# Package org.apache.sysds.hops.rewrite

Class Summary
HopDagValidator: This class allows to check hop dags for validity, e.g., parent-child linking.
HopRewriteRule: Base class for all hop rewrites in order to enable generic application of all rules.
HopRewriteUtils
MarkForLineageReuse
ProgramRewriter: This program rewriter applies a variety of rule-based rewrites on all hop dags of the given program in one pass over the entire program.
ProgramRewriteStatus
RewriteAlgebraicSimplificationDynamic: Rule: Algebraic Simplifications.
RewriteAlgebraicSimplificationStatic: Rule: Algebraic Simplifications.
RewriteBlockSizeAndReblock: Rule: BlockSizeAndReblock.
RewriteCommonSubexpressionElimination: Rule: CommonSubexpressionElimination.
RewriteCompressedReblock: Rule: Compressed Re block if config compressed.linalg is enabled, we inject compression directions after read of matrices if number of rows is above 1000 and cols at least 1.
RewriteConstantFolding: Rule: Constant Folding.
RewriteElementwiseMultChainOptimization: Prerequisite: RewriteCommonSubexpressionElimination must run before this rule.
RewriteForLoopVectorization: Rule: Simplify program structure by pulling if or else statement body out (removing the if statement block ifself) in order to allow intra-procedure analysis to propagate exact statistics.
RewriteGPUSpecificOps
RewriteHoistLoopInvariantOperations: Rule: Simplify program structure by hoisting loop-invariant operations out of while, for, or parfor loops.
RewriteIndexingVectorization: Rule: Indexing vectorization.
RewriteInjectSparkLoopCheckpointing: Rule: Insert checkpointing operations for caching purposes.
RewriteInjectSparkPReadCheckpointing: Rule: BlockSizeAndReblock.
RewriteMarkLoopVariablesUpdateInPlace: Rule: Mark loop variables that are only read/updated through cp left indexing for update in-place.
RewriteMatrixMultChainOptimization: Rule: Determine the optimal order of execution for a chain of matrix multiplications Solution: Classic Dynamic Programming Approach: Currently, the approach based only on matrix dimensions Goal: To reduce the number of computations in the run-time (map-reduce) layer
RewriteMatrixMultChainOptimizationSparse: Rule: Determine the optimal order of execution for a chain of matrix multiplications Solution: Classic Dynamic Programming Approach: Currently, the approach based only on matrix dimensions and sparsity estimates using the MNC sketch Goal: To reduce the number of computations in the run-time (map-reduce) layer
RewriteMergeBlockSequence: Rule: Simplify program structure by merging sequences of last-level statement blocks in order to create optimization opportunities.
RewriteRemoveDanglingParentReferences: This rewrite is a general-purpose cleanup pass that removes any dangling parent references in one pass through the hop DAG.
RewriteRemoveEmptyBasicBlocks: Rule: Simplify program structure by removing empty last-level blocks, which may originate from the original program or due to a sequence of rewrites (e.g., checkpoint injection and subsequent IPA).
RewriteRemoveForLoopEmptySequence: Rule: Simplify program structure by removing (par)for statements iterating over an empty sequence, i.e., (par)for-loops without a single iteration.
RewriteRemovePersistentReadWrite: This rewrite is a custom rewrite for JMLC in order to replace all persistent reads and writes with transient reads and writes from the symbol table.
RewriteRemoveReadAfterWrite: Rule: RemoveReadAfterWrite.
RewriteRemoveUnnecessaryBranches: Rule: Simplify program structure by pulling if or else statement body out (removing the if statement block ifself) in order to allow intra-procedure analysis to propagate exact statistics.
RewriteRemoveUnnecessaryCasts: Rule: RemoveUnnecessaryCasts.
RewriteSplitDagDataDependentOperators: Rule: Split Hop DAG after specific data-dependent operators.
RewriteSplitDagUnknownCSVRead: Rule: Split Hop DAG after CSV reads with unknown size.
RewriteTransientWriteParentHandling: Rule: Eliminate for Transient Write DataHops to have no parents Solution: Move parent edges of Transient Write Hop to parent of its child Reason: Transient Write not being a root messes up analysis for Lop's to Instruction translation (according to Amol)
StatementBlockRewriteRule: Base class for all hop rewrites in order to enable generic application of all rules.