[Bug rtl-optimization/27625] New: invalid loop transformation.

[ramana dot radhakrishnan at codito dot com]

Number of loop iterations is calculated wrongly in the following bit of code. 


extern char __dp0 ;
extern const long __reloc_table ;
extern const int __reloc_num ;




void
foo (void)
{
  register char *dp = 0;
  int cpu;
  const long *reloc_ptr;
  unsigned int num_relocs = 0;
  dp = &__dp0;



  for (reloc_ptr = &__reloc_table, num_relocs = (unsigned
int)&__reloc_num;num_relocs; reloc_ptr++,num_relocs--)
      *(long *)(dp + *reloc_ptr) += (long)dp;



}

Code generated for :  
./xgcc -B`pwd` -S -O3 -mregnames ~/tmp/fails.i

is 
foo:
        lis %r9,__dp0@ha
        lis %r11,__reloc_table@ha
        la %r8,__dp0@l(%r9)
        lis %r9,__reloc_num@ha
        la %r9,__reloc_num@l(%r9)
        la %r11,__reloc_table@l(%r11)
        mtctr %r9
        mr %r10,%r8
.L4:
        lwz %r9,0(%r11)
        addi %r11,%r11,4
        lwzx %r0,%r9,%r10
        add %r0,%r0,%r8
        stwx %r0,%r9,%r10
        bdnz .L4
        blr

This bug seems to appear after the ivopts backport. .08.jump has a check for
the loop counter to be 0 which 09.cse removes as trivially dead. I would expect
there to be a check for the loop counter to be zero before the body of the
loop.


-- 
           Summary: invalid loop transformation.
           Product: gcc
           Version: 4.1.1
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: rtl-optimization
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: ramana dot radhakrishnan at codito dot com
 GCC build triplet: i686-pc-linux
  GCC host triplet: i686-pc-linux
GCC target triplet: powerpc-elf


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=27625