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Date: Thu, 14 Oct 2004 19:48:00 -0000
From: "berndtrog at yahoo dot com" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Message-ID: <20041014194850.18002.berndtrog@yahoo.com>
Reply-To: gcc-bugzilla@gcc.gnu.org
Subject: [Bug target/18002] New:  [3.4/4.0 Regression] 'while' loop performace regression on avr target
X-Bugzilla-Reason: CC
X-SW-Source: 2004-10/txt/msg01989.txt.bz2
List-Id: <gcc-bugs.sourceware.org>

Hello,
when I compile(avr-gcc -c -Os -mmcu=atmega8 test.c) this code:

int main (void)
{
 while (((*(volatile unsigned char *)((0x0B) + 0x20)) & (1<<5)) == 0) {
  ;
 }

 return (0);
}

with gcc 3.3.1 I get this asm loop:

   8:   5d 9b           sbis    0x0b, 5 ; 11
   a:   fe cf           rjmp    .-4             ; 0x8


with gcc 3.4.2 or 4.0.0 I get this:

   8:   41 e0           ldi     r20, 0x01       ; 1
   a:   50 e0           ldi     r21, 0x00       ; 0 
   c:   8b b1           in      r24, 0x0b       ; 11
   e:   99 27           eor     r25, r25
  10:   25 e0           ldi     r18, 0x05       ; 5
  12:   96 95           lsr     r25
  14:   87 95           ror     r24
  16:   2a 95           dec     r18
  18:   e1 f7           brne    .-8             ; 0x12
  1a:   84 27           eor     r24, r20
  1c:   95 27           eor     r25, r21
  1e:   9c 01           movw    r18, r24
  20:   21 70           andi    r18, 0x01       ; 1
  22:   30 70           andi    r19, 0x00       ; 0
  24:   80 fd           sbrc    r24, 0
  26:   f2 cf           rjmp    .-28            ; 0xc

-- 
           Summary:  [3.4/4.0 Regression] 'while' loop performace regression
                    on avr target
           Product: gcc
           Version: 3.4.3
            Status: UNCONFIRMED
          Severity: normal
          Priority: P2
         Component: target
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: berndtrog at yahoo dot com
                CC: gcc-bugs at gcc dot gnu dot org
  GCC host triplet: i686-pc-linux-gnu
GCC target triplet: avr-elf


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=18002