search for: simpllfycfg

Hi, I was looking at Rust programs which are poorly optimized by LLVM, and one occasional factor is that LLVM allows for long-lived `br i1 false` instructions. The problem is that if a propagation pass discovers the condition of a branch, the branch itself will not be eliminated until a SimpllfyCfg pass is reached, of which there are few in the pipeline. One example is https://github.com/rust-lang/rust/issues/44041 - the branch conditions are found by loop unrolling, but the `br i1 false` instruction leaks to codegen. Another example is https://github.com/rust-lang/rust/issues/45466. In th...

...s which are poorly optimized by LLVM, and >> one occasional factor is that LLVM allows for long-lived `br i1 false` >> instructions. >> >> The problem is that if a propagation pass discovers the condition of a >> branch, the branch itself will not be eliminated until a SimpllfyCfg >> pass is reached, of which there are few in the pipeline. >> >> One example is https://github.com/rust-lang/rust/issues/44041 - the >> branch conditions are found by loop unrolling, but the `br i1 false` >> instruction leaks to codegen. >> >> Another exam...