[Haskell-cafe] GHC optimisations
stefanor at cox.net
Sun Aug 19 15:14:20 EDT 2007
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.)
> 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
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