bugAVR C Runtime Library - Bugs: bug #40003, Integer type promotion leads to...

 
 

bug #40003: Integer type promotion leads to inefficent code in wdt.h

Submitted by:  Joey Morin <joeymorin>
Submitted on:  Wed 11 Sep 2013 03:15:33 PM UTC  
 
Category: LibrarySeverity: 3 - Normal
Priority: 5 - NormalItem Group: Header files
Status: NonePercent Complete: 0%
Assigned to: NoneOpen/Closed: Open
Release: 1.8.0Fixed Release: None

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Wed 11 Sep 2013 03:23:28 PM UTC, comment #1:

Forgot to add an example:

In the case of wdt_enable(WDTO_15MS), the assembled output for targets such as the ATtiny85:
ldi r18, 0x08
ldi r24, 0x18
ldi r25, 0x00
in r0, 0x3f
cli
wdr
out 0x21, r24
out 0x3f, r0
out 0x21, r18

With the patch in place:
ldi r25, 0x08
ldi r24, 0x18
in r0, 0x3f
cli
wdr
out 0x21, r24
out 0x3f, r0
out 0x21, r25

Joey Morin <joeymorin>
Wed 11 Sep 2013 03:15:33 PM UTC, original submission:

Operands constructed in this fashion:
"r" (_BV(_WD_CHANGE_BIT) | _BV(WDE)),

...result in the use of two registers, one of which is loaded with 0x00 and never used.

Seems as though integer type promotion is responsible. A fix is as simple as casting to an 8-bit type:
"r" ((uint8_t)(_BV(_WD_CHANGE_BIT) | _BV(WDE))),

Indeed, most _asm_ statements in wdt.h are already taking this approach, but a couple are not.

Attached is a patch to resolve the issue.

I'm aware this is a minor issue, but as it is easy to resolve, I hope it will be accepted :)

Cheers,
JJ

Joey Morin <joeymorin>

 

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Attached Files
file #29105:  wdt.h.patch added by joeymorin (802B - text/x-patch)

 

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    Date Changed By Updated Field Previous Value => Replaced By
    Wed 11 Sep 2013 03:15:33 PM UTCjoeymorinAttached File-=>Added wdt.h.patch, #29105

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