Package at.dms.kjc.sir.lowering.fusion

Provides compiler passes to fuse (combine) a set of filters into a single filter.

See:
Description

Class Summary

FindVarDecls	Unused! Finds variable definitions and accesses that have type "Int" or "Float" and replaces them with numbered variables.
FuseAll	This class fuses all the pipelines that it can in a stream graph.
FusePipe	This is the high-level fusion class for pipelines.
FusePipelines	This class fuses sub-segments of pipelines with various characteristics.
FuseSimpleSplit	This flattens certain cases of split/joins into a single filter.
FuseSplit	This flattens any set of filters into a single splitjoin.
Lifter	Canonicalize stream structure eliminating some redundancies.
ReplaceVarDecls	Used by FindVarDecls.findAndReplace.

Package at.dms.kjc.sir.lowering.fusion Description

Provides compiler passes to fuse (combine) a set of filters into a single filter. Currently this transformation is applied for two reasons:

• To allow optimization across filter boundaries. After being fused into a single filter, optimizations such as constant propagation (and scalar replacement) can improve buffer-management code. See Section 5 of this LCTES'05 paper for more details.

• To provide load-balancing on a distributed target. If one employs a simple runtime system that runs only one filter per processor (for example, the space-multiplexing RawBackend), then fusion is needed to map multiple filters to that processor.

The main fusion classes are FusePipe and FuseSplit, which apply to pipelines and splitjoins, respectively. (Fusion of feedback loops is not yet implemented, though it should be straightforward to write.) There are two alternate implementations of pipeline fusion, as described in the LCTES'05 paper: one that uses modulo addressing (ModuloPipelineFusion) and one that avoids modulo operations (ShiftPipelineFusion). There is also an optimized splitjoin fusion (FuseSimpleSplit) for certain cases of splitjoins.

The FuseAll class can be used to fuse everything in a hierarchical stream graph. Lifter provides graph canonicalization (removing pipeline wrappers, for example) that are sometimes produced by fusion (as well as other transformations).

See Also:

at.dms.kjc.raw, at.dms.kjc.cluster, SJToPipe