RE: Optimized Allocation of Argument registers

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

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.

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.

Please let me know what do you think.

Thanks & Regards
Ajit