class LoopVersioning

Declaration

class LoopVersioning { /* full declaration omitted */ };

Description

This class emits a version of the loop where run-time checks ensure that may-alias pointers can't overlap. It currently only supports single-exit loops and assumes that the loop already has a preheader.

Declared at: llvm/include/llvm/Transforms/Utils/LoopVersioning.h:41

Member Variables

private llvm::Loop* VersionedLoop
The original loop. This becomes the "versioned" one. I.e., control flows here if pointers in the loop don't alias.
private llvm::Loop* NonVersionedLoop = nullptr
The fall-back loop. I.e. control flows here if pointers in the loop may alias (memchecks failed).
private llvm::ValueToValueMapTy VMap
This maps the instructions from VersionedLoop to their counterpart in NonVersionedLoop.
private SmallVector<llvm::RuntimePointerCheck, 4> AliasChecks
The set of alias checks that we are versioning for.
private const llvm::SCEVPredicate& Preds
The set of SCEV checks that we are versioning for.
private DenseMap<const llvm::Value*, const llvm::RuntimeCheckingPtrGroup*> PtrToGroup
Maps a pointer to the pointer checking group that the pointer belongs to.
private DenseMap<const llvm::RuntimeCheckingPtrGroup*, llvm::MDNode*> GroupToScope
The alias scope corresponding to a pointer checking group.
private DenseMap<const llvm::RuntimeCheckingPtrGroup*, llvm::MDNode*> GroupToNonAliasingScopeList
The list of alias scopes that a pointer checking group can't alias.
private const llvm::LoopAccessInfo& LAI
Analyses used.
private llvm::LoopInfo* LI
private llvm::DominatorTree* DT
private llvm::ScalarEvolution* SE

Method Overview

Methods

LoopVersioning(
    const llvm::LoopAccessInfo& LAI,
    ArrayRef<llvm::RuntimePointerCheck> Checks,
    llvm::Loop* L,
    llvm::LoopInfo* LI,
    llvm::DominatorTree* DT,
    llvm::ScalarEvolution* SE)

Description

Expects LoopAccessInfo, Loop, LoopInfo, DominatorTree as input. It uses runtime check provided by the user. If \p UseLAIChecks is true, we will retain the default checks made by LAI. Otherwise, construct an object having no checks and we expect the user to add them.

Declared at: llvm/include/llvm/Transforms/Utils/LoopVersioning.h:47

Parameters

const llvm::LoopAccessInfo& LAI
ArrayRef<llvm::RuntimePointerCheck> Checks
llvm::Loop* L
llvm::LoopInfo* LI
llvm::DominatorTree* DT
llvm::ScalarEvolution* SE

void addPHINodes(
    const SmallVectorImpl<llvm::Instruction*>&
        DefsUsedOutside)

Description

Adds the necessary PHI nodes for the versioned loops based on the loop-defined values used outside of the loop. This needs to be called after versionLoop if there are defs in the loop that are used outside the loop.

Declared at: llvm/include/llvm/Transforms/Utils/LoopVersioning.h:104

Parameters

const SmallVectorImpl<llvm::Instruction*>& DefsUsedOutside

void annotateInstWithNoAlias(
    llvm::Instruction* VersionedInst,
    const llvm::Instruction* OrigInst)

Description

Add the noalias annotations to \p VersionedInst. \p OrigInst is the instruction corresponding to \p VersionedInst in the original loop. Initialize the aliasing scopes with prepareNoAliasMetadata once before this can be called.

Declared at: llvm/include/llvm/Transforms/Utils/LoopVersioning.h:95

Parameters

llvm::Instruction* VersionedInst
const llvm::Instruction* OrigInst

void annotateInstWithNoAlias(llvm::Instruction* I)

Description

Add the noalias annotations to \p I. Initialize the aliasing scopes with prepareNoAliasMetadata once before this can be called.

Declared at: llvm/include/llvm/Transforms/Utils/LoopVersioning.h:108

Parameters

llvm::Instruction* I

void annotateLoopWithNoAlias()

Description

Annotate memory instructions in the versioned loop with no-alias metadata based on the memchecks issued. This is just wrapper that calls prepareNoAliasMetadata and annotateInstWithNoAlias on the instructions of the versioned loop.

Declared at: llvm/include/llvm/Transforms/Utils/LoopVersioning.h:84

llvm::Loop* getNonVersionedLoop()

Description

Returns the fall-back loop. Control flows here if pointers in the loop may alias (i.e. one of the memchecks failed).

Declared at: llvm/include/llvm/Transforms/Utils/LoopVersioning.h:77

llvm::Loop* getVersionedLoop()

Description

Returns the versioned loop. Control flows here if pointers in the loop don't alias (i.e. all memchecks passed). (This loop is actually the same as the original loop that we got constructed with.)

Declared at: llvm/include/llvm/Transforms/Utils/LoopVersioning.h:73

void prepareNoAliasMetadata()

Description

Set up the aliasing scopes based on the memchecks. This needs to be called before the first call to annotateInstWithNoAlias.

Declared at: llvm/include/llvm/Transforms/Utils/LoopVersioning.h:88

void versionLoop()

Description

Performs the CFG manipulation part of versioning the loop including the DominatorTree and LoopInfo updates. The loop that was used to construct the class will be the "versioned" loop i.e. the loop that will receive control if all the memchecks pass. This allows the loop transform pass to operate on the same loop regardless of whether versioning was necessary or not: for each loop L: analyze L if versioning is necessary version L transform L

Declared at: llvm/include/llvm/Transforms/Utils/LoopVersioning.h:64

void versionLoop(
    const SmallVectorImpl<llvm::Instruction*>&
        DefsUsedOutside)

Description

Same but if the client has already precomputed the set of values used outside the loop, this API will allows passing that.

Declared at: llvm/include/llvm/Transforms/Utils/LoopVersioning.h:68

Parameters

const SmallVectorImpl<llvm::Instruction*>& DefsUsedOutside