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The compilation scheme for Volatile accesses in the OpenJDK 9 HotSpot Java Virtual Machine has a major problem that persists despite a recent bug report and a long discussion. One of the suggested fixes is to let Java compile Volatile accesses in the same way as C/C++11. However, we show that this approach is invalid for Java. Indeed, we show a set of optimizations that is valid for C/C++11 but invalid for Java, while the compilation scheme is similar. We prove the correctness of the compilation scheme to Power and x86 and a suite of valid optimizations in Java. Our proofs are based on a language model that we validate by proving key properties such as the DRF-SC theorem and by running litmus tests via our implementation of Java in Herd7. 

Researchers have reported that static analysis tools rarely achieve a false-positive rate that would make them attractive to developers. We overcome this problem by a technique that leads to reporting fewer bugs but also much fewer false positives. Our technique prunes the static call graph that sits at the core of many static analyses. Specifically, static call-graph construction proceeds as usual, after which a call-graph pruner removes many false-positive edges but few true edges. The challenge is to strike a balance between being aggressive in removing false-positive edges but not so aggressive that no true edges remain. We achieve this goal by automatically producing a call-graph pruner through an automatic, ahead-of-time learning process. We added such a call-graph pruner to a software tool for null-pointer analysis and found that the false-positive rate decreased from 73% to 23%. This improvement makes the tool more useful to developers. 

The consequences of four-electron addition to [8]cycloparaphenylene ([8]CPP, 1 ) have been evaluated crystallographically, revealing a significant core deformation. The structural analysis exposes an elliptical distortion observed upon electron transfer, with the deformation parameter (D.P.) increased by 28% in comparison with neutral [8]CPP. The C–C bond length alteration pattern also indicates a quinoidal structural rearrangement upon four-fold reduction. The large internal cavity of [8]CPP 4− allows the encapsulation of two {K + (THF) 2 } cationic moieties with two additional cations bound externally in the solid-state structure of [{K + (THF) 2 } 4 ([8]CPP 4− )]. The experimental structural data have been used as a benchmark for the comprehensive theoretical description of the geometric changes and electronic properties of the highly-charged [8]CPP 4− nanohoop in comparison with its neutral parent. While neutral [8]CPP and the [8]CPP 2− anion clearly show aromatic behavior of all six-membered rings, subsequent addition of two more electrons completely reverses their aromatic character to afford the highly-antiaromatic [8]CPP 4− anion, as evidenced by structural, topological, and magnetic descriptors. The disentanglement of electron transfer from metal binding effects allowed their contributions to the overall core perturbation of the negatively-charged [8]CPP to be revealed. Consequently, the internal coordination of potassium cations is identified as the main driving force for drastic elliptic distortion of the macrocyclic framework upon reduction. 

One-electron reduction of bowl-shaped indenocorannulene, C 26 H 12 , with Rb metal in THF affords [{Rb + (18-crown-6)} 2 (C 26 H 12 –C 26 H 12 ) 2− ]·4THF, as confirmed by single-crystal X-ray diffraction. The product consists of a dimeric σ-bonded dianion (C–C, 1.568(7) Å) having two endo -η 6 coordinated {Rb + (18-crown-6)} moieties (Rb–C, 3.272(4)–3.561(4) Å). The (C 26 H 12 –C 26 H 12 ) 2− dimer represents the first crystallographically confirmed example of spontaneous coupling for indenocorannulene monoanion radicals, C 26 H 12 ˙ − . Comprehensive theoretical investigation of the new dimer confirms the single σ-bond character of the linker and reveals a significant increase of both thermodynamic and kinetic stability of [σ-(C 26 H 12 ) 2 ] 2− in comparison with analogues formed by such π-bowls as corannulene and its dibenzo-derivative. The in-depth computational analysis and direct comparison of the series demonstrates the effect of curvature on radical coupling processes, allowing control over stability and reactivity of bowl-shaped π-radicals. 

Abstract Chemical reduction of pentacene (C₂₂H₁₄,1) with Group 1 metals ranging from Li to Cs revealed that1readily undergoes a two‐fold reduction to afford a doubly‐reduced1²⁻anion in THF. With the help of 18‐crown‐6 ether used as a secondary coordinating agent, five π‐complexes of1²⁻with different alkali metal counterions have been isolated and fully characterized. This series of complexes enables the first evaluation of alkali‐metal ion binding patterns and structural changes of the1²⁻dianion based on the crystallographically confirmed examples. The difference in coordination of the smallest Li⁺ion vs. heavier Group 1 congeners has been demonstrated. In addition, the use of benzo‐15‐crown‐5 in the reaction of1with Na metal allowed the isolation of the unique solvent‐separated ion product with a “naked” dianion,1²⁻. The detailed structural analyses of the series revealed the C−C bond alteration and core deformation of pentacene upon two‐fold reduction and complexation. The negative charge localization at the central six‐membered ring of1²⁻identified by theoretical calculations corroborates with the X‐ray crystallographic results. Subsequent in‐depth theoretical analysis provided a detailed description of changes in the electronic structure and aromaticity of pentacene upon reduction. 

Abstract The stepwise chemical reduction of a molecular warped nanographene (WNG) having a negatively curved π‐surface and defined C₈₀H₃₀composition with Cs metal used as the reducing and complexing agent allowed the isolation of three different reduced states with one, two, and three electrons added to itsπ‐conjugated system. This provided a unique series of nanosized carbanions with increasing negative charge for in‐depth structural analysis of consequences of controlled electron charging of non‐planar nanographenes, using X‐ray crystallographic and computational tools. The 3D molecular electrostatic potential (MEP) maps identified the negative charge localization at the central part of the WNG surface where selective coordination of Cs⁺ions is confirmed crystallographically. In‐depth theoretical investigation revealed a complex response of the WNG to the stepwise electron acquisition. The extended and contorted π‐surface of the WNG undergoes subtle swinging distortions that are accompanied by notable changes in the electronic structure and site‐dependent aromaticity of the resulting carbanions.