forked from OSchip/llvm-project
6dc53ccb0b
Summary: When linking two llvm.used arrays, if the resulting merged array ends up with duplicated elements (with the same name) but with different types, the IRLinker was crashing. This was supposed to be legal, as the IRLinker bitcasts elements to match types in these situations. This bug was exposed by D56928 in clang to support attribute used in member functions of class templates. Crash happened when self-hosting with LTO. Since LLVM depends on attribute used to generate code for the dump() method, ubiquitous in the code base, many input bc had a definition of this method referenced in their llvm.used array. Some of these classes got optimized, changing the type of the first parameter (this) in the dump method, leading to a scenario with a pool of valid definitions but some with a different type, triggering this bug. This is a memory bug: ValueMapper depends on (calls) the materializer provided by IRLinker, and this materializer was freely calling RAUW methods whenever a global definition was updated in the temporary merged output file. However, replaceAllUsesWith may or may not destroy constants that use this global. If the linked definition has a type mismatch regarding the new def and the old def, the materializer would bitcast the old type to the new type and the elements of the llvm.used array, which already uses bitcast to i8*, would end up with elements cascading two bitcasts. RAUW would then indirectly call the constantfolder to update the constant to the new ref, which would, instead of updating the constant, destroy it to be able to create a new constant that folds the two bitcasts into one. The problem is that ValueMapper works with pointers to the same constants that may be getting destroyed by RAUW. Obviously, RAUW can update references in the Module to do not use the old destroyed constant, but it can't update ValueMapper's internal pointers to these constants, which are now invalid. The approach here is to move the task of RAUWing old definitions outside of the materializer. Test Plan: Added LIT test case, tested clang self-hosting with D56928 and verified it works Reviewed By: efriedma Differential Revision: https://reviews.llvm.org/D59552 llvm-svn: 356597 |
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| .. | ||
| CMakeLists.txt | ||
| IRMover.cpp | ||
| LLVMBuild.txt | ||
| LinkDiagnosticInfo.h | ||
| LinkModules.cpp | ||