[llvm-dev] [RISC-V V] How to read each bit of vbool8_t individually

[Shao-Ce Sun via llvm-dev]

Thanks for your help, and here is the code:


#include <stdio.h>
#include <riscv_vector.h>


#define N 5


int main(int argc, char **argv)
{
  signed char A[N] = {1, 2, 3, 4, 5};
  vint8m1_t B = vle8_v_i8m1(A, N);
  vbool8_t C = vmseq_vx_i8m1_b8(B, 3, N);
  int i;
  for (i = 0; i < N; ++i)
  {
    if (C[i])
      printf("INDEX:%d", i);
  }
}







------------------ Original ------------------
From:                                                                                                                        "Craig Topper"                                                                                    <craig.topper at gmail.com>;
Date: Fri, Jul 9, 2021 11:41 AM
To: "Shao-Ce Sun"<llvm at foxmail.com>;
Cc: "via llvm-dev"<llvm-dev at lists.llvm.org>;
Subject: Re: [llvm-dev] [RISC-V V] How to read each bit of vbool8_t individually



There aren't really any instructions for doing this in the ISA. Solutions I can think of are rounding vl to the next multiple of 8 and storing it to a uint8_t using vse8. Then reading it back by looping over the array and looking at all 8 bits of each uint8_t. Or you could use vmerge to turn into a vuint8m1_t vector of 1 and 0.


Perhaps if you shared your use case I might be able to come up with something else.

~Craig




On Thu, Jul 8, 2021 at 7:23 PM Shao-Ce Sun via llvm-dev <llvm-dev at lists.llvm.org> wrote:

Hi All,
  I have a question about RISC-V V, that is how to read each bit of vbool8_t individually, for example:
            vbool8_t A;
            bool B[8] = A;
Thanks!

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