LLVM miscompiles certain programs in C, C++, and Rust that use low-level language features such as raw pointers in Rust or conversion between integers and pointers in C or C++. The problem is that it is difficult for the compiler to implement aggressive, high-level memory optimizations while also respecting the guarantees made by the programming languages to low-level programs. A deeper problem is that the memory model for LLVM’s intermediate representation (IR) is informal and the semantics of corner cases are not always clear to all compiler developers.
We developed a novel memory model for LLVM IR and formalized it. The new model requires a handful of problematic IR-level optimizations to be removed, but it also supports the addition of new optimizations that were not previously legal. We have implemented the new model and shown that it fixes known memory-model-related miscompilations without impacting the quality of generated code.
Wed 7 Nov Times are displayed in time zone: Guadalajara, Mexico City, Monterrey change
|15:30 - 15:52|
|Format Abstraction for Sparse Tensor Algebra Compilers|
|15:52 - 16:15|
|ShareJIT: JIT Code Cache Sharing across Processes and its Practical Implementation|
|16:15 - 16:37|
|Reconciling High-level Optimizations and Low-level Code in LLVM|
|16:37 - 17:00|
|An Empirical Study of the Effect of Source-level Loop Transformations on Compiler Stability|
Zhangxiaowen GongUniversity of Illinois at Urbana-Champaign, Zhi ChenUniversity of California, Irvine, Justin SzadayUniversity of Illinois at Urbana-Champaign, David WongIntel, Zehra SuraIBM Research, Neftali Watkinson, Saeed MalekiMicrosoft Research, David PaduaUniversity of Illinois at Urbana-Champaign, Alexander VeidenbaumUniversity of California, Irvine, Alexandru NicolauUniversity of California, Irvine, Josep TorrellasUniversity of Illinois at Urbana-ChampaignMedia Attached