On 4/5/07, Simon Peyton-Jones
| 6. The inliner is a bit too greedy. Removing the slow-path code from | singleton doesn't help because popSingleton is only used once; but | if I explicitly {-# NOINLINE popSingleton #-}, the code for | singleton itself becomes much smaller, and inlinable (15% perf | gain). Plus the new singleton doesn't allocate memory, so I can | use even MORE realWorld#s.
That's a hard one! Inlining functions that are called just once is a huge win usually. I don't know how to spot what you did in an automated way.
I believe gcc uses __builtin_expect() (http://gcc.gnu.org/onlinedocs/gcc-4.1.2/gcc/Other-Builtins.html#index-g_t_00...) to let the programmer say that a branch is unlikely to be taken (i.e. is the slow path). If such a thing were available in GHC, Stefan wouldn't even have needed to pull the slow path code from singleton; the compiler could have done it for him. -- Namasté, Jeffrey Yasskin