#12603: INLINE and manually inlining produce different code -------------------------------------+------------------------------------- Reporter: bgamari | Owner: bgamari Type: task | Status: new Priority: normal | Milestone: 8.2.1 Component: Compiler | Version: 8.0.1 Resolution: | Keywords: Operating System: Unknown/Multiple | Architecture: | Unknown/Multiple Type of failure: None/Unknown | Test Case: Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Wiki Page: | -------------------------------------+------------------------------------- Comment (by simonpj):
When I INLINE the function, I get 3,421,310,504 bytes allocated in the heap (runtime 5.32s, but there is much wider measurement error margin that with allocation), when I NOINLINE it, I get 2,932,616,792 (5.17s) and when I leave it alone (I guess GHC inlines it somehow differently), I get 4,309,699,560 (5.57s).
This isn't necessarily surprising. Consider {{{ module M( f, g, h ) where f x = BIG g x = (f x, True) h x = ...(g x)... }}} Without an INLINE on `f`, GHC won't inline it (because it's big). But `g` is small, so it'll get inlined into `h`, and good things may happen because `h` can see the pair and `True`. But if you add an `INLINE` pragma to `f`, then `g` becomes big, so GHC won't inline it. These effects can be large, and are very hard to predict. GHC makes no guarantees, I'm afraid. It's a bit more puzzling that you say your big function is called only once; so it might come down to a race as to whether `f` gets auto-inlined before `g` does. That's a bit mysterious I admit. However a difference between 2.9G and 4.3G is very large, and it would be great to get more insight into why. I use `-ticky` to investigate this kind of thing. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/12603#comment:8 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler