Simon Peyton Jones pushed to branch wip/T23109a at Glasgow Haskell Compiler / GHC

Commits:

• ce5db8f6
  by Simon Peyton Jones at 2025-04-24T11:39:08+01:00

  Tiny change to saves_alloc
  
  Float lambdas (and PAPs) out of lambdas to top level
  This improves spectral/cse
  
  But the old comment was
          -- is_con_app: don't float PAPs to the top; they may well end
          -- up getting eta-expanded and re-inlined
          -- E.g.   f = \x -> (++) ys
          -- If we float, then eta-expand we get
          --      lvl = (++) ys
          --      f = \x \zs -> lvl zs
          -- and now we'll inline lvl.  Silly.
  
  Let's see what CI says
  

1 changed file:

• compiler/GHC/Core/Opt/SetLevels.hs

Changes:

     escapes_value_lam = dest_lvl `ltMajLvl` (le_ctxt_lvl env)

     -- See Note [Floating to the top]

-    is_con_app = isSaturatedConApp expr  -- True of literal strings too

+--    is_con_app = isSaturatedConApp expr  -- True of literal strings too

     saves_alloc = isTopLvl dest_lvl

                && (escapes_value_lam || floatConsts env)

                   -- Always float allocation out of a value lambda

                   --    if it gets to top level

-               && (not strict_ctxt || is_con_app || is_bot_lam)

+               && (not strict_ctxt || is_hnf || is_bot_lam)

         -- is_con_app: don't float PAPs to the top; they may well end

         -- up getting eta-expanded and re-inlined

         -- E.g.   f = \x -> (++) ys