Closed requested to merge hsyl20/ghc:hsyl20/perf/strlen into master
SDoc string literals created for example with `text "xyz"` are converted into `PtrString` (`Addr#` + size in bytes) with a rewrite rule to avoid allocating a String. Before this patch, the size in bytes was still computed at runtime. For every literal, we obtained the following pseudo STG: x :: Addr# x = "xzy"# s :: PtrString s = \u  case ffi:strlen [x realWorld#] of (# _, sz #) -> PtrString [x sz] But since GHC 9.0, we can use `cstringLength#` instead to get: x :: Addr# x = "xzy"# s :: PtrString s = PtrString! [x 3#] Literals become statically known constructor applications. Allocations seem to decrease a little in perf tests (between -0.1% and -0.7% on CI).