Andrew Pinski writes:
> On Tue, Jul 28, 2015 at 6:12 AM, Jiong Wang <jiong.w...@arm.com> wrote:
>>
>> The instruction sequences for preparing argument for TLS descriptor
>> runtime resolver and the later function call to resolver can actually be
>> hoisted out of the loop.
>>
>> Currently we can't because we have exposed the hard register X0 as
>> destination of "set". While GCC's RTL data flow infrastructure will
>> skip or do very conservative assumption when hard register involved in
>> and thus some loop IV opportunities are missed.
>>
>> This patch add another "tlsdesc_small_pseudo_<mode>" pattern, and avoid
>> expose x0 to gcc generic code.
>>
>> Generally, we define a new register class FIXED_R0 which only contains
>> register
>> 0, so the instruction sequences generated from the new add pattern is the
>> same
>> as tlsdesc_small_<mode>, while the operand 0 is wrapped as pseudo register
>> that
>> RTL IV opt can handle it.
>>
>> Ideally, we should allow operand 0 to be any pseudo register, but then
>> we can't model the override of x0 caused by the function call which is
>> hidded by the UNSPEC.
>>
>> So here, we restricting operand 0 to be x0, the override of x0 can be
>> reflected to the gcc.
>>
>> OK for trunk?
>
>
> This patch broke ILP32 because we used mode rather than ptr_mode for
> the psedu . I have an idea on how to fix it (like tlsie_small_sidi
> case) but I still need to test it fully.
Have done a quick re-visit the code, the use of "mode" instead of
"ptr_mode" looks OK to me.
While what looks strange to me is under ILP32 symbol_ref is DImode.
(symbol_ref:DI ("*.LANCHOR0")
My my understanding, the symbol_ref should be SI mode under ilp32
instead of DI mode.
So it's better to fix "create_block_symbol" in varasm, and we should let
it use ptr_mode instead of Pmode as Pmode is used to describe the
underline hardware mode instead of the mode view in C language level.
>
> This is the smallest testcase where the problem is:
> struct dtor_list
> {
> struct dtor_list *next;
> };
> static __thread struct dtor_list *tls_dtor_list;
> __cxa_thread_atexit_impl ( struct dtor_list *new)
> {
> new->next = tls_dtor_list;
> tls_dtor_list = new;
> }
>
>
> Thanks,
> Andrew
>
>>
>> 2015-07-28 Ramana Radhakrishnan <ramana.radhakrish...@arm.com>
>> Jiong Wang <jiong.w...@arm.com>
>>
>> gcc/
>> * config/aarch64/aarch64.d (tlsdesc_small_pseudo_<mode>): New pattern.
>> * config/aarch64/aarch64.h (reg_class): New enumeration FIXED_REG0.
>> (REG_CLASS_NAMES): Likewise.
>> (REG_CLASS_CONTENTS): Likewise.
>> * config/aarch64/aarch64.c (aarch64_class_max_nregs): Likewise.
>> (aarch64_register_move_cost): Likewise.
>> (aarch64_load_symref_appropriately): Invoke the new added pattern if
>> possible.
>> * config/aarch64/constraints.md (Uc0): New constraint.
>>
>> gcc/testsuite.
>> * gcc.target/aarch64/tlsdesc_hoist.c: New testcase.
>>
>> --
>> Regards,
>> Jiong
>>
--
Regards,
Jiong
