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[nvptx] Handle unused result in nvptx_unisimt_handle_set

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For an example:
...
  #pragma omp target map(tofrom: counter_N0)
  #pragma omp simd
  for (int i = 0 ; i < 1 ; i++ )
    {
      #pragma omp atomic update
      counter_N0 = counter_N0 + 1 ;
    }
...
I noticed that the result of the atomic update (%r30) is propagated:
...
  @%r33 atom.add.u32		_, [%r29], 1;
	shfl.sync.idx.b32	%r30, %r30, %r32, 31, 0xffffffff;
...
even though it is unused (which is why the bit bucket operand _ is used).

Fix this by not emitting the shuffle in this case, such that we have instead:
...
  @%r33 atom.add.u32	_, [%r29], 1;
	bar.warp.sync	0xffffffff;
...

Tested on nvptx.

gcc/ChangeLog:

2022-03-07  Tom de Vries  <tdevries@suse.de>

	* config/nvptx/nvptx.cc (nvptx_unisimt_handle_set): Handle unused
	result.

gcc/testsuite/ChangeLog:

2022-03-07  Tom de Vries  <tdevries@suse.de>

	* gcc.target/nvptx/uniform-simt-4.c: New test.
This commit is contained in:
Tom de Vries 2022-03-07 15:57:11 +01:00
parent 3ebcc053a4
commit 3e743d654b
2 changed files with 25 additions and 1 deletions
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4
gcc/config/nvptx/nvptx.cc
View File

@ -3274,7 +3274,9 @@ static bool
nvptx_unisimt_handle_set (rtx set, rtx_insn *insn, rtx master)
{
rtx reg;
if (GET_CODE (set) == SET && REG_P (reg = SET_DEST (set)))
if (GET_CODE (set) == SET
&& REG_P (reg = SET_DEST (set))
&& find_reg_note (insn, REG_UNUSED, reg) == NULL_RTX)
{
emit_insn_after (nvptx_gen_shuffle (reg, reg, master, SHUFFLE_IDX),
insn);

22
gcc/testsuite/gcc.target/nvptx/uniform-simt-4.c Normal file
View File

@ -0,0 +1,22 @@
/* { dg-do compile } */
/* { dg-options "-O2 -muniform-simt -mptx=_" } */
enum memmodel
{
MEMMODEL_RELAXED = 0
};
unsigned long long int *p64;
unsigned long long int v64;
int
main()
{
__atomic_fetch_add (p64, v64, MEMMODEL_RELAXED);
return 0;
}
/* { dg-final { scan-assembler-times "atom.add.u64\[\t \]+_," 1 } } */
/* { dg-final { scan-assembler-times "bar.warp.sync" 1 } } */
/* { dg-final { scan-assembler-not "shfl.sync.idx" } } */