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nir: Don't generate single iteration loops to zero-initialize memory

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If the stride we're adding to our loop counter is larger than the total
amount of shared local memory we're trying to initialize, we know the
loop will run at most one time.  So we can skip emitting a loop.

Loop unrolling appears to be unable to detect this currently.

Reviewed-by: Alyssa Rosenzweig <alyssa@rosenzweig.io>
Reviewed-by: Faith Ekstrand <faith.ekstrand@collabora.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/31312>
This commit is contained in:
Kenneth Graunke 2024-09-19 15:47:03 -07:00 • committed by Marge Bot
parent c1a44e8d43
commit 0b34a7aff0
1 changed files with 27 additions and 15 deletions
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42
src/compiler/nir/nir_lower_variable_initializers.c
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@ -153,6 +153,7 @@ nir_zero_initialize_shared_memory(nir_shader *shader,
const unsigned local_count = shader->info.workgroup_size[0] *
shader->info.workgroup_size[1] *
shader->info.workgroup_size[2];
const unsigned stride = chunk_size * local_count;
/* The initialization logic is simplified if we can always split the memory
* in full chunk_size units.
@ -161,30 +162,41 @@ nir_zero_initialize_shared_memory(nir_shader *shader,
const unsigned chunk_comps = chunk_size / 4;
nir_variable *it = nir_local_variable_create(b.impl, glsl_uint_type(),
"zero_init_iterator");
nir_def *local_index = nir_load_local_invocation_index(&b);
nir_def *first_offset = nir_imul_imm(&b, local_index, chunk_size);
nir_store_var(&b, it, first_offset, 0x1);
nir_loop *loop = nir_push_loop(&b);
{
nir_def *offset = nir_load_var(&b, it);
nir_push_if(&b, nir_uge_imm(&b, offset, shared_size));
if (stride >= shared_size) {
nir_push_if(&b, nir_ult_imm(&b, first_offset, shared_size));
{
nir_jump(&b, nir_jump_break);
nir_store_shared(&b, nir_imm_zero(&b, chunk_comps, 32), first_offset,
.align_mul = chunk_size,
.write_mask = ((1 << chunk_comps) - 1));
}
nir_pop_if(&b, NULL);
} else {
nir_variable *it = nir_local_variable_create(b.impl, glsl_uint_type(),
"zero_init_iterator");
nir_store_var(&b, it, first_offset, 0x1);
nir_store_shared(&b, nir_imm_zero(&b, chunk_comps, 32), offset,
.align_mul = chunk_size,
.write_mask = ((1 << chunk_comps) - 1));
nir_loop *loop = nir_push_loop(&b);
{
nir_def *offset = nir_load_var(&b, it);
nir_def *new_offset = nir_iadd_imm(&b, offset, chunk_size * local_count);
nir_store_var(&b, it, new_offset, 0x1);
nir_push_if(&b, nir_uge_imm(&b, offset, shared_size));
{
nir_jump(&b, nir_jump_break);
}
nir_pop_if(&b, NULL);
nir_store_shared(&b, nir_imm_zero(&b, chunk_comps, 32), offset,
.align_mul = chunk_size,
.write_mask = ((1 << chunk_comps) - 1));
nir_def *new_offset = nir_iadd_imm(&b, offset, stride);
nir_store_var(&b, it, new_offset, 0x1);
}
nir_pop_loop(&b, loop);
}
nir_pop_loop(&b, loop);
nir_barrier(&b, SCOPE_WORKGROUP, SCOPE_WORKGROUP, NIR_MEMORY_ACQ_REL,
nir_var_mem_shared);