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Date: Mon, 08 Mar 2004 02:13:00 -0000
From: "anton at samba dot org" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Message-ID: <20040308021331.14473.anton@samba.org>
Reply-To: gcc-bugzilla@gcc.gnu.org
Subject: [Bug c/14473] New: Failure to use count register
X-Bugzilla-Reason: CC
X-SW-Source: 2004-03/txt/msg00926.txt.bz2
List-Id: <gcc-bugs.sourceware.org>

I found this in ppc32 3.3.3 (Debian), it also appears in 3.4.0 20040215.

If the loop count is large enough, it wont use the count register in the second
loop. eg:

#if 1
#define LOOPS 100000
#else
#define LOOPS 10
#endif
                                                                                
int main()
{
        unsigned long i;
                                                                                
        i = LOOPS;
        while (i--) {
                asm volatile("":::"memory");
        }
                                                                                
        i = LOOPS;
        while (i--) {
                asm volatile("":::"memory");
        }
}

produces the following code:

        lis 0,0x1
        ori 0,0,34464
        mtctr 0
.L13:
        bdnz .L13
        lis 0,0x1
        ori 0,0,34464
.L12:
        addic. 0,0,-1
        bne+ 0,.L12
        blr

If you reduce COUNT it will use the count register for both loops as expected

-- 
           Summary: Failure to use count register
           Product: gcc
           Version: 3.4.0
            Status: UNCONFIRMED
          Severity: enhancement
          Priority: P2
         Component: c
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: anton at samba dot org
                CC: gcc-bugs at gcc dot gnu dot org
GCC target triplet: powerpc-unknown-linux-gnu


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=14473