[llvm-dev] Conditional Register Assignment based on the no of loop iterations

[hameeza ahmed via llvm-dev]

or should i write a condition in registerinfo.td; to define the registers
in object Reg_A in specific order according to loop iterations.

On Mon, Jul 10, 2017 at 9:17 AM, hameeza ahmed <hahmed2305 at gmail.com> wrote:

> hello,
>
> i have a situation where i have to assign the registers to instructions
> based on the loop iterations.
>
> for eg..
> the registers are:
> R_0_V_0, R_0_V_1, R_0_V_2, R_0_V_3,
> R_1_V_0, R_1_V_1, R_1_V_2, R_1_V_3,
> R_2_V_0, R_2_V_1, R_2_V_2, R_2_V_3.
> These registers defined in object Reg_A
>
> These are total 12 registers. will use them contiguously, here i  define
> it in above mentioned order i.e changing V first then R.
>
>
> for eg;
> if no of iterations>=4.
> 1st load will take place in R_0_V_0
> 2nd load will take place in R_0_V_1
> 3rd load will take place in R_0_V_2
> 4th load will take place in R_0_V_3
> I am getting this required behavior for iterations>=4. I want this to
> happen only if there are 4 or above iterations in loop.
>
>
> But if my iterations are less than 4 like 3
> again it will do the same thing;
> 1st load will take place in R_0_V_0
> 2nd load will take place in R_0_V_1
> 3rd load will take place in R_0_V_2
>
> Here i dont want the above to happen rather it should increment R instead
> of V in this case.
> It should do something as follows:
> 1st load to take place in R_0_V_0
> 2nd load to take place in R_1_V_0
> 3rd load to take place in R_2_V_0
>
> Now, how to achieve this?
>
> Can i mention some condition in instructioninfo.td file?
> and in registerinfo.td file instead of 1 object Reg_A, there will be 2
> objects Reg_A and Reg_B
> where Reg_B defines same registers but in different order.
>
> Reg_B;
>
> R_0_V_0, R_1_V_0, R_2_V_0,  //here R changes
> R_0_V_1, R_1_V_1, R_2_V_1,
> R_0_V_2, R_1_V_2, R_2_V_2,
> R_0_V_3, R_1_V_3, R_2_V_3.
>
> So that in instructioninfo.td file it will be something like;
>
> if (no of iterations>=4)
>
> load ................$Reg_A      ; here all register operands will come
> from Reg_A instance.
>
> if (no of iterations<4)
>
> load ................$Reg_B      ; here all register operands will come
> from Reg_B instance.
>
>
> Is the above approach possible??? if yes then how can we acquire the no of
> iterations in instructioninfo.td file??
>
> or can you suggest some better way?
>
> Looking forward to response
>
> Thank You.
>
>
>
>
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