[Top][All Lists]

[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

Re: [avr-gcc-list] AVR Libc int32_t and uint32_t typedefs areincorrect

From: Weddington, Eric
Subject: Re: [avr-gcc-list] AVR Libc int32_t and uint32_t typedefs areincorrect
Date: Thu, 12 Jan 2012 13:09:07 -0700

> -----Original Message-----
> From: Georg-Johann Lay
> Sent: Thursday, January 12, 2012 10:55 AM
> To: Weddington, Eric
> Cc: Joerg Wunsch; address@hidden
> Subject: Re: [avr-gcc-list] AVR Libc int32_t and uint32_t typedefs
> areincorrect
> sizeof(double) = 4 also breaks the standard...

Hence, one of the reasons to have correct doubles added to the backend.


> As said above, it's not only about optimization as such but also about
> promotion rules that cannot be optimized away in all situation. So if
> are
> on a target were each byte counts I guess developers will very much
> appreciate
>  -mint8, be it blessed by standard or not...


One of the biggest complaints from users has to do with promotion rules
being overly enforced during a set of operations, and then the result is
stored in some variable, typically of a smaller size (typically an
unsigned 8-bit variable), thereby truncating the value. In these
particular cases the enforcement of the promotion rules has no bearing
on the final outcome of the operations, but it does cause an unnecessary
increase in code size.

In these cases, is there a way to optimize the code such that these
promotion rules aren't strictly followed *when it does not affect the
outcome of the operation*?

The problem that I have with -mint8 is:
- it doesn't follow the standard
- it breaks avr-libc (or rather, avr-libc isn't adapted to it)
- people use it, because the backend hasn't been taught how to do the
right thing.

The thing is, is if the AVR backend knew how to optimize away these
superfluous promotions, then I really don't think that -mint8 would ever
really be needed. Why should a user have to specify a switch to get the
compiler to do the right thing?

How can we get to this point?

reply via email to

[Prev in Thread] Current Thread [Next in Thread]