Mikolaj Konarski pushed to branch wip/T28016-inline-boring-work-free at Glasgow Haskell Compiler / GHC

Commits:

• 06d164e6
  by Mikolaj Konarski at 2026-10-26T22:11:40+01:00

  Experiment: inline 0-ary bindings in boring contexts only if work-free
  
  Not for merging. tryUnfolding inlines an INLINE binding
  with no arguments in a boring context only if its template is work-free,
  so that no work is duplicated. The test is in tryUnfolding and
  not in mkInlineUnfoldingWithArity, because simplStableUnfolding only
  ever turns ug_boring_ok on, while a template can become work-free when
  it is simplified.
  
  This is for #28016, where an INLINE [1] constant inlined after the first
  float-out is computed at every call.
  
  Assisted-by: Claude Opus 5.5
  

1 changed file:

• compiler/GHC/Core/Opt/Simplify/Inline.hs

Changes:

      UnfNever -> traceInline logger opts id str (text "UnfNever") Nothing

      UnfWhen { ug_arity = uf_arity, ug_unsat_ok = unsat_ok, ug_boring_ok = boring_ok }

-        | enough_args && (boring_ok || some_benefit || unfoldingVeryAggressive opts)

+        | enough_args && ((boring_ok && (uf_arity > 0 || is_wf))

+                          || some_benefit || unfoldingVeryAggressive opts)

                 -- See Note [INLINE for small functions] (3)

+                -- EXPERIMENT (#28016): a binding with no arguments is

+                -- inlined in a boring context only if that duplicates no work.

         -> traceInline logger opts id str (mk_doc some_benefit empty True) (Just unf_template)

         | otherwise

         -> traceInline logger opts id str (mk_doc some_benefit empty False) Nothing