[Bug target/70630] New: [6 regression] sparc bootstrap failure: sparc.c:4919:6: error: suggest explicit braces to avoid ambiguous 'else'

["mikpelinux at gmail dot com" <gcc-bugzilla at gcc dot gnu dot org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=70630

            Bug ID: 70630
           Summary: [6 regression] sparc bootstrap failure:
                    sparc.c:4919:6: error: suggest explicit braces to
                    avoid ambiguous 'else'
           Product: gcc
           Version: 6.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: target
          Assignee: unassigned at gcc dot gnu.org
          Reporter: mikpelinux at gmail dot com
  Target Milestone: ---

Attempting to bootstrap gcc-6-20160410 on sparc-linux fails with:

/mnt/scratch/gcc-6-20160410/gcc/config/sparc/sparc.c: In function 'long long
int sparc_compute_frame_size(long long int, int)':
/mnt/scratch/gcc-6-20160410/gcc/config/sparc/sparc.c:4919:6: error: suggest
explicit braces to avoid ambiguous 'else' [-Werror=parentheses]
   if (TARGET_ARCH64)
      ^
cc1plus: all warnings being treated as errors
make[3]: *** [sparc.o] Error 1
make[3]: *** Waiting for unfinished jobs....
make[3]: Leaving directory `/mnt/scratch/objdir6/gcc'
make[2]: *** [all-stage2-gcc] Error 2
make[2]: Leaving directory `/mnt/scratch/objdir6'
make[1]: *** [stage2-bubble] Error 2
make[1]: Leaving directory `/mnt/scratch/objdir6'
make: *** [bootstrap] Error 2

What it's complaining about is:

if (TARGET_ARCH64)
    for (i = 0; i < 8; i++)
      if (save_global_or_fp_reg_p (i, 0))
        n_global_fp_regs += 2;
  else
    for (i = 0; i < 8; i += 2)
      if (save_global_or_fp_reg_p (i, 0) || save_global_or_fp_reg_p (i + 1, 0))
        n_global_fp_regs += 2;

which seems highly dubious to me (the else should probably go with the outer
not the inner if).
gcc-6-20160403 bootstrapped fine.  Strangely enough, it contains the exact same
code here, so I don't know why gcc didn't complain before.

Configured as:
/mnt/scratch/gcc-6-20160410/configure --prefix=/mnt/scratch/install6
--with-gmp=/home/mikpe/pkgs/linux-sparc64/gmp-6.1.0
--with-mpfr=/home/mikpe/pkgs/linux-sparc64/mpfr-3.1.4
--with-mpc=/home/mikpe/pkgs/linux-sparc64/mpc-1.0.3 --enable-multilib
--disable-plugin --disable-lto --disable-nls --enable-threads=posix
--enable-checking=release --disable-libmudflap --enable-languages=c,ada,c++
--build=sparc-unknown-linux --target=sparc-unknown-linux --with-cpu=ultrasparc
--enable-targets=all