[Bug tree-optimization/20231] New: missed optimization of loop IV modulus

astrange at ithinksw dot com gcc-bugzilla@gcc.gnu.org
Sun Feb 27 17:23:00 GMT 2005


[zebes:~] astrange% /usr/local/bin/gcc -v
Using built-in specs.
Target: powerpc-apple-darwin7.7.0
Configured with: ../configure --enable-threads=posix --with-threads=posix
Thread model: posix
gcc version 4.1.0 20050226 (experimental)

Command line: /usr/local/bin/gcc -O3 -mcpu=7400 -mtune=7400 -fdump-tree-optimized -c 
mod_loop.c

Code:
void mod_loop(unsigned char *array, int len, unsigned char repeat)
{
        unsigned char i;
        for (i = 0; i < len; i++) array[i] = i%repeat;
}

void mod_loop2(unsigned char *array, int len, unsigned char repeat)
{
        unsigned char i,i2=0;
        for (i = 0; i < len; i++) {array[i] = i2++; if (i2 == repeat) i2 = 0;}
}

Although the two functions are equivalent and mod_loop2 is better (avoiding an expensive divide), GCC 
doesn't transform the first into the second.

-- 
           Summary: missed optimization of loop IV modulus
           Product: gcc
           Version: 4.1.0
            Status: UNCONFIRMED
          Severity: enhancement
          Priority: P2
         Component: tree-optimization
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: astrange at ithinksw dot com
                CC: gcc-bugs at gcc dot gnu dot org
 GCC build triplet: powerpc-apple-darwin7.7.0
  GCC host triplet: powerpc-apple-darwin7.7.0
GCC target triplet: powerpc-apple-darwin7.7.0


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=20231



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