[Bug bootstrap/51872] New: [4.7 Regression] Shrink-wrapping with -mminimal-toc causes bootstrap failure

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

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=51872

             Bug #: 51872
           Summary: [4.7 Regression] Shrink-wrapping with -mminimal-toc
                    causes bootstrap failure
    Classification: Unclassified
           Product: gcc
           Version: 4.7.0
            Status: UNCONFIRMED
          Keywords: wrong-code
          Severity: normal
          Priority: P3
         Component: bootstrap
        AssignedTo: unassigned@gcc.gnu.org
        ReportedBy: jakub@gcc.gnu.org
                CC: amodra@gcc.gnu.org, bernds@gcc.gnu.org,
                    dje@gcc.gnu.org
            Target: powerpc64-linux


powerpc64-linux doesn't bootstrap with -mminimal-toc in CFLAGS/CXXFLAGS, due to
shrink-wrapping, as crtbegin.o is miscompiled.

Short testcase for -m64 -O2 -mminimal-toc:
static void *var[] __attribute__ ((used, section("jlist"),
aligned(sizeof(void*)))) = { };
extern void bar (void *) __attribute__ ((weak));

static void __attribute__((noinline, noclone))
baz (void)
{
  asm volatile ("" : : : "memory");
}

void
foo (void)
{
  if (var[0])
    {
      void (*register_classes) (void *) = bar;
      __asm ("" : "+r" (register_classes));
      if (register_classes)
       register_classes (var);
    }
  baz ();
}

The problem is that the TOC register (r30) isn't added to the
set_up_by_prologue
regset (flag_pic is 0, TARGET_MINIMAL_TOC is true and the prologue computes the
TOC_REGISTER).  I wonder if we don't need a target hook that will add
additional registers to set_up_by_prologue regset.