[Bug tree-optimization/72785] New: [7 Regression] kernel build error since r236831

["trippels at gcc dot gnu.org" <gcc-bugzilla at gcc dot gnu dot org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=72785

            Bug ID: 72785
           Summary: [7 Regression] kernel build error since r236831
           Product: gcc
           Version: 7.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: tree-optimization
          Assignee: unassigned at gcc dot gnu.org
          Reporter: trippels at gcc dot gnu.org
                CC: law at gcc dot gnu.org
  Target Milestone: ---

Since r236831 I get:
...
  LD      init/built-in.o
kernel/built-in.o:memremap.c:function update_wall_time: error: undefined
reference to '____ilog2_NaN'
make: *** [Makefile:955: vmlinux] Error 1


markus@x4 linux % cat timekeeping.i
int a, b;
extern int ____ilog2_NaN(void);
void by(void) {
  int c = 1;
  b = a ?: c;
  __builtin_constant_p(b) ? b ? ____ilog2_NaN() : 0 : 0;
}

markus@x4 linux % icc -O2 -c timekeeping.i -S -o - | grep ____ilog2_NaN
markus@x4 linux % clang -O2 -c timekeeping.i -S -o - | grep ____ilog2_NaN
markus@x4 linux % gcc-6 -O2 -c timekeeping.i -S -o - | grep ____ilog2_NaN
markus@x4 linux % gcc-trunk -O2 -c timekeeping.i -S -o - | grep ____ilog2_NaN
        jmp     ____ilog2_NaN