On Thu, Jan 29, 2015 at 4:12 PM, Richard Biener
<richard.guent...@gmail.com> wrote:
> On Thu, Jan 29, 2015 at 4:05 PM, Richard Biener
> <richard.guent...@gmail.com> wrote:
>> On Thu, Jan 29, 2015 at 3:14 PM, Alan Modra <amo...@gmail.com> wrote:
>>> Here is the completed patch. Bootstrapped and regression tested
>>> powerpc64-linux. Is this OK to apply? If not now, then when gcc is
>>> in stage1 again?
>>
>> It's ok to apply as it is a wrong-code fix. It would also be ok to backport
>> if needed.
>>
>> Did you check whether other targets have function descriptors (seem
>> to remember the Itanic here at least)?
>>
>> The middle-end changes are ok, I defer to David for the rs6000 changes.
>>
>> I am also curious of the .029t.ealias dump from
>>
>> gcc -O -fdump-tree-ealias-details-alias
>>
>> on (the nonsensical)
>>
>> void x(void);
>> int y;
>> int main()
>> {
>> void *p = x;
>> p+=y;
>> return *(int *)p;
>> }
>
> Just checked myself with the host gcc 4.8 on gcc111. It looks like
> function descriptors are not exposed in GIMPLE:
>
> void * p;
> sizetype y.1;
> int y.0;
> int _6;
>
> <bb 2>:
> y.0_3 = y;
> y.1_4 = (sizetype) y.0_3;
> # PT =
> p_5 = x + y.1_4;
> _6 = MEM[(int *)p_5];
> return _6;
>
> thus when the function address-taking happens in the same function
> as the call there will be no aliasing as it points to nothing (points-to
> doesn't track function decls). And if it's flowing in from the outside
> you get "all globals".
>
> This means that you still will be able to create a testcase that is
> miscompiled with exposing the address-taking to points-to analysis.
> And it means that indirect calls to const functions are severely
> pessimized (not that it matters?) as they effectively become pure calls.
Btw, with gimple_call_fntype available I was hoping to eventually get
rid of the required conversion between ptr and function ptr:
/* We need to take special care recursing to pointed-to types. */
else if (POINTER_TYPE_P (inner_type)
&& POINTER_TYPE_P (outer_type))
{
/* Do not lose casts to function pointer types. */
if ((TREE_CODE (TREE_TYPE (outer_type)) == FUNCTION_TYPE
|| TREE_CODE (TREE_TYPE (outer_type)) == METHOD_TYPE)
&& !(TREE_CODE (TREE_TYPE (inner_type)) == FUNCTION_TYPE
|| TREE_CODE (TREE_TYPE (inner_type)) == METHOD_TYPE))
return false;
/* We do not care for const qualification of the pointed-to types
as const qualification has no semantic value to the middle-end. */
/* Otherwise pointers/references are equivalent. */
return true;
which means call in the testcase in the PR would become
(&opd) (dl_hwcap);
just as I mentioned in my initial review (you can try removing the above
check to see that).
I wonder if we have targets where a conversion between type T and
a function pointer generates actual code.
Richard.
> Richard.
>
>> Thanks,
>> Richard.
>>
>>> gcc/
>>> PR target/64703
>>> * target.def (has_function_descriptors): New hook.
>>> * doc/tm.texi.in: Add TARGET_HAS_FUNCTION_DESCRIPTORS.
>>> * doc/tc.texi: Regenerate.
>>> * tree-ssa-alias.c (pt_solution_includes_base): New function,
>>> extracted from..
>>> (ref_maybe_used_by_call_p_1): ..here. Handle potential memory
>>> reference by indirect calls on targets using function descriptors.
>>> * config/rs6000/rs6000.c (TARGET_HAS_FUNCTION_DESCRIPTORS): Define.
>>> (rs6000_has_function_descriptors): New function.
>>> gcc/testsuite/
>>> * gcc.target/powerpc/pr64703.c: New.
>>>
>>> Index: gcc/target.def
>>> ===================================================================
>>> --- gcc/target.def (revision 220025)
>>> +++ gcc/target.def (working copy)
>>> @@ -2821,6 +2821,15 @@ The default value of this hook is based on target'
>>> bool, (void),
>>> default_has_ifunc_p)
>>>
>>> +/* True if target defines the address of a function as that of a
>>> + function descriptor. */
>>> +DEFHOOK
>>> +(has_function_descriptors,
>>> + "True if target has function descriptors and defines the address\n\
>>> +of a function as that of a function descriptor.",
>>> + bool, (void),
>>> + hook_bool_void_false)
>>> +
>>> /* True if it is OK to do sibling call optimization for the specified
>>> call expression EXP. DECL will be the called function, or NULL if
>>> this is an indirect call. */
>>> Index: gcc/doc/tm.texi.in
>>> ===================================================================
>>> --- gcc/doc/tm.texi.in (revision 220025)
>>> +++ gcc/doc/tm.texi.in (working copy)
>>> @@ -8175,6 +8175,8 @@ and the associated definitions of those functions.
>>>
>>> @hook TARGET_HAS_IFUNC_P
>>>
>>> +@hook TARGET_HAS_FUNCTION_DESCRIPTORS
>>> +
>>> @hook TARGET_ATOMIC_ALIGN_FOR_MODE
>>>
>>> @hook TARGET_ATOMIC_ASSIGN_EXPAND_FENV
>>> Index: gcc/doc/tm.texi
>>> ===================================================================
>>> --- gcc/doc/tm.texi (revision 220025)
>>> +++ gcc/doc/tm.texi (working copy)
>>> @@ -11510,6 +11510,11 @@ The support includes the assembler, linker and dyn
>>> The default value of this hook is based on target's libc.
>>> @end deftypefn
>>>
>>> +@deftypefn {Target Hook} bool TARGET_HAS_FUNCTION_DESCRIPTORS (void)
>>> +True if target has function descriptors and defines the address
>>> +of a function as that of a function descriptor.
>>> +@end deftypefn
>>> +
>>> @deftypefn {Target Hook} {unsigned int} TARGET_ATOMIC_ALIGN_FOR_MODE
>>> (machine_mode @var{mode})
>>> If defined, this function returns an appropriate alignment in bits for an
>>> atomic object of machine_mode @var{mode}. If 0 is returned then the
>>> default alignment for the specified mode is used.
>>> @end deftypefn
>>> Index: gcc/tree-ssa-alias.c
>>> ===================================================================
>>> --- gcc/tree-ssa-alias.c (revision 220025)
>>> +++ gcc/tree-ssa-alias.c (working copy)
>>> @@ -1532,6 +1532,25 @@ refs_output_dependent_p (tree store1, tree store2)
>>> return refs_may_alias_p_1 (&r1, &r2, false);
>>> }
>>>
>>> +/* Return true if the points-to solution *PT includes the object BASE. */
>>> +
>>> +static bool
>>> +pt_solution_includes_base (struct pt_solution *pt, tree base)
>>> +{
>>> + if (DECL_P (base))
>>> + return pt_solution_includes (pt, base);
>>> +
>>> + if ((TREE_CODE (base) == MEM_REF
>>> + || TREE_CODE (base) == TARGET_MEM_REF)
>>> + && TREE_CODE (TREE_OPERAND (base, 0)) == SSA_NAME)
>>> + {
>>> + struct ptr_info_def *pi = SSA_NAME_PTR_INFO (TREE_OPERAND (base, 0));
>>> + if (pi)
>>> + return pt_solutions_intersect (pt, &pi->pt);
>>> + }
>>> + return true;
>>> +}
>>> +
>>> /* If the call CALL may use the memory reference REF return true,
>>> otherwise return false. */
>>>
>>> @@ -1542,6 +1561,22 @@ ref_maybe_used_by_call_p_1 (gcall *call, ao_ref *r
>>> unsigned i;
>>> int flags = gimple_call_flags (call);
>>>
>>> + callee = gimple_call_fn (call);
>>> + if (callee && TREE_CODE (callee) == SSA_NAME
>>> + && targetm.has_function_descriptors ())
>>> + {
>>> + /* Handle indirect call. When a target defines the address of a
>>> + function as that of a function descriptor, then dereferencing
>>> + a function pointer implicitly references memory. */
>>> + struct ptr_info_def *pi = SSA_NAME_PTR_INFO (callee);
>>> + if (pi)
>>> + {
>>> + base = ao_ref_base (ref);
>>> + if (pt_solution_includes_base (&pi->pt, base))
>>> + return true;
>>> + }
>>> + }
>>> +
>>> /* Const functions without a static chain do not implicitly use memory.
>>> */
>>> if (!gimple_call_chain (call)
>>> && (flags & (ECF_CONST|ECF_NOVOPS)))
>>> @@ -1564,7 +1599,7 @@ ref_maybe_used_by_call_p_1 (gcall *call, ao_ref *r
>>> && !is_global_var (base))
>>> goto process_args;
>>>
>>> - callee = gimple_call_fndecl (call);
>>> + callee = gimple_call_addr_fndecl (callee);
>>>
>>> /* Handle those builtin functions explicitly that do not act as
>>> escape points. See tree-ssa-structalias.c:find_func_aliases
>>> @@ -1803,23 +1838,7 @@ ref_maybe_used_by_call_p_1 (gcall *call, ao_ref *r
>>> }
>>>
>>> /* Check if the base variable is call-used. */
>>> - if (DECL_P (base))
>>> - {
>>> - if (pt_solution_includes (gimple_call_use_set (call), base))
>>> - return true;
>>> - }
>>> - else if ((TREE_CODE (base) == MEM_REF
>>> - || TREE_CODE (base) == TARGET_MEM_REF)
>>> - && TREE_CODE (TREE_OPERAND (base, 0)) == SSA_NAME)
>>> - {
>>> - struct ptr_info_def *pi = SSA_NAME_PTR_INFO (TREE_OPERAND (base, 0));
>>> - if (!pi)
>>> - return true;
>>> -
>>> - if (pt_solutions_intersect (gimple_call_use_set (call), &pi->pt))
>>> - return true;
>>> - }
>>> - else
>>> + if (pt_solution_includes_base (gimple_call_use_set (call), base))
>>> return true;
>>>
>>> /* Inspect call arguments for passed-by-value aliases. */
>>> Index: gcc/config/rs6000/rs6000.c
>>> ===================================================================
>>> --- gcc/config/rs6000/rs6000.c (revision 220025)
>>> +++ gcc/config/rs6000/rs6000.c (working copy)
>>> @@ -1490,6 +1490,9 @@ static const struct attribute_spec rs6000_attribut
>>> #undef TARGET_ASM_CAN_OUTPUT_MI_THUNK
>>> #define TARGET_ASM_CAN_OUTPUT_MI_THUNK
>>> hook_bool_const_tree_hwi_hwi_const_tree_true
>>>
>>> +#undef TARGET_HAS_FUNCTION_DESCRIPTORS
>>> +#define TARGET_HAS_FUNCTION_DESCRIPTORS rs6000_has_function_descriptors
>>> +
>>> #undef TARGET_FUNCTION_OK_FOR_SIBCALL
>>> #define TARGET_FUNCTION_OK_FOR_SIBCALL rs6000_function_ok_for_sibcall
>>>
>>> @@ -22099,6 +22102,14 @@ rs6000_return_addr (int count, rtx frame)
>>> return get_hard_reg_initial_val (Pmode, LR_REGNO);
>>> }
>>>
>>> +/* Return true if we use function descriptors. */
>>> +
>>> +static bool
>>> +rs6000_has_function_descriptors (void)
>>> +{
>>> + return DEFAULT_ABI == ABI_AIX;
>>> +}
>>> +
>>> /* Say whether a function is a candidate for sibcall handling or not. */
>>>
>>> static bool
>>> Index: gcc/testsuite/gcc.target/powerpc/pr64703.c
>>> ===================================================================
>>> --- gcc/testsuite/gcc.target/powerpc/pr64703.c (revision 0)
>>> +++ gcc/testsuite/gcc.target/powerpc/pr64703.c (working copy)
>>> @@ -0,0 +1,36 @@
>>> +/* { dg-do compile { target { powerpc*-*-* && lp64 } } } */
>>> +/* { dg-skip-if "" { powerpc*-*-darwin* } { "*" } { "" } } */
>>> +/* { dg-options "-O2 -mabi=elfv1" } */
>>> +/* { dg-final { scan-assembler "std .\*,112\\(1\\)" } } */
>>> +/* { dg-final { scan-assembler "std .\*,120\\(1\\)" } } */
>>> +/* { dg-final { scan-assembler "std .\*,128\\(1\\)" } } */
>>> +/* { dg-final { scan-assembler "addi .\*,1,112" } } */
>>> +
>>> +/* Testcase taken from glibc, powerpc64 dl-machine.h. */
>>> +
>>> +typedef struct {
>>> + unsigned long fd_func;
>>> + unsigned long fd_toc;
>>> + unsigned long fd_aux;
>>> +} Elf64_FuncDesc;
>>> +
>>> +extern unsigned long dl_hwcap;
>>> +
>>> +unsigned long
>>> +resolve_ifunc (unsigned long value, unsigned long adjust)
>>> +{
>>> + Elf64_FuncDesc opd;
>>> +
>>> + if (adjust)
>>> + {
>>> + Elf64_FuncDesc *func = (Elf64_FuncDesc *) value;
>>> + opd.fd_func = func->fd_func + adjust;
>>> + opd.fd_toc = func->fd_toc + adjust;
>>> + opd.fd_aux = func->fd_aux;
>>> + value = (unsigned long) &opd;
>>> + }
>>> +#if 0
>>> + __asm__ ("#%0" : : "r" (value));
>>> +#endif
>>> + return ((unsigned long (*) (unsigned long)) value) (dl_hwcap);
>>> +}
>>>
>>> --
>>> Alan Modra
>>> Australia Development Lab, IBM
