RE: Optimized Allocation of Argument registers

[Ajit Kumar Agarwal <ajit dot kumar dot agarwal at xilinx dot com>]

-----Original Message-----
From: Vladimir Makarov [mailto:vmakarov@redhat.com] 
Sent: Tuesday, November 18, 2014 1:57 AM
To: Ajit Kumar Agarwal; gcc Mailing List
Cc: Vinod Kathail; Shail Aditya Gupta; Vidhumouli Hunsigida; Nagaraju Mekala
Subject: Re: Optimized Allocation of Argument registers

On 2014-11-17 8:13 AM, Ajit Kumar Agarwal wrote:
> Hello All:
>
> I was looking at the optimized usage and allocation to argument registers. There are two aspects to it as follows.
>
> 1. We need to specify the argument registers as followed by ABI in the target specific code. Based on the function
>   argument registers defined in the target dependent code the function argument registers are passed. If the
>   number of argument registers defined in the Architecture is large say 6/8 function argument registers.
> Most of the time in the benchmarks we don't pass so many arguments and the number of arguments passed
>   is quite less. Since we reserve the function arguments as specified 
> in the target specific code for the given architecture, leads to unoptimized usage as this function argument registers will not be used in the function.
> Thus we need to steal some of the arguments registers and have the 
> usage of those in the function depending on the support of the number of function argument registers. The stealing of function argument registers will
>   lead more number of registers available that are to be used in the function and leading to less spill and fetch.
>

>>The argument registers should be not reserved.  They should be present in RTL and RA allocator will figure out itself when it can use them. 
>>That is how other ports work.

Thanks Vladimir for Clarifications.

> 2. The other aspect of the function argument registers is not spill 
> and fetch the argument registers as they are live across the function 
> call. But the liveness is limited to certain point of the called 
> function after that point the function argument registers are not live 
> and can be used inside the called function. Other aspect is if there is a shortage of registers than can the function argument registers should be used as spill candidate? Will this lead to the optimized code.
>
>

>>You can remove unnecessary code to save/restore arg registers around calls if you can figure out that they are not used in called functions. 
 >> There is already code for this written by Tom de Vries.  So you can use it.

Is the code written by Tom de Vries already a part of trunk?  Could you please give the pointer to this part of code.

Thanks & Regards
Ajit