Re: Cmm code of `id` function referring to `breakpoint`?

That's because of the CSE (common subexpression elimination) pass. Here's an example: module Lib where foo :: a -> a foo x = x bar :: a -> a bar x = x Build with -O -ddump-stg and you'll see something like: Lib.foo :: forall a. a -> a [GblId, Arity=1, Caf=NoCafRefs, Str=, Unf=OtherCon []] = [] \r [x_s1bB] x_s1bB; Lib.bar :: forall a. a -> a [GblId, Arity=1, Caf=NoCafRefs, Str=, Unf=OtherCon []] = [] \r [eta_B1] Lib.foo eta_B1; Without -O or with -fno-cse this does not happen. This is quite unexpected, but maybe not harmful. Ömer Shao, Cheng , 6 Şub 2019 Çar, 08:35 tarihinde şunu yazdı:

Hi devs,

I just found that the Cmm code of `GHC.Base.id` refers to `breakpoint` in the same module, however, in the Haskell source of `GHC.Base`, the definition of `id` and `breakpoint` are totally unrelated:

``` id :: a -> a id x = x

breakpoint :: a -> a breakpoint r = r ```

And here's the pretty-printed Cmm code:

``` base_GHCziBase_id_entry() // [R2] { [] } {offset chwa: // global R2 = R2; call base_GHCziBase_breakpoint_entry(R2) args: 8, res: 0, upd: 8; } base_GHCziBase_breakpoint_entry() // [R2] { [] } {offset chvW: // global R1 = R2; call stg_ap_0_fast(R1) args: 8, res: 0, upd: 8; } ```

This looks suspicious. I'm curious if this is intended behavior of ghc.

Regards, Shao Cheng _______________________________________________ ghc-devs mailing list ghc-devs@haskell.org http://mail.haskell.org/cgi-bin/mailman/listinfo/ghc-devs