[Bug c/49642] New: constant part of a macro not optimized away as expected due to splitter

[marcus at jet dot franken.de]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=49642

           Summary: constant part of a macro not optimized away as
                    expected due to splitter
           Product: gcc
           Version: tree-ssa
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c
        AssignedTo: unassigned@gcc.gnu.org
        ReportedBy: marcus@jet.franken.de


my Linux kernel builds on gcc 4.6 pcc64 fail with:

ERROR: ".____ilog2_NaN" [drivers/infiniband/hw/ehca/ib_ehca.ko] undefined!

This comes from include/linux/log2.h which uses a large macro with
builtin_constant_p() to optimize constant ilog2 calls.

I have reduced it to the attached testcase.

$ gcc -m64 -O2 -fno-inline-functions-called-once -c ehca_mrmw.i ; objdump -dr
ehca_mrmw.o |grep NaN
                        1a8: R_PPC64_REL24      ____ilog2_NaN
                        1cc: R_PPC64_REL24      ____ilog2_NaN
$ 

It should not report NaN as that is in a if
(__builtin_constant_p(shca->hca_cap_mr_pgsize)) expression.