[Bug c/43904] New: Wrong code with -foptimize-sibling-calls and memcpy on x86_64

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

On x86_64, gcc 4.5.0, this code generates bad assembly:

--- C code ---
typedef unsigned long size_t;
void *memcpy(void *dest, const void *src, size_t n);

void
buggy_init(void *ptr, size_t size)
{
  const char *str = "Hello world!";
  memcpy(ptr, &str, size);
}
--------------

Compiled with gcc -O -foptimize-sibling-calls, the generated assembly looks
like this:

--------------
buggy_init:
        movq    %rsi, %rdx
        movq    $.LC0, -16(%rsp)
        leaq    -16(%rsp), %rsi
        jmp     memcpy
--------------

which passes rsp-16 as memcpy's second argument.  memcpy overwrites this part
of the stack, and copies the wrong value, which causes a crash later.


-- 
           Summary: Wrong code with -foptimize-sibling-calls and memcpy on
                    x86_64
           Product: gcc
           Version: 4.5.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: tavianator at gmail dot com
 GCC build triplet: x86_64-unknown-linux-gnu
  GCC host triplet: x86_64-unknown-linux-gnu
GCC target triplet: x86_64-unknown-linux-gnu


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=43904