Survey on Combinatorial Register Allocation and Instruction Scheduling

Register allocation (mapping variables to processor registers or memory) and instruction scheduling (reordering instructions to increase instruction-level parallelism) are essential tasks for generating efficient assembly code in a compiler. In the last three decades, combinatorial optimization has emerged as an alternative to traditional, heuristic algorithms for these two tasks. Combinatorial optimization approaches can deliver optimal solutions according to a model, can precisely capture trade-offs between conflicting decisions, and are more flexible at the expense of increased compilation time. This paper provides an exhaustive literature review and a classification of combinatorial optimization approaches to register allocation and instruction scheduling, with a focus on the techniques that are most applied in this context: integer programming, constraint programming, partitioned Boolean quadratic programming, and enumeration. Researchers in compilers and combinatorial optimization can benefit from identifying developments, trends, and challenges in the area; compiler practitioners may discern opportunities and grasp the potential benefit of applying combinatorial optimization

Parameterization and adaptive search for graph coloring register allocation

Graph coloring register allocators use heuristics for register coalescing and allocation, which are relevant to the number of physical registers that a group of virtual registers will use after allocation. They cannot be determined accurately in allocation, thus we made them tunable by introducing new parameters as the thresholds for coalescing and the thresholds for defining constrained live intervals in simplification. Experiments demonstrated neither the aggressive method nor the conservative method can outperform the other for all tests and the best parameters vary significantly among programs. This parameterization is profitable because the best running time reached by varying the parameters is up to 16% faster than the best of fixed-parameter methods. Hill-climbing and random probe algorithms were used to find good parameters, and the later performed better. Further analysis reveals the search space has many irregular fluctuations that are not suitable for the hill-climber

Moccasin: Efficient Tensor Rematerialization for Neural Networks

The deployment and training of neural networks on edge computing devices pose many challenges. The low memory nature of edge devices is often one of the biggest limiting factors encountered in the deployment of large neural network models. Tensor rematerialization or recompute is a way to address high memory requirements for neural network training and inference. In this paper we consider the problem of execution time minimization of compute graphs subject to a memory budget. In particular, we develop a new constraint programming formulation called \textsc{Moccasin} with only $O(n)$ integer variables, where $n$ is the number of nodes in the compute graph. This is a significant improvement over the works in the recent literature that propose formulations with $O(n^2)$ Boolean variables. We present numerical studies that show that our approach is up to an order of magnitude faster than recent work especially for large-scale graphs

Survey on Instruction Selection: An Extensive and Modern Literature Review

Instruction selection is one of three optimisation problems involved in the code generator backend of a compiler. The instruction selector is responsible of transforming an input program from its target-independent representation into a target-specific form by making best use of the available machine instructions. Hence instruction selection is a crucial part of efficient code generation. Despite on-going research since the late 1960s, the last, comprehensive survey on the field was written more than 30 years ago. As new approaches and techniques have appeared since its publication, this brings forth a need for a new, up-to-date review of the current body of literature. This report addresses that need by performing an extensive review and categorisation of existing research. The report therefore supersedes and extends the previous surveys, and also attempts to identify where future research should be directed.Comment: Major changes: - Merged simulation chapter with macro expansion chapter - Addressed misunderstandings of several approaches - Completely rewrote many parts of the chapters; strengthened the discussion of many approaches - Revised the drawing of all trees and graphs to put the root at the top instead of at the bottom - Added appendix for listing the approaches in a table See doc for more inf

Analysing Finnish Multi-Word Expressions with Word Embeddings

Sanayhdistelmät ovat useamman sanan kombinaatioita, jotka ovat jollakin tavalla jähmeitä ja/tai idiomaattisia. Tutkimuksessa tarkastellaan suomen kielen verbaalisia idiomeja sanaupotusmenetelmän (word2vec) avulla. Työn aineistona käytetään Gutenberg-projektista haettuja suomenkielisiä kirjoja. Työssä tutkitaan pääosin erityisesti idiomeja, joissa esiintyy suomen kielen sana ‘silmä’. Niiden idiomaattisuutta mitataan komposiittisuuden (kuinka hyvin sanayhdistelmän merkitys vastaa sen komponenttien merkitysten kombinaatiota) ja jähmeyttä leksikaalisen korvaustestin avulla. Vastaavat testit tehdään myös sanojen sisäisen rakenteen huomioonottavan fastText-algoritmin avulla. Työssä on myös luotu Gutenberg-korpuksen perusteella pienehkö luokiteltu lausejoukko, jota lajitellaan neuroverkkopohjaisen luokittelijan avulla. Tämä lisäksi työssä tunnustellaan eri ominaisuuksien kuten sijamuodon vaikutusta idiomin merkitykseen. Mittausmenetelmien tulokset ovat yleisesti ottaen varsin kirjavia. fastText-algoritmin suorituskyky on yleisesti ottaen hieman parempi kuin perusmenetelmän; sen lisäksi sanaupotusten laatu on parempi. Leksikaalinen korvaustesti antaa parhaimmat tulokset, kun vain lähin naapuri otetaan huomioon. Sijamuodon todettiin olevan varsin tärkeä idiomin merkityksen määrittämiseen. Mittauksien heikot tulokset voivat johtua monesta tekijästä, kuten siitä, että idiomien semanttisen läpinäkyvyyden aste voi vaihdella. Sanaupotusmenetelmä ei myöskään normaalisti ota huomioon sitä, että myös sanayhdistelmillä voi olla useita merkityksiä (kirjaimellinen ja idiomaattinen/kuvaannollinen). Suomen kielen rikas morfologia asettaa menetelmälle myös ylimääräisiä haasteita. Tuloksena voidaan sanoa, että sanaupotusmenetelmä on jokseenkin hyödyllinen suomen kielen idiomien tutkimiseen. Testattujen mittausmenetelmien käyttökelpoisuus yksin käytettynä on rajallinen, mutta ne saattaisivat toimia paremmin osana laajempaa tutkimusmekanismia

Essays on Inflation in Emerging Markets and Developing Countries

This dissertation consists of three self-contained chapters contributing to the analysis in monetary macroeconomics. In these chapters concerning with research questions on inflation in emerging markets and developing countries, I aim to better understand the redistributive effects of anticipated inflation on individual behaviours together with welfare consequences; proximate, socio-economical and political drivers of inflation; and the best response of monetary policy makers with respect to monetary targets in foreign aid-recipient countries. Chapter 2 shows that anticipated inflation rate has long-run real impacts, disproportionately affects heterogeneous households by redistributing from lenders to borrowers; and whether the inflation rate can be used as an instrument to improve utilitarian welfare relies on the presence of money demand in the form of money-in-utility model, the concern with pro-lender/borrower bias, the relationship between intertemporal elasticity of substitutions and the heterogeneous productivity levels. In other words, the policy planner should be concerned about these features when targeting an inflation rate to account for the welfare effects of that policy implication. Chapter 3 incorporates different theories which refer to the proximate determinants; and socio-economical and political determinants to improve the knowledge on inflation dynamics. Inflation is stressed to be mainly driven by money growth and inflation persistence. From the political perspective, greater democratization is found to lead to inflation as the inequality gap rises. The insignificance of the impact from de juro central bank independence on inflation is supported. Inflation inertia with its greatest magnitude and significance suggest that the inflationary expectations and indexations schemes in price and wage are the most critical determinants of inflation in emerging and developing economies. Chapter 4 optimizes the policy parameters of the Taylor rule, namely interest rate smoothing, inflation targeting and output growth targeting in order to maximize unconditional welfare under three cases: only cost-push shock (CP), only foreign aid shock (FA); and cost-push and foreign aid shocks (CP+FA). The findings demonstrate that aid recipient developing countries also face a trade-off between stabilizing the inflation rate and output growth in the presence of cost push shock while the foreign aid shock is found to resolve this trade-off, leading to the conclusion that foreign aid recipient developing countries should act in favor of the inflation targeting as in industrialized countries

Building a network of excellence in artificial intelligence in Sub-Saharan Africa : final technical report

The report provides a summary of project activities, milestones, achievements, outcomes and outputs. The project drew from the Global South ecosystem mapping, and facilitated a bottom-up network/community of researchers who investigated and provided recommendations on how future artificial intelligence for development (AI4D) networks’ research should be shaped. The project acknowledges the growing importance of funding Networks and domain-specific research relevant to African researchers and practitioners, with a focus on the ethical, legal and social aspects of AI research. One of the major results works towards addressing language barriers through machine translation

Determinants of the Generalized Trust Radius in Scripted Fragile Sub-Saharan African States

Trust between strangers does not come easily in collectivist societies governed by coercive institutions and subject to unstable market forces. More than one-third of all states are fragile, yet the trust literature has shown little interest in explaining the variability of generalized trust among them; instead fixating on social capital, the consequence of the expansion of generalized trust, putting the cart before the horse and leaving unexamined many of its causes. The enhanced accuracy of the reconfigured World Values Survey trust question has generated new research opportunities to address this concern. This dissertation advances the trust literature through identifying, measuring, and explaining the full social effect on generalized trust in fragile states through group proximity and civil society power differential. Sociological institutionalism and social capital theory provide the theoretical framework for modeling and explaining structural social effects leading to the improbable expansion of generalized trust in the highly scripted fragile sub-Saharan African states of Burkina Faso, Ethiopia, and Nigeria. These purposefully deviant and least likely test cases are examined using within- and cross-case analysis of necessary and sufficient conditions through most similar multiple comparative case analysis, affirming or confirming most hypotheses. The expansion of generalized trust requires sustained and usually incentivized positive inter-group interaction. In fragile states, most inter-group interaction is conflictual and occurs through civil society because individuals have little capital with which to engage in the market and the state is dysfunctional. The generalized trust radius is likely to widen the more proximate and consociational its civil society is, regardless of how fragile the state is. This dissertation enlarges and strengthens the social explanation for generalized trust variability in fragile states, filling a significant gap in the literature and establishing a research design and model for future research to replicate in other fragile regions