[Bug tree-optimization/57830] New: fold_builtin_memory_op expands memcpy without regard to -Os

[amylaar at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=57830

            Bug ID: 57830
           Summary: fold_builtin_memory_op expands memcpy without regard
                    to -Os
           Product: gcc
           Version: 4.8.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: tree-optimization
          Assignee: unassigned at gcc dot gnu.org
          Reporter: amylaar at gcc dot gnu.org

I see that the memcpy call at the end of gcc.dg/strlenopt-10.c:fn2.c
is expanded for the avr target (which has "#define BIGGEST_ALIGNMENT 8",
 i.e. the "dest_align < TYPE_ALIGN (desttype)" test at builtins.c:8923
 succeeds) irrespective of -Os or the size of the copied object.
So this generates 20 loads, 20 stores, ancillary address arithmetic,
and sky-high register pressure with 18 call-saved registers saved in
the prologue and restored in the epilogue.
Just leaving the call to memcpy alone would generate shorter code.