Optimized Cmm containing useless blocks

[Johan Tibell]

This was my mess-up (see previous email). Sorry for the noise.


On Mon, Mar 10, 2014 at 9:30 AM, Simon Peyton Jones
<simonpj at microsoft.com>wrote:

> That doesn't look right.  Are you using -O?
>
> If so, perhaps open a ticket explaining how to reproduce, and including
> the results of -ddump-cmm.
>
> (Don't use module Main, because it's irrelevant to this question, and
> generate a certain amount of auxiliary goop.)
>
> Thanks
>
> SImon
>
> | -----Original Message-----
> | From: ghc-devs [mailto:ghc-devs-bounces at haskell.org] On Behalf Of Karel
> | Gardas
> | Sent: 09 March 2014 21:40
> | To: Johan Tibell
> | Cc: ghc-devs at haskell.org
> | Subject: Re: Optimized Cmm containing useless blocks
> |
> |
> | If I may add to this, then I'm curious why there is something like:
> |
> |   I64[BaseReg + 784] = I64[BaseReg + 784];
> |
> | presented in Cmm optimized code. Since I don't know Cmm enough I've
> | verified if the semantics is really C like by looking into generated asm
> | and indeed it looks so. This costs 5 isns of sparc asm btw.
> |
> | If someone is interested to duplicate this, then use sparc or ppc 32 bit
> | registerised target and Haskell code:
> |
> | module Main where
> |
> | import Data.Int
> |
> | main = print ( ( 2 ^ 6 ) :: Int64 )
> |
> | Karel
> |
> | On 03/ 8/14 09:21 AM, Johan Tibell wrote:
> | > While looking at some generated Cmm I saw things like this
> | >
> | > c1Cm:
> | >      goto c1Cq;
> | > c1Cq:
> | >
> | > i.e. useless basic blocks that haven't been optimized away. Is this to
> | > be expected?
> | >
> | > -- Johan
> | >
> | >
> | >
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> |
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