachingDefinition(Stmt);
return give(isl_map_intersect_range(StmtResult.take(), DomainDef.take()));
}
/// Create a statement-to-unknown value mapping.
///
/// @param Stmt The statement whose instances are mapped to unknown.
///
/// @return { Domain[] -> ValInst[] }
isl::map makeUnknownForDomain(ScopStmt *Stmt) const {
return ::makeUnknownForDomain(getDomainFor(Stmt));
}
/// Create an isl_id that represents @p V.
isl::id makeValueId(Value *V) {
if (!V)
return nullptr;
auto &Id = ValueIds[V];
if (Id.is_null()) {
auto Name = getIslCompatibleName("Val_", V, ValueIds.size() - 1,
std::string(), UseInstructionNames);
Id = give(isl_id_alloc(IslCtx.get(), Name.c_str(), V));
}
return Id;
}
/// Create the space for an llvm::Value that is available everywhere.
isl::space makeValueSpace(Value *V) {
auto Result = give(isl_space_set_from_params(ParamSpace.copy()));
return give(isl_space_set_tuple_id(Result.take(), isl_dim_set,
makeValueId(V).take()));
}
/// Create a set with the llvm::Value @p V which is available everywhere.
isl::set makeValueSet(Value *V) {
auto Space = makeValueSpace(V);
return give(isl_set_universe(Space.take()));
}
/// Create a mapping from a statement instance to the instance of an
/// llvm::Value that can be used in there.
///
/// Although LLVM IR uses single static assignment, llvm::Values can have
/// different contents in loops, when they get redefined in the last
/// iteration. This function tries to get the statement instance of the
/// previous definition, relative to a user.
///
/// Example:
/// for (int i = 0; i < N; i += 1) {
/// DEF:
/// int v = A[i];
/// USE:
/// use(v);
/// }
///
/// The value instance used by statement instance USE[i] is DEF[i]. Hence,
/// makeValInst returns:
///
/// { USE[i] -> [DEF[i] -> v[]] : 0 <= i < N }
///
/// @param Val The value to get the instance of.
/// @param UserStmt The statement that uses @p Val. Can be nullptr.
/// @param Scope Loop the using instruction resides in.
/// @param IsCertain Pass true if the definition of @p Val is a
/// MUST_WRITE or false if the write is conditional.
///
/// @return { DomainUse[] -> ValInst[] }
isl::map makeValInst(Value *Val, ScopStmt *UserStmt, Loop *Scope,
bool IsCertain = true) {
// When known knowledge is disabled, just return the unknown value. It will
// either get filtered out or conflict with itself.
if (!DelicmComputeKnown)
return makeUnknownForDomain(UserStmt);
// If the definition/write is conditional, the value at the location could
// be either the written value or the old value. Since we cannot know which
// one, consider the value to be unknown.
if (!IsCertain)
return makeUnknownForDomain(UserStmt);
auto DomainUse = getDomainFor(UserStmt);
auto VUse = VirtualUse::create(S, UserStmt, Scope, Val, true);
switch (VUse.getKind()) {
case VirtualUse::Constant:
case VirtualUse::Block:
case VirtualUse::Hoisted:
case VirtualUse::ReadOnly: {
// The definition does not depend on the statement which uses it.
auto ValSet = makeValueSet(Val);
return give(
isl_map_from_domain_and_range(DomainUse.take(), ValSet.take()));
}
case VirtualUse::Synthesizable: {
auto *ScevExpr = VUse.getScevExpr();
auto UseDomainSpace = give(isl_set_get_space(DomainUse.keep()));
// Construct the SCEV space.
// TODO: Add only the induction variables referenced in SCEVAddRecExpr
// expressions, not just all of them.
auto ScevId = give(isl_id_alloc(UseDomainSpace.get_ctx().get(), nullptr,
const_cast<SCEV *>(ScevExpr)));
auto ScevSpace =
give(isl_space_drop_dims(UseDomainSpace.copy(), isl_dim_set, 0, 0));
ScevSpace = give(
isl_space_set_tuple_id(ScevSpace.take(), isl_dim_set, ScevId.copy()));
// { DomainUse[] -> ScevExpr[] }
auto ValInst = give(isl_map_identity(isl_space_map_from_domain_and_range(
UseDomainSpace.copy(), ScevSpace.copy())));
return ValInst;
}
case VirtualUse::Intra: {
// Definition and use is in the same statement. We do not need to compute
// a reaching definition.
// { llvm::Value }
auto ValSet = makeValueSet(Val);
// { UserDomain[] -> llvm::Value }
auto ValInstSet =
give(isl_map_from_domain_and_range(DomainUse.take(), ValSet.take()));
// { UserDomain[] -> [UserDomain[] - >llvm::Value] }
auto Result =
give(isl_map_reverse(isl_map_domain_map(ValInstSet.take())));
simplify(Result);
return Result;
}
case VirtualUse::Inter: {
// The value is defined in a different statement.
auto *Inst = cast<Instruction>(Val);
auto *ValStmt = S->getStmtFor(Inst);
// If the llvm::Value is defined in a removed Stmt, we cannot derive its
// domain. We could use an arbitrary statement, but this could result in
// different ValInst[] for the same llvm::Value.
if (!ValStmt)
return ::makeUnknownForDomain(DomainUse);
// { DomainDef[] }
auto DomainDef = getDomainFor(ValStmt);
// { Scatter[] -> DomainDef[] }
auto ReachDef = getScalarReachingDefinition(DomainDef);
// { DomainUse[] -> Scatter[] }
auto UserSched = getScatterFor(DomainUse);
// { DomainUse[] -> DomainDef[] }
auto UsedInstance =
give(isl_map_apply_range(UserSched.take(), ReachDef.take()));
// { llvm::Value }
auto ValSet = makeValueSet(Val);
// { DomainUse[] -> llvm::Value[] }
auto ValInstSet =
give(isl_map_from_domain_and_range(DomainUse.take(), ValSet.take()));
// { DomainUse[] -> [DomainDef[] -> llvm::Value] }
auto Result =
give(isl_map_range_product(UsedInstance.take(), ValInstSet.take()));
simplify(Result);
return Result;
}
}
llvm_unreachable("Unhandled use type");
}
/// Compute the different zones.
void computeCommon() {
AllReads = makeEmptyUnionMap();
AllMayWrites = makeEmptyUnionMap();
AllMustWrites = makeEmptyUnionMap();
AllWriteValInst = makeEmptyUnionMap();
for (auto &Stmt : *S) {
for (auto *MA : Stmt) {
if (!MA->isLatestArrayKind())
continue;
if (MA->isRead())
addArrayReadAccess(MA);
if (MA->isWrite())
addArrayWriteAccess(MA);
}
}
// { DomainWrite[] -> Element[] }
auto AllWrites =
give(isl_union_map_union(AllMustWrites.copy(), AllMayWrites.copy()));
// { [Element[] -> Zone[]] -> DomainWrite[] }
WriteReachDefZone =
computeReachingDefinition(Schedule, AllWrites, false, true);
simplify(WriteReachDefZone);
}
/// Print the current state of all MemoryAccesses to @p.
void printAccesses(llvm::raw_ostream &OS, int Indent = 0) const {
OS.indent(Indent) << "After accesses {\n";
for (auto &Stmt : *S) {
OS.indent(Indent + 4) << Stmt.getBaseName() << "\n";
for (auto *MA : Stmt)
MA->print(OS);
}
OS.indent(Indent) << "}\n";
}
public:
/// Return the SCoP this object is analyzing.
Scop *getScop() const { return S; }
};
/// Implementation of the DeLICM/DePRE transformation.
class DeLICMImpl : public ZoneAlgorithm {
private:
/// Knowledge before any transformation took place.
Knowledge OriginalZone;
/// Current knowledge of the SCoP including all already applied
/// transformations.
Knowledge Zone;
/// For getting the MemoryAccesses that write or read a given scalar.
ScalarDefUseChains DefUse;
/// Number of StoreInsts something can be mapped to.
int NumberOfCompatibleTargets = 0;
/// The number of StoreInsts to which at least one value or PHI has been
/// mapped to.
int NumberOfTargetsMapped = 0;
/// The number of llvm::Value mapped to some array element.
int NumberOfMappedValueScalars = 0;
/// The number of PHIs mapped to some array element.
int NumberOfMappedPHIScalars = 0;
/// Determine whether two knowledges are conflicting with each other.
///
/// @see Knowledge::isConflicting
bool isConflicting(const Knowledge &Proposed) {
raw_ostream *OS = nullptr;
DEBUG(OS = &llvm::dbgs());
return Knowledge::isConflicting(Zone, Proposed, OS, 4);
}
/// Determine whether @p SAI is a scalar that can be mapped to an array
/// element.
bool isMappable(const ScopArrayInfo *SAI) {
assert(SAI);
if (SAI->isValueKind()) {
auto *MA = DefUse.getValueDef(SAI);
if (!MA) {
DEBUG(dbgs()
<< " Reject because value is read-only within the scop\n");
return false;
}
// Mapping if value is used after scop is not supported. The code
// generator would need to reload the scalar after the scop, but it
// does not have the information to where it is mapped to. Only the
// MemoryAccesses have that information, not the ScopArrayInfo.
auto Inst = MA->getAccessInstruction();
for (auto User : Inst->users()) {
if (!isa<Instruction>(User))
return false;
auto UserInst = cast<Instruction>(User);
if (!S->contains(UserInst)) {
DEBUG(dbgs() << " Reject because value is escaping\n");
return false;
}
}
return true;
}
if (SAI->isPHIKind()) {
auto *MA = DefUse.getPHIRead(SAI);
assert(MA);
// Mapping of an incoming block from before the SCoP is not supported by
// the code generator.
auto PHI = cast<PHINode>(MA->getAccessInstruction());
for (auto Incoming : PHI->blocks()) {
if (!S->contains(Incoming)) {
DEBUG(dbgs() << " Reject because at least one incoming block is "
"not in the scop region\n");
return false;
}
}
return true;
}
DEBUG(dbgs() << " Reject ExitPHI or other non-value\n");
return false;
}
/// Compute the uses of a MemoryKind::Value and its lifetime (from its
/// definition to the last use).
///
/// @param SAI The ScopArrayInfo representing the value's storage.
///
/// @return { DomainDef[] -> DomainUse[] }, { DomainDef[] -> Zone[] }
/// First element is the set of uses for each definition.
/// The second is the lifetime of each definition.
std::tuple<isl::union_map, isl::map>
computeValueUses(const ScopArrayInfo *SAI) {
assert(SAI->isValueKind());
// { DomainRead[] }
auto Reads = makeEmptyUnionSet();
// Find all uses.
for (auto *MA : DefUse.getValueUses(SAI))
Reads =
give(isl_union_set_add_set(Reads.take(), getDomainFor(MA).take()));
// { DomainRead[] -> Scatter[] }
auto ReadSchedule = getScatterFor(Reads);
auto *DefMA = DefUse.getValueDef(SAI);
assert(DefMA);
// { DomainDef[] }
auto Writes = getDomainFor(DefMA);
// { DomainDef[] -> Scatter[] }
auto WriteScatter = getScatterFor(Writes);
// { Scatter[] -> DomainDef[] }
auto ReachDef = getScalarReachingDefinition(DefMA->getStatement());
// { [DomainDef[] -> Scatter[]] -> DomainUse[] }
auto Uses = give(
isl_union_map_apply_range(isl_union_map_from_map(isl_map_range_map(
isl_map_reverse(ReachDef.take()))),
isl_union_map_reverse(ReadSchedule.take())));
// { DomainDef[] -> Scatter[] }
auto UseScatter =
singleton(give(isl_union_set_unwrap(isl_union_map_domain(Uses.copy()))),
give(isl_space_map_from_domain_and_range(
isl_set_get_space(Writes.keep()), ScatterSpace.copy())));
// { DomainDef[] -> Zone[] }
auto Lifetime = betweenScatter(WriteScatter, UseScatter, false, true);
// { DomainDef[] -> DomainRead[] }
auto DefUses = give(isl_union_map_domain_factor_domain(Uses.take()));
return std::make_pair(DefUses, Lifetime);
}
/// For each 'execution' of a PHINode, get the incoming block that was
/// executed before.
///
/// For each PHI instance we can directly determine which was the incoming
/// block, and hence derive which value the PHI has.
///
/// @param SAI The ScopArrayInfo representing the PHI's storage.
///
/// @return { DomainPHIRead[] -> DomainPHIWrite[] }
isl::union_map computePerPHI(const ScopArrayInfo *SAI) {
assert(SAI->isPHIKind());
// { DomainPHIWrite[] -> Scatter[] }
auto PHIWriteScatter = makeEmptyUnionMap();
// Collect all incoming block timepoint.
for (auto *MA : DefUse.getPHIIncomings(SAI)) {
auto Scatter = getScatterFor(MA);
PHIWriteScatter =
give(isl_union_map_add_map(PHIWriteScatter.take(), Scatter.take()));
}
// { DomainPHIRead[] -> Scatter[] }
auto PHIReadScatter = getScatterFor(DefUse.getPHIRead(SAI));
// { DomainPHIRead[] -> Scatter[] }
auto BeforeRead = beforeScatter(PHIReadScatter, true);
// { Scatter[] }
auto WriteTimes = singleton(
give(isl_union_map_range(PHIWriteScatter.copy())), ScatterSpace);
// { DomainPHIRead[] -> Scatter[] }
auto PHIWriteTimes =
give(isl_map_intersect_range(BeforeRead.take(), WriteTimes.take()));
auto LastPerPHIWrites = give(isl_map_lexmax(PHIWriteTimes.take()));
// { DomainPHIRead[] -> DomainPHIWrite[] }
auto Result = give(isl_union_map_apply_range(
isl_union_map_from_map(LastPerPHIWrites.take()),
isl_union_map_reverse(PHIWriteScatter.take())));
assert(isl_union_map_is_single_valued(Result.keep()) == isl_bool_true);
assert(isl_union_map_is_injective(Result.keep()) == isl_bool_true);
return Result;
}
/// Try to map a MemoryKind::Value to a given array element.
///
/// @param SAI Representation of the scalar's memory to map.
/// @param TargetElt { Scatter[] -> Element[] }
/// Suggestion where to map a scalar to when at a timepoint.
///
/// @return true if the scalar was successfully mapped.
bool tryMapValue(const ScopArrayInfo *SAI, isl::map TargetElt) {
assert(SAI->isValueKind());
auto *DefMA = DefUse.getValueDef(SAI);
assert(DefMA->isValueKind());
assert(DefMA->isMustWrite());
auto *V = DefMA->getAccessValue();
auto *DefInst = DefMA->getAccessInstruction();
// Stop if the scalar has already been mapped.
if (!DefMA->getLatestScopArrayInfo()->isValueKind())
return false;
// { DomainDef[] -> Scatter[] }
auto DefSched = getScatterFor(DefMA);
// Where each write is mapped to, according to the suggestion.
// { DomainDef[] -> Element[] }
auto DefTarget = give(isl_map_apply_domain(
TargetElt.copy(), isl_map_reverse(DefSched.copy())));
simplify(DefTarget);
DEBUG(dbgs() << " Def Mapping: " << DefTarget << '\n');
auto OrigDomain = getDomainFor(DefMA);
auto MappedDomain = give(isl_map_domain(DefTarget.copy()));
if (!isl_set_is_subset(OrigDomain.keep(), MappedDomain.keep())) {
DEBUG(dbgs()
<< " Reject because mapping does not encompass all instances\n");
return false;
}
// { DomainDef[] -> Zone[] }
isl::map Lifetime;
// { DomainDef[] -> DomainUse[] }
isl::union_map DefUses;
std::tie(DefUses, Lifetime) = computeValueUses(SAI);
DEBUG(dbgs() << " Lifetime: " << Lifetime << '\n');
/// { [Element[] -> Zone[]] }
auto EltZone = give(
isl_map_wrap(isl_map_apply_domain(Lifetime.copy(), DefTarget.copy())));
simplify(EltZone);
// { DomainDef[] -> ValInst[] }
auto ValInst = makeValInst(V, DefMA->getStatement(),
LI->getLoopFor(DefInst->getParent()));
// { DomainDef[] -> [Element[] -> Zone[]] }
auto EltKnownTranslator =
give(isl_map_range_product(DefTarget.copy(), Lifetime.copy()));
// { [Element[] -> Zone[]] -> ValInst[] }
auto EltKnown =
give(isl_map_apply_domain(ValInst.copy(), EltKnownTranslator.take()));
simplify(EltKnown);
// { DomainDef[] -> [Element[] -> Scatter[]] }
auto WrittenTranslator =
give(isl_map_range_product(DefTarget.copy(), DefSched.take()));
// { [Element[] -> Scatter[]] -> ValInst[] }
auto DefEltSched =
give(isl_map_apply_domain(ValInst.copy(), WrittenTranslator.take()));
simplify(DefEltSched);
Knowledge Proposed(EltZone, nullptr, filterKnownValInst(EltKnown),
DefEltSched);
if (isConflicting(Proposed))
return false;
// { DomainUse[] -> Element[] }
auto UseTarget = give(
isl_union_map_apply_range(isl_union_map_reverse(DefUses.take()),
isl_union_map_from_map(DefTarget.copy())));
mapValue(SAI, std::move(DefTarget), std::move(UseTarget),
std::move(Lifetime), std::move(Proposed));
return true;
}
/// After a scalar has been mapped, update the global knowledge.
void applyLifetime(Knowledge Proposed) {
Zone.learnFrom(std::move(Proposed));
}
/// Map a MemoryKind::Value scalar to an array element.
///
/// Callers must have ensured that the mapping is valid and not conflicting.
///
/// @param SAI The ScopArrayInfo representing the scalar's memory to
/// map.
/// @param DefTarget { DomainDef[] -> Element[] }
/// The array element to map the scalar to.
/// @param UseTarget { DomainUse[] -> Element[] }
/// The array elements the uses are mapped to.
/// @param Lifetime { DomainDef[] -> Zone[] }
/// The lifetime of each llvm::Value definition for
/// reporting.
/// @param Proposed Mapping constraints for reporting.
void mapValue(const ScopArrayInfo *SAI, isl::map DefTarget,
isl::union_map UseTarget, isl::map Lifetime,
Knowledge Proposed) {
// Redirect the read accesses.
for (auto *MA : DefUse.getValueUses(SAI)) {
// { DomainUse[] }
auto Domain = getDomainFor(MA);
// { DomainUse[] -> Element[] }
auto NewAccRel = give(isl_union_map_intersect_domain(
UseTarget.copy(), isl_union_set_from_set(Domain.take())));
simplify(NewAccRel);
assert(isl_union_map_n_map(NewAccRel.keep()) == 1);
MA->setNewAccessRelation(isl_map_from_union_map(NewAccRel.take()));
}
auto *WA = DefUse.getValueDef(SAI);
WA->setNewAccessRelation(DefTarget.copy());
applyLifetime(Proposed);
MappedValueScalars++;
NumberOfMappedValueScalars += 1;
}
/// Express the incoming values of a PHI for each incoming statement in an
/// isl::union_map.
///
/// @param SAI The PHI scalar represented by a ScopArrayInfo.
///
/// @return { PHIWriteDomain[] -> ValInst[] }
isl::union_map determinePHIWrittenValues(const ScopArrayInfo *SAI) {
auto Result = makeEmptyUnionMap();
// Collect the incoming values.
for (auto *MA : DefUse.getPHIIncomings(SAI)) {
// { DomainWrite[] -> ValInst[] }
isl::union_map ValInst;
auto *WriteStmt = MA->getStatement();
auto Incoming = MA->getIncoming();
assert(!Incoming.empty());
if (Incoming.size() == 1) {
ValInst = makeValInst(Incoming[0].second, WriteStmt,
LI->getLoopFor(Incoming[0].first));
} else {
// If the PHI is in a subregion's exit node it can have multiple
// incoming values (+ maybe another incoming edge from an unrelated
// block). We cannot directly represent it as a single llvm::Value.
// We currently model it as unknown value, but modeling as the PHIInst
// itself could be OK, too.
ValInst = makeUnknownForDomain(WriteStmt);
}
Result = give(isl_union_map_union(Result.take(), ValInst.take()));
}
assert(isl_union_map_is_single_valued(Result.keep()) == isl_bool_true &&
"Cannot have multiple incoming values for same incoming statement");
return Result;
}
/// Try to map a MemoryKind::PHI scalar to a given array element.
///
/// @param SAI Representation of the scalar's memory to map.
/// @param TargetElt { Scatter[] -> Element[] }
/// Suggestion where to map the scalar to when at a
/// timepoint.
///
/// @return true if the PHI scalar has been mapped.
bool tryMapPHI(const ScopArrayInfo *SAI, isl::map TargetElt) {
auto *PHIRead = DefUse.getPHIRead(SAI);
assert(PHIRead->isPHIKind());
assert(PHIRead->isRead());
// Skip if already been mapped.
if (!PHIRead->getLatestScopArrayInfo()->isPHIKind())
return false;
// { DomainRead[] -> Scatter[] }
auto PHISched = getScatterFor(PHIRead);
// { DomainRead[] -> Element[] }
auto PHITarget =
give(isl_map_apply_range(PHISched.copy(), TargetElt.copy()));
simplify(PHITarget);
DEBUG(dbgs() << " Mapping: " << PHITarget << '\n');
auto OrigDomain = getDomainFor(PHIRead);
auto MappedDomain = give(isl_map_domain(PHITarget.copy()));
if (!isl_set_is_subset(OrigDomain.keep(), MappedDomain.keep())) {
DEBUG(dbgs()
<< " Reject because mapping does not encompass all instances\n");
return false;
}
// { DomainRead[] -> DomainWrite[] }
auto PerPHIWrites = computePerPHI(SAI);
// { DomainWrite[] -> Element[] }
auto WritesTarget = give(isl_union_map_reverse(isl_union_map_apply_domain(
PerPHIWrites.copy(), isl_union_map_from_map(PHITarget.copy()))));
simplify(WritesTarget);
// { DomainWrite[] }
auto UniverseWritesDom = give(isl_union_set_empty(ParamSpace.copy()));
for (auto *MA : DefUse.getPHIIncomings(SAI))
UniverseWritesDom = give(isl_union_set_add_set(UniverseWritesDom.take(),
getDomainFor(MA).take()));
auto RelevantWritesTarget = WritesTarget;
if (DelicmOverapproximateWrites)
WritesTarget = expandMapping(WritesTarget, UniverseWritesDom);
auto ExpandedWritesDom = give(isl_union_map_domain(WritesTarget.copy()));
if (!DelicmPartialWrites &&
!isl_union_set_is_subset(UniverseWritesDom.keep(),
ExpandedWritesDom.keep())) {
DEBUG(dbgs() << " Reject because did not find PHI write mapping for "
"all instances\n");
if (DelicmOverapproximateWrites)
DEBUG(dbgs() << " Relevant Mapping: " << RelevantWritesTarget
<< '\n');
DEBUG(dbgs() << " Deduced Mapping: " << WritesTarget << '\n');
DEBUG(dbgs() << " Missing instances: "
<< give(isl_union_set_subtract(UniverseWritesDom.copy(),
ExpandedWritesDom.copy()))
<< '\n');
return false;
}
// { DomainRead[] -> Scatter[] }
auto PerPHIWriteScatter = give(isl_map_from_union_map(
isl_union_map_apply_range(PerPHIWrites.copy(), Schedule.copy())));
// { DomainRead[] -> Zone[] }
auto Lifetime = betweenScatter(PerPHIWriteScatter, PHISched, false, true);
simplify(Lifetime);
DEBUG(dbgs() << " Lifetime: " << Lifetime << "\n");
// { DomainWrite[] -> Zone[] }
auto WriteLifetime = give(isl_union_map_apply_domain(
isl_union_map_from_map(Lifetime.copy()), PerPHIWrites.copy()));
// { DomainWrite[] -> ValInst[] }
auto WrittenValue = determinePHIWrittenValues(SAI);
// { DomainWrite[] -> [Element[] -> Scatter[]] }
auto WrittenTranslator =
give(isl_union_map_range_product(WritesTarget.copy(), Schedule.copy()));
// { [Element[] -> Scatter[]] -> ValInst[] }
auto Written = give(isl_union_map_apply_domain(WrittenValue.copy(),
WrittenTranslator.copy()));
simplify(Written);
// { DomainWrite[] -> [Element[] -> Zone[]] }
auto LifetimeTranslator = give(
isl_union_map_range_product(WritesTarget.copy(), WriteLifetime.copy()));
// { DomainWrite[] -> ValInst[] }
auto WrittenKnownValue = filterKnownValInst(WrittenValue);
// { [Element[] -> Zone[]] -> ValInst[] }
auto EltLifetimeInst = give(isl_union_map_apply_domain(
WrittenKnownValue.copy(), LifetimeTranslator.copy()));
simplify(EltLifetimeInst);
// { [Element[] -> Zone[] }
auto Occupied = give(isl_union_map_range(LifetimeTranslator.copy()));
simplify(Occupied);
Knowledge Proposed(Occupied, nullptr, EltLifetimeInst, Written);
if (isConflicting(Proposed))
return false;
mapPHI(SAI, std::move(PHITarget), std::move(WritesTarget),
std::move(Lifetime), std::move(Proposed));
return true;
}
/// Map a MemoryKind::PHI scalar to an array element.
///
/// Callers must have ensured that the mapping is valid and not conflicting
/// with the common knowledge.
///
/// @param SAI The ScopArrayInfo representing the scalar's memory to
/// map.
/// @param ReadTarget { DomainRead[] -> Element[] }
/// The array element to map the scalar to.
/// @param WriteTarget { DomainWrite[] -> Element[] }
/// New access target for each PHI incoming write.
/// @param Lifetime { DomainRead[] -> Zone[] }
/// The lifetime of each PHI for reporting.
/// @param Proposed Mapping constraints for reporting.
void mapPHI(const ScopArrayInfo *SAI, isl::map ReadTarget,
isl::union_map WriteTarget, isl::map Lifetime,
Knowledge Proposed) {
// Redirect the PHI incoming writes.
for (auto *MA : DefUse.getPHIIncomings(SAI)) {
// { DomainWrite[] }
auto Domain = getDomainFor(MA);
// { DomainWrite[] -> Element[] }
auto NewAccRel = give(isl_union_map_intersect_domain(
WriteTarget.copy(), isl_union_set_from_set(Domain.take())));
simplify(NewAccRel);
assert(isl_union_map_n_map(NewAccRel.keep()) == 1);
MA->setNewAccessRelation(isl_map_from_union_map(NewAccRel.take()));
}
// Redirect the PHI read.
auto *PHIRead = DefUse.getPHIRead(SAI);
PHIRead->setNewAccessRelation(ReadTarget.copy());
applyLifetime(Proposed);
MappedPHIScalars++;
NumberOfMappedPHIScalars++;
}
/// Search and map scalars to memory overwritten by @p TargetStoreMA.
///
/// Start trying to map scalars that are used in the same statement as the
/// store. For every successful mapping, try to also map scalars of the
/// statements where those are written. Repeat, until no more mapping
/// opportunity is found.
///
/// There is currently no preference in which order scalars are tried.
/// Ideally, we would direct it towards a load instruction of the same array
/// element.
bool collapseScalarsToStore(MemoryAccess *TargetStoreMA) {
assert(TargetStoreMA->isLatestArrayKind());
assert(TargetStoreMA->isMustWrite());
auto TargetStmt = TargetStoreMA->getStatement();
// { DomTarget[] }
auto TargetDom = getDomainFor(TargetStmt);
// { DomTarget[] -> Element[] }
auto TargetAccRel = getAccessRelationFor(TargetStoreMA);
// { Zone[] -> DomTarget[] }
// For each point in time, find the next target store instance.
auto Target =
computeScalarReachingOverwrite(Schedule, TargetDom, false, true);
// { Zone[] -> Element[] }
// Use the target store's write location as a suggestion to map scalars to.
auto EltTarget =
give(isl_map_apply_range(Target.take(), TargetAccRel.take()));
simplify(EltTarget);
DEBUG(dbgs() << " Target mapping is " << EltTarget << '\n');
// Stack of elements not yet processed.
SmallVector<MemoryAccess *, 16> Worklist;
// Set of scalars already tested.
SmallPtrSet<const ScopArrayInfo *, 16> Closed;
// Lambda to add all scalar reads to the work list.
auto ProcessAllIncoming = [&](ScopStmt *Stmt) {
for (auto *MA : *Stmt) {
if (!MA->isLatestScalarKind())
continue;
if (!MA->isRead())
continue;
Worklist.push_back(MA);
}
};
auto *WrittenVal = TargetStoreMA->getAccessInstruction()->getOperand(0);
if (auto *WrittenValInputMA = TargetStmt->lookupInputAccessOf(WrittenVal))
Worklist.push_back(WrittenValInputMA);
else
ProcessAllIncoming(TargetStmt);
auto AnyMapped = false;
auto &DL = S->getRegion().getEntry()->getModule()->getDataLayout();
auto StoreSize =
DL.getTypeAllocSize(TargetStoreMA->getAccessValue()->getType());
while (!Worklist.empty()) {
auto *MA = Worklist.pop_back_val();
auto *SAI = MA->getScopArrayInfo();
if (Closed.count(SAI))
continue;
Closed.insert(SAI);
DEBUG(dbgs() << "\n Trying to map " << MA << " (SAI: " << SAI
<< ")\n");
// Skip non-mappable scalars.
if (!isMappable(SAI))
continue;
auto MASize = DL.getTypeAllocSize(MA->getAccessValue()->getType());
if (MASize > StoreSize) {
DEBUG(dbgs() << " Reject because storage size is insufficient\n");
continue;
}
// Try to map MemoryKind::Value scalars.
if (SAI->isValueKind()) {
if (!tryMapValue(SAI, EltTarget))
continue;
auto *DefAcc = DefUse.getValueDef(SAI);
ProcessAllIncoming(DefAcc->getStatement());
AnyMapped = true;
continue;
}
// Try to map MemoryKind::PHI scalars.
if (SAI->isPHIKind()) {
if (!tryMapPHI(SAI, EltTarget))
continue;
// Add inputs of all incoming statements to the worklist. Prefer the
// input accesses of the incoming blocks.
for (auto *PHIWrite : DefUse.getPHIIncomings(SAI)) {
auto *PHIWriteStmt = PHIWrite->getStatement();
bool FoundAny = false;
for (auto Incoming : PHIWrite->getIncoming()) {
auto *IncomingInputMA =
PHIWriteStmt->lookupInputAccessOf(Incoming.second);
if (!IncomingInputMA)
continue;
Worklist.push_back(IncomingInputMA);
FoundAny = true;
}
if (!FoundAny)
ProcessAllIncoming(PHIWrite->getStatement());
}
AnyMapped = true;
continue;
}
}
if (AnyMapped) {
TargetsMapped++;
NumberOfTargetsMapped++;
}
return AnyMapped;
}
/// Compute when an array element is unused.
///
/// @return { [Element[] -> Zone[]] }
isl::union_set computeLifetime() const {
// { Element[] -> Zone[] }
auto ArrayUnused = computeArrayUnused(Schedule, AllMustWrites, AllReads,
false, false, true);
auto Result = give(isl_union_map_wrap(ArrayUnused.copy()));
simplify(Result);
return Result;
}
/// Compute which value an array element stores at every instant.
///
/// @return { [Element[] -> Zone[]] -> ValInst[] }
isl::union_map computeKnown() const {
// { [Element[] -> Zone[]] -> [Element[] -> DomainWrite[]] }
auto EltReachdDef =
distributeDomain(give(isl_union_map_curry(WriteReachDefZone.copy())));
// { [Element[] -> DomainWrite[]] -> ValInst[] }
auto AllKnownWriteValInst = filterKnownValInst(AllWriteValInst);
// { [Element[] -> Zone[]] -> ValInst[] }
return EltReachdDef.apply_range(AllKnownWriteValInst);
}
/// Determine when an array element is written to, and which value instance is
/// written.
///
/// @return { [Element[] -> Scatter[]] -> ValInst[] }
isl::union_map computeWritten() const {
// { [Element[] -> Scatter[]] -> ValInst[] }
auto EltWritten = applyDomainRange(AllWriteValInst, Schedule);
simplify(EltWritten);
return EltWritten;
}
/// Determine whether an access touches at most one element.
///
/// The accessed element could be a scalar or accessing an array with constant
/// subscript, such that all instances access only that element.
///
/// @param MA The access to test.
///
/// @return True, if zero or one elements are accessed; False if at least two
/// different elements are accessed.
bool isScalarAccess(MemoryAccess *MA) {
auto Map = getAccessRelationFor(MA);
auto Set = give(isl_map_range(Map.take()));
return isl_set_is_singleton(Set.keep()) == isl_bool_true;
}
/// Print mapping statistics to @p OS.
void printStatistics(llvm::raw_ostream &OS, int Indent = 0) const {
OS.indent(Indent) << "Statistics {\n";
OS.indent(Indent + 4) << "Compatible overwrites: "
<< NumberOfCompatibleTargets << "\n";
OS.indent(Indent + 4) << "Overwrites mapped to: " << NumberOfTargetsMapped
<< '\n';
OS.indent(Indent + 4) << "Value scalars mapped: "
<< NumberOfMappedValueScalars << '\n';
OS.indent(Indent + 4) << "PHI scalars mapped: "
<< NumberOfMappedPHIScalars << '\n';
OS.indent(Indent) << "}\n";
}
/// Return whether at least one transformation been applied.
bool isModified() const { return NumberOfTargetsMapped > 0; }
public:
DeLICMImpl(Scop *S, LoopInfo *LI) : ZoneAlgorithm(S, LI) {}
/// Calculate the lifetime (definition to last use) of every array element.
///
/// @return True if the computed lifetimes (#Zone) is usable.
bool computeZone() {
// Check that nothing strange occurs.
if (!isCompatibleScop()) {
DeLICMIncompatible++;
return false;
}
DefUse.compute(S);
isl::union_set EltUnused;
isl::union_map EltKnown, EltWritten;
{
IslMaxOperationsGuard MaxOpGuard(IslCtx.get(), DelicmMaxOps);
computeCommon();
EltUnused = computeLifetime();
EltKnown = computeKnown();
EltWritten = computeWritten();
}
DeLICMAnalyzed++;
if (!EltUnused || !EltKnown || !EltWritten) {
assert(isl_ctx_last_error(IslCtx.get()) == isl_error_quota &&
"The only reason that these things have not been computed should "
"be if the max-operations limit hit");
DeLICMOutOfQuota++;
DEBUG(dbgs() << "DeLICM analysis exceeded max_operations\n");
DebugLoc Begin, End;
getDebugLocations(getBBPairForRegion(&S->getRegion()), Begin, End);
OptimizationRemarkAnalysis R(DEBUG_TYPE, "OutOfQuota", Begin,
S->getEntry());
R << "maximal number of operations exceeded during zone analysis";
S->getFunction().getContext().diagnose(R);
return false;
}
Zone = OriginalZone = Knowledge(nullptr, EltUnused, EltKnown, EltWritten);
DEBUG(dbgs() << "Computed Zone:\n"; OriginalZone.print(dbgs(), 4));
assert(Zone.isUsable() && OriginalZone.isUsable());
return true;
}
/// Try to map as many scalars to unused array elements as possible.
///
/// Multiple scalars might be mappable to intersecting unused array element
/// zones, but we can only chose one. This is a greedy algorithm, therefore
/// the first processed element claims it.
void greedyCollapse() {
bool Modified = false;
for (auto &Stmt : *S) {
for (auto *MA : Stmt) {
if (!MA->isLatestArrayKind())
continue;
if (!MA->isWrite())
continue;
if (MA->isMayWrite()) {
DEBUG(dbgs() << "Access " << MA
<< " pruned because it is a MAY_WRITE\n");
OptimizationRemarkMissed R(DEBUG_TYPE, "TargetMayWrite",
MA->getAccessInstruction());
R << "Skipped possible mapping target because it is not an "
"unconditional overwrite";
S->getFunction().getContext().diagnose(R);
continue;
}
if (Stmt.getNumIterators() == 0) {
DEBUG(dbgs() << "Access " << MA
<< " pruned because it is not in a loop\n");
OptimizationRemarkMissed R(DEBUG_TYPE, "WriteNotInLoop",
MA->getAccessInstruction());
R << "skipped possible mapping target because it is not in a loop";
S->getFunction().getContext().diagnose(R);
continue;
}
if (isScalarAccess(MA)) {
DEBUG(dbgs() << "Access " << MA
<< " pruned because it writes only a single element\n");
OptimizationRemarkMissed R(DEBUG_TYPE, "ScalarWrite",
MA->getAccessInstruction());
R << "skipped possible mapping target because the memory location "
"written to does not depend on its outer loop";
S->getFunction().getContext().diagnose(R);
continue;
}
NumberOfCompatibleTargets++;
DEBUG(dbgs() << "Analyzing target access " << MA << "\n");
if (collapseScalarsToStore(MA))
Modified = true;
}
}
if (Modified)
DeLICMScopsModified++;
}
/// Dump the internal information about a performed DeLICM to @p OS.
void print(llvm::raw_ostream &OS, int Indent = 0) {
if (!Zone.isUsable()) {
OS.indent(Indent) << "Zone not computed\n";
return;
}
printStatistics(OS, Indent);
if (!isModified()) {
OS.indent(Indent) << "No modification has been made\n";
return;
}
printAccesses(OS, Indent);
}
};
class DeLICM : public ScopPass {
private:
DeLICM(const DeLICM &) = delete;
const DeLICM &operator=(const DeLICM &) = delete;
/// The pass implementation, also holding per-scop data.
std::unique_ptr<DeLICMImpl> Impl;
void collapseToUnused(Scop &S) {
auto &LI = getAnalysis<LoopInfoWrapperPass>().getLoopInfo();
Impl = make_unique<DeLICMImpl>(&S, &LI);
if (!Impl->computeZone()) {
DEBUG(dbgs() << "Abort because cannot reliably compute lifetimes\n");
return;
}
DEBUG(dbgs() << "Collapsing scalars to unused array elements...\n");
Impl->greedyCollapse();
DEBUG(dbgs() << "\nFinal Scop:\n");
DEBUG(S.print(dbgs()));
}
public:
static char ID;
explicit DeLICM() : ScopPass(ID) {}
virtual void getAnalysisUsage(AnalysisUsage &AU) const override {
AU.addRequiredTransitive<ScopInfoRegionPass>();
AU.addRequired<LoopInfoWrapperPass>();
AU.setPreservesAll();
}
virtual bool runOnScop(Scop &S) override {
// Free resources for previous scop's computation, if not yet done.
releaseMemory();
collapseToUnused(S);
return false;
}
virtual void printScop(raw_ostream &OS, Scop &S) const override {
if (!Impl)
return;
assert(Impl->getScop() == &S);
OS << "DeLICM result:\n";
Impl->print(OS);
}
virtual void releaseMemory() override { Impl.reset(); }
};
char DeLICM::ID;
} // anonymous namespace
Pass *polly::createDeLICMPass() { return new DeLICM(); }
INITIALIZE_PASS_BEGIN(DeLICM, "polly-delicm", "Polly - DeLICM/DePRE", false,
false)
INITIALIZE_PASS_DEPENDENCY(ScopInfoWrapperPass)
INITIALIZE_PASS_DEPENDENCY(LoopInfoWrapperPass)
INITIALIZE_PASS_END(DeLICM, "polly-delicm", "Polly - DeLICM/DePRE", false,
false)
bool polly::isConflicting(
isl::union_set ExistingOccupied, isl::union_set ExistingUnused,
isl::union_map ExistingKnown, isl::union_map ExistingWrites,
isl::union_set ProposedOccupied, isl::union_set ProposedUnused,
isl::union_map ProposedKnown, isl::union_map ProposedWrites,
llvm::raw_ostream *OS, unsigned Indent) {
Knowledge Existing(std::move(ExistingOccupied), std::move(ExistingUnused),
std::move(ExistingKnown), std::move(ExistingWrites));
Knowledge Proposed(std::move(ProposedOccupied), std::move(ProposedUnused),
std::move(ProposedKnown), std::move(ProposedWrites));
return Knowledge::isConflicting(Existing, Proposed, OS, Indent);
}