An Analysis of the Search Spaces for Generate and Validate Patch Generation Systems

We present the first systematic analysis of the characteristics of patch search spaces for automatic patch generation systems. We analyze the search spaces of two current state-of-the-art systems, SPR and Prophet, with 16 different search space configurations. Our results are derived from an analysis of 1104 different search spaces and 768 patch generation executions. Together these experiments consumed over 9000 hours of CPU time on Amazon EC2. The analysis shows that 1) correct patches are sparse in the search spaces (typically at most one correct patch per search space per defect), 2) incorrect patches that nevertheless pass all of the test cases in the validation test suite are typically orders of magnitude more abundant, and 3) leveraging information other than the test suite is therefore critical for enabling the system to successfully isolate correct patches. We also characterize a key tradeoff in the structure of the search spaces. Larger and richer search spaces that contain correct patches for more defects can actually cause systems to find fewer, not more, correct patches. We identify two reasons for this phenomenon: 1) increased validation times because of the presence of more candidate patches and 2) more incorrect patches that pass the test suite and block the discovery of correct patches. These fundamental properties, which are all characterized for the first time in this paper, help explain why past systems often fail to generate correct patches and help identify challenges, opportunities, and productive future directions for the field

An Analysis of the Search Spaces for Generate and Validate Patch Generation Systems

We present the first systematic analysis of the characteristics of patch search spaces for automatic patch generation systems. We analyze the search spaces of two current state-of- the-art systems, SPR and Prophet, with 16 different search space configurations. Our results are derived from an analysis of 1104 different search spaces and 768 patch generation executions. Together these experiments consumed over 9000 hours of CPU time on Amazon EC2.The analysis shows that 1) correct patches are sparse in the search spaces (typically at most one correct patch per search space per defect), 2) incorrect patches that nevertheless pass all of the test cases in the validation test suite are typically orders of magnitude more abundant, and 3) leveraging information other than the test suite is therefore critical for enabling the system to successfully isolate correct patches.We also characterize a key tradeoff in the structure of the search spaces. Larger and richer search spaces that contain correct patches for more defects can actually cause systems to find fewer, not more, correct patches. We identify two reasons for this phenomenon: 1) increased validation times because of the presence of more candidate patches and 2) more incorrect patches that pass the test suite and block the discovery of correct patches. These fundamental properties, which are all characterized for the first time in this paper, help explain why past systems often fail to generate correct patches and help identify challenges, opportunities, and productive future directions for the field

Abstract Learning Frameworks for Synthesis

We develop abstract learning frameworks (ALFs) for synthesis that embody the principles of CEGIS (counter-example based inductive synthesis) strategies that have become widely applicable in recent years. Our framework defines a general abstract framework of iterative learning, based on a hypothesis space that captures the synthesized objects, a sample space that forms the space on which induction is performed, and a concept space that abstractly defines the semantics of the learning process. We show that a variety of synthesis algorithms in current literature can be embedded in this general framework. While studying these embeddings, we also generalize some of the synthesis problems these instances are of, resulting in new ways of looking at synthesis problems using learning. We also investigate convergence issues for the general framework, and exhibit three recipes for convergence in finite time. The first two recipes generalize current techniques for convergence used by existing synthesis engines. The third technique is a more involved technique of which we know of no existing instantiation, and we instantiate it to concrete synthesis problems

Verifying and Synthesizing Software with Recursive Functions

Our goal is to help people construct software that does what they wish. We develop tools and algorithms that span static and dynamic verification, constraint solving, and program synthesis. I will outline the current state our verification and synthesis system, Leon, which translates software into a functional language and uses SMT solvers to reason about paths in programs and specifications. Certain completeness results partly explain the effectiveness of verification and synthesis procedures implemented within Leon, in particular results on decidability of sufficiently surjective abstraction functions, and the framework of complete functional synthesis

Deductive Program Repair

Abstract. We present an approach to program repair and its applica-tion to programs with recursive functions over unbounded data types. Our approach formulates program repair in the framework of deductive synthesis that uses existing program structure as a hint to guide synthe-sis. We introduce a new specification construct for symbolic tests. We rely on such user-specified tests as well as automatically generated ones to localize the fault and speed up synthesis. Our implementation is able to eliminate errors within seconds from a variety of functional programs, including symbolic computation code and implementations of functional data structures. The resulting programs are formally verified by the Leon system.

Prediction of fetal death in monochorionic twin pregnancies complicated by Type-III selective fetal growth restriction

Objective : Monochorionic diamniotic twin pregnancies complicated by Type-III selective fetal growth restriction (sFGR) are at high risk of fetal death. The aim of this study was to identify predictors of fetal death in these pregnancies. Methods : This was an international multicenter retrospective cohort study. Type-III sFGR was defined as fetal estimated fetal weight (EFW) of one twin below the 10th percentile and intertwin EFW discordance of ≥ 25% in combination with intermittent absent or reversed end-diastolic flow in the umbilical artery of the smaller fetus. Predictors of fetal death were recorded longitudinally throughout gestation and assessed in univariable and multivariable logistic regression models. The classification and regression trees (CART) method was used to construct a prediction model of fetal death using significant predictors derived from the univariable analysis. Results : A total of 308 twin pregnancies (616 fetuses) were included in the analysis. In 273 (88.6%) pregnancies, both twins were liveborn, whereas 35 pregnancies had single (n = 19 (6.2%)) or double (n = 16 (5.2%)) fetal death. On univariable analysis, earlier gestational age at diagnosis of Type-III sFGR, oligohydramnios in the smaller twin and deterioration in umbilical artery Doppler flow were associated with an increased risk of fetal death, as was larger fetal EFW discordance, particularly between 24 and 32 weeks' gestation. None of the parameters identified on univariable analysis maintained statistical significance on multivariable analysis. The CART model allowed us to identify three risk groups: a low-risk group (6.8% risk of fetal death), in which umbilical artery Doppler did not deteriorate; an intermediate-risk group (16.3% risk of fetal death), in which umbilical artery Doppler deteriorated but the diagnosis of sFGR was made at or after 16 + 5 weeks' gestation; and a high-risk group (58.3% risk of fetal death), in which umbilical artery Doppler deteriorated and gestational age at diagnosis was < 16 + 5 weeks' gestation. Conclusions : Type-III sFGR is associated with a high risk of fetal death. A prediction algorithm can help to identify the highest-risk group, which is characterized by Doppler deterioration and early referral. Further studies should investigate the potential benefit of fetal surveillance and intervention in this cohort

Outcomes of monochorionic twin pregnancies complicated by Type-III selective fetal growth restriction.

OBJECTIVE: Type III selective intrauterine growth restriction (sIUGR) is associated with a high and unpredictable risk of fetal death and fetal brain injury. Our objective was to describe the prospective risk of fetal death and the risk of adverse neonatal outcomes in a contemporary cohort. METHODS: We retrospectively reviewed all monochorionic diamniotic twin pregnancies complicated by type III sIUGR managed at nine fetal centers over a 12-year time period. Higher order multiples, major fetal anomalies or other monochorionicity related complications at initial presentation were excluded. Fetal and neonatal outcomes were collected and management strategies were reviewed. Composite adverse neonatal outcome was defined as neonatal death, invasive ventilation beyond the resuscitation period, culture proven sepsis, necrotizing enterocolitis (NEC) requiring treatment, intraventricular hemorrhage (IVH) >grade I, retinopathy of prematurity (ROP) >stage II or periventricular leukomalacia (PVL). The prospective risk of fetal death and the risk of neonatal complications at each gestational age were evaluated. RESULTS: We collected data on 328 pregnancies (656 fetuses). After exclusion of pregnancies which underwent selective reduction (n=18, 5.5%), there were 51 (8.3%) non-iatrogenic fetal deaths in 35 pregnancies (11.3%). Single deaths occurred in 19 (5.8%) pregnancies and double deaths in 16 (4.9%) pregnancies. The prospective risk of non-iatrogenic fetal death per fetus declined from 8.1% (95% CI 5.95-10.26) at 16 weeks, to less than 2% (95% CI 0.59-2.79) after 28.4 weeks and to less than 1% (95% CI -0.30-1.89) beyond 32.6 weeks. In otherwise uncomplicated type III sIUGR, delivery was generally planned at 32 weeks, at which time the risk of composite adverse neonatal outcomes was 29% (31/107 neonates). For twin pregnancies that continued to 34 weeks there was a very low risk of fetal demise (0.7%) and a low risk of adverse outcomes (11%). CONCLUSIONS: In this contemporary cohort from tertiary fetal centers, the risk of fetal death in type III sIUGR was lower than previously reported. Further efforts should be directed at identifying predictors of fetal death and optimal antenatal surveillance strategies to select a cohort of pregnancies that can safely continue beyond 33 weeks of gestation. This article is protected by copyright. All rights reserved.status: Published onlin

Outcome of monochorionic twin pregnancy complicated by Type-III selective intrauterine growth restriction.

Type-III selective intrauterine growth restriction (sIUGR) is associated with a high and unpredictable risk of fetal death and fetal brain injury. The objective of this study was to describe the prospective risk of fetal death and the risk of adverse neonatal outcome in a cohort of twin pregnancies complicated by Type-III sIUGR and treated according to up-to-date guidelines. We reviewed retrospectively all monochorionic diamniotic twin pregnancies complicated by Type-III sIUGR managed at nine fetal centers over a 12-year period. Higher-order multiple gestations and pregnancies with major fetal anomalies or other monochorionicity-related complications at initial presentation were excluded. Data on fetal and neonatal outcomes were collected and management strategies reviewed. Composite adverse neonatal outcome was defined as neonatal death, invasive ventilation beyond the resuscitation period, culture-proven sepsis, necrotizing enterocolitis requiring treatment, intraventricular hemorrhage Grade &gt; I, retinopathy of prematurity Stage &gt; II or cystic periventricular leukomalacia. The prospective risk of intrauterine death (IUD) and the risk of neonatal complications according to gestational age were evaluated. We collected data on 328 pregnancies (656 fetuses). After exclusion of pregnancies that underwent selective reduction (n = 18 (5.5%)), there were 51/620 (8.2%) non-iatrogenic IUDs in 35/310 (11.3%) pregnancies. Single IUD occurred in 19/328 (5.8%) pregnancies and double IUD in 16/328 (4.9%). The prospective risk of non-iatrogenic IUD per fetus declined from 8.1% (95% CI, 5.95-10.26%) at 16 weeks, to less than 2% (95% CI, 0.59-2.79%) after 28.4 weeks and to less than 1% (95% CI, -0.30 to 1.89%) beyond 32.6 weeks. In otherwise uncomplicated pregnancies with Type-III sIUGR, delivery was generally planned at 32 weeks, at which time the risk of composite adverse neonatal outcome was 29.0% (31/107 neonates). In twin pregnancies that continued to 34 weeks, there was a very low risk of IUD (0.7%) and a low risk of composite adverse neonatal outcome (11%). In this cohort of twin pregnancies complicated by Type-III sIUGR and treated at several tertiary fetal centers, the risk of fetal death was lower than that reported previously. Further efforts should be directed at identifying predictors of fetal death and optimal antenatal surveillance strategies to select a cohort of pregnancies that can continue safely beyond 33 weeks' gestation. © 2020 International Society of Ultrasound in Obstetrics and Gynecology