[llvm-dev] load instruction to gather intrinsics

[陳韋任 via llvm-dev]

2017-05-06 7:41 GMT+08:00 zhi chen <zchenhn at gmail.com>:

> The frontend would generate the load in the IR. I am using IRBuilder to
> generate gather. I know it is mainly for discontinuous memory locations.
> It's a long story why I want to use this. I want to gather some memory
> locations. Suppose there are an array A, I manually duplicated it somewhere
> with an offset x. Now, we have two arrays A and A', where A'[i] - A[i] =
> offset. I want to gather the two values at A+i and A+i whenever there was a
> load instruction to get a value from A+i.
>
> It is easy to do this if the code was not vectorized, but it become tricky
> when they are vectorized. If there is a load %1 = load <2 x i64>* %Ai,
> align 8, which loads two consecutive values at Ai, I need to gather the
> values from A'i as well. So I think I need to use gather to get values from
> A+i, A+i+1, A'+i, A'+i+1.
>
​
I think you can use `getelementptr` to calculate ​the address needed
by the gather
intrinsic, though I don't know
if there is better way to achieve your goal.

-- 
Wei-Ren Chen (陳韋任)
Homepage: https://people.cs.nctu.edu.tw/~chenwj
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