Generating Litmus Tests for Contrasting Memory Consistency Models - Extended Version

Well-defined memory consistency models are necessary for writing correct parallel software. Developing and understanding formal specifications of hardware memory models is a challenge due to the subtle differences in allowed reorderings and different specification styles. To facilitate exploration of memory model specifications, we have developed a technique for systematically comparing hardware memory models specified using both operational and axiomatic styles. Given two specifications, our approach generates all possible multi-threaded programs up to a specified bound, and for each such program, checks if one of the models can lead to an observable behavior not possible in the other model. When the models differs, the tool finds a minimal “litmus test” program that demonstrates the difference. A number of optimizations reduce the number of programs that need to be examined. Our prototype implementation has successfully compared both axiomatic and operational specifications of six different hardware memory models. We describe two case studies: (1) development of a non-store atomic variant of an existing memory model, which illustrates the use of the tool while developing a new memory model, and (2) identification of a subtle specification mistake in a recently published axiomatic specification of TSO

Non-Existential Indefinites and Semantic Incorporation of PP Complements

This paper studies some newly observed phenomena with indefinite descriptions when they appear as complements of prepositional phrases (PPs). We show that in many such cases the indefinite does not receive the traditional existential interpretation, and its quantificational force is sensitive to the identity of the preposition. Such cases of quantificational variability are explained by elaborating previous theories of semantic incorporation. In our proposal, predicative indefinites are direct arguments of the spatial component in the semantics of the PP. The semantics of spatial prepositions is directly responsible for the quantificational interpretation of predicative indefinites that appear as PP complements. Using earlier studies of locative prepositions, especially (Zwarts and Winter 2000), we analyze the effects that monotonicity and (anti-)additivity of prepositions have on the quantificational interpretation of predicative indefinites in their complement. These semantic observations are supported by standard tests from entailments and acceptability with negative polarity items. 1

Far From Obvious: the Semantics of Locative Indefinites

Locative sentences containing a indefinites exhibit a variety of non-existential interpretations. This understudied phenomenon is especially problematic for traditional theories that treat indefinites as denoting existential quantifiers. We propose a solution where indefinites denote properties and are assigned locations similarly to other spatial descriptions. This property-based analysis accounts for new observations about the correlation between non-existential interpretations of locative indefinites and similar geometrical effects with entity-denoting NPs. Thereby, the proposal opens up a new empirical domain for property-based theories of indefinites, with implications for the analysis of generics, collective descriptions, negative polarity items and part-whole structure.

Far from obvious: the semantics of locative indefinites

Simple locative sentences show a variety of pseudo-quantificational interpretations. Some locatives give the impression of universal quantification over parts of objects, others involve existential quantification, and yet others cannot be characterized by either of these quantificational terms. This behavior is explained by virtually all semantic theories of locatives. What has not been previously observed is that similar quantificational variability is also exhibited by locative sentences containing indefinites with the ‘a’ article. This phenomenon is especially problematic for traditional existential treatments of indefinites. We propose a solution where indefinites denote properties and are assigned locations similarly to other spatial descriptions. This Property-Eigenspace Hypothesis accounts for the correlation between the interpretations of locative indefinites and the pseudo-quantificational effects with simple entity-denoting NPs. Thereby, the proposal opens up a new empirical domain for property-based theories of indefinites, with implications for the analysis of collective descriptions, generics, negative polarity items and part–whole structure