Rust Performance Is Getting Hurt On LLVM 10 With Noticeably Longer Build Times

While our benchmarks of Clang 10.0 have generally been favorable or at least no big regressions compared to LLVM/Clang 9.0, it seems the same can't be said for Rust when shifting their compiler base to LLVM 10.0.

Rust developer Josh Stone of Red Hat raised the alarms on Friday that LLVM 10.0 through their Git master is seeing not only longer build times and much greater number of instructions when compiling the same code-base.

Stone and other developers have found LLVM 10.0 to lead to slower Rust compile times in the area of 7~8% compared to using LLVM 9.0. In a mailing list post he found from LLVM 9.x to 10.x was around 5.3% more instructions being generated on a test code-base and another 4.8% hit when it came from LLVM 10.x to LLVM 11 Git master.

Given the sizable hit and multiple Rust developers seeing this same behavior out of LLVM 10, hopefully it won't be long before it's addressed.