radv: add support for push constants inlining when possible

This removes some scalar loads from shaders, but it increases
the number of SET_SH_REG packets. This is currently basic but
it could be improved if needed. Inlining dynamic offsets might
also help.

Original idea from Dave Airlie.

29077 shaders in 15096 tests
Totals:
SGPRS: 1321325 -> 1357101 (2.71 %)
VGPRS: 936000 -> 932576 (-0.37 %)
Spilled SGPRs: 24804 -> 24791 (-0.05 %)
Code Size: 49827960 -> 49642232 (-0.37 %) bytes
Max Waves: 242007 -> 242700 (0.29 %)

Totals from affected shaders:
SGPRS: 290989 -> 326765 (12.29 %)
VGPRS: 244680 -> 241256 (-1.40 %)
Spilled SGPRs: 1442 -> 1429 (-0.90 %)
Code Size: 8126688 -> 7940960 (-2.29 %) bytes
Max Waves: 80952 -> 81645 (0.86 %)

Signed-off-by: Samuel Pitoiset <samuel.pitoiset@gmail.com>
Reviewed-by: Bas Nieuwenhuizen <bas@basnieuwenhuizen.nl>

src/amd/common/ac_nir_to_llvm.c

@@ -1392,10 +1392,31 @@ static LLVMValueRef visit_load_push_constant(struct ac_nir_context *ctx,
                                              nir_intrinsic_instr *instr)
 {
 	LLVMValueRef ptr, addr;
+	LLVMValueRef src0 = get_src(ctx, instr->src[0]);
+	unsigned index = nir_intrinsic_base(instr);
 
-	addr = LLVMConstInt(ctx->ac.i32, nir_intrinsic_base(instr), 0);
+	addr = LLVMConstInt(ctx->ac.i32, index, 0);
-	addr = LLVMBuildAdd(ctx->ac.builder, addr,
+	addr = LLVMBuildAdd(ctx->ac.builder, addr, src0, "");
-			    get_src(ctx, instr->src[0]), "");
+
+	/* Load constant values from user SGPRS when possible, otherwise
+	 * fallback to the default path that loads directly from memory.
+	 */
+	if (LLVMIsConstant(src0) &&
+	    instr->dest.ssa.bit_size == 32) {
+		unsigned count = instr->dest.ssa.num_components;
+		unsigned offset = index;
+
+		offset += LLVMConstIntGetZExtValue(src0);
+		offset /= 4;
+
+		offset -= ctx->abi->base_inline_push_consts;
+
+		if (offset + count <= ctx->abi->num_inline_push_consts) {
+			return ac_build_gather_values(&ctx->ac,
+						      ctx->abi->inline_push_consts + offset,
+						      count);
+		}
+	}
 
 	ptr = ac_build_gep0(&ctx->ac, ctx->abi->push_constants, addr);
 

src/amd/common/ac_shader_abi.h

@@ -32,6 +32,8 @@ struct nir_variable;
 
 #define AC_LLVM_MAX_OUTPUTS (VARYING_SLOT_VAR31 + 1)
 
+#define AC_MAX_INLINE_PUSH_CONSTS 8
+
 enum ac_descriptor_type {
 	AC_DESC_IMAGE,
 	AC_DESC_FMASK,
@@ -66,6 +68,9 @@ struct ac_shader_abi {
 
 	/* Vulkan only */
 	LLVMValueRef push_constants;
+	LLVMValueRef inline_push_consts[AC_MAX_INLINE_PUSH_CONSTS];
+	unsigned num_inline_push_consts;
+	unsigned base_inline_push_consts;
 	LLVMValueRef view_index;
 
 	LLVMValueRef outputs[AC_LLVM_MAX_OUTPUTS * 4];

src/amd/vulkan/radv_cmd_buffer.c

@@ -628,6 +628,23 @@ radv_emit_descriptor_pointers(struct radv_cmd_buffer *cmd_buffer,
 	}
 }
 
+static void
+radv_emit_inline_push_consts(struct radv_cmd_buffer *cmd_buffer,
+			     struct radv_pipeline *pipeline,
+			     gl_shader_stage stage,
+			     int idx, int count, uint32_t *values)
+{
+	struct radv_userdata_info *loc = radv_lookup_user_sgpr(pipeline, stage, idx);
+	uint32_t base_reg = pipeline->user_data_0[stage];
+	if (loc->sgpr_idx == -1)
+		return;
+
+	assert(loc->num_sgprs == count);
+
+	radeon_set_sh_reg_seq(cmd_buffer->cs, base_reg + loc->sgpr_idx * 4, count);
+	radeon_emit_array(cmd_buffer->cs, values, count);
+}
+
 static void
 radv_update_multisample_state(struct radv_cmd_buffer *cmd_buffer,
 			      struct radv_pipeline *pipeline)
@@ -1901,6 +1918,7 @@ radv_flush_constants(struct radv_cmd_buffer *cmd_buffer,
 		radv_get_descriptors_state(cmd_buffer, bind_point);
 	struct radv_pipeline_layout *layout = pipeline->layout;
 	struct radv_shader_variant *shader, *prev_shader;
+	bool need_push_constants = false;
 	unsigned offset;
 	void *ptr;
 	uint64_t va;
@@ -1910,37 +1928,56 @@ radv_flush_constants(struct radv_cmd_buffer *cmd_buffer,
 	    (!layout->push_constant_size && !layout->dynamic_offset_count))
 		return;
 
-	if (!radv_cmd_buffer_upload_alloc(cmd_buffer, layout->push_constant_size +
-					  16 * layout->dynamic_offset_count,
-					  256, &offset, &ptr))
-		return;
-
-	memcpy(ptr, cmd_buffer->push_constants, layout->push_constant_size);
-	memcpy((char*)ptr + layout->push_constant_size,
-	       descriptors_state->dynamic_buffers,
-	       16 * layout->dynamic_offset_count);
-
-	va = radv_buffer_get_va(cmd_buffer->upload.upload_bo);
-	va += offset;
-
-	MAYBE_UNUSED unsigned cdw_max = radeon_check_space(cmd_buffer->device->ws,
-	                                                   cmd_buffer->cs, MESA_SHADER_STAGES * 4);
-
-	prev_shader = NULL;
 	radv_foreach_stage(stage, stages) {
-		shader = radv_get_shader(pipeline, stage);
+		if (!pipeline->shaders[stage])
+			continue;
 
-		/* Avoid redundantly emitting the address for merged stages. */
+		need_push_constants |= pipeline->shaders[stage]->info.info.loads_push_constants;
-		if (shader && shader != prev_shader) {
+		need_push_constants |= pipeline->shaders[stage]->info.info.loads_dynamic_offsets;
-			radv_emit_userdata_address(cmd_buffer, pipeline, stage,
-						   AC_UD_PUSH_CONSTANTS, va);
 
-			prev_shader = shader;
+		uint8_t base = pipeline->shaders[stage]->info.info.base_inline_push_consts;
+		uint8_t count = pipeline->shaders[stage]->info.info.num_inline_push_consts;
+
+		radv_emit_inline_push_consts(cmd_buffer, pipeline, stage,
+					     AC_UD_INLINE_PUSH_CONSTANTS,
+					     count,
+					     (uint32_t *)&cmd_buffer->push_constants[base * 4]);
+	}
+
+	if (need_push_constants) {
+		if (!radv_cmd_buffer_upload_alloc(cmd_buffer, layout->push_constant_size +
+						  16 * layout->dynamic_offset_count,
+						  256, &offset, &ptr))
+			return;
+
+		memcpy(ptr, cmd_buffer->push_constants, layout->push_constant_size);
+		memcpy((char*)ptr + layout->push_constant_size,
+		       descriptors_state->dynamic_buffers,
+		       16 * layout->dynamic_offset_count);
+
+		va = radv_buffer_get_va(cmd_buffer->upload.upload_bo);
+		va += offset;
+
+		MAYBE_UNUSED unsigned cdw_max =
+			radeon_check_space(cmd_buffer->device->ws,
+	                                   cmd_buffer->cs, MESA_SHADER_STAGES * 4);
+
+		prev_shader = NULL;
+		radv_foreach_stage(stage, stages) {
+			shader = radv_get_shader(pipeline, stage);
+
+			/* Avoid redundantly emitting the address for merged stages. */
+			if (shader && shader != prev_shader) {
+				radv_emit_userdata_address(cmd_buffer, pipeline, stage,
+							   AC_UD_PUSH_CONSTANTS, va);
+
+				prev_shader = shader;
+			}
 		}
+		assert(cmd_buffer->cs->cdw <= cdw_max);
 	}
 
 	cmd_buffer->push_constant_stages &= ~stages;
-	assert(cmd_buffer->cs->cdw <= cdw_max);
 }
 
 static void

src/amd/vulkan/radv_nir_to_llvm.c

@@ -627,6 +627,50 @@ count_vs_user_sgprs(struct radv_shader_context *ctx)
 	return count;
 }
 
+static void allocate_inline_push_consts(struct radv_shader_context *ctx,
+					struct user_sgpr_info *user_sgpr_info)
+{
+	uint8_t remaining_sgprs = user_sgpr_info->remaining_sgprs;
+
+	/* Only supported if shaders use push constants. */
+	if (ctx->shader_info->info.min_push_constant_used == UINT8_MAX)
+		return;
+
+	/* Only supported if shaders don't have indirect push constants. */
+	if (ctx->shader_info->info.has_indirect_push_constants)
+		return;
+
+	/* Only supported for 32-bit push constants. */
+	if (!ctx->shader_info->info.has_only_32bit_push_constants)
+		return;
+
+	uint8_t num_push_consts =
+		(ctx->shader_info->info.max_push_constant_used -
+		 ctx->shader_info->info.min_push_constant_used) / 4;
+
+	/* Check if the number of user SGPRs is large enough. */
+	if (num_push_consts < remaining_sgprs) {
+		ctx->shader_info->info.num_inline_push_consts = num_push_consts;
+	} else {
+		ctx->shader_info->info.num_inline_push_consts = remaining_sgprs;
+	}
+
+	/* Clamp to the maximum number of allowed inlined push constants. */
+	if (ctx->shader_info->info.num_inline_push_consts > AC_MAX_INLINE_PUSH_CONSTS)
+		ctx->shader_info->info.num_inline_push_consts = AC_MAX_INLINE_PUSH_CONSTS;
+
+	if (ctx->shader_info->info.num_inline_push_consts == num_push_consts &&
+	    !ctx->shader_info->info.loads_dynamic_offsets) {
+		/* Disable the default push constants path if all constants are
+		 * inlined and if shaders don't use dynamic descriptors.
+		 */
+		ctx->shader_info->info.loads_push_constants = false;
+	}
+
+	ctx->shader_info->info.base_inline_push_consts =
+		ctx->shader_info->info.min_push_constant_used / 4;
+}
+
 static void allocate_user_sgprs(struct radv_shader_context *ctx,
 				gl_shader_stage stage,
 				bool has_previous_stage,
@@ -706,6 +750,8 @@ static void allocate_user_sgprs(struct radv_shader_context *ctx,
 	} else {
 		user_sgpr_info->remaining_sgprs = remaining_sgprs - num_desc_set;
 	}
+
+	allocate_inline_push_consts(ctx, user_sgpr_info);
 }
 
 static void
@@ -735,6 +781,13 @@ declare_global_input_sgprs(struct radv_shader_context *ctx,
 		add_arg(args, ARG_SGPR, type, &ctx->abi.push_constants);
 	}
 
+	for (unsigned i = 0; i < ctx->shader_info->info.num_inline_push_consts; i++) {
+		add_arg(args, ARG_SGPR, ctx->ac.i32,
+			&ctx->abi.inline_push_consts[i]);
+	}
+	ctx->abi.num_inline_push_consts = ctx->shader_info->info.num_inline_push_consts;
+	ctx->abi.base_inline_push_consts = ctx->shader_info->info.base_inline_push_consts;
+
 	if (ctx->shader_info->info.so.num_outputs) {
 		add_arg(args, ARG_SGPR,
 			ac_array_in_const32_addr_space(ctx->ac.v4i32),
@@ -853,6 +906,11 @@ set_global_input_locs(struct radv_shader_context *ctx,
 		set_loc_shader_ptr(ctx, AC_UD_PUSH_CONSTANTS, user_sgpr_idx);
 	}
 
+	if (ctx->shader_info->info.num_inline_push_consts) {
+		set_loc_shader(ctx, AC_UD_INLINE_PUSH_CONSTANTS, user_sgpr_idx,
+			       ctx->shader_info->info.num_inline_push_consts);
+	}
+
 	if (ctx->streamout_buffers) {
 		set_loc_shader_ptr(ctx, AC_UD_STREAMOUT_BUFFERS,
 			       user_sgpr_idx);

src/amd/vulkan/radv_shader.h

@@ -129,10 +129,11 @@ struct radv_nir_compiler_options {
 enum radv_ud_index {
 	AC_UD_SCRATCH_RING_OFFSETS = 0,
 	AC_UD_PUSH_CONSTANTS = 1,
-	AC_UD_INDIRECT_DESCRIPTOR_SETS = 2,
+	AC_UD_INLINE_PUSH_CONSTANTS = 2,
-	AC_UD_VIEW_INDEX = 3,
+	AC_UD_INDIRECT_DESCRIPTOR_SETS = 3,
-	AC_UD_STREAMOUT_BUFFERS = 4,
+	AC_UD_VIEW_INDEX = 4,
-	AC_UD_SHADER_START = 5,
+	AC_UD_STREAMOUT_BUFFERS = 5,
+	AC_UD_SHADER_START = 6,
 	AC_UD_VS_VERTEX_BUFFERS = AC_UD_SHADER_START,
 	AC_UD_VS_BASE_VERTEX_START_INSTANCE,
 	AC_UD_VS_MAX_UD,
@@ -167,6 +168,8 @@ struct radv_shader_info {
 	uint8_t max_push_constant_used;
 	bool has_only_32bit_push_constants;
 	bool has_indirect_push_constants;
+	uint8_t num_inline_push_consts;
+	uint8_t base_inline_push_consts;
 	uint32_t desc_set_used_mask;
 	bool needs_multiview_view_index;
 	bool uses_invocation_id;