[PATCH] D41949: [RISCV] implement li pseudo instruction

[Sameer AbuAsal via Phabricator via llvm-commits]

sabuasal added a comment.

Hi,

This patch causes repeated LUI generation for the following test case :

void  foo (int num, int* addr) {

  addr[0] = num*4097;
  addr[1] = num*4098;
  addr[2] = num*4099;
  addr[3] = num*4100;

}

Without patch:

  1.	lui       a0, 1
  2.	addi      a3, a0, 2
  3.	mul       a3, a1, a3
  4.	sw         a3, 4(a2)
  5.	addi      a3, a0, 1
  6.	mul       a3, a1, a3
  7.	sw         a3, 0(a2)
  8.	addi      a3, a0, 3
  9.	mul       a3, a1, a3
  10.	sw         a3, 8(a2)
  11.	addi      a0, a0, 4
  12.	mul       a0, a1, a0
  13.	sw         a0, 12(a2)
  14.	ret

with patch:

  1.	lui        a0, 1
  2.	addi       a0, a0, 2
  3.	mul        a0, a1, a0
  4.	sw a0, 4(a2)
  5.	lui       a0, 1           repeated lui!
  6.	addi       a0, a0, 1
  7.	mul        a0, a1, a0
  8.	sw a0, 0(a2)
  9.	 lui       a0, 1   ---> repeated load
  10.	addi       a0, a0, 3
  11.	mul        a0, a1, a0
  12.	sw a0, 8(a2)
  13.	lui        a0, 1      ---> repeated load
  14.	addi       a0, a0, 4
  15.	mul        a0, a1, a0
  16.	sw a0, 12(a2)
  17.	ret

I think this is bacuse we are hiding the %hi part f the immediate from the Selection Dag so it doesn't optimize it away.

Sorry for the late reply. I thought you were going to hold off committing this till the compression issue is addressed.


Repository:
  rL LLVM

https://reviews.llvm.org/D41949