-----Original Message----- From: Vladimir Makarov [mailto:vmaka...@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
