[Bug rtl-optimization/19580] New: [3.4/4.0 Regression] poor register allocation

[belyshev at depni dot sinp dot msu dot ru]

------------------------------------------------------------------------------
int r[6];

void f (int n)
{
  while (-- n)
    {
      r [0] += r [5];
      r [1] += r [0];
      r [2] += r [1];
      r [3] += r [2];
      r [4] += r [3];
      r [5] += r [4];
    }
}
------------------------------------------------------------------------------

On i386 with -O2 -fomit-frame-pointer we get:

.L4:
	movl	20(%esp), %ebp
	movl	8(%esp), %eax
	movl	16(%esp), %ebx
	incl	24(%esp)
	addl	%edi, %ebp
	leal	(%ebp,%eax), %esi
	movl	12(%esp), %eax
	movl	%ebp, 20(%esp)
	leal	(%esi,%ebx), %ecx
	movl	4(%esp), %ebx
	movl	%esi, 8(%esp)
	leal	(%ecx,%eax), %edx
	movl	%ecx, 16(%esp)
	leal	(%edx,%ebx), %eax
	movl	24(%esp), %ebx
	cmpl	%ebx, 28(%esp)
	movl	%edx, 12(%esp)
	leal	(%eax,%edi), %edi
	movl	%eax, 4(%esp)
	movl	%edi, (%esp)
	jne	.L4

workaround: -fno-gcse

-- 
           Summary: [3.4/4.0 Regression] poor register allocation
           Product: gcc
           Version: 4.0.0
            Status: UNCONFIRMED
          Keywords: missed-optimization, ra
          Severity: normal
          Priority: P2
         Component: rtl-optimization
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: belyshev at depni dot sinp dot msu dot ru
                CC: gcc-bugs at gcc dot gnu dot org


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=19580