GHC does some constant folding, but little by way of strength reduction, or using shifts instead of multiplication. It's pretty easy to add more: it's all done in a single module. Look at primOpRules in the module PrelRules. Patches welcome! But please also supply test-suite tests that check the correctness of the rules. Simon | -----Original Message----- | From: haskell-cafe-bounces@haskell.org [mailto:haskell-cafe- | bounces@haskell.org] On Behalf Of Stefan O'Rear | Sent: 19 August 2007 20:14 | To: Andrew Coppin | Cc: haskell-cafe@haskell.org | Subject: Re: [Haskell-cafe] GHC optimisations | | 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 | 12...) | | Stefan