# Iterated register coalescing

@article{George1996IteratedRC, title={Iterated register coalescing}, author={Lal George and Andrew W. Appel}, journal={ACM Trans. Program. Lang. Syst.}, year={1996}, volume={18}, pages={300-324} }

An important function of any register allocator is to target registers so as to eliminate copy instructions. Graph-coloring register allocation is an elegant approach to this problem. If the source and destination of a move instruction do not interfere, then their nodes can be coalesced in the interference graph. Chaitin's coalescing heuristic could make a graph uncolorable (i.e., introduce spills); Briggs et al. demonstrated a conservative coalescing heuristic that preserves colorability. But…

## 218 Citations

### Improvements to Conservative and Optimistic Register Coalescing ?

- Computer Science
- 2007

It is shown that, with a more involved conservative strategy, incremental conservative coalescing can be as e ( cid:14) cient as optimistic coalescing, and a more aggressive optimistic approach with a di (cid:11) erent de-coalescing phase is developed.

### Register allocation for programs in SSA form

- Computer ScienceCC
- 2006

A novel register allocation architecture for programs in SSA-form is presented which simplifies register allocation significantly and a heuristic methods for spilling and coalescing are compared to an optimal method based on integer linear programming.

### Optimistic coalescing for heterogeneous register architectures

- Computer ScienceLCTES
- 2007

A modified algorithm for optimal coalescing is developed that helps a register allocator for an embedded processor to better handle such heterogeneity of the register architecture.

### Optimal spilling for CISC machines with few registers

- Computer SciencePLDI '01
- 2001

This work shows how to optimally split live ranges and optimally use addressing modes, and shows a variant of Park and Moon's optimistic coalescing algorithm that does a very good (though not provably optimal) job of removing the register-register moves.

### Register coalescing techniques for heterogeneous register architecture with copy sifting

- Computer ScienceTECS
- 2009

It is shown that optimistic coalescing is also useful for an embedded processor to better handle such heterogeneity of the register architecture, and a modified algorithm for optimal coalescing that helps a register allocator is developed.

### Advanced conservative and optimistic register coalescing

- Environmental ScienceCASES '08
- 2008

The results show that optimistic strategies do not outperform conservative ones, and incremental conservative coalescing performs even better than the improved de-coalescing scheme and leads to about 15% improvement compared to the state-of-the-art optimistic coalescing.

### Copy elimination on data dependence graphs

- Computer ScienceSAC '12
- 2012

This work presents an extension of a local recoloring technique called Parallel Copy Motion that performs code motion on data dependence graphs in order to eliminate useless copies and reorder instructions, while at the same time a valid register assignment is preserved.

### On the Complexity of Register Coalescing

- Computer ScienceInternational Symposium on Code Generation and Optimization (CGO'07)
- 2007

This paper is devoted to the complexity of the coalescing phase, in particular in the light of recent developments on the SSA form, and almost completely classify the NP-completeness of these problems, discussing also on the structure of the interference graph.

### Parallel Copy Elimination on Data Dependence Graphs

- Computer Science
- 2011

This work presents an extension of a local recoloring technique called Parallel Copy Motion that performs code motion on data dependence graphs in order to eliminate useless copies and reorder instructions, while at the same time a valid register assignment is preserved.

### Comparing conservative coalescing criteria

- EconomicsTOPL
- 2005

It is shown that for coalescing with precolored nodes, the full George criterion is strictly more powerful than the full Briggs criterion, while offering an equally strong safety guarantee, and a number of theorems characterizing the form of safety that each achieves.

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