Re: PR/46898 CVS commit: src/sys/arch/arm/include

[Matt Thomas <matt%3am-software.com@localhost>]

On Sep 4, 2012, at 11:40 PM, David Laight wrote:

> The following reply was made to PR port-arm/46898; it has been noted by GNATS.
> 
> From: David Laight <david%l8s.co.uk@localhost>
> To: gnats-bugs%NetBSD.org@localhost
> Cc: 
> Subject: Re: PR/46898 CVS commit: src/sys/arch/arm/include
> Date: Wed, 5 Sep 2012 07:29:40 +0100
> 
> On Wed, Sep 05, 2012 at 01:05:03AM +0000, Matt Thomas wrote:
>> Disable arm32 __asm for _byte_swap_u16_variable since gcc4.5 produces
>> decent code for it.  Fixes PR/46898.
> 
> Presumably there was also something badly wrong with it as well?
> That is likely to be replicated and will crop up elsewhere.

the uint16_t was causing the compiler to assume the upper 16-bits
didn't matter which int fact they did.  So unexpected got mixed
into the result resulting in a bad value.  Hence the adding of a
uint32_t temporary to cause the compiler to do the right thing.  But
after examining the code that generated again the naive C code, i
found the the normal optimizer did a decent enough job that the asm
wasn't needed.