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Support whole program devirtualization #68262
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A-LLVMArea: Code generation parts specific to LLVM. Both correctness bugs and optimization-related issues.Area: Code generation parts specific to LLVM. Both correctness bugs and optimization-related issues.A-trait-systemArea: Trait systemArea: Trait systemC-enhancementCategory: An issue proposing an enhancement or a PR with one.Category: An issue proposing an enhancement or a PR with one.C-optimizationCategory: An issue highlighting optimization opportunities or PRs implementing suchCategory: An issue highlighting optimization opportunities or PRs implementing suchT-compilerRelevant to the compiler team, which will review and decide on the PR/issue.Relevant to the compiler team, which will review and decide on the PR/issue.
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A-LLVMArea: Code generation parts specific to LLVM. Both correctness bugs and optimization-related issues.Area: Code generation parts specific to LLVM. Both correctness bugs and optimization-related issues.A-trait-systemArea: Trait systemArea: Trait systemC-enhancementCategory: An issue proposing an enhancement or a PR with one.Category: An issue proposing an enhancement or a PR with one.C-optimizationCategory: An issue highlighting optimization opportunities or PRs implementing suchCategory: An issue highlighting optimization opportunities or PRs implementing suchT-compilerRelevant to the compiler team, which will review and decide on the PR/issue.Relevant to the compiler team, which will review and decide on the PR/issue.
When doing LTO, LLVM supports a devirtualization pass that converts some indirect calls to static, inlineable calls. This can unlock a lot of optimizations when dynamic dispatch is used frequently in a program.
I don't know how hard this would be to support in Rust. Clang has a flag
-fwhole-program-vtableswhich we would need to emulate. From there it seems like it might "just work". I'm opening this issue to start collecting more information.I also found #11915 which mentions this, but not sure if any of the information there is still accurate.