On Mon, Oct 09, 2006 at 10:33:47AM -0400, roconnor@theorem.ca wrote:
On Mon, 9 Oct 2006, Simon Peyton-Jones wrote:
Turns out that 'shift' is just too big to be inlined. (It's only called once, but you have exported it too.)
You can see GHC's inlining decisions by saying -ddump-inlinings.
To make GHC keener to inline, use an INLINE pragma, or increase the inlining size threshold e.g. -funfolding-threshold=12
Okay, when I force inlining for shift, (and I even need to do it for shiftR!) then the code is inlined in C. However this isn't the behaviour I want. Ideally the inlining should only happen when/because the second argument of shift is constant and the system knows that it can evaluate the case analysis away and that makes the function small.
Am I being too naive on what to expect from my complier or is this reasonable?
It might be possible, but it sounds tricky. I guess it would have to go something like "try inlining this, run the simplifier, see if it got small enough, if not back out", which could waste a lot of work if it fails in lots of cases.
PS, is there a way to mark an imported instance of a class function (Data.Bits.shift for Data.Word.Word32) to be inlined?
You can use GHC.Exts.inline in 6.6: http://www.haskell.org/ghc/dist/current/docs/users_guide/special-ids.html#id... but note the restriction in the final paragraph. Thanks Ian