Re: optimization/10620: for(i=25000;i;i--) {} generates wrong assembly source in avr-gcc with -O2

[Nagy Endre <gumo@lucifer.kgt.bme.hu>]

The following reply was made to PR optimization/10620; it has been noted by GNATS.

From: Nagy Endre <gumo@lucifer.kgt.bme.hu>
To: Dara Hazeghi <dhazeghi@yahoo.com>
Cc: gcc-gnats@gcc.gnu.org
Subject: Re: optimization/10620: for(i=25000;i;i--) {} generates wrong assembly
 source in avr-gcc with -O2
Date: Fri, 9 May 2003 10:53:41 +0200 (CEST)

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 > could the submitter of this bug please include a full testcase that
 > demonstrates the bug (ie something that will compile without
 > additions). I cannot replicate the assembly in question using 3.3
 > branch and:
 > void main(){int i;for(i=25000;i;i--){}}
 
 Yes, of course.
 The simplest case is:
 
 =================================
 int main(void) {
     unsigned int i,j;
     for(j=500;j;j--) {
         for(i=25000;i;i--) {}
     }
     return 0;
 }
 =================================
 
 So that i is allocated in narrow registers. The resulting asm code
 varies depending on the initial value of i, if it is less than 32768.
 
 The inner loop will be:
 
 .L10:
         subi r18,lo8(-(-25))
         sbci r19,hi8(-(-25))
         brne .L10
 
 Where -25 varies depending on i.
 
 The compiler command:
 avr-gcc -g -Wall -O2 -mmcu=at90s8515 -S -o test2.S test2.c
 (see attachments)
 
 I've used the gcc-3.3 prerelease included in WinAVR:
 http://prdownloads.sourceforge.net/winavr/WinAVR-20030424-bin-install.exe?download
 
 Excuse me for being inaccurate.
 
 Thanks,
 Gumo
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