[Bug regression/20372] New: Reversed branch-on-count loop (DoLoop)

["pthaugen at us dot ibm dot com" <gcc-bugzilla at gcc dot gnu dot org>]

Noticed a regression relative to 4.0 on the code generated for one of the loops
in zaxpy.f of the SPEC wupwise benchark. The loop is transformed into a
branch-on-count loop, but the target on the branch is the loop exit (return in
this case) instead of the loop start. The 'bct' is immediately followed by an
unconditional branch to the loop start.

Here's a snippet of the generated code (this is for the first loop in the
source, even though it appears as the second loop in the generated code). 'L18'
is the epilog block.

.L15:

	addi %r0,%r7,-1	 # D.511, ix,
        ...
        ...
	stfdx %f11,%r11,%r31	 # (* zy), SR.12
	bdz .L18
	b .L15

-- 
           Summary: Reversed branch-on-count loop (DoLoop)
           Product: gcc
           Version: 4.1.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P2
         Component: regression
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: pthaugen at us dot ibm dot com
                CC: gcc-bugs at gcc dot gnu dot org
 GCC build triplet: powerpc*-*-*
  GCC host triplet: powerpc*-*-*
GCC target triplet: powerpc*-*-*


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=20372