On Jan 8, 2018, at 8:06 AM, Richard Earnshaw (lists) <richard.earns...@arm.com>
wrote:
>
> On 08/01/18 02:20, Bill Schmidt wrote:
>> Hi Richard,
>>
>> Unfortunately, I don't see any way that this will be useful for the ppc
>> targets. We don't
>> have a way to force resolution of a condition prior to continuing
>> speculation, so this
>> will just introduce another comparison that we would speculate past. For
>> our mitigation
>> we will have to introduce an instruction that halts all speculation at that
>> point, and place
>> it in front of all dangerous loads. I wish it were otherwise.
>
> So can't you make the builtin expand to (in pseudo code):
>
> if (bounds_check)
> {
> __asm ("barrier");
> result = *ptr;
> }
> else
> result = failval;
Could, but this just generates unnecessary code for Power. We would instead
generate
__asm ("barrier");
result = *ptr;
without any checks. We would ignore everything but the first argument.
Thanks,
Bill
>
> R.
>
>>
>> Thanks,
>> Bill
>>
>>> On Jan 4, 2018, at 7:58 AM, Richard Earnshaw <richard.earns...@arm.com>
>>> wrote:
>>>
>>>
>>> This patch adds generic support for the new builtin
>>> __builtin_load_no_speculate. It provides the overloading of the
>>> different access sizes and a default fall-back expansion for targets
>>> that do not support a mechanism for inhibiting speculation.
>>>
>>> * builtin_types.def (BT_FN_I1_CONST_VPTR_CONST_VPTR_CONST_VPTR_VAR):
>>> New builtin type signature.
>>> (BT_FN_I2_CONST_VPTR_CONST_VPTR_CONST_VPTR_VAR): Likewise.
>>> (BT_FN_I4_CONST_VPTR_CONST_VPTR_CONST_VPTR_VAR): Likewise.
>>> (BT_FN_I8_CONST_VPTR_CONST_VPTR_CONST_VPTR_VAR): Likewise.
>>> (BT_FN_I16_CONST_VPTR_CONST_VPTR_CONST_VPTR_VAR): Likewise.
>>> * builtins.def (BUILT_IN_LOAD_NO_SPECULATE_N): New builtin.
>>> (BUILT_IN_LOAD_NO_SPECULATE_1): Likewise.
>>> (BUILT_IN_LOAD_NO_SPECULATE_2): Likewise.
>>> (BUILT_IN_LOAD_NO_SPECULATE_4): Likewise.
>>> (BUILT_IN_LOAD_NO_SPECULATE_8): Likewise.
>>> (BUILT_IN_LOAD_NO_SPECULATE_16): Likewise.
>>> * target.def (inhibit_load_speculation): New hook.
>>> * doc/tm.texi.in (TARGET_INHIBIT_LOAD_SPECULATION): Add to
>>> documentation.
>>> * doc/tm.texi: Regenerated.
>>> * doc/cpp.texi: Document __HAVE_LOAD_NO_SPECULATE.
>>> * doc/extend.texi: Document __builtin_load_no_speculate.
>>> * c-family/c-common.c (load_no_speculate_resolve_size): New function.
>>> (load_no_speculate_resolve_params): New function.
>>> (load_no_speculate_resolve_return): New function.
>>> (resolve_overloaded_builtin): Handle overloading
>>> __builtin_load_no_speculate.
>>> * builtins.c (expand_load_no_speculate): New function.
>>> (expand_builtin): Handle new no-speculation builtins.
>>> * targhooks.h (default_inhibit_load_speculation): Declare.
>>> * targhooks.c (default_inhibit_load_speculation): New function.
>>> ---
>>> gcc/builtin-types.def | 16 +++++
>>> gcc/builtins.c | 99 ++++++++++++++++++++++++++
>>> gcc/builtins.def | 22 ++++++
>>> gcc/c-family/c-common.c | 164
>>> ++++++++++++++++++++++++++++++++++++++++++++
>>> gcc/c-family/c-cppbuiltin.c | 5 +-
>>> gcc/doc/cpp.texi | 4 ++
>>> gcc/doc/extend.texi | 53 ++++++++++++++
>>> gcc/doc/tm.texi | 6 ++
>>> gcc/doc/tm.texi.in | 2 +
>>> gcc/target.def | 20 ++++++
>>> gcc/targhooks.c | 69 +++++++++++++++++++
>>> gcc/targhooks.h | 3 +
>>> 12 files changed, 462 insertions(+), 1 deletion(-)
>>>
>>> <0001-builtins-Generic-support-for-__builtin_load_no_specu.patch>
>>
>
