Re: Generating host code in TCG mode

[沈梦姣]

Thanks Peter

> 在 2023年3月19日，上午2:52，Peter Maydell <peter.maydell@linaro.org> 写道：
> 
> On Fri, 17 Mar 2023 at 21:01, 沈梦姣 <shen.mengjiao3@icloud.com> wrote:
>> TCG knows what registers may be clobbered by a call into
>> host C code (this is set up in the tcg_target_call_clobber_regs
>> regset by code in tcg_target_init()), so the register allocator
>> will either avoid using those registers
>> 
>> Look at tcg_target_reg_alloc_order in i386 host, it has these
>> clobber registers though it first allocates callee saved registers.
> 
> Yes, that's the sensible order to allocate in.
> 
>> for values that must
>> be preserved across the call, or else it will spill them to
>> memory.
>> 
>> I didn’t see these clobber registers being saved to memory
>> before call/jmp Host C code in i386(x86-64) host, and copy
>> these memory value back to these registers
> 
> If they were not saved to memory, then there must not have
> been a 'live' value in them in the example you were looking
> at.
> If TCG didn't correctly handle registers that are clobbered
> by calls, then it would not work at all.
Yes, but it will be helpful if someone provides some hints though I’m still 
reviewing the code. Thanks 

BR
> 
> thanks
> -- PMM