1) LLVM does not use pull-request and code-review isn't mandatory for the main contributors.
2) until a few months ago LLVM didn't even have any testing system before the code is pushed to the master branch: folks just push code directly after (hopefully) building/testing locally.
The real root cause is that no one cares enough to really invest deeply into this. There is also not a clear community guideline on what is acceptable (can I regress O2 compile time by 1% if I improve "some" benchmarks by 1%? Who defines the benchmarks suite? etc.)
To your last paragraph, there's no real technical leadership in LLVM because none of the original contributors are good project stewards, e.g. Lattner is just chasing the next shiny.
There are occasionally some feeble attempts to improve that, but of course people are wary of the potential politics.
1) LLVM does not use pull-request and code-review isn't mandatory for the main contributors.
2) until a few months ago LLVM didn't even have any testing system before the code is pushed to the master branch: folks just push code directly after (hopefully) building/testing locally.
The real root cause is that no one cares enough to really invest deeply into this. There is also not a clear community guideline on what is acceptable (can I regress O2 compile time by 1% if I improve "some" benchmarks by 1%? Who defines the benchmarks suite? etc.)