[Mesa-dev] [RFC PATCH 2/2] ac/nir: Don't treat each element as a vec4 in compute shared memory
Connor Abbott
cwabbott0 at gmail.com
Tue Jul 4 03:32:30 UTC 2017
I'm going to do a full CTS run later this week before I send the
patches to the list, but can you confirm that this series fixes your
problems: https://cgit.freedesktop.org/~cwabbott0/mesa/log/?h=radv-rewrite-vars
(it passes all the CTS dEQP.compute.* tests, but that's not saying
much...)
On Mon, Jul 3, 2017 at 6:33 PM, Connor Abbott <cwabbott0 at gmail.com> wrote:
> I think a better approach would be to translate the NIR variables
> directly to LLVM variables instead of creating one giant LLVM
> variable. I have a series coming up that does a similar thing for
> local variables, I can try and convert shared variables too.
>
> On Tue, Jun 27, 2017 at 8:53 AM, Alex Smith <asmith at feralinteractive.com> wrote:
>> Currently every element in shared memory (including individual elements
>> of an array) are treated as a vec4. For example, the following:
>>
>> shared uint array[1024];
>>
>> gets treated as an array of 1024 vec4s with only the first component
>> ever used.
>>
>> This can be highly wasteful of LDS space. We have a shader which only
>> really requires ~24KB of shared memory, but since scalars are being
>> padded to vec4, it actually ends up needing 96KB. This is more than
>> the hardware supports, and leads to an LLVM compilation failure.
>>
>> Therefore, instead pack data in LDS according to the std430 layout.
>>
>> Signed-off-by: Alex Smith <asmith at feralinteractive.com>
>> ---
>> RFC since I'm not sure whether this is the best approach to handle this,
>> and there may be something I've missed.
>>
>> No regressions seen in Mad Max or Dawn of War 3, which both have a few
>> shaders which use shared memory. Also no regressions in the CTS
>> 'dEQP-VK.compute.*' tests.
>>
>> I've also checked over various test cases using arrays/structs/etc. in
>> shared memory, and as far as I can tell the generated LLVM/GCN code is
>> correct.
>> ---
>> src/amd/common/ac_nir_to_llvm.c | 55 ++++++++++++++++++++++-------------------
>> 1 file changed, 29 insertions(+), 26 deletions(-)
>>
>> diff --git a/src/amd/common/ac_nir_to_llvm.c b/src/amd/common/ac_nir_to_llvm.c
>> index 468ce4d..a48bb3b 100644
>> --- a/src/amd/common/ac_nir_to_llvm.c
>> +++ b/src/amd/common/ac_nir_to_llvm.c
>> @@ -397,7 +397,7 @@ static LLVMValueRef get_shared_memory_ptr(struct nir_to_llvm_context *ctx,
>> LLVMValueRef ptr;
>> int addr_space;
>>
>> - offset = LLVMConstInt(ctx->i32, idx * 16, false);
>> + offset = LLVMConstInt(ctx->i32, idx, false);
>>
>> ptr = ctx->shared_memory;
>> ptr = LLVMBuildGEP(ctx->builder, ptr, &offset, 1, "");
>> @@ -2404,7 +2404,7 @@ static LLVMValueRef visit_load_ubo_buffer(struct nir_to_llvm_context *ctx,
>>
>> static void
>> radv_get_deref_offset(struct nir_to_llvm_context *ctx, nir_deref_var *deref,
>> - bool vs_in, unsigned *vertex_index_out,
>> + bool vs_in, bool compute_shared, unsigned *vertex_index_out,
>> LLVMValueRef *vertex_index_ref,
>> unsigned *const_out, LLVMValueRef *indir_out)
>> {
>> @@ -2445,7 +2445,14 @@ radv_get_deref_offset(struct nir_to_llvm_context *ctx, nir_deref_var *deref,
>> if (tail->deref_type == nir_deref_type_array) {
>> nir_deref_array *deref_array = nir_deref_as_array(tail);
>> LLVMValueRef index, stride, local_offset;
>> - unsigned size = glsl_count_attribute_slots(tail->type, vs_in);
>> +
>> + /* For compute LDS, data is packed rather than treating
>> + * each individual element as a vec4. The returned
>> + * index is used to index into an i32 array so divide
>> + * by 4.
>> + */
>> + unsigned size = compute_shared ? glsl_get_std430_array_stride(tail->type, false) / 4
>> + : glsl_count_attribute_slots(tail->type, vs_in);
>>
>> const_offset += size * deref_array->base_offset;
>> if (deref_array->deref_array_type == nir_deref_array_type_direct)
>> @@ -2465,7 +2472,11 @@ radv_get_deref_offset(struct nir_to_llvm_context *ctx, nir_deref_var *deref,
>>
>> for (unsigned i = 0; i < deref_struct->index; i++) {
>> const struct glsl_type *ft = glsl_get_struct_field(parent_type, i);
>> - const_offset += glsl_count_attribute_slots(ft, vs_in);
>> +
>> + /* Same as above. */
>> + unsigned size = compute_shared ? glsl_get_std430_array_stride(ft, false) / 4
>> + : glsl_count_attribute_slots(tail->type, vs_in);
>> + const_offset += size;
>> }
>> } else
>> unreachable("unsupported deref type");
>> @@ -2641,7 +2652,7 @@ load_tcs_input(struct nir_to_llvm_context *ctx,
>> const bool is_compact = instr->variables[0]->var->data.compact;
>> param = shader_io_get_unique_index(instr->variables[0]->var->data.location);
>> radv_get_deref_offset(ctx, instr->variables[0],
>> - false, NULL, per_vertex ? &vertex_index : NULL,
>> + false, false, NULL, per_vertex ? &vertex_index : NULL,
>> &const_index, &indir_index);
>>
>> stride = unpack_param(ctx, ctx->tcs_in_layout, 13, 8);
>> @@ -2673,7 +2684,7 @@ load_tcs_output(struct nir_to_llvm_context *ctx,
>> const bool is_compact = instr->variables[0]->var->data.compact;
>> param = shader_io_get_unique_index(instr->variables[0]->var->data.location);
>> radv_get_deref_offset(ctx, instr->variables[0],
>> - false, NULL, per_vertex ? &vertex_index : NULL,
>> + false, false, NULL, per_vertex ? &vertex_index : NULL,
>> &const_index, &indir_index);
>>
>> if (!instr->variables[0]->var->data.patch) {
>> @@ -2712,7 +2723,7 @@ store_tcs_output(struct nir_to_llvm_context *ctx,
>> const bool is_compact = instr->variables[0]->var->data.compact;
>>
>> radv_get_deref_offset(ctx, instr->variables[0],
>> - false, NULL, per_vertex ? &vertex_index : NULL,
>> + false, false, NULL, per_vertex ? &vertex_index : NULL,
>> &const_index, &indir_index);
>>
>> param = shader_io_get_unique_index(instr->variables[0]->var->data.location);
>> @@ -2779,7 +2790,7 @@ load_tes_input(struct nir_to_llvm_context *ctx,
>> const bool is_compact = instr->variables[0]->var->data.compact;
>>
>> radv_get_deref_offset(ctx, instr->variables[0],
>> - false, NULL, per_vertex ? &vertex_index : NULL,
>> + false, false, NULL, per_vertex ? &vertex_index : NULL,
>> &const_index, &indir_index);
>> param = shader_io_get_unique_index(instr->variables[0]->var->data.location);
>> if (instr->variables[0]->var->data.location == VARYING_SLOT_CLIP_DIST0 &&
>> @@ -2808,7 +2819,7 @@ load_gs_input(struct nir_to_llvm_context *ctx,
>> LLVMValueRef value[4], result;
>> unsigned vertex_index;
>> radv_get_deref_offset(ctx, instr->variables[0],
>> - false, &vertex_index, NULL,
>> + false, false, &vertex_index, NULL,
>> &const_index, &indir_index);
>> vtx_offset_param = vertex_index;
>> assert(vtx_offset_param < 6);
>> @@ -2849,8 +2860,9 @@ static LLVMValueRef visit_load_var(struct nir_to_llvm_context *ctx,
>> unsigned const_index;
>> bool vs_in = ctx->stage == MESA_SHADER_VERTEX &&
>> instr->variables[0]->var->data.mode == nir_var_shader_in;
>> - radv_get_deref_offset(ctx, instr->variables[0], vs_in, NULL, NULL,
>> - &const_index, &indir_index);
>> + bool compute_shared = instr->variables[0]->var->data.mode == nir_var_shared;
>> + radv_get_deref_offset(ctx, instr->variables[0], vs_in, compute_shared,
>> + NULL, NULL, &const_index, &indir_index);
>>
>> if (instr->dest.ssa.bit_size == 64)
>> ve *= 2;
>> @@ -2925,9 +2937,6 @@ static LLVMValueRef visit_load_var(struct nir_to_llvm_context *ctx,
>> LLVMValueRef ptr = get_shared_memory_ptr(ctx, idx, ctx->i32);
>> LLVMValueRef derived_ptr;
>>
>> - if (indir_index)
>> - indir_index = LLVMBuildMul(ctx->builder, indir_index, LLVMConstInt(ctx->i32, 4, false), "");
>> -
>> for (unsigned chan = 0; chan < ve; chan++) {
>> LLVMValueRef index = LLVMConstInt(ctx->i32, chan, false);
>> if (indir_index)
>> @@ -2955,7 +2964,8 @@ visit_store_var(struct nir_to_llvm_context *ctx,
>> int writemask = instr->const_index[0];
>> LLVMValueRef indir_index;
>> unsigned const_index;
>> - radv_get_deref_offset(ctx, instr->variables[0], false,
>> + bool compute_shared = instr->variables[0]->var->data.mode == nir_var_shared;
>> + radv_get_deref_offset(ctx, instr->variables[0], false, compute_shared,
>> NULL, NULL, &const_index, &indir_index);
>>
>> if (get_elem_bits(ctx, LLVMTypeOf(src)) == 64) {
>> @@ -3040,9 +3050,6 @@ visit_store_var(struct nir_to_llvm_context *ctx,
>> case nir_var_shared: {
>> LLVMValueRef ptr = get_shared_memory_ptr(ctx, idx, ctx->i32);
>>
>> - if (indir_index)
>> - indir_index = LLVMBuildMul(ctx->builder, indir_index, LLVMConstInt(ctx->i32, 4, false), "");
>> -
>> for (unsigned chan = 0; chan < 8; chan++) {
>> if (!(writemask & (1 << chan)))
>> continue;
>> @@ -5756,9 +5763,9 @@ handle_shader_outputs_post(struct nir_to_llvm_context *ctx)
>>
>> static void
>> handle_shared_compute_var(struct nir_to_llvm_context *ctx,
>> - struct nir_variable *variable, uint32_t *offset, int idx)
>> + struct nir_variable *variable, uint32_t *offset)
>> {
>> - unsigned size = glsl_count_attribute_slots(variable->type, false);
>> + unsigned size = glsl_get_std430_array_stride(variable->type, false);
>> variable->data.driver_location = *offset;
>> *offset += size;
>> }
>> @@ -5926,16 +5933,12 @@ LLVMModuleRef ac_translate_nir_to_llvm(LLVMTargetMachineRef tm,
>> nir_foreach_variable(variable, &nir->shared)
>> num_shared++;
>> if (num_shared) {
>> - int idx = 0;
>> uint32_t shared_size = 0;
>> LLVMValueRef var;
>> LLVMTypeRef i8p = LLVMPointerType(ctx.i8, LOCAL_ADDR_SPACE);
>> - nir_foreach_variable(variable, &nir->shared) {
>> - handle_shared_compute_var(&ctx, variable, &shared_size, idx);
>> - idx++;
>> - }
>> + nir_foreach_variable(variable, &nir->shared)
>> + handle_shared_compute_var(&ctx, variable, &shared_size);
>>
>> - shared_size *= 16;
>> var = LLVMAddGlobalInAddressSpace(ctx.module,
>> LLVMArrayType(ctx.i8, shared_size),
>> "compute_lds",
>> --
>> 2.9.4
>>
>> _______________________________________________
>> mesa-dev mailing list
>> mesa-dev at lists.freedesktop.org
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