Stefan O'Rear wrote:
On Sun, Aug 19, 2007 at 12:53:07PM +0100, Andrew Coppin wrote:
Does GHC do stuff like converting (2*) into (shift 1) or converting x + x into 2*x?
For a good time, compile some code which uses even or odd :: Int -> Bool using -O2 -fasm -ddump-asm... The compiler *really* shouldn't be using 'idivl'.
(If you use -fvia-C -optc-O2, the C compiler will notice the operations and optimize it itself. This is one of the very few areas where -fvia-C is still better.)
The way I heard it is that compilation via C is "always better", though they "plan" to change that some day. I don't know how true that is...
If I do x * sin 12, is GHC likely to compute sin 12 at compile-time?
Also try -ddump-simpl-stats and -ddump-simpl-iterations if you want to know *why*. (The extremely obscure 'full laziness' transformation performed by GHC has a fundamental effect on the compilation of x * sin 12...)
Hmm, OK.