[llvm-dev] which pass can do following optimization? gvn-sink?

[Fangqing Du via llvm-dev]

Dear all,

Imagine we have following code:

  1 #define ny 10

  2 #define Batch_Size 10

  3

  4 typedef float data_t;

  5

  6 void foo(data_t out[ny][Batch_Size], data_t max[Batch_Size]);

  7

  8 void Softmax_Activation(data_t l_Z2[ny][Batch_Size],

  9                         data_t out[ny][Batch_Size]) {

 10

 11   data_t max[Batch_Size];

 12

 13 SA_MAX2:

 14   for (int i = 0; i < Batch_Size; i++) {

 15     max[i] = 0;

 16   SA_MAX1:

 17     for (int j = 0; j < ny; j++) {

 18       if (l_Z2[j][i] > max[i])

 19         max[i] = l_Z2[j][i];

 20     }

 21   }

 22   foo(out, max);

 23 }
we can see 'max[i]' is an invariant variable to loop 'SA_MAX1', so I want
to know which pass can following following transformation/optimization:

  1 #define ny 10


  2 #define Batch_Size 10


  3


  4 typedef float data_t;


  5


  6 void foo(data_t out[ny][Batch_Size], data_t max[Batch_Size]);


  7


  8 void Softmax_Activation(data_t l_Z2[ny][Batch_Size],


  9                         data_t out[ny][Batch_Size]) {


 10


 11   data_t max[Batch_Size];


 12


 13 SA_MAX2:


 14   for (int i = 0; i < Batch_Size; i++) {


 15     data_t Max = 0;


 16   SA_MAX1:


 17     for (int j = 0; j < ny; j++) {


 18       if (l_Z2[j][i] > Max)


 19         Max = l_Z2[j][i];


 20     }


 21     max[i] = Max;


 22   }


 23   foo(out, max);


 24 }
Which will use a local scalar 'Max' to replace the original 'max[i]', and
sink the original write out of the loop 'SA_MAX1'.

I did some experiment with godbolt, looks like currently we don't have such
kind of optimization.
https://godbolt.org/z/9PK3hYvPs

Do you know which pass can do this? Or it's not necessary for CPU?

Thanks,
Fangqing
Xilinx Inc.
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.llvm.org/pipermail/llvm-dev/attachments/20210730/d9c41805/attachment.html>