> there aren't many complaints that other compilers using LLVM are slow.
Practically every VM that tried to use LLVM as a JIT gave up as it was too slow. WebKit eventually abandoned their LLVM backend and wrote their own, B3.
JITs are of course a specialized use case, but there are also known issues with compilation speed in LLVM. For example, LLVM is single-threaded, so compiling a single very large compilation module can be much slower than it needs to be - and this is an issue hit by Rust due to how crates are designed. But you are also very correct that Rust is generating overly-complex LLVM IR for LLVM to compile, which is another problem there.
Also worth noting that while once clang beat gcc in compilation speed, as clang's optimizations have caught up to gcc the difference has vanished, and on many benchmarks today gcc compiles more quickly.
> Practically every VM that tried to use LLVM as a JIT gave up as it was too slow.
And it doesn't even seem to work effectively as a target for JIT. It can do the machine code emitting part of a JIT well, but that wasn't really the problem and it doesn't seem to work well at the real problem of optimising code for a high-level language. You need to optimise yourself, by writing basically your own compiler pipeline, before emitting LLVM.
See for example the Rubinius implementation of Ruby.
Practically every VM that tried to use LLVM as a JIT gave up as it was too slow. WebKit eventually abandoned their LLVM backend and wrote their own, B3.
JITs are of course a specialized use case, but there are also known issues with compilation speed in LLVM. For example, LLVM is single-threaded, so compiling a single very large compilation module can be much slower than it needs to be - and this is an issue hit by Rust due to how crates are designed. But you are also very correct that Rust is generating overly-complex LLVM IR for LLVM to compile, which is another problem there.
Also worth noting that while once clang beat gcc in compilation speed, as clang's optimizations have caught up to gcc the difference has vanished, and on many benchmarks today gcc compiles more quickly.