[#llvm-SCEVExpander]
= xref:llvm.adoc[llvm]::SCEVExpander
:relfileprefix: ../
:mrdocs:

This class uses information about analyze scalars to rewrite expressions in canonical form.

== Synopsis

Declared in `<llvm/Transforms/Utils/ScalarEvolutionExpander.h>`

[source,cpp,subs="verbatim,replacements,macros,-callouts"]
----
class SCEVExpander
    : public xref:llvm/SCEVUseVisitor-00.adoc[SCEVUseVisitor<SCEVExpander, Value*>]
----

== Description

Clients should create an instance of this class when rewriting is needed, and destroy it when finished to allow the release of the associated memory.

== Base Classes

[cols="1,4"]
|===
| Name| Description
| `xref:llvm/SCEVUseVisitor-00.adoc[SCEVUseVisitor<SCEVExpander, Value*>]`
| A visitor class for SCEVUse.
|===

== Member Functions

[cols="1,4"]
|===
| Name| Description
| xref:llvm/SCEVExpander/2constructor.adoc[`SCEVExpander`]         [.small]#[constructor]#
| Construct a SCEVExpander in "canonical" mode.
| xref:llvm/SCEVExpander/2destructor.adoc[`~SCEVExpander`] [.small]#[destructor]#
| Destroy the expander and assert that insert‐point guards were balanced.
| xref:llvm/SCEVExpander/SetCurrentDebugLocation.adoc[`SetCurrentDebugLocation`] 
| Set location information used by debugging information.
| xref:llvm/SCEVExpander/clear.adoc[`clear`] 
| Clear cached expansions and inserted‐value tracking.
| xref:llvm/SCEVExpander/clearInsertPoint.adoc[`clearInsertPoint`] 
| Clear the current insertion point. This is useful if the instruction that had been serving as the insertion point may have been deleted.
| xref:llvm/SCEVExpander/clearPostInc.adoc[`clearPostInc`] 
| Disable all post‐inc expansion.
| xref:llvm/SCEVExpander/disableCanonicalMode.adoc[`disableCanonicalMode`] 
| Disable the behavior of expanding expressions in canonical form rather than in a more literal form. Non‐canonical mode is useful for late optimization passes.
| xref:llvm/SCEVExpander/enableLSRMode.adoc[`enableLSRMode`] 
| Enable strength‐reduction mode for loop strength reduction.
| xref:llvm/SCEVExpander/eraseDeadInstructions.adoc[`eraseDeadInstructions`] 
| Remove inserted instructions that are dead, e.g. due to InstSimplifyFolder simplifications. `Root` is assumed to be used and won't be removed.
| xref:llvm/SCEVExpander/expandCodeFor-04.adoc[`expandCodeFor`] 
| `expandCodeFor` overloads
| xref:llvm/SCEVExpander/expandCodeForPredicate.adoc[`expandCodeForPredicate`] 
| Expand `Pred` to an i1 value inserted at `Loc.`
| xref:llvm/SCEVExpander/expandComparePredicate.adoc[`expandComparePredicate`] 
| A specialized variant of expandCodeForPredicate, handling the case when we are expanding code for a SCEVComparePredicate.
| xref:llvm/SCEVExpander/expandUnionPredicate.adoc[`expandUnionPredicate`] 
| A specialized variant of expandCodeForPredicate, handling the case when we are expanding code for a SCEVUnionPredicate.
| xref:llvm/SCEVExpander/expandWrapPredicate.adoc[`expandWrapPredicate`] 
| A specialized variant of expandCodeForPredicate, handling the case when we are expanding code for a SCEVWrapPredicate.
| xref:llvm/SCEVExpander/findInsertPointAfter.adoc[`findInsertPointAfter`] 
| Returns a suitable insert point after `I,` that dominates `MustDominate.` Skips instructions inserted by the expander.
| xref:llvm/SCEVExpander/generateOverflowCheck.adoc[`generateOverflowCheck`] 
| Generates code that evaluates if the `AR` expression will overflow.
| xref:llvm/SCEVExpander/getAllInsertedInstructions.adoc[`getAllInsertedInstructions`] 
| Return a vector containing all instructions inserted during expansion.
| xref:llvm/SCEVExpander/getCurrentDebugLocation.adoc[`getCurrentDebugLocation`] 
| Get location information used by debugging information.
| xref:llvm/SCEVExpander/getIVIncOperand.adoc[`getIVIncOperand`] 
| Return the induction variable increment's IV operand.
| xref:llvm/SCEVExpander/getInsertedIVs.adoc[`getInsertedIVs`] 
| Return the induction variables created during expansion.
| xref:llvm/SCEVExpander/getSE.adoc[`getSE`] 
| Return the ScalarEvolution instance used by this expander.
| xref:llvm/SCEVExpander/hasRelatedExistingExpansion.adoc[`hasRelatedExistingExpansion`] 
| Determine whether there is an existing expansion of S that can be reused. This is used to check whether S can be expanded cheaply.
| xref:llvm/SCEVExpander/hoistIVInc.adoc[`hoistIVInc`] 
| Hoist `IncV` and its required subexpressions before `InsertPos.`
| xref:llvm/SCEVExpander/isHighCostExpansion.adoc[`isHighCostExpansion`] 
| Return true for expressions that can't be evaluated at runtime within given *Budget.*
| xref:llvm/SCEVExpander/isInsertedInstruction.adoc[`isInsertedInstruction`] 
| Return true if the specified instruction was inserted by the code rewriter.
| xref:llvm/SCEVExpander/isSafeToExpand.adoc[`isSafeToExpand`] 
| Return true if `S` is safe to expand anywhere its operands are defined.
| xref:llvm/SCEVExpander/isSafeToExpandAt.adoc[`isSafeToExpandAt`] 
| Return true if `S` is safe to expand at `InsertionPoint.`
| xref:llvm/SCEVExpander/replaceCongruentIVs.adoc[`replaceCongruentIVs`] 
| replace congruent phis with their most canonical representative. Return the number of phis eliminated.
| xref:llvm/SCEVExpander/setChainedPhi.adoc[`setChainedPhi`] 
| Record `PN` as completing an IV chain so it can be reused.
| xref:llvm/SCEVExpander/setIVIncInsertPos.adoc[`setIVIncInsertPos`] 
| Set the current IV increment loop and position.
| xref:llvm/SCEVExpander/setInsertPoint-06.adoc[`setInsertPoint`] 
| `setInsertPoint` overloads
| xref:llvm/SCEVExpander/setPostInc.adoc[`setPostInc`] 
| Enable post‐inc expansion for addrecs referring to the given loops. Post‐inc expansion is only supported in non‐canonical mode.
| xref:llvm/SCEVExpander/visit.adoc[`visit`] 
| Dispatch to the typed visit method for SCEVUse `S.`
| xref:llvm/SCEVExpander/visitCouldNotCompute.adoc[`visitCouldNotCompute`] 
| Default handler for SCEVCouldNotCompute uses; aborts on use.
|===


== Static Member Functions

[cols="1,4"]
|===
| Name| Description
| xref:llvm/SCEVExpander/canReuseFlagsFromOriginalIVInc.adoc[`canReuseFlagsFromOriginalIVInc`] 
| Return true if original and wide IV increments can share poison flags.
| xref:llvm/SCEVExpander/dropPoisonGeneratingAnnotationsAndReinfer.adoc[`dropPoisonGeneratingAnnotationsAndReinfer`] 
| Drop poison‐generating flags from `I,` then try re‐infer via SCEV.
| xref:llvm/SCEVExpander/findReusableCastForPtrToAddr.adoc[`findReusableCastForPtrToAddr`] 
| Find an existing cast among `PtrOp's` users that computes the same value as a `ptrtoaddr` of `PtrOp` to `Ty` and can be reused when expanding ptrtoaddr.
|===


== Friends

[cols="1,4"]
|===
| Name| Description
| `xref:llvm/SCEVUseVisitor-00.adoc[llvm::SCEVUseVisitor]`
| A visitor class for SCEVUse.
| `xref:llvm/SCEVExpanderCleaner.adoc[llvm::SCEVExpanderCleaner]`
| Helper to remove instructions inserted during SCEV expansion, unless they are marked as used.
|===


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