[Bug c/21626] New: Do not create very big empty structure to initialise stack

["etienne_lorrain at yahoo dot fr" <gcc-bugzilla at gcc dot gnu dot org>]

etienne@cygne:~/projet/gujin$ cat tmp.c
typedef struct {
        enum { INIT = 0 } mode;
        unsigned          very_big_array[4096];
        struct short_struct { int a,b,c; } str[5];
        } z_stream;

struct short_struct fct (unsigned val) {
        z_stream gzlib = { .mode = INIT }; /* everything is null */
        return gzlib.str[val];
}
etienne@cygne:~/projet/gujin$ gcc -v
Reading specs from /usr/lib/gcc-lib/i486-linux/3.3.6/specs
Configured with: ../src/configure -v --enable-
languages=c,c++,java,f77,pascal,objc,ada,treelang --prefix=/usr --
mandir=/usr/share/man --infodir=/usr/share/info --with-gxx-include-
dir=/usr/include/c++/3.3 --enable-shared --enable-__cxa_atexit --with-system-
zlib --enable-nls --without-included-gettext --enable-clocale=gnu --enable-
debug --enable-java-gc=boehm --enable-java-awt=xlib --enable-objc-gc i486-linux
Thread model: posix
gcc version 3.3.6 (Debian 1:3.3.6-5)
etienne@cygne:~/projet/gujin$ gcc -Os -c tmp.c -o tmp.o
etienne@cygne:~/projet/gujin$ size tmp.o
   text    data     bss     dec     hex filename
     71       0       0      71      47 tmp.o
etienne@cygne:~/projet/gujin$ ../toolchain-4.0/bin/gcc -v
Using built-in specs.
Target: i686-pc-linux-gnu
Configured with: ../configure --prefix=/home/etienne/projet/toolchain --enable-
languages=c
Thread model: posix
gcc version 4.0.0
etienne@cygne:~/projet/gujin$ ../toolchain-4.0/bin/gcc  -Os -c tmp.c -o tmp.o
etienne@cygne:~/projet/gujin$ size tmp.o
   text    data     bss     dec     hex filename
  16509       0       0   16509    407d tmp.o
etienne@cygne:~/projet/gujin$ ../toolchain-4.0/bin/gcc  -Os -S tmp.c -o tmp.s
etienne@cygne:~/projet/gujin$ cat tmp.s
        .file   "tmp.c"
        .section        .rodata
        .align 32
        .type   C.0.1145, @object
        .size   C.0.1145, 16448
C.0.1145:
        .zero   16448
        .text
.globl fct
        .type   fct, @function
fct:
        pushl   %ebp
        movl    %esp, %ebp
        pushl   %ebx
        subl    $16448, %esp
        pushl   $16448
        movl    8(%ebp), %ebx
        pushl   $C.0.1145
        leal    -16452(%ebp), %eax
        pushl   %eax
        call    memcpy
        imull   $12, 12(%ebp), %eax
        pushl   $12
        leal    -64(%eax,%ebp), %eax
        pushl   %eax
        pushl   %ebx
        call    memcpy
        movl    %ebx, %eax
        movl    -4(%ebp), %ebx
        leave
        ret     $4
        .size   fct, .-fct
        .ident  "GCC: (GNU) 4.0.0"
        .section        .note.GNU-stack,"",@progbits
etienne@cygne:~/projet/gujin$

-- 
           Summary: Do not create very big empty structure to initialise
                    stack
           Product: gcc
           Version: 4.0.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P2
         Component: c
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: etienne_lorrain at yahoo dot fr
                CC: gcc-bugs at gcc dot gnu dot org
 GCC build triplet: i686-pc-linux-gnu
  GCC host triplet: i686-pc-linux-gnu
GCC target triplet: i686-pc-linux-gnu


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=21626