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//===- polly/ScopBuilder.h --------------------------------------*- C++ -*-===//
//
// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
// See https://llvm.org/LICENSE.txt for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
//
//===----------------------------------------------------------------------===//
//
// Create a polyhedral description for a static control flow region.
//
// The pass creates a polyhedral description of the Scops detected by the SCoP
// detection derived from their LLVM-IR code.
//
//===----------------------------------------------------------------------===//
#ifndef POLLY_SCOPBUILDER_H
#define POLLY_SCOPBUILDER_H
#include "polly/ScopInfo.h"
#include "polly/Support/ScopHelper.h"
#include "llvm/ADT/ArrayRef.h"
#include "llvm/ADT/SetVector.h"
namespace polly {
class ScopDetection;
/// Command line switch whether to model read-only accesses.
extern bool ModelReadOnlyScalars;
/// Build the Polly IR (Scop and ScopStmt) on a Region.
class ScopBuilder {
/// The AliasAnalysis to build AliasSetTracker.
AliasAnalysis &AA;
/// Target data for element size computing.
const DataLayout &DL;
/// DominatorTree to reason about guaranteed execution.
DominatorTree &DT;
/// LoopInfo for information about loops.
LoopInfo &LI;
/// Valid Regions for Scop
ScopDetection &SD;
/// The ScalarEvolution to help building Scop.
ScalarEvolution &SE;
/// An optimization diagnostic interface to add optimization remarks.
OptimizationRemarkEmitter &ORE;
/// Set of instructions that might read any memory location.
SmallVector<std::pair<ScopStmt *, Instruction *>, 16> GlobalReads;
/// Set of all accessed array base pointers.
SmallSetVector<Value *, 16> ArrayBasePointers;
// The Scop
std::unique_ptr<Scop> scop;
// Methods for pattern matching against Fortran code generated by dragonegg.
// @{
/// Try to match for the descriptor of a Fortran array whose allocation
/// is not visible. That is, we can see the load/store into the memory, but
/// we don't actually know where the memory is allocated. If ALLOCATE had been
/// called on the Fortran array, then we will see the lowered malloc() call.
/// If not, this is dubbed as an "invisible allocation".
///
/// "<descriptor>" is the descriptor of the Fortran array.
///
/// Pattern match for "@descriptor":
/// 1. %mem = load double*, double** bitcast (%"struct.array1_real(kind=8)"*
/// <descriptor> to double**), align 32
///
/// 2. [%slot = getelementptr inbounds i8, i8* %mem, i64 <index>]
/// 2 is optional because if you are writing to the 0th index, you don't
/// need a GEP.
///
/// 3.1 store/load <memtype> <val>, <memtype>* %slot
/// 3.2 store/load <memtype> <val>, <memtype>* %mem
///
/// @see polly::MemoryAccess, polly::ScopArrayInfo
///
/// @note assumes -polly-canonicalize has been run.
///
/// @param Inst The LoadInst/StoreInst that accesses the memory.
///
/// @returns Reference to <descriptor> on success, nullptr on failure.
Value *findFADAllocationInvisible(MemAccInst Inst);
/// Try to match for the descriptor of a Fortran array whose allocation
/// call is visible. When we have a Fortran array, we try to look for a
/// Fortran array where we can see the lowered ALLOCATE call. ALLOCATE
/// is materialized as a malloc(...) which we pattern match for.
///
/// Pattern match for "%untypedmem":
/// 1. %untypedmem = i8* @malloc(...)
///
/// 2. %typedmem = bitcast i8* %untypedmem to <memtype>
///
/// 3. [%slot = getelementptr inbounds i8, i8* %typedmem, i64 <index>]
/// 3 is optional because if you are writing to the 0th index, you don't
/// need a GEP.
///
/// 4.1 store/load <memtype> <val>, <memtype>* %slot, align 8
/// 4.2 store/load <memtype> <val>, <memtype>* %mem, align 8
///
/// @see polly::MemoryAccess, polly::ScopArrayInfo
///
/// @note assumes -polly-canonicalize has been run.
///
/// @param Inst The LoadInst/StoreInst that accesses the memory.
///
/// @returns Reference to %untypedmem on success, nullptr on failure.
Value *findFADAllocationVisible(MemAccInst Inst);
// @}
// Build the SCoP for Region @p R.
void buildScop(Region &R, AssumptionCache &AC);
/// Adjust the dimensions of @p Dom that was constructed for @p OldL
/// to be compatible to domains constructed for loop @p NewL.
///
/// This function assumes @p NewL and @p OldL are equal or there is a CFG
/// edge from @p OldL to @p NewL.
isl::set adjustDomainDimensions(isl::set Dom, Loop *OldL, Loop *NewL);
/// Compute the domain for each basic block in @p R.
///
/// @param R The region we currently traverse.
/// @param InvalidDomainMap BB to InvalidDomain map for the BB of current
/// region.
///
/// @returns True if there was no problem and false otherwise.
bool buildDomains(Region *R,
DenseMap<BasicBlock *, isl::set> &InvalidDomainMap);
/// Compute the branching constraints for each basic block in @p R.
///
/// @param R The region we currently build branching conditions
/// for.
/// @param InvalidDomainMap BB to InvalidDomain map for the BB of current
/// region.
///
/// @returns True if there was no problem and false otherwise.
bool buildDomainsWithBranchConstraints(
Region *R, DenseMap<BasicBlock *, isl::set> &InvalidDomainMap);
/// Build the conditions sets for the terminator @p TI in the @p Domain.
///
/// This will fill @p ConditionSets with the conditions under which control
/// will be moved from @p TI to its successors. Hence, @p ConditionSets will
/// have as many elements as @p TI has successors.
bool buildConditionSets(BasicBlock *BB, Instruction *TI, Loop *L,
__isl_keep isl_set *Domain,
DenseMap<BasicBlock *, isl::set> &InvalidDomainMap,
SmallVectorImpl<__isl_give isl_set *> &ConditionSets);
/// Build the conditions sets for the branch condition @p Condition in
/// the @p Domain.
///
/// This will fill @p ConditionSets with the conditions under which control
/// will be moved from @p TI to its successors. Hence, @p ConditionSets will
/// have as many elements as @p TI has successors. If @p TI is nullptr the
/// context under which @p Condition is true/false will be returned as the
/// new elements of @p ConditionSets.
bool buildConditionSets(BasicBlock *BB, Value *Condition, Instruction *TI,
Loop *L, __isl_keep isl_set *Domain,
DenseMap<BasicBlock *, isl::set> &InvalidDomainMap,
SmallVectorImpl<__isl_give isl_set *> &ConditionSets);
/// Build the conditions sets for the switch @p SI in the @p Domain.
///
/// This will fill @p ConditionSets with the conditions under which control
/// will be moved from @p SI to its successors. Hence, @p ConditionSets will
/// have as many elements as @p SI has successors.
bool buildConditionSets(BasicBlock *BB, SwitchInst *SI, Loop *L,
__isl_keep isl_set *Domain,
DenseMap<BasicBlock *, isl::set> &InvalidDomainMap,
SmallVectorImpl<__isl_give isl_set *> &ConditionSets);
/// Build condition sets for unsigned ICmpInst(s).
/// Special handling is required for unsigned operands to ensure that if
/// MSB (aka the Sign bit) is set for an operands in an unsigned ICmpInst
/// it should wrap around.
///
/// @param IsStrictUpperBound holds information on the predicate relation
/// between TestVal and UpperBound, i.e,
/// TestVal < UpperBound OR TestVal <= UpperBound
__isl_give isl_set *buildUnsignedConditionSets(
BasicBlock *BB, Value *Condition, __isl_keep isl_set *Domain,
const SCEV *SCEV_TestVal, const SCEV *SCEV_UpperBound,
DenseMap<BasicBlock *, isl::set> &InvalidDomainMap,
bool IsStrictUpperBound);
/// Propagate the domain constraints through the region @p R.
///
/// @param R The region we currently build branching
/// conditions for.
/// @param InvalidDomainMap BB to InvalidDomain map for the BB of current
/// region.
///
/// @returns True if there was no problem and false otherwise.
bool propagateDomainConstraints(
Region *R, DenseMap<BasicBlock *, isl::set> &InvalidDomainMap);
/// Propagate domains that are known due to graph properties.
///
/// As a CFG is mostly structured we use the graph properties to propagate
/// domains without the need to compute all path conditions. In particular,
/// if a block A dominates a block B and B post-dominates A we know that the
/// domain of B is a superset of the domain of A. As we do not have
/// post-dominator information available here we use the less precise region
/// information. Given a region R, we know that the exit is always executed
/// if the entry was executed, thus the domain of the exit is a superset of
/// the domain of the entry. In case the exit can only be reached from
/// within the region the domains are in fact equal. This function will use
/// this property to avoid the generation of condition constraints that
/// determine when a branch is taken. If @p BB is a region entry block we
/// will propagate its domain to the region exit block. Additionally, we put
/// the region exit block in the @p FinishedExitBlocks set so we can later
/// skip edges from within the region to that block.
///
/// @param BB The block for which the domain is currently
/// propagated.
/// @param BBLoop The innermost affine loop surrounding @p BB.
/// @param FinishedExitBlocks Set of region exits the domain was set for.
/// @param InvalidDomainMap BB to InvalidDomain map for the BB of current
/// region.
void propagateDomainConstraintsToRegionExit(
BasicBlock *BB, Loop *BBLoop,
SmallPtrSetImpl<BasicBlock *> &FinishedExitBlocks,
DenseMap<BasicBlock *, isl::set> &InvalidDomainMap);
/// Propagate invalid domains of statements through @p R.
///
/// This method will propagate invalid statement domains through @p R and at
/// the same time add error block domains to them. Additionally, the domains
/// of error statements and those only reachable via error statements will
/// be replaced by an empty set. Later those will be removed completely.
///
/// @param R The currently traversed region.
/// @param InvalidDomainMap BB to InvalidDomain map for the BB of current
/// region.
//
/// @returns True if there was no problem and false otherwise.
bool propagateInvalidStmtDomains(
Region *R, DenseMap<BasicBlock *, isl::set> &InvalidDomainMap);
/// Compute the union of predecessor domains for @p BB.
///
/// To compute the union of all domains of predecessors of @p BB this
/// function applies similar reasoning on the CFG structure as described for
/// @see propagateDomainConstraintsToRegionExit
///
/// @param BB The block for which the predecessor domains are collected.
/// @param Domain The domain under which BB is executed.
///
/// @returns The domain under which @p BB is executed.
isl::set getPredecessorDomainConstraints(BasicBlock *BB, isl::set Domain);
/// Add loop carried constraints to the header block of the loop @p L.
///
/// @param L The loop to process.
/// @param InvalidDomainMap BB to InvalidDomain map for the BB of current
/// region.
///
/// @returns True if there was no problem and false otherwise.
bool addLoopBoundsToHeaderDomain(
Loop *L, DenseMap<BasicBlock *, isl::set> &InvalidDomainMap);
/// Compute the isl representation for the SCEV @p E in this BB.
///
/// @param BB The BB for which isl representation is to be
/// computed.
/// @param InvalidDomainMap A map of BB to their invalid domains.
/// @param E The SCEV that should be translated.
/// @param NonNegative Flag to indicate the @p E has to be
/// non-negative.
///
/// Note that this function will also adjust the invalid context
/// accordingly.
__isl_give isl_pw_aff *
getPwAff(BasicBlock *BB, DenseMap<BasicBlock *, isl::set> &InvalidDomainMap,
const SCEV *E, bool NonNegative = false);
/// Create equivalence classes for required invariant accesses.
///
/// These classes will consolidate multiple required invariant loads from the
/// same address in order to keep the number of dimensions in the SCoP
/// description small. For each such class equivalence class only one
/// representing element, hence one required invariant load, will be chosen
/// and modeled as parameter. The method
/// Scop::getRepresentingInvariantLoadSCEV() will replace each element from an
/// equivalence class with the representing element that is modeled. As a
/// consequence Scop::getIdForParam() will only return an id for the
/// representing element of each equivalence class, thus for each required
/// invariant location.
void buildInvariantEquivalenceClasses();
/// Try to build a multi-dimensional fixed sized MemoryAccess from the
/// Load/Store instruction.
///
/// @param Inst The Load/Store instruction that access the memory
/// @param Stmt The parent statement of the instruction
///
/// @returns True if the access could be built, False otherwise.
bool buildAccessMultiDimFixed(MemAccInst Inst, ScopStmt *Stmt);
/// Try to build a multi-dimensional parametric sized MemoryAccess.
/// from the Load/Store instruction.
///
/// @param Inst The Load/Store instruction that access the memory
/// @param Stmt The parent statement of the instruction
///
/// @returns True if the access could be built, False otherwise.
bool buildAccessMultiDimParam(MemAccInst Inst, ScopStmt *Stmt);
/// Try to build a MemoryAccess for a memory intrinsic.
///
/// @param Inst The instruction that access the memory
/// @param Stmt The parent statement of the instruction
///
/// @returns True if the access could be built, False otherwise.
bool buildAccessMemIntrinsic(MemAccInst Inst, ScopStmt *Stmt);
/// Try to build a MemoryAccess for a call instruction.
///
/// @param Inst The call instruction that access the memory
/// @param Stmt The parent statement of the instruction
///
/// @returns True if the access could be built, False otherwise.
bool buildAccessCallInst(MemAccInst Inst, ScopStmt *Stmt);
/// Build a single-dimensional parametric sized MemoryAccess
/// from the Load/Store instruction.
///
/// @param Inst The Load/Store instruction that access the memory
/// @param Stmt The parent statement of the instruction
void buildAccessSingleDim(MemAccInst Inst, ScopStmt *Stmt);
/// Finalize all access relations.
///
/// When building up access relations, temporary access relations that
/// correctly represent each individual access are constructed. However, these
/// access relations can be inconsistent or non-optimal when looking at the
/// set of accesses as a whole. This function finalizes the memory accesses
/// and constructs a globally consistent state.
void finalizeAccesses();
/// Update access dimensionalities.
///
/// When detecting memory accesses different accesses to the same array may
/// have built with different dimensionality, as outer zero-values dimensions
/// may not have been recognized as separate dimensions. This function goes
/// again over all memory accesses and updates their dimensionality to match
/// the dimensionality of the underlying ScopArrayInfo object.
void updateAccessDimensionality();
/// Fold size constants to the right.
///
/// In case all memory accesses in a given dimension are multiplied with a
/// common constant, we can remove this constant from the individual access
/// functions and move it to the size of the memory access. We do this as this
/// increases the size of the innermost dimension, consequently widens the
/// valid range the array subscript in this dimension can evaluate to, and
/// as a result increases the likelihood that our delinearization is
/// correct.
///
/// Example:
///
/// A[][n]
/// S[i,j] -> A[2i][2j+1]
/// S[i,j] -> A[2i][2j]
///
/// =>
///
/// A[][2n]
/// S[i,j] -> A[i][2j+1]
/// S[i,j] -> A[i][2j]
///
/// Constants in outer dimensions can arise when the elements of a parametric
/// multi-dimensional array are not elementary data types, but e.g.,
/// structures.
void foldSizeConstantsToRight();
/// Fold memory accesses to handle parametric offset.
///
/// As a post-processing step, we 'fold' memory accesses to parametric
/// offsets in the access functions. @see MemoryAccess::foldAccess for
/// details.
void foldAccessRelations();
/// Assume that all memory accesses are within bounds.
///
/// After we have built a model of all memory accesses, we need to assume
/// that the model we built matches reality -- aka. all modeled memory
/// accesses always remain within bounds. We do this as last step, after
/// all memory accesses have been modeled and canonicalized.
void assumeNoOutOfBounds();
/// Mark arrays that have memory accesses with FortranArrayDescriptor.
void markFortranArrays();
/// Build the alias checks for this SCoP.
bool buildAliasChecks();
/// A vector of memory accesses that belong to an alias group.
using AliasGroupTy = SmallVector<MemoryAccess *, 4>;
/// A vector of alias groups.
using AliasGroupVectorTy = SmallVector<AliasGroupTy, 4>;
/// Build a given alias group and its access data.
///
/// @param AliasGroup The alias group to build.
/// @param HasWriteAccess A set of arrays through which memory is not only
/// read, but also written.
//
/// @returns True if __no__ error occurred, false otherwise.
bool buildAliasGroup(AliasGroupTy &AliasGroup,
DenseSet<const ScopArrayInfo *> HasWriteAccess);
/// Build all alias groups for this SCoP.
///
/// @returns True if __no__ error occurred, false otherwise.
bool buildAliasGroups();
/// Build alias groups for all memory accesses in the Scop.
///
/// Using the alias analysis and an alias set tracker we build alias sets
/// for all memory accesses inside the Scop. For each alias set we then map
/// the aliasing pointers back to the memory accesses we know, thus obtain
/// groups of memory accesses which might alias. We also collect the set of
/// arrays through which memory is written.
///
/// @returns A pair consistent of a vector of alias groups and a set of arrays
/// through which memory is written.
std::tuple<AliasGroupVectorTy, DenseSet<const ScopArrayInfo *>>
buildAliasGroupsForAccesses();
/// Split alias groups by iteration domains.
///
/// We split each group based on the domains of the minimal/maximal accesses.
/// That means two minimal/maximal accesses are only in a group if their
/// access domains intersect. Otherwise, they are in different groups.
///
/// @param AliasGroups The alias groups to split
void splitAliasGroupsByDomain(AliasGroupVectorTy &AliasGroups);
/// Build an instance of MemoryAccess from the Load/Store instruction.
///
/// @param Inst The Load/Store instruction that access the memory
/// @param Stmt The parent statement of the instruction
void buildMemoryAccess(MemAccInst Inst, ScopStmt *Stmt);
/// Analyze and extract the cross-BB scalar dependences (or, dataflow
/// dependencies) of an instruction.
///
/// @param UserStmt The statement @p Inst resides in.
/// @param Inst The instruction to be analyzed.
void buildScalarDependences(ScopStmt *UserStmt, Instruction *Inst);
/// Build the escaping dependences for @p Inst.
///
/// Search for uses of the llvm::Value defined by @p Inst that are not
/// within the SCoP. If there is such use, add a SCALAR WRITE such that
/// it is available after the SCoP as escaping value.
///
/// @param Inst The instruction to be analyzed.
void buildEscapingDependences(Instruction *Inst);
/// Create MemoryAccesses for the given PHI node in the given region.
///
/// @param PHIStmt The statement @p PHI resides in.
/// @param PHI The PHI node to be handled
/// @param NonAffineSubRegion The non affine sub-region @p PHI is in.
/// @param IsExitBlock Flag to indicate that @p PHI is in the exit BB.
void buildPHIAccesses(ScopStmt *PHIStmt, PHINode *PHI,
Region *NonAffineSubRegion, bool IsExitBlock = false);
/// Build the access functions for the subregion @p SR.
void buildAccessFunctions();
/// Should an instruction be modeled in a ScopStmt.
///
/// @param Inst The instruction to check.
/// @param L The loop in which context the instruction is looked at.
///
/// @returns True if the instruction should be modeled.
bool shouldModelInst(Instruction *Inst, Loop *L);
/// Create one or more ScopStmts for @p BB.
///
/// Consecutive instructions are associated to the same statement until a
/// separator is found.
void buildSequentialBlockStmts(BasicBlock *BB, bool SplitOnStore = false);
/// Create one or more ScopStmts for @p BB using equivalence classes.
///
/// Instructions of a basic block that belong to the same equivalence class
/// are added to the same statement.
void buildEqivClassBlockStmts(BasicBlock *BB);
/// Create ScopStmt for all BBs and non-affine subregions of @p SR.
///
/// @param SR A subregion of @p R.
///
/// Some of the statements might be optimized away later when they do not
/// access any memory and thus have no effect.
void buildStmts(Region &SR);
/// Build the access functions for the statement @p Stmt in or represented by
/// @p BB.
///
/// @param Stmt Statement to add MemoryAccesses to.
/// @param BB A basic block in @p R.
/// @param NonAffineSubRegion The non affine sub-region @p BB is in.
void buildAccessFunctions(ScopStmt *Stmt, BasicBlock &BB,
Region *NonAffineSubRegion = nullptr);
/// Create a new MemoryAccess object and add it to #AccFuncMap.
///
/// @param Stmt The statement where the access takes place.
/// @param Inst The instruction doing the access. It is not necessarily
/// inside @p BB.
/// @param AccType The kind of access.
/// @param BaseAddress The accessed array's base address.
/// @param ElemType The type of the accessed array elements.
/// @param Affine Whether all subscripts are affine expressions.
/// @param AccessValue Value read or written.
/// @param Subscripts Access subscripts per dimension.
/// @param Sizes The array dimension's sizes.
/// @param Kind The kind of memory accessed.
///
/// @return The created MemoryAccess, or nullptr if the access is not within
/// the SCoP.
MemoryAccess *addMemoryAccess(ScopStmt *Stmt, Instruction *Inst,
MemoryAccess::AccessType AccType,
Value *BaseAddress, Type *ElemType, bool Affine,
Value *AccessValue,
ArrayRef<const SCEV *> Subscripts,
ArrayRef<const SCEV *> Sizes, MemoryKind Kind);
/// Create a MemoryAccess that represents either a LoadInst or
/// StoreInst.
///
/// @param Stmt The statement to add the MemoryAccess to.
/// @param MemAccInst The LoadInst or StoreInst.
/// @param AccType The kind of access.
/// @param BaseAddress The accessed array's base address.
/// @param ElemType The type of the accessed array elements.
/// @param IsAffine Whether all subscripts are affine expressions.
/// @param Subscripts Access subscripts per dimension.
/// @param Sizes The array dimension's sizes.
/// @param AccessValue Value read or written.
///
/// @see MemoryKind
void addArrayAccess(ScopStmt *Stmt, MemAccInst MemAccInst,
MemoryAccess::AccessType AccType, Value *BaseAddress,
Type *ElemType, bool IsAffine,
ArrayRef<const SCEV *> Subscripts,
ArrayRef<const SCEV *> Sizes, Value *AccessValue);
/// Create a MemoryAccess for writing an llvm::Instruction.
///
/// The access will be created at the position of @p Inst.
///
/// @param Inst The instruction to be written.
///
/// @see ensureValueRead()
/// @see MemoryKind
void ensureValueWrite(Instruction *Inst);
/// Ensure an llvm::Value is available in the BB's statement, creating a
/// MemoryAccess for reloading it if necessary.
///
/// @param V The value expected to be loaded.
/// @param UserStmt Where to reload the value.
///
/// @see ensureValueStore()
/// @see MemoryKind
void ensureValueRead(Value *V, ScopStmt *UserStmt);
/// Create a write MemoryAccess for the incoming block of a phi node.
///
/// Each of the incoming blocks write their incoming value to be picked in the
/// phi's block.
///
/// @param PHI PHINode under consideration.
/// @param IncomingStmt The statement to add the MemoryAccess to.
/// @param IncomingBlock Some predecessor block.
/// @param IncomingValue @p PHI's value when coming from @p IncomingBlock.
/// @param IsExitBlock When true, uses the .s2a alloca instead of the
/// .phiops one. Required for values escaping through a
/// PHINode in the SCoP region's exit block.
/// @see addPHIReadAccess()
/// @see MemoryKind
void ensurePHIWrite(PHINode *PHI, ScopStmt *IncomintStmt,
BasicBlock *IncomingBlock, Value *IncomingValue,
bool IsExitBlock);
/// Add user provided parameter constraints to context (command line).
void addUserContext();
/// Add user provided parameter constraints to context (source code).
void addUserAssumptions(AssumptionCache &AC,
DenseMap<BasicBlock *, isl::set> &InvalidDomainMap);
/// Add all recorded assumptions to the assumed context.
void addRecordedAssumptions();
/// Create a MemoryAccess for reading the value of a phi.
///
/// The modeling assumes that all incoming blocks write their incoming value
/// to the same location. Thus, this access will read the incoming block's
/// value as instructed by this @p PHI.
///
/// @param PHIStmt Statement @p PHI resides in.
/// @param PHI PHINode under consideration; the READ access will be added
/// here.
///
/// @see ensurePHIWrite()
/// @see MemoryKind
void addPHIReadAccess(ScopStmt *PHIStmt, PHINode *PHI);
/// Wrapper function to calculate minimal/maximal accesses to each array.
bool calculateMinMaxAccess(AliasGroupTy AliasGroup,
Scop::MinMaxVectorTy &MinMaxAccesses);
/// Build the domain of @p Stmt.
void buildDomain(ScopStmt &Stmt);
/// Fill NestLoops with loops surrounding @p Stmt.
void collectSurroundingLoops(ScopStmt &Stmt);
/// Check for reductions in @p Stmt.
///
/// Iterate over all store memory accesses and check for valid binary
/// reduction like chains. For all candidates we check if they have the same
/// base address and there are no other accesses which overlap with them. The
/// base address check rules out impossible reductions candidates early. The
/// overlap check, together with the "only one user" check in
/// collectCandidateReductionLoads, guarantees that none of the intermediate
/// results will escape during execution of the loop nest. We basically check
/// here that no other memory access can access the same memory as the
/// potential reduction.
void checkForReductions(ScopStmt &Stmt);
/// Verify that all required invariant loads have been hoisted.
///
/// Invariant load hoisting is not guaranteed to hoist all loads that were
/// assumed to be scop invariant during scop detection. This function checks
/// for cases where the hoisting failed, but where it would have been
/// necessary for our scop modeling to be correct. In case of insufficient
/// hoisting the scop is marked as invalid.
///
/// In the example below Bound[1] is required to be invariant:
///
/// for (int i = 1; i < Bound[0]; i++)
/// for (int j = 1; j < Bound[1]; j++)
/// ...
void verifyInvariantLoads();
/// Hoist invariant memory loads and check for required ones.
///
/// We first identify "common" invariant loads, thus loads that are invariant
/// and can be hoisted. Then we check if all required invariant loads have
/// been identified as (common) invariant. A load is a required invariant load
/// if it was assumed to be invariant during SCoP detection, e.g., to assume
/// loop bounds to be affine or runtime alias checks to be placeable. In case
/// a required invariant load was not identified as (common) invariant we will
/// drop this SCoP. An example for both "common" as well as required invariant
/// loads is given below:
///
/// for (int i = 1; i < *LB[0]; i++)
/// for (int j = 1; j < *LB[1]; j++)
/// A[i][j] += A[0][0] + (*V);
///
/// Common inv. loads: V, A[0][0], LB[0], LB[1]
/// Required inv. loads: LB[0], LB[1], (V, if it may alias with A or LB)
void hoistInvariantLoads();
/// Add invariant loads listed in @p InvMAs with the domain of @p Stmt.
void addInvariantLoads(ScopStmt &Stmt, InvariantAccessesTy &InvMAs);
/// Check if @p MA can always be hoisted without execution context.
bool canAlwaysBeHoisted(MemoryAccess *MA, bool StmtInvalidCtxIsEmpty,
bool MAInvalidCtxIsEmpty,
bool NonHoistableCtxIsEmpty);
/// Return true if and only if @p LI is a required invariant load.
bool isRequiredInvariantLoad(LoadInst *LI) const {
return scop->getRequiredInvariantLoads().count(LI);
}
/// Check if the base ptr of @p MA is in the SCoP but not hoistable.
bool hasNonHoistableBasePtrInScop(MemoryAccess *MA, isl::union_map Writes);
/// Return the context under which the access cannot be hoisted.
///
/// @param Access The access to check.
/// @param Writes The set of all memory writes in the scop.
///
/// @return Return the context under which the access cannot be hoisted or a
/// nullptr if it cannot be hoisted at all.
isl::set getNonHoistableCtx(MemoryAccess *Access, isl::union_map Writes);
/// Collect loads which might form a reduction chain with @p StoreMA.
///
/// Check if the stored value for @p StoreMA is a binary operator with one or
/// two loads as operands. If the binary operand is commutative & associative,
/// used only once (by @p StoreMA) and its load operands are also used only
/// once, we have found a possible reduction chain. It starts at an operand
/// load and includes the binary operator and @p StoreMA.
///
/// Note: We allow only one use to ensure the load and binary operator cannot
/// escape this block or into any other store except @p StoreMA.
void collectCandidateReductionLoads(MemoryAccess *StoreMA,
SmallVectorImpl<MemoryAccess *> &Loads);
/// Build the access relation of all memory accesses of @p Stmt.
void buildAccessRelations(ScopStmt &Stmt);
/// Canonicalize arrays with base pointers from the same equivalence class.
///
/// Some context: in our normal model we assume that each base pointer is
/// related to a single specific memory region, where memory regions
/// associated with different base pointers are disjoint. Consequently we do
/// not need to compute additional data dependences that model possible
/// overlaps of these memory regions. To verify our assumption we compute
/// alias checks that verify that modeled arrays indeed do not overlap. In
/// case an overlap is detected the runtime check fails and we fall back to
/// the original code.
///
/// In case of arrays where the base pointers are know to be identical,
/// because they are dynamically loaded by accesses that are in the same
/// invariant load equivalence class, such run-time alias check would always
/// be false.
///
/// This function makes sure that we do not generate consistently failing
/// run-time checks for code that contains distinct arrays with known
/// equivalent base pointers. It identifies for each invariant load
/// equivalence class a single canonical array and canonicalizes all memory
/// accesses that reference arrays that have base pointers that are known to
/// be equal to the base pointer of such a canonical array to this canonical
/// array.
///
/// We currently do not canonicalize arrays for which certain memory accesses
/// have been hoisted as loop invariant.
void canonicalizeDynamicBasePtrs();
/// Construct the schedule of this SCoP.
void buildSchedule();
/// A loop stack element to keep track of per-loop information during
/// schedule construction.
using LoopStackElementTy = struct LoopStackElement {
// The loop for which we keep information.
Loop *L;
// The (possibly incomplete) schedule for this loop.
isl::schedule Schedule;
// The number of basic blocks in the current loop, for which a schedule has
// already been constructed.
unsigned NumBlocksProcessed;
LoopStackElement(Loop *L, isl::schedule S, unsigned NumBlocksProcessed)
: L(L), Schedule(S), NumBlocksProcessed(NumBlocksProcessed) {}
};
/// The loop stack used for schedule construction.
///
/// The loop stack keeps track of schedule information for a set of nested
/// loops as well as an (optional) 'nullptr' loop that models the outermost
/// schedule dimension. The loops in a loop stack always have a parent-child
/// relation where the loop at position n is the parent of the loop at
/// position n + 1.
using LoopStackTy = SmallVector<LoopStackElementTy, 4>;
/// Construct schedule information for a given Region and add the
/// derived information to @p LoopStack.
///
/// Given a Region we derive schedule information for all RegionNodes
/// contained in this region ensuring that the assigned execution times
/// correctly model the existing control flow relations.
///
/// @param R The region which to process.
/// @param LoopStack A stack of loops that are currently under
/// construction.
void buildSchedule(Region *R, LoopStackTy &LoopStack);
/// Build Schedule for the region node @p RN and add the derived
/// information to @p LoopStack.
///
/// In case @p RN is a BasicBlock or a non-affine Region, we construct the
/// schedule for this @p RN and also finalize loop schedules in case the
/// current @p RN completes the loop.
///
/// In case @p RN is a not-non-affine Region, we delegate the construction to
/// buildSchedule(Region *R, ...).
///
/// @param RN The RegionNode region traversed.
/// @param LoopStack A stack of loops that are currently under
/// construction.
void buildSchedule(RegionNode *RN, LoopStackTy &LoopStack);
public:
explicit ScopBuilder(Region *R, AssumptionCache &AC, AliasAnalysis &AA,
const DataLayout &DL, DominatorTree &DT, LoopInfo &LI,
ScopDetection &SD, ScalarEvolution &SE,
OptimizationRemarkEmitter &ORE);
ScopBuilder(const ScopBuilder &) = delete;
ScopBuilder &operator=(const ScopBuilder &) = delete;
~ScopBuilder() = default;
/// Try to build the Polly IR of static control part on the current
/// SESE-Region.
///
/// @return Give up the ownership of the scop object or static control part
/// for the region
std::unique_ptr<Scop> getScop() { return std::move(scop); }
};
} // end namespace polly
#endif // POLLY_SCOPBUILDER_H
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