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PLDI 2020
Mon 15 - Fri 19 June 2020
Thu 18 Jun 2020 13:40 - 14:00 at PLDI Research Papers live stream - Code Generation Chair(s): Fan Long

Function merging is an important optimization for reducing code size. This technique eliminates redundant code across functions by merging them into a single function. While initially limited to identical or trivially similar functions, the most recent approach can identify all merging opportunities in arbitrary pairs of functions. However, this approach has a serious limitation which prevents it from reaching its full potential. Because it cannot handle phi-nodes, the state-of-the-art applies register demotion to eliminate them before applying its core algorithm. While a superficially minor workaround, this has a three-fold negative effect: by artificially lengthening the instruction sequences to be aligned, it hinders the identification of mergeable instruction; it prevents a vast number of functions from being profitably merged; it increases compilation overheads, both in terms of compile-time and memory usage.

We present SalSSA, a novel approach that fully supports the SSA form, removing any need for register demotion. By doing so, we notably increase the number of profitably merged functions. We implement SalSSA in LLVM and apply it to the SPEC 2006 and 2017 suites. Experimental results show that our approach delivers on average, 7.9% to 9.7% reduction on the final size of the compiled code. This translates to around 2x more code size reduction over the state-of-the-art. Moreover, as a result of aligning shorter sequences of instructions and reducing the number of wasteful merge operations, our new approach incurs an average compile-time overhead of only 5%, 3x less than the state-of-the-art, while also reducing memory usage by over 2x.

Conference Day
Thu 18 Jun

Displayed time zone: Pacific Time (US & Canada) change

13:00 - 14:00
13:00
20m
Talk
Automatic Generation of Efficient Sparse Tensor Format Conversion Routines
PLDI Research Papers
Stephen ChouMassachusetts Institute of Technology, USA, Fredrik KjolstadStanford University, Saman AmarasingheMassachusetts Institute of Technology, USA
Pre-print
13:20
20m
Talk
OOElala: Order-of-Evaluation Based Alias Analysis for Compiler Optimization
PLDI Research Papers
Ankush PhuliaIIT Delhi, India, Vaibhav BhageeIIT Delhi, India, Sorav BansalIIT Delhi, India
13:40
20m
Talk
Effective Function Merging in the SSA Form
PLDI Research Papers
Rodrigo C. O. RochaUniversity of Edinburgh, UK, Pavlos PetoumenosUniversity of Manchester, UK, Zheng WangUniversity of Leeds, UK, Murray ColeUniversity of Edinburgh, UK, Hugh LeatherUniversity of Edinburgh, UK