On Fri, Jan 25, 2013 at 8:02 PM, Richard Biener
<richard.guent...@gmail.com> wrote:
> On Fri, Jan 25, 2013 at 3:05 PM, Sudakshina Das
> <sudakshina1...@gmail.com> wrote:
>> On Fri, Jan 25, 2013 at 9:46 AM, Sudakshina Das
>> <sudakshina1...@gmail.com> wrote:
>>>
>>> On Thu, Jan 24, 2013 at 5:15 PM, Richard Biener
>>> <richard.guent...@gmail.com> wrote:
>>> >
>>> > On Thu, Jan 24, 2013 at 7:06 AM, Sudakshina Das
>>> > <sudakshina1...@gmail.com> wrote:
>>> > > Dear all,
>>> > >
>>> > > I am currently updating a pass that was made for gcc-4.6.*, so that it
>>> > > works for gcc.4.7.2.
>>> > >
>>> > > In the pass for gcc-4.6.*, a code fragment from tree-ssa-structalias.c
>>> > > was picked up and used.
>>> > > Given below is the fragment taken form create_function_info_for () .
>>> > > This fragment was used to create variable information for the function
>>> > > and it was picked up to perform a similar operation in the added pass
>>> > > as well.
>>> > >
>>> > > But in gcc-4.7.2 some changes are introduced in the fragment. The code
>>> > > given below shows the changes that have been introduced in
>>> > > create_function_info_for () of tree-ssa-structalias.c in gcc-4.7.2
>>> > > along with the original code in the comments.
>>> > >
>>> > > /* Add one representative for all further args. */
>>> > > if (is_varargs)
>>> > > {
>>> > > varinfo_t argvi;
>>> > > const char *newname;
>>> > > char *tempname;
>>> > > tree decl;
>>> > >
>>> > > asprintf (&tempname, "%s.varargs", name);
>>> > > newname = ggc_strdup (tempname);
>>> > > free (tempname);
>>> > >
>>> > > /* We need sth that can be pointed to for va_start. */
>>> > >
>>> > > /**************** CHANGED CODE in GCC-4.7.2 ***************/
>>> > > decl = build_fake_var_decl (ptr_type_node);
>>> > >
>>> > > /************ ORIGINAL CODE in GCC-4.6.2 *******************
>>> > > /* decl = create_tmp_var_raw (ptr_type_node, name);
>>> > > get_var_ann (decl);
>>> > > */
>>> > >
>>> > > argvi = new_var_info (decl, newname);
>>> > > argvi->offset = fi_parm_base + num_args;
>>> > > argvi->size = ~0;
>>> > > argvi->is_full_var = true;
>>> > > argvi->is_heap_var = true;
>>> > > argvi->fullsize = vi->fullsize;
>>> > > gcc_assert (prev_vi->offset < argvi->offset);
>>> > > prev_vi->next = argvi;
>>> > > prev_vi = argvi;
>>> > > }
>>> > >
>>> > > return vi;
>>> > >
>>> > >
>>> > > So I made the same changes in the pass where this fragment was used.
>>> > > But after making the changes the pass is now giving an "internal
>>> > > compiler error" and a "segmentation fault" at runtime.
>>> > >
>>> > > After debugging I could narrow it down to the function
>>> > > build_fake_var_decl() and to be specific at the memory allocation
>>> > > statement highlighted below.
>>> > >
>>> > >
>>> > > tree
>>> > > build_fake_var_decl (tree type)
>>> > > {
>>> > > /************************ My debugging showed that the control came
>>> > > here *********************/
>>> > > tree decl = (tree) XOBNEW (&fake_var_decl_obstack, struct
>>> > > tree_var_decl);
>>> > > /************************ But did not come here
>>> > > **********************************************************/
>>> > > memset (decl, 0, sizeof (struct tree_var_decl));
>>> > > TREE_SET_CODE (decl, VAR_DECL);
>>> > > TREE_TYPE (decl) = type;
>>> > > DECL_UID (decl) = allocate_decl_uid ();
>>> > > SET_DECL_PT_UID (decl, -1);
>>> > > layout_decl (decl, 0);
>>> > > return decl;
>>> > > }
>>> > >
>>> > > The builf_fake_var_decl() function is a gcc function defined in
>>> > > tree-ssa-structalias.c. To be able to use it in my pass, I removed the
>>> > > keyword static in its definition.
>>> > >
>>> > > I cannot figure out what can possibly cause this error in the XOBNEW
>>> > > function.
>>> > >
>>> > > Please help!!!
>>> >
>>> > Don't use build_fake_var_decl, use what 4.6 did, create_tmp_var_raw.
>>> >
>>> > Richard.
>>> >
>>> >
>>>
>>> But 4.6 used get_var_ann() also along with create_tmp_var_raw() which
>>> has been removed from 4.7.
>>
>>
>> I would like to clarify my above statement by saying that 4.6 used 2
>> functions [ie. create_tmp_var_raw() and get_var_ann()] whereas 4.7
>> used only one function [build_fake_var_decl()] for the same purpose.
>> Now in 4.7 get_var_ann() is unavailable. So is it safe to use only
>> create_tmp_var_raw(). In other words, was get_var_ann() a redundant
>> function in 4.6?
>
> The whole function is very special for tree-ssa-structalias.c. I have no idea
> what your pass does, but unless it closely resembles tree-ssa-structalias.c
> and shares its internal data structures you shouldn't blindly copy over what
> tree-ssa-structalias.c does (well, at least not without understanding what you
> are doing).
>
> What do you think you are doing with the copy of that code?
>
> Richard.
>
>>
>>>
The copy of the above code is from function create_function_info_for()
in tree-ssa-structalias.c which is used to create variables for a
function in its tree. In the pass there is a similar function named
cs_create_func_info_for() used for the same purpose, except it does
not create variables for all the cases. In other words some portions
from the original function is omitted. Also the data structure
varinfo_t is modified a bit to suite the pass and renamed as
csvarinfo_t. I have copied the function from my pass below,
highlighting the difference from the original function using comments.
/* Creation function node for DECL, using NAME, and return the index
of the variable we've created for the function. */
static csvarinfo_t
cs_create_func_info_for (tree decl, const char *name)
{
csvarinfo_t vi, prev_vi;
tree arg;
unsigned int i;
bool is_varargs = false;
unsigned int num_args = count_num_arguments (decl, &is_varargs);
/* Create the variable info. */
vi = cs_new_var_info (decl, name);
vi->offset = 0;
vi->size = 1;
vi->fullsize = num_args + 1;
vi->may_have_pointers = false;
if (is_varargs)
vi->fullsize = ~0;
cs_insert_vi_for_tree (vi->decl, vi);
prev_vi = vi
/************ There were portions in original code with the
following comments: **************
1. Create a variable for things the function clobbers and one
for things the function uses.
2. And one for the static chain.
3. Create a variable for the return var.
*******************************************************************************************************/
/* Set up variables for each argument. */
arg = DECL_ARGUMENTS (decl);
for (i = 1; i < num_args + 1; i++) {
csvarinfo_t argvi;
tree argdecl = decl;
if (arg)
argdecl = arg;
argvi = cs_new_var_info (argdecl, alias_get_name (argdecl));
argvi->offset = i;
argvi->size = 1;
argvi->is_full_var = true;
argvi->fullsize = vi->fullsize;
if (arg)
argvi->may_have_pointers = true;
gcc_assert (prev_vi->offset < argvi->offset);
prev_vi->next = argvi;
prev_vi = argvi;
if (arg) {
cs_insert_vi_for_tree (arg, argvi);
arg = DECL_CHAIN (arg);
}
}
/* Add one representative for all further args. */
if (is_varargs) {
csvarinfo_t argvi;
const char *newname;
char *tempname;
tree decl;
asprintf (&tempname, "%s.varargs", name);
newname = ggc_strdup (tempname);
free (tempname);
/* We need sth that can be pointed to for va_start. */
decl = create_tmp_var_raw (ptr_type_node, name);
get_var_ann (decl);
argvi = cs_new_var_info (decl, newname);
argvi->offset = 1 + num_args;
argvi->size = ~0;
argvi->is_full_var = true;
argvi->is_heap_var = true;
argvi->fullsize = vi->fullsize;
gcc_assert (prev_vi->offset < argvi->offset);
prev_vi->next = argvi;
prev_vi = argvi;
}
return vi;
}
Sudakshina Das
