[Bug c/28887] New: generates invalid code for -O1 -fprefetch-loop-arrays

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

Alleged bug goes away if ommitting -fprefetch-loop-arrays.

Trying to compile binutils-2.17.50.0.3 (gdb-6.4 also exhibits this alleged bug)
with gcc-trunk from 20060828, i get errors of the form:

make[3]: Entering directory
`/root/src/buildroot/build_x86_64/binutils-2.17.50.0.3-target/libiberty'
if [ x"" != x ] && [ ! -d pic ]; then \
          mkdir pic; \
        else true; fi
touch stamp-picdir
if [ x"" != x ]; then \
          x86_64-linux-uclibc-gcc -c -DHAVE_CONFIG_H -O2 -fPIC
-ftree-loop-optimize -ftree-vectorize -ftree-vect-loop-version -funroll-loops
-freorder-blocks -freorder-blocks-and-partition -mtune=nocona -march=nocona
-msse -msse2 -msse3 -mfpmath=sse -fprefetch-loop-arrays -funswitch-loops
-fbranch-target-load-optimize -ftree-loop-linear -ftree-loop-im
-ftree-loop-ivcanon -fgcse-after-reload -fvariable-expansion-in-unroller
-fivopts  -I.
-I/root/src/buildroot/toolchain_build_x86_64/binutils-2.17.50.0.3/libiberty/../include
 -W -Wall -pedantic -Wwrite-strings -Wstrict-prototypes -Wc++-compat 
/root/src/buildroot/toolchain_build_x86_64/binutils-2.17.50.0.3/libiberty/regex.c
-o pic/regex.o; \
        else true; fi
x86_64-linux-uclibc-gcc -c -DHAVE_CONFIG_H -O2 -fPIC -ftree-loop-optimize
-ftree-vectorize -ftree-vect-loop-version -funroll-loops -freorder-blocks
-freorder-blocks-and-partition -mtune=nocona -march=nocona -msse -msse2 -msse3
-mfpmath=sse -fprefetch-loop-arrays -funswitch-loops
-fbranch-target-load-optimize -ftree-loop-linear -ftree-loop-im
-ftree-loop-ivcanon -fgcse-after-reload -fvariable-expansion-in-unroller
-fivopts  -I.
-I/root/src/buildroot/toolchain_build_x86_64/binutils-2.17.50.0.3/libiberty/../include
 -W -Wall -pedantic -Wwrite-strings -Wstrict-prototypes -Wc++-compat
/root/src/buildroot/toolchain_build_x86_64/binutils-2.17.50.0.3/libiberty/regex.c
-o regex.o
/root/src/buildroot/toolchain_build_x86_64/binutils-2.17.50.0.3/libiberty/regex.c:
In function 'byte_re_match_2_internal':
/root/src/buildroot/toolchain_build_x86_64/binutils-2.17.50.0.3/libiberty/regex.c:5549:
error: cannot take address of bit-field 'match_null_string_p'
/root/src/buildroot/toolchain_build_x86_64/binutils-2.17.50.0.3/libiberty/regex.c:5549:
error: cannot take address of bit-field 'match_null_string_p'
/root/src/buildroot/toolchain_build_x86_64/binutils-2.17.50.0.3/libiberty/regex.c:5549:
error: cannot take address of bit-field 'match_null_string_p'
make[3]: *** [regex.o] Error 1
make[3]: Leaving directory
`/root/src/buildroot/build_x86_64/binutils-2.17.50.0.3-target/libiberty'
make[2]: *** [all-libiberty] Error 2
make[2]: Leaving directory
`/root/src/buildroot/build_x86_64/binutils-2.17.50.0.3-target'
make[1]: *** [all] Error 2
make[1]: Leaving directory
`/root/src/buildroot/build_x86_64/binutils-2.17.50.0.3-target'
make: ***
[/root/src/buildroot/build_x86_64/binutils-2.17.50.0.3-target/binutils/objdump]
Error 2



Reduced testcase:
# cat c.i                                                                      
    typedef long unsigned int size_t;                                          
    struct re_pattern_buffer                                                   
    {
  size_t re_nsub;
};
typedef enum
{
  start_memory,
} re_opcode_t;
typedef union
{
  struct
  {
    unsigned matched_something:1;
  } bits;
} byte_register_info_type;
byte_re_match_2_internal (struct re_pattern_buffer *bufp)
{
  int mcnt;
  size_t num_regs = bufp->re_nsub + 1;
  byte_register_info_type *reg_info;
  for (mcnt = 1; (unsigned) mcnt < num_regs; mcnt++)
    {
      ((reg_info[mcnt]).bits.matched_something) = 0;
    }
}


x86_64-linux-uclibc-gcc -O1 -fprefetch-loop-arrays c.i -c -o regex.o -v 
Using built-in specs.
Target: x86_64-linux-uclibc
Configured with: /root/src/buildroot/toolchain_build_x86_64/gcc-4.2.0/configure
--prefix=/root/src/buildroot/build_x86_64/staging_dir
--build=x86_64-pc-linux-gnu --host=x86_64-pc-linux-gnu
--target=x86_64-linux-uclibc --enable-languages=c,c++ --enable-shared
--disable-__cxa_atexit --enable-target-optspace --with-gnu-ld --disable-nls
--enable-threads --disable-multilib
Thread model: posix
gcc version 4.2.0 20060828 (experimental)

/root/src/buildroot/build_x86_64/staging_dir/libexec/gcc/x86_64-linux-uclibc/4.2.0/cc1
-fpreprocessed c.i -quiet -dumpbase c.i -mtune=generic -auxbase-strip regex.o
-O1 -version -fprefetch-loop-arrays -o /tmp/ccwSTKtj.s
GNU C version 4.2.0 20060828 (experimental) (x86_64-linux-uclibc)
        compiled by GNU C version 4.1.2 20060613 (prerelease) (Debian 4.1.1-5).
GGC heuristics: --param ggc-min-expand=30 --param ggc-min-heapsize=4096
Compiler executable checksum: 7dbca204c110dec99203ab2b693d4e2f
c.i: In function 'byte_re_match_2_internal':
c.i:18: error: cannot take address of bit-field 'matched_something'
c.i:18: error: cannot take address of bit-field 'matched_something'
c.i:18: error: cannot take address of bit-field 'matched_something'


-- 
           Summary: generates invalid code for -O1 -fprefetch-loop-arrays
           Product: gcc
           Version: 4.2.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: aldot at gcc dot gnu dot org
 GCC build triplet: x86_64-linux-gnu
  GCC host triplet: x86_64-linux-gnu
GCC target triplet: x86_64-linux-gnu


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=28887