Re: Question about TCG liveness_pass_1

[LIU Zhiwei]

On 2023/3/17 22:02, Richard Henderson wrote:
> On 3/16/23 19:57, LIU Zhiwei wrote:
> > Hi Richard,
> >
> > When I read the tcg code, I find a corner case which may be a bug in 
> > liveness_pass_1.
> >
> > I see all TEMP_TBs or global temps are set to TS_DEAD | TS_MEM when 
> > enter liveness_pass_1. Think about the  sequence.
> >
> >
> > 1)Write_global_temp_0 // 0->TS_DEAD, but not recorded in arg_life
>
> Here TS_MEM->TS_DEAD, so *is* recorded in arg_life.
>
> > 2)INDEX_op_qemu_st   //trigger an exception here.
>
> Here TCG_OPF_SIDE_EFFECTS is set, so call la_global_sync, so 0->TS_MEM.

Oops! I missed this. Thanks.

> > 3)Ref_global_temp_0   // TS_DEAD->0
> >
> > 4)Write_global_temp_0 // TS_DEAD | TS_MEM -> TS_DEAD
> >
> > As 1) will not write to memory, its register will be reused by the 
> > 3). I think it may miss a write to global_temp_0 when enter an 
> > exception.
>
> Was there a specific test case that you find is miscompiled?

No.

Best Regards,
Zhiwei

> r~