llvm-project

1f38d49e - ValueMapper: Delete unused initializers of replaced appending globals.

ValueMapper: Delete unused initializers of replaced appending globals. A full LTO link time performance and memory regression was introduced by #137081 in cases where the modules contain large quantities of llvm.used globals. This was unnoticed because it was not expected that this would be a typical case, but this is exactly what coverage collection does, and when this feature is enabled together with full LTO we end up with quadratic memory consumption (from the unused constants) and quadratic complexity in the function Verifier::visitGlobalValue (which visits all the unused constants in the use list of each global value). This is a targeted fix that avoids reintroducing the quadratic complexity from before #137081, by having ValueMapper delete the old initializer of an appending global if it is unused, instead of visiting every global in the context after every link. The repro-cfi-64 reproducer from #167037 before and after this change: ``` Elapsed time Max RSS (KB) Before 12:05.11 52537184 After 3:27.68 7520696 ``` Fixes #167037. Reviewers: nikic, teresajohnson Reviewed By: teresajohnson Pull Request: https://github.com/llvm/llvm-project/pull/167629