[Git][ghc/ghc][wip/T21470] Wibble

[Simon Peyton Jones (@simonpj)]

Simon Peyton Jones pushed to branch wip/T21470 at Glasgow Haskell Compiler / GHC


Commits:
f7a033ac by Simon Peyton Jones at 2022-09-28T13:54:57+01:00
Wibble

Fix Specialiser for dead binders

(todo: merge with previous commit)

- - - - -


1 changed file:

- compiler/GHC/Core/Opt/Specialise.hs


Changes:

=====================================
compiler/GHC/Core/Opt/Specialise.hs
=====================================
@@ -2458,6 +2458,7 @@ specHeader env (bndr : bndrs) (UnspecType : args)
 -- a wildcard binder to match the dictionary (See Note [Specialising Calls] for
 -- the nitty-gritty), as a LHS rule and unfolding details.
 specHeader env (bndr : bndrs) (SpecDict d : args)
+  | not (isDeadBinder bndr)
   = do { (env1, bndr') <- newDictBndr env bndr -- See Note [Zap occ info in rule binders]
        ; let (env2, dx_bind, spec_dict) = bindAuxiliaryDict env1 bndr bndr' d
        ; (_, env3, leftover_bndrs, rule_bs, rule_es, bs', dx, spec_args)
@@ -2474,15 +2475,18 @@ specHeader env (bndr : bndrs) (SpecDict d : args)
               )
        }
 
--- Finally, we have the unspecialised argument 'i'. We need to produce
--- a binder, LHS and RHS argument for the RULE, and a binder for the
--- specialised body.
+-- Finally, we don't want to specialise on this argument 'i':
+--   - It's an UnSpecArg, or
+--   - It's a dead dictionary
+-- We need to produce a binder, LHS and RHS argument for the RULE, and
+-- a binder for the specialised body.
 --
 -- NB: Calls to 'specHeader' will trim off any trailing 'UnspecArg's, which is
 -- why 'i' doesn't appear in our RULE above. But we have no guarantee that
 -- there aren't 'UnspecArg's which come /before/ all of the dictionaries, so
 -- this case must be here.
-specHeader env (bndr : bndrs) (UnspecArg : args)
+specHeader env (bndr : bndrs) (_ : args)
+    -- The "_" can be UnSpecArg, or SpecDict where the bndr is dead
   = do { -- see Note [Zap occ info in rule binders]
          let (env', bndr') = substBndr env (zapIdOccInfo bndr)
        ; (useful, env'', leftover_bndrs, rule_bs, rule_es, bs', dx, spec_args)



View it on GitLab: https://gitlab.haskell.org/ghc/ghc/-/commit/f7a033ac30301c942594c59e8ad5f03a3e2ecd3e

-- 
View it on GitLab: https://gitlab.haskell.org/ghc/ghc/-/commit/f7a033ac30301c942594c59e8ad5f03a3e2ecd3e
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