Get rid of the release flag (#3160)

* Get rid of the `release` flag

Problem: `kore.cabal` contains `release` flag which is off by default.
When it's disabled, code is compiled without `specialise` optimization.
The flag is a bit weird: it's not clear why one may want to disable
only this specific optimization. It indeed makes compilation faster
and runtime slower, but if you want that, you may simply disable all
optimizations.

Solution:
1. We have tested whether enabling more optimizations (`-O2`) can
improve performance compared to the default configuration.
Our results indicate that the difference is negligible.
2. Since default configuration produces optimal performance, we don't
need an extra flag to determine whether we want to compile code faster
or to have faster runtime. Both `stack` and `cabal` have an easy way
to enable/disable optimizations.
3. For the reasons above, we are removing this flag from `kore.cabal`.
Now default build process should produce optimal executable (with all
`-O1` optimizations enabled which should be sufficient).
4. We are also updating the README file to mention how one can build
code faster (and get slower runtime).

Resolves #3135

* Materialize Nix expressions

Co-authored-by: github-actions <github-actions@github.com>
Co-authored-by: ana-pantilie <45069775+ana-pantilie@users.noreply.github.com>

Author: 3 people

README.md

@@ -43,6 +43,8 @@ cabal build kore
 ```
 
 If using `cabal`, version 3.0 or later is recommended.
+You may pass `--fast` to `stack build` or `-O0` to `cabal build` in order to
+disable compiler optimizations and make build faster at the cost of slower runtime.
 
 Using [make]:
 

kore/kore.cabal

@@ -19,11 +19,6 @@ source-repository head
   type: git
   location: https://github.com/runtimeverification/haskell-backend
 
-flag release
-  description: Build a faster runtime, at the expense of a slower build.
-  manual: True
-  default: False
-
 flag threaded
   description: Use the threaded runtime. Recommended to disable for profiling.
   manual: True
@@ -587,8 +582,6 @@ library
   hs-source-dirs:
     src
     app/share
-  if !flag(release)
-    ghc-options: -fno-specialise
 
 executable kore-exec
   import: haskell

nix/kore-ghc8107.nix.d/kore.nix

@@ -8,7 +8,7 @@
   , config
   , ... }:
   {
-    flags = { release = false; threaded = true; };
+    flags = { threaded = true; };
     package = {
       specVersion = "2.2";
       identifier = { name = "kore"; version = "0.60.0.0"; };