Re: How to make IRA not to move an instruction

["H.J. Lu" <hjl dot tools at gmail dot com>]

On Fri, May 28, 2010 at 3:03 PM, Jeff Law <law@redhat.com> wrote:
> On 05/28/10 10:38, H.J. Lu wrote:
>>
>> Hi,
>>
>> I want to generate vzeroupper when I know upper 128bits aren't used. I
>> can't find
>> a way to mark an pattern which zeros upper 128bits. So I added
>>
>
> Presumably you can't use a zero_extract?
>
> [ ... ]

I tried something similar. But it doesn't work since register
allocator will try to allocate all 8/16 SSE registers to vzeroupper.

>
>> before IRA,
>>
>> (insn 2 4 3 2 x.i:9 (set (reg/v:V8SF 59 [ y ])
>> ? ? ? ? (reg:V8SF 21 xmm0 [ y ])) 1036 {*avx_movv8sf_internal}
>> (expr_list:REG_DEAD (reg:V8SF 21 xmm0 [ y ])
>> ? ? ? ? (nil)))
>>
>> (note 3 2 6 2 NOTE_INSN_FUNCTION_BEG)
>>
>> (insn 6 3 7 2 x.i:10 (unspec_volatile [
>> ? ? ? ? ? ? (const_int 0 [0])
>> ? ? ? ? ] 17) 1960 {avx_vzeroupper_nop} (nil))
>>
>> (call_insn 7 6 8 2 x.i:10 (call (mem:QI (symbol_ref:DI ("bar2") [flags
>> 0x41]<function_decl 0x7ffa930ecd00 bar2>) [0 S1 A8])
>> ? ? ? ? (const_int 0 [0])) 599 {*call_0} (nil)
>> ? ? (nil))
>>
>>
>> after IRA,
>>
>> (insn 6 3 20 2 x.i:10 (unspec_volatile [
>> ? ? ? ? ? ? (const_int 0 [0])
>> ? ? ? ? ] 17) 1960 {avx_vzeroupper_nop} (nil))
>>
>> (insn 20 6 7 2 x.i:10 (set (mem/c:V8SF (reg/f:DI 7 sp) [3 S32 A256])
>> ? ? ? ? (reg:V8SF 21 xmm0)) 1036 {*avx_movv8sf_internal} (nil))
>>
>> (call_insn 7 20 21 2 x.i:10 (call (mem:QI (symbol_ref:DI ("bar2")
>> [flags 0x41]<function_decl 0x7ffa930ecd00 bar2>) [0 S1 A8])
>> ? ? ? ? (const_int 0 [0])) 599 {*call_0} (nil)
>> ? ? (nil))
>>
>> Since vzeroupper will change xmm0/ymm0, the value saved on stack is wrong.
>> Is that a way to tell IRA not to move an instruction?
>>
>
> You need to expose those operands so that the dataflow information is
> correct.
>

I couldn't find a way to do so. I am adding a pass to move
avx_vzeroupper_nop just before a jump.



-- 
H.J.